Description:TECHNICAL FIELD
The present disclosure relates to the field of hydrogen detection and leak monitoring. Moreover, the present disclosure relates to a method for the fabrication of a flexible hydrogen detection sensor.
BACKGROUND
Hydrogen is a widely used raw material in various industries and serves as a fuel for fuel-cell vehicles and space exploration. However, hydrogen's highly flammable nature and extensive flammability range (4% v/v to 75% v/v in air) pose significant safety risks. As a colourless and odourless gas, hydrogen is difficult to detect visually or by smell, and its lightness allows it to leak through the smallest openings, potentially forming explosive mixtures with air. The necessity for fast-responding hydrogen sensors is evident in environments where hydrogen is utilized. Effective hydrogen leak detection systems are crucial in preventing accidents.
Existing hydrogen sensors often utilize palladium-based sensing elements due to their excellent selectivity and sensitivity to hydrogen at room temperature. The existing hydrogen sensors generally operate on the principle of chemoresistance, where the electrical resistance of the palladium changes upon exposure to hydrogen. Despite their effectiveness, conventional hydrogen sensors often face limitations in terms of mechanical rigidity, which restricts their ability to conform to irregular or flexible surfaces such as pipe fittings where leaks are likely to occur. This has led to an increasing interest in the development of flexible sensors that can better accommodate these challenging environments. While several methods for fabricating flexible hydrogen sensors have been explored, including sputtering, lithographically patterned nano-electrodeposition, and hydrothermal synthesis, these techniques often require complex equipment, operate under extreme conditions, or are time-consuming. Additionally, current flexible sensors, like those based on colour-changing tape, are limited by the need for manual inspection and single-use functionality.
Therefore, in light of the foregoing discussion, there exists a need to overcome the aforementioned drawbacks.
SUMMARY
The present disclosure provides a method for fabrication of a flexible hydrogen detection sensor. The present disclosure provides a solution to the technical problem of how to create a hydrogen detection sensor that combines high sensitivity, fast response time, and mechanical flexibility, allowing the hydrogen detection sensor to be easily integrated into various industrial settings, particularly in areas with irregular or non-rigid surfaces like pipelines and joints. An aim of the present disclosure is to provide a solution that overcomes at least partially the problems encountered in the prior art and provide an improved method that not only synthesizes flexible hydrogen detection sensor that is cost-effective but the method that may be easily adopted. Thus, the method of the present disclosure manifests a technical advancement as well as economic benefits.
One or more objectives of the present disclosure is achieved by the solutions provided in the enclosed independent claims. Advantageous implementations of the present disclosure are further defined in the dependent claims.
In one aspect, the present disclosure provides a method for fabrication of a flexible hydrogen detection sensor. The method includes preparing a polyimide-substrate assembly and pre-treating the polyimide-substrate assembly with an alkaline solution. Further, the method includes creating an aluminium-polyimide assembly by affixing an aluminium tape to the pre-treated polyimide-substrate assembly. The method further includes preparing a precursor solution comprising palladium and platinum compounds and applying the precursor solution to the aluminium-polyimide assembly, allowing the precursor solution to contact the aluminium tape. Further, the method includes allowing a reaction between the precursor solution and the aluminium tape to proceed for a first predetermined time period and removing the precursor solution and separating the aluminium tape from the polyimide-substrate assembly to reveal an electrically conductive metal nanoparticle deposit on a surface of the polyimide-substrate assembly. Furthermore, the method includes performing a post-treatment step by applying a fresh batch of the precursor solution to the electrically conductive metal nanoparticle deposit for a second predetermined time period. The electrically conductive metal nanoparticle deposit forms an electrically conductive network on the polyimide-substrate assembly, and the electrically conductive network formed by the electrically conductive metal nanoparticle deposit exhibits a measurable change in electrical resistance upon exposure to hydrogen, said change being correlatable to hydrogen concentration.
The method of the present disclosure for the fabrication of the flexible hydrogen detection sensor has several significant technical effects.
The use of a polyimide-substrate assembly and aluminium tape enables the flexible hydrogen detection sensor to be flexible and conform to a variety of shapes and surfaces. The flexibility is particularly beneficial for applications on curved or irregular surfaces, such as pipe flanges and joints, where traditional rigid sensors cannot be effectively used. The electrically conductive metal nanoparticle deposit, formed from palladium and platinum compounds, offers high sensitivity to hydrogen. The combination of palladium and platinum compounds allows the flexible hydrogen detection sensor to detect low concentrations of the hydrogen gas quickly, significantly reducing the risk of undetected leaks and potential explosions. The method involves simple steps, such as pre-treating the substrate with the alkaline solution and applying the precursor solution. The steps do not require expensive or complex equipment, making the fabrication process cost-effective and potentially scalable for mass production. The use of palladium and platinum in the precursor solution enhances the selectivity for hydrogen while maintaining stability under various environmental conditions. This ensures reliable and accurate detection over extended periods. The simplicity of the method allows for adjustments in the precursor solution or substrate materials to customize the flexible hydrogen detection sensor for different applications or specific performance requirements, enhancing its versatility. The post-treatment reinforces the electrically conductive metal nanoparticle network, ensuring that the flexible hydrogen detection sensor maintains its performance over multiple detection cycles. The reliable performance reduces the need for frequent replacements and maintenance. By providing fast and accurate detection of hydrogen leaks, the flexible hydrogen detection sensor significantly enhances safety in environments where the hydrogen gas is used, protecting both personnel and equipment from potential hazards. The fabrication process operates at ambient conditions, reducing energy consumption and environmental impact compared to methods requiring elevated temperatures or pressures. The straightforward and reproducible nature of the fabrication process ensures ease of manufacturing and deployment in various industrial settings, enabling widespread adoption and integration into existing safety systems.
It is to be appreciated that all the aforementioned implementation forms can be combined. All steps which are performed by the various entities described in the present application as well as the functionalities described to be performed by the various entities are intended to mean that the respective entity is adapted to or configured to perform the respective steps and functionalities. It will be appreciated that features of the present disclosure are susceptible to being combined in various combinations without departing from the scope of the present disclosure as defined by the appended claims.
Additional aspects, advantages, features, and objects of the present disclosure would be made apparent from the drawings and the detailed description of the illustrative implementations construed in conjunction with the appended claims that follow.
BRIEF DESCRIPTION OF THE DRAWINGS
The summary above, as well as the following detailed description of illustrative embodiments, is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the present disclosure, exemplary constructions of the disclosure are shown in the drawings. However, the present disclosure is not limited to specific methods and instrumentalities disclosed herein. Moreover, those skilled in the art will understand that the drawings are not to scale. Wherever possible, like elements have been indicated by identical numbers.
Embodiments of the present disclosure will now be described, by way of example only, with reference to the following diagrams wherein:
FIG. 1 is a flowchart depicting a method for fabrication of a flexible hydrogen detection sensor, in accordance with an embodiment of the present disclosure;
FIGs. 2A, 2B, 2C and 2D depict schematic views of various steps for setting an inverted assembly, in accordance with an embodiment of the present disclosure.;
FIG. 3 is an exemplary diagram illustrating a schematic of a side view of the inverted assembly, in accordance with an embodiment of the present disclosure;
FIGs. 4A, 4B and 4C depict schematic views of various steps for setting an upright assembly, in accordance with another embodiment of the present disclosure;
FIG. 5 is an exemplary diagram illustrating the schematic of a side view of the upright assembly, in accordance with an embodiment of the present disclosure.;
FIGs. 6A and 6B are the graphical representations illustrating the response of the flexible hydrogen detection sensor with respect to different gases, in accordance with an embodiment of the present disclosure;
FIGs. 7A and 7B are graphical representations illustrating the performance of the flexible hydrogen detection sensor, in accordance with an embodiment of the present disclosure;
FIGs. 8A and 8B are graphical representations illustrating the behaviour of the flexible hydrogen detection sensor with the molecular sieve coating on exposure to interference gases, in accordance with an embodiment of the disclosure;
FIGs. 8C and 8D are graphical representations illustrating the behaviour of the flexible hydrogen detection sensor without the molecular sieve coating on exposure to interference gases, in accordance with an embodiment of the disclosure;
FIGs. 9A and 9B are graphical representations illustrating the six-month stability of the flexible hydrogen detection sensor with the molecular sieve coating;
FIGs. 9C and 9D are graphical representations illustrating the six-month stability of the flexible hydrogen detection sensor without the molecular sieve coating, in accordance with an embodiment of the present disclosure;
FIGs 10A and 10B are graphical representations illustrating the response of the flexible hydrogen detection sensor with the molecular sieve coating under tension and compression, in accordance with an embodiment of the present disclosure;
FIGs 10C and 10D are graphical representations illustrating the response of the flexible hydrogen detection sensor without the molecular sieve coating under tension and compression, in accordance with an embodiment of the present disclosure;
FIGs. 11A and 11B are graphical representations illustrating the effect of platinum content on the flexible hydrogen detection sensor with molecular sieve coating, in accordance with an embodiment of the present disclosure;
FIGs. 12A and 12B are graphical representations illustrating the limit of detection of the hydrogen gas by flexible hydrogen detection sensor with molecular sieve coating, in accordance with an embodiment of the present disclosure; and
FIGs. 12C and 12D are graphical representations illustrating the limit of detection of the hydrogen gas by flexible hydrogen detection sensor without the molecular sieve coating, in accordance with an embodiment of the present disclosure.
In the accompanying drawings, an underlined number is employed to represent an item over which the underlined number is positioned or an item to which the underlined number is adjacent. A non-underlined number relates to an item identified by a line linking the non-underlined number to the item. When a number is non-underlined and accompanied by an associated arrow, the non-underlined number is used to identify a general item at which the arrow is pointing.
DETAILED DESCRIPTION OF EMBODIMENTS
The following detailed description illustrates embodiments of the present disclosure and ways in which they can be implemented. Although some modes of carrying out the present disclosure have been disclosed, those skilled in the art would recognize that other embodiments for carrying out or practicing the present disclosure are also possible.
FIG. 1 is a flowchart depicting a method for fabrication of a flexible hydrogen detection sensor, in accordance with an embodiment of the present disclosure. With reference to FIG. 1, there is shown a flowchart of a method 100. In some implementations, the method 100 is executed by a skilled person. The method 100 may include steps 102 to 116.
At step 102, the method 100 includes preparing a polyimide-substrate assembly. The polyimide is a type of polymer characterized by imide monomers in its chemical structure and due to their excellent insulating properties and flexibility. In some examples, the polyimide is used in the manufacture of flexible electronic devices and sensors. Throughout the present disclosure, the term “polyimide-substrate assembly” refers to a composite structure where a polyimide tape is adhered to a supporting substrate, which is a flexible polymer. In an example, a plastic tray is filled with tap water and a suitable amount of a cleaning agent (for example, Labolene) is added to the tap water. The mixture of the tap water and the cleaning agent is stirred gently to create a uniform, soapy solution. The polyimide tape is cut and immersed into the uniform, soapy solution, ensuring the polyimide tape becomes completely wet. The immersion of the polyimide tape in the soapy solution temporarily weakens the adhesive, preventing the polyimide tape from sticking to itself. The wet polyimide tape is removed from the soapy solution.
In an implementation, preparing the polyimide-substrate assembly includes adhering a polyimide tape to a polyester. In some implementations, the wet polyimide tape is laid on a transparent polyester sheet (for example, PET), ensuring it is smooth and free of air bubbles or wrinkles. Further, the polyimide-substrate assembly is rinsed with running tap water to flush out any remaining soapy solution from between the polyimide tape and the polyester sheet. In some examples, a paperweight may be used to press out the trapped water between the polyimide tape and the polyester sheet. The paperweight is moved across the surface of the polyimide tape, applying even pressure to ensure all excess water is expelled. The polyimide-substrate assembly is cleaned with a tissue paper to absorb any remaining moisture. Later, the polyimide-substrate assembly is allowed to dry overnight to ensure that any residual water is fully absorbed and evaporated, leaving the polyimide firmly adhered to the polyester sheet. The temporary weakening of the adhesive effect by the cleaning agent enables smooth application and ensures the durability of the polyimide-substrate assembly.
At step 104, the method 100 includes pre-treating the polyimide-substrate assembly with an alkaline solution. The polyimide-substrate assembly is cut into smaller pieces and immersed in a solution of cleaning agent and deionized water. Further, the pieces of the polyimide-substrate assembly are washed thoroughly with deionized water and treated with an alkaline solution. In some implementations, the alkaline solution is a potassium hydroxide solution. In an example, the potassium hydroxide solution is prepared by mixing 0.4-0.6 M of potassium hydroxide with 18 -20 ml of deionized water. The potassium hydroxide treatment implants K+ ions into a polyimide surface of the polyimide-substrate assembly, which are replaced with metal ions, forming a metal interlayer that enhances the adhesion of electrically conductive metal nanoparticle deposits. After treating the pieces of the polyimide-substrate assembly with the alkaline solution, the pre-treated polyimide-substrate assembly is washed with the deionized water.
In some examples, the alkaline solution may include, but not limited to, a sodium hydroxide solution, a calcium hydroxide solution, a lithium hydroxide solution, a potassium carbonate solution, an ammonium hydroxide solution, a sodium phosphate solution, or a sodium aluminate solution. In some other examples, the alkaline solution may include an alkali solution, an alkali metal hydroxide, or any other solution with an abrasive nature.
At step 106, the method 100 includes creating an aluminium-polyimide assembly by affixing an aluminium tape to the pre-treated polyimide-substrate assembly. The aluminium tape has an aluminium side and an adhesive side with a paper backing on an opposite side of the aluminium tape. The paper backing from the aluminium tape is removed and replaced with a cello tape, ensuring that the adhesive side of the aluminium tape sticks to the cello tape. The aluminium tape is cut to the predefined length. In some examples, the aluminium tape is wiped with an ethanol-soaked tissue to clear any dust. Further, a pen knife may be used to cut along the edge using multiple strokes gently. After that, the aluminium tape is placed on the pre-treated polyimide-substrate assembly, ensuring the aluminium side faces the polyimide side of the pre-treated polyimide-substrate assembly. The aluminium-polyimide assembly provides a stable and durable platform for various applications, including the fabrication of flexible sensors and other electronic devices.
At step 108, the method 100 includes preparing a precursor solution including palladium and platinum compounds. In some implementations, one or more components, such as ethanol, deionized water, hydrochloric acid, and palladium chloride, are mixed together to form a palladium chloride solution. The palladium chloride solution is kept sit overnight to ensure complete dissolution. Further, potassium tetrachloroplatinate is dissolved in the deionized water to create a potassium tetrachloroplatinate solution. In addition, potassium bromide (KBr) is mixed with the deionized water to form a potassium bromide (KBr) solution. Finally, predefined volumes of the palladium chloride solution, the potassium tetrachloroplatinate solution, the potassium bromide (KBr) solution, acidic ethanol (ethanol mixed with an acid), and the deionized water are mixed together to form the precursor solution.
In an implementation, the precursor solution includes 35.4 volume/volume percentage (%v/v) of palladium chloride and 2.1 %v/v of potassium tetrachloroplatinate. In some implementations, the precursor solution may include 28 to 38 %v/v of palladium chloride and 1.5 to 2.5 %v/v of potassium tetrachloroplatinate. Specifically, in some other implementations, the precursor solution includes 35.4 %v/v of palladium chloride solution, 2.1 %v/v of potassium tetrachloroplatinate solution, 12.5 %v/v of potassium bromide solution, 25 %v/v of the acidic ethanol, and 25 %v/v of the deionized water. The high concentration of palladium chloride provides a sufficient amount of palladium, a metal known for its excellent hydrogen absorption properties. The absorption enhances the sensitivity of the flexible to hydrogen gas by enabling a more significant change in electrical resistance upon hydrogen exposure. The inclusion of potassium tetrachloroplatinate in a lower concentration contributes to improved deposition efficiency and faster response time eventually.
At step 110, the method 100 includes applying the precursor solution to the aluminium-polyimide assembly, allowing the precursor solution to contact the aluminium tape. The precursor solution is applied uniformly over the aluminium-polyimide assembly. The application can be done using various techniques, such as drop-casting, spin-coating, or dipping, depending on the predefined thickness and uniformity of the metal nanoparticle layer.
At step 112, the method 100 includes allowing a reaction between the precursor solution and the aluminium tape to proceed for a first predetermined time period. The assembly is left undisturbed to allow the precursor solution to come into contact with the aluminium tape. During this period, the metal ions in the solution are reduced by the aluminium, leading to the formation of metal nanoparticles. As the precursor solution contacts the aluminium tape, a redox reaction occurs. The aluminium reacts with the precursor solution and indirectly reduces the metal ions to their metallic state. This results in the deposition of metal nanoparticles on the polyimide surface. In some implementations, the first predetermined time period is between 60 to 1200 seconds. In some other implementations, the first predetermined time period may be between 240 to 300 seconds. The controlled time period ensures that the metal nanoparticles are uniformly distributed across the polyimide surface of the polyimide-substrate assembly. The duration helps in achieving the predefined thickness of the electrically conductive metal nanoparticle deposit metal nanoparticle layer, which is essential for the sensitivity and response time of the flexible hydrogen detection sensor. A well-regulated deposition time promotes the formation of continuous and conductive nanoparticle networks. This enhances the electrical conductivity of the flexible hydrogen detection sensor, which is vital for detecting hydrogen gas through resistance changes.
At step 114, the method 100 includes removing the precursor solution and separating the aluminium tape from the polyimide-substrate assembly to reveal an electrically conductive metal nanoparticle deposit on the surface of the polyimide-substrate assembly. Once the precursor solution has sufficiently reacted with the aluminium tape, resulting in the deposition of metal nanoparticles on the polyimide surface, the next step is to remove the remaining precursor solution.
In an implementation, the method further includes washing the electrically conductive metal nanoparticle deposit with deionized water after removing the precursor solution and before performing the post-treatment step. The aluminium polyimide assembly is rinsed with the deionized water to remove any excess precursor solution. Rinsing ensures that no unreacted metal salts or other contaminants remain on the polyimide surface. After rinsing, the aluminium polyimide assembly is dried. In an example, drying may be performed using air drying, a gentle stream of nitrogen gas, or a low-temperature oven. Proper drying is essential to ensure that the metal nanoparticles remain firmly adhered to the polyimide surface. Once the precursor solution is removed and the assembly is dried, the aluminium tape needs to be carefully separated from the polyimide substrate. Separation must be done cautiously to avoid damaging the newly formed metal nanoparticle layer. The aluminium tape is gently peeled off from the polyimide substrate. The polyimide tape, now with an electrically conductive layer of metal nanoparticles deposited on its surface, is revealed. The polyimide-substrate assembly is inspected to ensure a uniform and intact layer of electrically conductive metal nanoparticles. The electrically conductive metal nanoparticles, which have been deposited through the reduction process, form an electrically conductive layer on the polyimide surface. The electrically conductive layer is crucial for the functionality of the hydrogen sensor, as it allows the detection of hydrogen gas through changes in electrical resistance.
At step 116, the method 100 includes performing a post-treatment step by applying a fresh batch of the precursor solution to the electrically conductive metal nanoparticle deposit for a second predetermined time period. A fresh batch of the precursor solution further refined the nanoparticle deposit. The fresh batch of the precursor solution uniformly over the already deposited electrically conductive metal nanoparticles on the polyimide substrate. This can be achieved through techniques such as drop-casting, spin-coating, or dipping. Allow the precursor solution to remain in contact with the electrically conductive nanoparticle deposit for the second predetermined time period, which is optimized for the predefined enhancement effects. The second predetermined time period typically varies based on the specific requirements of the performance of the flexible hydrogen detection sensor. During the second predetermined time period, the fresh precursor solution inhibits the atmospheric oxidation of the metal nanoparticle deposits to a certain degree. After the second predetermined time period, the polyimide substrate is rinsed with a suitable solvent to remove any excess precursor solution. The polyimide substrate is thoroughly dried using air drying, a gentle stream of nitrogen gas, or a low-temperature oven. In an implementation, the second predetermined time period is 10 to 1000 seconds. In some other implementations, the second predetermined time period is 50 to 70 seconds.
In an implementation, the concentration of the precursor solution used in the post-treatment step is the same as the concentration used when initially applying the precursor solution to the aluminium-polyimide assembly. Maintaining the same concentration ensures uniform deposition of palladium and platinum nanoparticles throughout the fabrication process. The use of the potassium bromide in the post-treatment precursor solution for the post-treatment step enables the electrically conductive deposits for hydrogen sensing, such that the change in their electrical resistance can be correlated with the exposed the hydrogen gas concentration in the environment of air. The incorporation of the platinum and the palladium salts, along with the potassium bromide in the post-treatment solution, improves the hydrogen sensitivity further. Therefore, all the three component solutions, i.e. the potassium bromide, the palladium chloride, and the potassium tetra chloroplatinate are required to be present in the solution for the post-treatment step. To simplify, the fresh precursor solution itself was used for the post-treatment step.
The electrically conductive metal nanoparticle deposit forms an electrically conductive network on the polyimide-substrate assembly, and the electrically conductive metal nanoparticle deposit exhibits a measurable change in electrical resistance upon exposure to hydrogen, said change being correlatable to hydrogen concentration. During the initial deposition process, metal nanoparticles (e.g., palladium and platinum) are deposited onto the polyimide substrate through a reduction reaction facilitated by the aluminium tape. The fresh batch of the precursor solution is applied in a post-treatment step, enhancing the density and uniformity of the electrically conductive metal nanoparticle layer. The electrically conductive metal nanoparticles form a continuous, interconnected network on the polyimide substrate. The interconnected network is essential for creating a path for electron flow, making the substrate electrically conductive. The controlled deposition and post-treatment steps ensure that the electrically conductive metal nanoparticle layer is uniform and dense, contributing to stable electrical properties. When the flexible hydrogen detection sensor is exposed to hydrogen gas, hydrogen molecules adsorb onto the surface of the metal nanoparticles. This interaction is particularly strong with metals like palladium, which can absorb hydrogen into their lattice structure. The adsorption of hydrogen onto the electrically conductive metal nanoparticles alters their electronic structure, leading to a change in electrical resistance. The change in electrical resistance occurs due to the formation of metal hydrides and changes in the charge carrier density within the conductive network. The change in resistance is measurable using standard electrical measurement techniques. This measurable change is a direct indicator of the presence and concentration of hydrogen gas.
The flexible hydrogen detection sensor can be calibrated to establish a relationship between the change in electrical resistance and the concentration of hydrogen. The calibration involves measuring the resistance change at known hydrogen concentrations to create a calibration curve. The sensitivity of the flexible hydrogen detection sensor is determined by the magnitude of the resistance change in response to a given concentration of hydrogen. A more sensitive sensor will show a more significant resistance change for a smaller amount of hydrogen.
In some implementations, attaching electrical contacts to the electrically conductive metal nanoparticle deposit to measure the change in electrical resistance. Attaching electrical contacts to the electrically conductive metal nanoparticle deposit enables the measurement of changes in electrical resistance, which occurs when the sensor is exposed to hydrogen. These contacts serve as interfaces between the sensor material and external measurement equipment, allowing for accurate detection and quantification of hydrogen concentration based on the resistance change. This setup is essential for converting the chemical interaction of hydrogen with the sensor into a measurable electrical signal.
The method 100 further includes applying a molecular sieve coating to the electrically conductive metal nanoparticle deposit after the post-treatment step to enhance selectivity for hydrogen detection. A molecular sieve is a material with pores of uniform size that selectively adsorbs molecules based on their size and shape. Common materials used as molecular sieves include zeolites and metal-organic frameworks (MOFs). The deposit consists of metal nanoparticles (e.g., palladium and platinum) on a polyimide substrate, forming an electrically conductive network. The network changes its electrical resistance upon exposure to hydrogen gas. The molecular sieve coating is applied to increase the selectivity of the flexible hydrogen detection sensor towards the hydrogen gas over other gases. Hydrogen gas molecules are smaller and can pass through the pores of the molecular sieve, while larger molecules are excluded.
In practical applications, various gases might be present in the environment. The molecular sieve coating helps to filter out larger, non-target gas molecules that could otherwise interfere with the readings of the flexible hydrogen detection sensor, ensuring more accurate hydrogen detection. By selectively allowing only hydrogen molecules to reach the metal nanoparticles, the sensor provides more precise measurements. The sieve coating enhances the reliability of the flexible hydrogen detection sensor in diverse and potentially contaminated environments by minimizing false positives and negatives. The molecular sieve layer helps discriminate against interference gases.
In an example, in order to prepare a molecular sieve solution, a solution containing the molecular sieve material is prepared. This may involve dissolving or dispersing the material in a suitable solvent. The molecular sieve solution is uniformly applied to the surface of the electrically conductive metal nanoparticle deposit. This can be done using techniques such as dip-coating, spin-coating, or spray-coating to ensure even coverage. The thickness of the sieve coating is carefully controlled to maintain the balance between selectivity and accessibility. The coating must be thick enough to filter out larger molecules but thin enough to allow hydrogen molecules to reach the nanoparticles. After application, the sieve coating is dried to remove the solvent, leaving behind a uniform layer of the molecular sieve material. Curing processes such as heat treatment may be employed to enhance the stability and adherence of the molecular sieve coating to the nanoparticle layer. The pore size and distribution of the molecular sieve are verified to ensure they match the predefined specifications for selective hydrogen detection. The flexible hydrogen detection sensor is tested to confirm that the molecular sieve coating effectively enhances selectivity for hydrogen while maintaining the sensitivity and response time of the flexible hydrogen detection sensor.
The steps 102 to 116 are only illustrative, and other alternatives can also be provided where one or more steps are added, one or more steps are removed, or one or more steps are provided in a different sequence without departing from the scope of the claims herein.
FIG. 2A, 2B, 2C and 2D depict schematic views of various steps for setting an inverted assembly, in accordance with an embodiment of the present disclosure. FIGs. 2A to 2D are described in conjunction with elements from FIG. 1. With reference to FIG. 2A, there is shown a base assembly 200A that includes a base 202A, a first piece of double-sided tape 204A and a second piece of double-sided tape 206A. With reference to FIG. 2B, there is shown an aluminium-polyimide assembly 200B including a polyimide substrate assembly including a polyimide tape 202B and a polyester sheet 206B on which the polyimide tape 202B is adhered. The aluminium-polyimide assembly 200B further includes an aluminium tape 204B including an aluminium side and the adhesive side. With reference to FIG. 2C, there is shown a combined assembly 200C including the aluminium-polyimide assembly 200B attached to the base assembly 200A. With reference to FIG. 2D, there is shown an inverted assembly 200D, in which the aluminium-polyimide assembly 200B is placed in an inverted orientation with the aluminium side of the aluminium tape 204B facing upward, i.e., towards the polyimide tape 202B and the polyimide tape is 202B facing the base 202A during the application of the precursor solution. The application of the precursor solution is shown by a shaded area 202D in FIG. 2D. The inverted assembly 200D allows the precursor solution to interact uniformly with the aluminium side of the aluminium tape 204B, promoting even deposition of electrically conductive metal nanoparticles on the polyimide-substrate assembly. The aluminium acts as a temporary surface for the chemical reaction, which facilitates the transfer of metal ions from the precursor solution onto the polyimide-substrate assembly. The reaction between the aluminium and the precursor solution produces bubbles, assumed to be of the hydrogen gas. These bubbles are thought to play a significant role in creating the deposits on polyimide or any other substrate as well. The inverted assembly approach is designed in such a way that the bubbles are able to do their job much more efficiently. By placing the aluminium side of aluminium polyimide assembly 200B upward, gravity helps to keep the bubbles in contact with the polyimide surface, ensuring consistent exposure and reaction time.
FIG. 3 is an exemplary diagram illustrating a schematic of a side view of the inverted assembly. FIG. 3 is described in conjunction with elements from FIGs. 1 to 2D. With reference to FIG. 3, there is shown an exemplary diagram 300 depicting the side view of the inverted assembly 200D. The exemplary diagram 300 includes the polyester sheet 206B, the polyimide tape 202B, the base 202A, the aluminium side of the aluminium tape 204B, the cello-tape backing 302, a clearance 304 between the aluminium tape and the base 202A.
In an implementation, the applying the precursor solution to the aluminium-polyimide assembly 200B includes securing the aluminium-polyimide assembly 200B in an inverted orientation with the aluminium side of the aluminium tape 204B facing upward, i.e., towards the polyimide tape 202B, creating the clearance 304 between the aluminium side of the aluminium tape 204B and the supporting surface (i.e., the base 202A); applying the precursor solution to fill the clearance 304; and allowing the precursor solution to react with the aluminium side of the aluminium tape 204B in the inverted orientation.
The aluminium-polyimide assembly 200B, which includes the aluminium side of the aluminium tape 204B and the polyimide-substrate assembly, is positioned in an inverted orientation, which means that the aluminium side of the aluminium tape 204B faces upward. i.e., towards the polyimide tape 202B. In contrast, the polyimide-substrate assembly is oriented downward. The clearance 304 is established between the aluminium side of the aluminium tape 204B and the base 202A below it. The clearance 304 acts as a controlled space for holding the precursor solution. The clearance 304 may be achieved by raising the aluminium-polyimide assembly 200B slightly above the base 202A, ensuring that the precursor solution can be contained within this space without spilling. The precursor solution, containing palladium and platinum compounds, is then carefully applied to fill the clearance 304. The application is done in such a way that the entire aluminium surface is covered with the precursor solution. The application ensures uniform exposure of the aluminium side of the aluminium tape 204B to the precursor solution, which is critical for consistent nanoparticle formation. Once the precursor solution is in place, it is allowed to react with the aluminium side of the aluminium tape 204B. In the inverted orientation, gravity assists in maintaining the bubbles’ contact with the aluminium surface. The reaction between the precursor solution and the aluminium side of the aluminium tape 204B results in the deposition of electrically conductive metal nanoparticles onto the polyimide-substrate assembly, forming an electrically conductive layer. This reaction is typically controlled for a specific period to achieve the predefined properties of the nanoparticle layer.
In an implementation, the volume of precursor solution applied is proportional to the length of the aluminium tape 204B used in the aluminium-polyimide assembly 200B. By scaling the volume of the precursor solution with the length of the aluminium tape, an entire surface of the aluminium tape 204B may be uniformly covered, ensuring consistent exposure across the entire area. The uniformity is vital for achieving an even deposition of nanoparticles. Proportionally adjusting the volume of the precursor solution helps in optimizing the use of materials. It ensures that sufficient precursor solution is available to react with the entire length of the aluminium tape 204B without wastage. Maintaining a proportional relationship between the precursor solution volume and aluminium tape length allows for better control over the thickness and uniformity of the deposited electrically conductive metal nanoparticle layer. This control is essential for achieving predefined electrical properties, such as consistent conductivity and resistance, which directly impact the performance of the flexible hydrogen detection sensor.
FIGs 4A, 4B, and 4C depict an exemplary scenario for setting an upright assembly, in accordance with an embodiment of the present disclosure. FIG. 4A to 4C are described in conjunction with elements from FIG. 1 to FIG. 3. With reference to FIG. 4A, there is shown an aluminium polyimide assembly 200B, including a polyimide tape 202B, a polyester sheet 206B, and the aluminium side of the aluminium tape 204B. The polyimide tape 202B refers to a specific type of tape that consists of a polyimide film coated with an adhesive layer, often with a protective backing that can be removed before application. The polyester sheet 206B refers to a specific sheet made from polyester material, known for its durability, chemical resistance, and mechanical strength.
With reference to FIG. 4B, there is shown an exemplary diagram 400B including a container frame 402B that is stuck around the aluminium tape. With reference to FIG. 4C, there is shown an upright assembly 400C, in which the aluminium-polyimide assembly 200B is placed in an upright orientation with the aluminium side of the aluminium tape 204B facing downward during the application of the precursor solution. The aluminium-polyimide assembly 200B is positioned vertically, the aluminium side of the aluminium tape 204B facing downward, i.e. towards the polyimide tape 202B. The orientation ensures that the aluminium surface is directly exposed to the precursor solution. The precursor solution is then introduced into a space 402C, created by the container - frame 402B. This can be done by applying the solution so that it comes into contact with the downward-facing aluminium surface. The precursor solution comes into direct contact with the aluminium side of the aluminium tape 204B, allowing the chemical reaction to occur. Gravity assists in keeping the solution in contact with the aluminium surface, helping to maintain a consistent and uniform reaction. The reaction leads to the deposition of electrically conductive metal nanoparticles on the polyimide-substrate assembly.
In an implementation, applying the precursor solution to the aluminium-polyimide assembly comprises creating the container frame 402B around the aluminium tape 204B on the polyimide-substrate assembly, filling the container-frame with the precursor solution, and allowing the precursor solution to react with the aluminium side of the aluminium tape 204B in the upright orientation.
The process of applying the precursor solution to the aluminium-polyimide assembly 200B involves several detailed steps to ensure controlled and uniform deposition of the electrically conductive metal nanoparticle layer. The container frame 402B is constructed around the aluminium tape, which is adhered to the polyimide-substrate assembly. The container frame 402B acts as a boundary or barrier to contain the precursor solution. The container frame 402B is positioned in such a way that it surrounds the aluminium side of the aluminium tape 204B and forms a shallow container above it. The container frame 402B can be made of a chemically inert material that does not react with the precursor solution. Once the container frame 402B is securely in place, the precursor solution is carefully poured into the frame, filling it to a level that submerges the aluminium tape. The container frame 402B ensures that the precursor solution is evenly distributed across the surface of the aluminium side of the aluminium tape 204B. The amount of precursor solution used should be sufficient to completely cover the aluminium side of the aluminium tape 204B, ensuring uniform exposure. With the aluminium-polyimide assembly 200B in an upright orientation (aluminium side facing downward), the precursor solution within the container frame 402B is allowed to interact with the aluminium side of the aluminium tape 204B.
During this reaction, the palladium and platinum compounds in the precursor solution react with the aluminium surface, leading to the formation and deposition of electrically conductive metal nanoparticles onto the polyimide-substrate assembly. This reaction typically takes place over a specific period, during which the solution remains in contact with the aluminium tape. It creates a controlled environment where the precursor solution is stayed connected with the aluminium tape, ensuring consistent exposure and reaction. The frame prevents the precursor solution from spilling or spreading beyond the intended area, leading to more efficient use of the solution. By containing the solution directly over the aluminium tape, the container-frame 402B helps achieve uniform deposition of nanoparticles, which is critical for the electrical and functional properties of the flexible hydrogen detection sensor.
FIG. 5 is an exemplary diagram illustrating a schematic of a side view of the upright assembly. FIG. 5 is described in conjunction with elements from FIGs. 1 to 4B. With reference to FIG. 5, there is shown an exemplary diagram 500 depicting a side view of the upright assembly. The exemplary diagram 500 includes the polyester sheet 206B, the polyimide tape 202B, the aluminium side of the aluminium tape 204B, and a cello-tape backing 302. The upright orientation allows for precise control over the application of the precursor solution. The use of gravity ensures that the solution remains in contact with the aluminium surface, facilitating uniform distribution and reaction across the entire tape. By positioning the aluminium surface downward, the upward assembly allows for better contacting between the hydrogen gas bubbles and the polyimide tape 202B in comparison to a situation if the aluminium were to face upwards. If the aluminium were to face upwards (instead of downwards) in the upright orientation method, there would be no “sandwiching” of the bubbles between the aluminium and the polyimide tape 202B. The reason is that the bubbles would originate from the aluminium and directly float away without even touching the polyimide, thereby not creating any deposition whatsoever.
The downward-facing aluminium surface benefits from a consistent and stable reaction environment. The precursor solution is evenly distributed across the aluminium surface, aided by gravity, leading to a uniform reaction and consistent nanoparticle layer formation. This uniformity is vital for the electrical characteristics of the sensor, ensuring reliable detection of hydrogen gas. After the reaction, the excess precursor solution can be efficiently removed by draining it away from the aluminium surface. This prevents excess precursor solution from pooling or creating inconsistencies in the nanoparticle layer. Nanoparticle deposition is essential for the performance and reliability of flexible hydrogen sensors.
FIGs. 6A and 6B are the graphical representations illustrating the response of the flexible hydrogen detection sensor to different gases, in accordance with an embodiment of the present disclosure. FIGs. 6A and 6B are described in conjunction with elements from the FIGs. 1 to 5. With reference to FIG. 6A, there is shown a graphical representation 600A when the flexible hydrogen detection sensor is exposed to nitrogen gas and hydrogen gas. The graphical representation 600A includes three regions, namely a region 602A, a region 604A and a region 606A. The regions 602A and the region 606A correspond to the time duration when the flexible hydrogen detection sensor is exposed to only background nitrogen gas flowing at 8 litres per minute (LPM). The region 604A corresponds to the time duration when the flexible hydrogen detection sensor is exposed to 3% hydrogen gas with nitrogen gas flowing in the background at 8 litres per minute (LPM).
When the hydrogen gas is introduced sharp increase in sensitivity is observed, and peak sensitivity reaches approximately 4.8%. Further, the sensitivity plateaus within about 50 seconds, i.e., the flexible hydrogen detection sensor achieves quick saturation., maintains high sensitivity during hydrogen gas exposure, rapid decrease in sensitivity upon removal of the hydrogen gas.
With reference to FIG. 6B, there is shown a graphical representation 600B depicting the response of the flexible hydrogen detection sensor to the same conditions as illustrated by the graphical representation 600A after four days. The graphical representation 600B includes. The graphical representation 600B includes three regions, namely a region 602B, a region 604B and a region 606B. The regions 602B and the region 606B correspond to the time duration when the flexible hydrogen detection sensor is exposed to only background nitrogen gas flowing at 8 litres per minute (LPM). The region 604B corresponds to the time duration when the flexible hydrogen detection sensor is exposed to 3% hydrogen gas with nitrogen gas flowing in the background at 8 litres per minute (LPM).
The graphical representation 600B depicts consistent behaviour of the flexible hydrogen detection sensor similar to the shown by the graphical representation 600A. There is a slight decrease in sensitivity observed (peak sensitivity reaches about 3.5%), a similar response profile is obtained and an effective recovery. The flexible hydrogen detection sensor maintains its overall response characteristics after four days, indicating good short-term stability. While there is a slight decrease in peak sensitivity (from ~4.8% to ~3.5%), the sensor remains highly responsive to the hydrogen gas. Both the graphical representations 600A and 600B show rapid response to hydrogen gas introduction and quick recovery upon removal of the hydrogen gas, demonstrating consistent kinetics.
Further, the graphical representations 600A and 600B exhibit low noise and clear distinction between without hydrogen gas exposure and hydrogen gas exposure phases. These results demonstrate that the presence of bimetallic palladium and platinum in the flexible hydrogen detection sensor effectively mitigates hydrogen embrittlement issues commonly associated with pure palladium sensors. The flexible hydrogen detection sensor maintains high sensitivity, rapid response, and quick recovery over multiple days of testing. The performance stability suggests that the palladium and the platinum nanoparticle structure are more resistant to structural changes induced by repeated hydrogen exposure, making it a promising candidate for long-term, reliable hydrogen sensing applications.
FIGs. 7A and 7B are graphical representations illustrating the performance of the flexible hydrogen detection sensor, in accordance with an embodiment of the disclosure. FIGs. 7A and 7B are described in conjunction with elements from FIGs. 1 to 6B. With reference to FIG. 7A, there is shown a graphical representation 700A depicting the response of the flexible hydrogen detection sensor when exposed to 3.28% hydrogen in the air background. The time is measured in seconds (sec) in an abscissa axis (X-axis). The sensitivity is expressed in percentage in an ordinate axis (Y-axis).
The graphical representation 700A includes a curve 702A, a curve 704A and a curve 706A. The curve 702A represents the initial sensitivity, which is close to 0%. The curve 704A represents a sharp increase in sensitivity, which occurs at around 100 seconds. The sensitivity peaks at about 3.5% when exposed to 3.28% of hydrogen gas. Further, the curve 706 represents a rapid decrease in sensitivity.
With reference to FIG. 7B, there is shown a graphical representation 700B depicting the response of the flexible hydrogen detection sensor when exposed to multiple cycles of different hydrogen gas concentrations. The time is measured in seconds (sec) in an abscissa axis (X-axis). The sensitivity is expressed in percentage in an ordinate axis (Y-axis).
The graphical representation 700B includes a first region 702B, a second region 708B, a third region 714B and a fourth region 720B. The first region 702B, corresponds time duration for which the flexible hydrogen detection sensor is exposed to 3.28% of hydrogen gas in the air background. The first region 702B, includes a curve 704B and a curve 706B. The curve 704B corresponds to a rise in sensitivity, and the curve 706B corresponds to a fall in sensitivity. The second region 708B, corresponds to the time duration for which the flexible hydrogen detection sensor is exposed to 1.27% of the hydrogen gas in the air background. The second region 708B, includes a curve 710B and a curve 712B. The curve 710B and the curve 712B corresponds to rise in sensitivity and fall in sensitivity, respectively. The third region 714B, corresponds to the time duration for which the flexible hydrogen detection sensor is exposed to 0.64% of the hydrogen gas in the air background. The third region 714B, includes a curve 716B, representing a rise in sensitivity, and a curve 718B, representing a fall in sensitivity. The fourth region 720B, corresponds to the time duration for which the flexible hydrogen detection sensor is exposed to 2.41% of the hydrogen gas in the air background. The fourth region 720B, includes a curve 722B, representing a rise in sensitivity and a curve 724B, representing a fall in sensitivity. Each exposure results in a peak in sensitivity, with higher concentrations producing larger peaks. The sensor shows good recovery between exposures, returning close to the baseline.
The graphical representation 700A shows a smaller response, due to initial oxide removal. The graphical representation 700B shows consistent and repeatable responses. The flexible hydrogen detection sensor demonstrates a clear concentration-dependent response, with higher hydrogen gas concentrations producing larger sensitivity peaks. The flexible hydrogen detection sensor exhibits good recovery between exposures, indicating reversibility. The presence of potassium bromide in the precursor solution has enabled oxide-resistant nanoparticles, as evidenced by the consistent increase in electrical resistance (i.e., positive sensitivity) for all hydrogen gas exposures. The slightly lower initial resistance in the graphical representation 700A is due to the oxide removal during the first exposure. The graphical representations 700A and 700B demonstrate that the flexible hydrogen detection sensor consisting of palladium and platinum with potassium bromide treatment shows good sensitivity, repeatability, and concentration-dependent response to hydrogen gas.
FIGs. 8A and 8B are graphical representations illustrating the behaviour of the flexible hydrogen detection sensor with the molecular sieve coating on exposure to interference gases, in accordance with an embodiment of the disclosure. FIGs. 8A and 8B are described in conjunction with elements from FIGs. 1 to 7B. With reference to FIG. 8A, there is shown a graphical representation 800A illustrating the relative change in sensitivity of the flexible hydrogen detection sensor before and after exposure to interference gases. The flexible hydrogen detection sensor is subjected to 1 hour of interference gas flow at a rate of 5.5 LPM. The abscissa axis represents the square root of the hydrogen gas concentration expressed in percentage. The ordinate axis represents the ratio of change in the average sensitivity before and after the exposure relative to the initial average sensitivity at a given concentration of the hydrogen gas. Further, different interference gases, i.e., hydrogen sulphide (H2S), sulphur dioxide (SO2), Hexamethyldisilazane (HMDS), carbon monoxide (CO) and isooctane, methane (CH4), and nitrogen dioxide (NO2) are shown in the FIG. 8A with different patterns.
The graphical representation 800A includes a first region 802A, a second region 804A, a third region 806A and a fourth region 810A. The first region 802A, corresponds behaviour of the flexible hydrogen detection sensor at 3.23 % of the hydrogen gas. The second region 804A, corresponds behaviour of the flexible hydrogen detection sensor at 2.38 % of the hydrogen gas. The third region 806A, corresponds behaviour of the flexible hydrogen detection sensor at 1.23% of the hydrogen gas. The fourth region 808A, corresponds behaviour of the flexible hydrogen detection sensor at 0.63% of the hydrogen gas.
With reference to FIG. 8B, there is shown a graphical representation 800B illustrating the change in sensitivity of the flexible hydrogen detection sensor (with the molecular sieve coating) before and after exposure to interference gases. The flexible hydrogen detection sensor is subjected to 5 minutes of interference gas flow rate of 4 LPM. The abscissa axis represents the square root (sqrt) of the hydrogen gas concentration expressed in percentage. The ordinate axis represents the ratio of change in the average sensitivity before and after the exposure relative to the initial average sensitivity at a given concentration of the hydrogen gas.
The graphical representation 800B includes a first region 802B, a second region 804B, a third region 806B and a fourth region 810B. The first region 802B, corresponds behaviour of the flexible hydrogen detection sensor at 3.23 % of the hydrogen gas. The second region 804B, corresponds behaviour of the flexible hydrogen detection sensor at 2.38 vol% of the hydrogen gas. The third region 806B, corresponds behaviour of the flexible hydrogen detection sensor at 1.23% of the hydrogen gas. The fourth region 808B, corresponds behaviour of the flexible hydrogen detection sensor at 0.63% of the hydrogen gas. Further, different interference gases, i.e., hydrogen sulphide (H2S), sulphur dioxide (SO2), Hexamethyldisilazane (HMDS), carbon monoxide (CO) and isooctane, methane (CH4), and nitrogen dioxide (NO2) are shown in the FIG. 8A with different patterns.
The flexible hydrogen detection sensor (with the molecular sieve coating) is resistant to gases such as the hydrogen sulphide (H2S), sulphur dioxide (SO2), HMDS, CO, and isooctane for the 1-hour exposure. In the case of the methane (CH4), a slight increase in sensitivity after exposure is observed, while in the case of nitrogen dioxide (NO2) exposure, the sensitivity diminished by more than 20% for the 1-hour exposure.
FIGs. 8C and 8D are graphical representations illustrating the behaviour of the flexible hydrogen detection sensor without the molecular sieve coating on exposure to interference gases, in accordance with an embodiment of the disclosure. FIGs. 8C and 8D are described in conjunction with elements from FIGs. 1 to 8B. With reference to FIG. 8C, there is shown a graphical representation 800C illustrating the change in sensitivity of the flexible hydrogen detection sensor before and after exposure to interference gases. The flexible hydrogen detection sensor is subjected to 1 hour of interference gas flow at a rate of 5.5 LPM. The abscissa axis represents the square root (sqrt) of the hydrogen gas concentration expressed in percentage. The ordinate axis represents the ratio of change in the average sensitivity before and after the exposure relative to the initial average sensitivity at a given concentration of the hydrogen gas. Further different interference gases, i.e., hydrogen sulphide (H2S), sulphur dioxide (SO2), Hexamethyldisilazane (HMDS), carbon monoxide (CO) and isooctane methane (CH4), and nitrogen dioxide (NO2) are represented by the different patterns as shown in the FIG. 8A.
With reference to FIG. 8D, there is shown a graphical representation 800D illustrating the change in sensitivity of the flexible hydrogen detection sensor (without the molecular sieve coating) before and after exposure to interference gases. The flexible hydrogen detection sensor is subjected to 5 minutes of interference gas flow at a rate of 4 LPM. The abscissa axis represents the square root (sqrt) of the hydrogen gas concentration expressed in percentage. The ordinate axis represents the ratio of change in the average sensitivity before and after the exposure to the initial average sensitivity at a given concentration of the hydrogen gas. Further, different interference gases, i.e., hydrogen sulphide (H2S), sulphur dioxide (SO2), Hexamethyldisilazane (HMDS), carbon monoxide (CO) and isooctane, methane (CH4), and nitrogen dioxide (NO2) are represented by the different patterns as shown in the FIG. 8A.
The graphical representation 800D includes a first region 802D, a second region 804D, a third region 806D and a fourth region 810D. The first region 802D, corresponds behaviour of the flexible hydrogen detection sensor at 3.23% of the hydrogen gas. The second region 804D, corresponds behaviour of the flexible hydrogen detection sensor at 2.38 vol% of the hydrogen gas. The third region 806D, corresponds behaviour of the flexible hydrogen detection sensor at 1.23% of the hydrogen gas. The fourth region 808D, corresponds behaviour of the flexible hydrogen detection sensor at 0.63% of the hydrogen gas. Further, different interference gases, i.e., hydrogen sulphide (H2S), sulphur dioxide (SO2), Hexamethyldisilazane (HMDS), carbon monoxide (CO) and isooctane, methane (CH4), and nitrogen dioxide (NO2) are shown in the FIG. 8A with different patterns. The flexible hydrogen detection sensor (without the molecular sieve coating) is also resistant to all the interference gases except the hydrogen sulphide, which resulted in a more than 20% drop in sensitivity after exposure.
FIGs. 9A and 9B are graphical representations illustrating the six-month stability of the flexible hydrogen detection sensor with the molecular sieve coating, in accordance with an embodiment of the present disclosure. FIGs. 9A and 9B are described in conjunction with elements from FIGs. 1 to 9B. With reference to FIG. 9A, there is shown a graphical representation 900A illustrating the comparison between the average sensitivity of the flexible hydrogen detection sensor with the molecular sieve coating, as observed at the beginning versus at the end of the six-month period. The abscissa axis represents the square root of the hydrogen gas concentration expressed in percentage. The ordinate axis represents the average sensitivity expressed in percentage.
The graphical representation 900A includes a first curve 902A, and a second curve 904A. The first curve 902A represents the performance of the flexible hydrogen detection sensor at the beginning of the six-month period, i.e., May month. The second curve 904A represents the performance of the flexible hydrogen detection sensor at the end of the six-month period, i.e., December month.
The first curve 902A shows a steady increase in the sensitivity as hydrogen gas concentration increases. The sensitivity ranges from about 1.7% at the lowest hydrogen gas concentration to 4% at the highest hydrogen gas concentration. The second curve 904A also shows an increasing trend in sensitivity with hydrogen gas concentration. The sensitivity ranges from about 1.8% at the lowest concentration to 4.7% at the highest hydrogen gas concentration. The first curve 902A, and the second curve 904A show similar trends, indicating consistent behaviour of the flexible hydrogen detection sensor over time. The second curve 904A shows slightly higher sensitivity across all hydrogen gas concentrations, suggesting an improvement in the performance of the flexible hydrogen detection sensor over the six-month period. The difference in sensitivity becomes more pronounced at higher hydrogen gas concentrations.
With reference to FIG. 9B, there is shown a graphical representation 900B illustrating the comparison between the average response time of the flexible hydrogen detection sensor with the molecular sieve coating, as observed at the beginning vs at the end of the six-month period. The abscissa axis represents the hydrogen gas concentration expressed in volume percentage. The ordinate axis represents the average response time expressed in seconds.
The graphical representation 900B includes a first curve 902B and a second curve 904B. The first curve 902B, represents the performance of the flexible hydrogen detection sensor at the beginning of the six-month period, i.e., May month. The second curve 904B, represents the performance of the flexible hydrogen detection sensor at the end of the six-month period, i.e., December month. The first curve 902B, shows a decreasing trend in response time as hydrogen gas concentration increases. The response time decreases from about 7.5 seconds at 0.63 % of the hydrogen gas to 3.5 seconds at 3.23 % of the hydrogen gas. The second curve 904B, also shows a general decreasing trend in response time with increasing hydrogen gas concentration. The response time decreases from about 10.5 seconds at 0.63 % of the hydrogen gas concentration to 6 seconds at 3.23 % of the hydrogen gas concentration.
Both the curves, i.e., the first curve 902B and the second curve 904B, show faster response times at higher hydrogen gas concentrations. The second curve 904B, shows consistently longer response times compared to the first curve 902B. The difference in response times is more pronounced at lower hydrogen gas concentrations. The flexible hydrogen detection sensor with the molecular sieve coating maintains its functionality over a six-month period. The sensitivity slightly improves over time, particularly at higher hydrogen gas concentrations. The response time increases over the six-month period, indicating a slight decrease in the speed of response time. The trade-off between improved sensitivity and slightly slower response time suggests some changes in the characteristics over time of the flexible hydrogen detection sensor with the molecular sieve coating, due to ageing effects or environmental factors.
The graphical representation 900A and the graphical representation 900B demonstrate the long-term stability and performance evolution of the flexible hydrogen detection sensor with the molecular sieve coating, which is crucial information for assessing its suitability for practical, long-term hydrogen sensing applications.
FIGs. 9C and 9D are graphical representations illustrating the six-month stability of the flexible hydrogen detection sensor without the molecular sieve coating, in accordance with an embodiment of the present disclosure. FIGs. 9C and 9D are described in conjunction with elements from FIGs. 1 to 9B. With reference to FIG. 9C, there is shown a graphical representation 900C illustrating the comparison between the average sensitivity of the flexible hydrogen detection sensor without the molecular sieve coating, as observed at the beginning versus at the end of the six-month period. The abscissa axis represents the square root of the hydrogen gas concentration expressed in percentage. The ordinate axis represents the average sensitivity expressed in percentage.
The graphical representation 900C includes a first curve 902C and a second curve 904C. The first curve 902C represents the performance of the flexible hydrogen detection sensor at the beginning of the six-month period, i.e., May month. The second curve 904C represents the performance of the flexible hydrogen detection sensor at the end of the six-month period, i.e., December month.
Both the curves, i.e., the first curve 902C and the second curve 904C, show a linear increase in the sensitivity as the hydrogen gas concentration increases. The first curve 902C, and the second curve 904C, are almost overlapping each other, suggesting little change in sensitivity over the six-month period. The sensitivity ranges from about 2% at low hydrogen gas concentrations to about 5.5% at high hydrogen gas concentrations.
With reference to FIG. 9D, there is shown a graphical representation 900D illustrating the comparison between the average response time of the flexible hydrogen detection sensor without the molecular sieve coating, as observed at the beginning versus at the end of the six-month period. The abscissa axis represents the hydrogen gas concentration expressed in volume percentage. The ordinate axis represents the average response time expressed in seconds.
The graphical representation 900D includes a first curve 902D and a second curve 904D. The first curve 902D represents the performance of the flexible hydrogen detection sensor at the beginning of the six-month period, i.e., May month. The second curve 904D represents the performance of the flexible hydrogen detection sensor at the end of the six-month period, i.e., December month.
Both the curves, i.e., the first curve 902D and the second curve 904D, show a general trend of decreasing response time as the hydrogen gas concentration increases. The first curve 902D shows a more pronounced decrease in the response time, especially at higher hydrogen gas concentrations. The second curve 904D shows a slight upturn in the response time at the highest hydrogen concentration.
Overall, the graphical representation 900C and the graphical representation 900D suggest that while the sensitivity of the flexible hydrogen detection sensor without the molecular sieve coating remained stable over the six-month period, but response time characteristics changed with slight variations.
FIGs 10A and 10B are graphical representations illustrating the response of the flexible hydrogen detection sensor with the molecular sieve coating under tension and compression, in accordance with an embodiment of the present disclosure. FIGs. 10A and 10B are described in conjunction with elements from FIGs. 1 to 9D. With reference to FIG. 10A, there is shown a graphical representation 1000A illustrating the comparison between the average sensitivity of the flexible hydrogen detection sensor with the molecular sieve coating under tension and compression. The abscissa axis represents the square root of the hydrogen gas concentration expressed in percentage. The ordinate axis represents the average sensitivity expressed in percentage.
The graphical representation 1000A includes a first curve 1002A, and a second curve 1004A. The first curve 1002A depicts the response of the flexible hydrogen detection sensor with the molecular sieve coating under compression. The second curve 1004A depicts the response of the flexible hydrogen detection sensor with the molecular sieve coating under tension.
Both the curves, i.e., the first curve 1002A and the second curve 1004A, show increasing sensitivity with increasing hydrogen concentration. The second curve 1004A, consistently shows slightly higher sensitivity than the first curve 1002A, across all hydrogen gas concentrations. The sensitivity ranges from about 2% at low hydrogen gas concentrations to about 5-5.5% at high hydrogen gas concentrations. The difference in sensitivity between tension and compression becomes more pronounced at higher hydrogen gas concentrations.
With reference to FIG. 10B, there is shown a graphical representation 1000B illustrating the comparison between the average response time of the flexible hydrogen detection sensor with the molecular sieve coating under tension versus compression. The abscissa axis represents the hydrogen gas concentration expressed in volume percentage. The ordinate axis represents the average response time expressed in seconds.
The graphical representation 1000B includes a first curve 1002B, and a second curve 1004B. The first curve 1002B, depicts the average response time of the flexible hydrogen detection sensor with the molecular sieve coating under compression as a function of hydrogen gas concentration. The second curve 1004B, depicts the average response time of the flexible hydrogen detection sensor with the molecular sieve coating under tension as a function of hydrogen gas concentration.
Both curves, i.e., the first curve 1002B and the second curve 1004B, show a general trend of decreasing response time with increasing hydrogen gas concentration. The second curve 1004B, consistently shows longer average response times as compared to the first curve 1002B. Average response times range from about 18 seconds at low hydrogen gas concentrations to 9-12 seconds at higher hydrogen gas concentrations. The difference in response time between tension and compression is most pronounced at lower hydrogen concentrations and becomes smaller at higher concentrations.
FIGs 10C and 10D are graphical representations illustrating the response of the flexible hydrogen detection sensor without the molecular sieve coating under tension and compression, in accordance with an embodiment of the present disclosure. FIGs. 10C and 10D are described in conjunction with elements from FIGs. 1 to 10B. With reference to FIG. 10C, there is shown a graphical representation 1000C illustrating the response of the flexible hydrogen detection sensor without the molecular sieve coating (with reference to average sensitivity) under tension and compression. The abscissa axis represents the square root of the hydrogen gas concentration expressed in percentage. The ordinate axis represents the average sensitivity expressed in percentage.
The graphical representation 1000C includes a first curve 1002C and a second curve 1004C. The first curve 1002C depicts the response of the flexible hydrogen detection sensor (without the molecular sieve coating) under compression. The second curve 1004C depicts the response time of the flexible hydrogen detection sensor without the molecular sieve coating under tension.
Both the first curve 1002C, and the second curve 1004C show increasing sensitivity with increasing hydrogen concentration. The second curve 1004C shows slightly higher sensitivity than the first curve 1002C, but the difference is less pronounced compared to the flexible hydrogen detection sensor (without the molecular sieve coating). The sensitivity ranges from about 2% at low hydrogen gas concentrations to about 5-5.5% at high hydrogen gas concentrations.
With reference to FIG. 10D, there is shown a graphical representation 1000D illustrating the comparison between the average response time of the flexible hydrogen detection sensor (without the molecular sieve coating) under tension and compression. The abscissa axis represents the hydrogen gas concentration expressed in volume percentage. The ordinate axis represents the average response time expressed in seconds.
The graphical representation 1000D includes a first curve 1002D and a second curve 1004D. The first curve 1002D depicts the average response time of the flexible hydrogen detection sensor (without the molecular sieve coating) under compression as a function of hydrogen gas concentration. The second curve 1004D depicts the average response time of the flexible hydrogen detection sensor (without the molecular sieve coating) under tension as a function of hydrogen gas concentration.
Both the curves, i.e., the first curve 1002D and the second curve 1004D, show a general trend of decreasing average response time with increasing hydrogen gas concentration. The first curve 1002D shows longer response times compared to the second curve 1004D, but the difference is less pronounced than in the flexible hydrogen detection sensor with molecular sieve coating. Response times range from about 14-18 seconds at low concentrations to 9-12 seconds at high hydrogen gas concentrations. The difference in response time between tension and compression is consistent across all hydrogen gas concentrations. The molecular sieve coating does not significantly affect the sensitivity of the first curve 1002D and the second curve 1004D but does impact the response time. The flexible hydrogen detection sensor with and without molecular sieve coating shows higher sensitivity and longer response times under tension compared to compression.
The molecular sieve coating amplifies the differences in average response time between tension and compression, especially at lower hydrogen gas concentrations. Overall, the mechanical strain (tension vs compression) affects the performance of the flexible hydrogen detection sensor, and the molecular sieve coating interacts with mechanical strain, particularly in terms of response time.
FIGs. 11A and 11B are graphical representations illustrating the effect of platinum content on the flexible hydrogen detection sensor having the molecular sieve coating, in accordance with an embodiment of the present disclosure. FIGs 11A and 11B are described in conjunction with elements from the FIGs 1 to 10D. With reference to FIG. 11A, there is shown a response of the flexible hydrogen detection sensor containing 10 mol% of platinum and 90 mol% of the palladium. With reference to FIG. 11A, there is shown a graphical representation 1100A depicting the response of the flexible hydrogen detection sensor when exposed to two different hydrogen gas concentrations, with three cycles for each hydrogen gas concentration. The time is measured in seconds (sec) in an abscissa axis. The sensitivity is expressed in percentage in an ordinate axis.
The graphical representation 1100A includes a region 1102A depicting exposure to 3.25 % of hydrogen gas concentration and a region 1104A depicting exposure to 0.63% of hydrogen gas concentration. For the region 1102A, sensitivity ranges from about -1% to 2%. The region 1102A shows larger amplitude changes compared to region 1104A. The overall trend shows a gradual decrease in baseline sensitivity over time.
With reference to FIG. 11B, there is shown a response of the flexible hydrogen detection sensor containing 5 mol% of platinum and 95 mol% of the palladium. With reference to FIG. 11B, there is shown a graphical representation 1100B depicting the response of the flexible hydrogen detection sensor when exposed to two cycles of different hydrogen gas concentrations. The time is measured in seconds in an abscissa axis. The sensitivity is expressed in percentage in an ordinate axis.
The graphical representation 1100B includes a region 1102B depicting exposure to 3.25 % of hydrogen gas concentration, a region 1104B depicting exposure to 1.27% of hydrogen gas concentration, a region 1106B depicting exposure to 0.63% of hydrogen gas concentration and a region 1108B depicting exposure to 2.42% of hydrogen gas concentration.
The flexible hydrogen detection sensor containing 5 mol% of platinum and 95 mol% of the palladium (represented by FIG. 11B) shows higher sensitivity (larger resistance changes) for both the hydrogen gas concentrations compared to the flexible hydrogen detection sensor containing 10 mol% of platinum and 90 mol% of the palladium (represented by FIG. 11A).
The response time of the flexible hydrogen detection sensor containing 10 mol% of platinum and 90 mol% of palladium has a slightly faster response time than the flexible hydrogen detection sensor with 5 mol% of platinum and 95 mol% of the palladium, but the flexible hydrogen detection sensor with 5 mol% of platinum and 95 mol% of the palladium sensor shows more pronounced changes in sensitivity.
FIGs. 12A and 12B are graphical representations illustrating the limit of detection of the hydrogen gas by flexible hydrogen detection sensor with molecular sieve coating, in accordance with an embodiment of the present disclosure. With reference to FIG. 12A, there is shown a graphical representation 1200A depicting the response curve for exposure of deposition of molecular sieve for two hours. The time is measured in seconds in an abscissa axis. The sensitivity is expressed in percentage in an ordinate axis. The hydrogen concentration peaks at about 0.10%. The response curve is smoother and less reactive.
With reference to FIG. 12B, there are shown two graphical representations a first graphical representation 1200B and a second graphical representation 1202B, when the flexible hydrogen gas detection sensor with molecular sieve coating is exposed to hydrogen gas for forty-five minutes. The time is measured in seconds in an abscissa axis. The sensitivity is expressed in percentage in an ordinate axis. The second graphical representation 1202B depicts multiple cycles are visible, with peaks at 3.26% of hydrogen gas concentration, 1.26% of hydrogen concentration, 0.64% of hydrogen gas concentration, and 2.41% of hydrogen gas concentration. The flexible hydrogen gas detection sensor responds quickly to changes in hydrogen gas concentration, shown by sharp changes in electrical resistance. The second graphical representation 1202B, depicts sensitivity for lower hydrogen gas concentration, i.e. 0.1%.
Overall, the flexible hydrogen detection sensor is responsive to both high and low hydrogen gas concentrations Response is faster and more pronounced for higher concentrations (as shown in 1200B). The flexible hydrogen detection sensor shows good repeatability across multiple cycles. For 45-minute exposure, the molecular sieve coating allows detection of both high hydrogen concentrations (for example, 3.26% of hydrogen gas) and low hydrogen gas concentrations (for example, 0.10% of hydrogen gas).
FIGs. 12C and 12D are graphical representations illustrating the limit of detection of the hydrogen gas by flexible hydrogen detection sensor without the molecular sieve coating, in accordance with an embodiment of the present disclosure. With reference to FIG. 12C, there is shown a graphical representation 1200C depicting response curve. The time is measured in seconds in an abscissa axis. The sensitivity is expressed in percentage in an ordinate axis. The graphical representation 1200C depicts multiple cycles are visible with peaks at 3.28% of hydrogen gas, 1.27% of hydrogen gas, 0.64% of hydrogen gas, and 2.41% of hydrogen gas. Sharp changes in electrical resistance indicate rapid response to changes in hydrogen gas concentration.
With reference to FIG. 12D, there is shown a graphical representation 1200D depicting response curve. The time is measured in seconds in an abscissa axis. The sensitivity is expressed in percentage in an ordinate axis. The graphical representation 1200D depicts sensitivity for lower hydrogen concentration (i.e., 0.10% of hydrogen gas).
The flexible hydrogen detection sensor without molecular sieve coating is highly responsive to both high and low hydrogen gas concentrations. Response amplitude obtained without molecular sieve coating is larger compared to the with molecular sieve coatings. The flexible hydrogen detection sensor without molecular sieve coating shows good repeatability across multiple cycles, and the recovery phases are more pronounced, especially for the low concentrations.
Example 1
An example illustrating the fabrication of the flexible hydrogen detection sensor through a series of steps:
I. Preparing the polyimide-polyester assembly:
Material used: A polyimide tape, transparent polyester sheet, plastic tray, Labolene or any other soap, paperweight.
Steps to prepare polyimide-polyester assembly:
1) Some labolene detergent was put in the plastic tray and then filled with tap water.
2) A piece of polyimide tape was cut and immersed in the tray so that it became completely wet
3) The polyimide tape was removed and laid flat on the polyester sheet. The composite sheet was kept under running tap water to flush out the detergent solution.
4) Since there still was water between the polyimide and the polyester sheet, it was pressed out by moving a paperweight on the polyimide sheet.
5) The composite sheet was covered with tissue paper to absorb any leftover water between the tape and the sheet. Paperweights were kept on top to prevent the tissues from flying off. After overnight drying, the polyimide and polyester composite sheet were ready for further processing.
II. KOH pre-treatment
The polyimide and polyester composite sheet were pre-treated with a solution of KOH in the following manner, as per an adaptation of the procedure:
1) The polyimide was cut into smaller pieces and immersed for 15 minutes in a detergent solution by mixing 825 mg of LaboleneTM in 30 ml of deionized water.
2) The polyimide pieces were removed and washed thoroughly with deionized water to flush out all the detergent solution.
3) 0.5 M KOH solution was prepared by adding 20 ml of deionized water to 560 mg KOH in a petri dish. The polyimide pieces were immersed in this solution and kept for 15 minutes.
4) The polyimide pieces were thoroughly washed with deionized water and then stored in a desiccator for future use.
III. Preparing the aluminium-polyimide assembly
The aluminium tape consisted of aluminium on one side and an adhesive with a paper backing on the other. The backing was removed, and a cello tape was stuck instead. After the aluminium was stuck on the cello-tape, the sides of this assembly were cut with scissors to expose the aluminium edges. The length of the electrically conductive metal nanoparticle deposits predefined depended on the aluminium tape used. So, the assembly was cut further as per a predefined length.
Cutting the aluminium tape involves the following steps:
1. The aluminium tape was placed flat on a rubber mat (for example, AnezusTM self-healing cutting mat, A3 size, PVC, green) and wiped with an ethanol-soaked tissue to clear any dust.
2. A ruler was taken and positioned 1 mm off the aluminium edge.
3. A pen knife was used to gently cut in the direction along the edge using multiple strokes. The ruler was firmly held in place so that it would not move while the penknife was being used along its edge.
4. The pen knife blade was wiped with an ethanol-soaked tissue before use to clear any dust that may have accumulated during storage. A slightly blunt blade was advisable, as brand-new sharp blades tended not to move freely while cutting. Hence, whenever a new blade was fitted in the pen knife, it was used several times on spare aluminium tapes to make it blunt enough for our use.
IV. Aluminium-polyimide assembly:
1. A piece of cello tape was stuck on one end of the strip, and the strip was then placed on polyimide
2. The cello tape was stuck so that it would hold the aluminium strip in place
3. The aluminium strip was then flattened with a roller (in our case, we used the core of a cello-tape roll), and another piece of cello tape was stuck at the other end to yield the aluminium-polyimide assembly
V. Preparing the “inverted assembly” setup:
The procedure for creating the inverter assembly is mentioned below.
1. A double-sided tape was cut into two pieces; each stuck some distance apart. The distance between these pieces was determined by the length of the aluminium-polyimide assembly.
2. The aluminium-polyimide assembly was placed so each end rested on the double-sided tape pieces. It must be noted that the aluminium-polyimide assembly was positioned such that the aluminium tape faced downwards.
3. A precursor solution was prepared:
To prepare 250 mM of palladium chloride (For 1 ml of precursor solution), 0.8 ml of ethanol, 0.2 ml of deionized water, 25 µl of hydrochloric acid and 44 mg of the palladium chloride were mixed, and the palladium chloride solution was left undisturbed overnight in ambient conditions so that pallidum chloride would dissolve completely. To prepare 200 mM of potassium tetrachloroplatinate (for 1 ml of precursor solution), 1 ml of deionized water and 83 mg of potassium tetrachloroplatinate are mixed together to form a potassium tetrachloroplatinate solution. To prepare 4 M potassium bromide, 1 ml of deionized water and 476 mg of potassium bromide were mixed to form a potassium bromide solution. Further, acidic ethanol was obtained by mixing 1 ml of ethanol and 200 µl of hydrochloric acid. The standard precursor solution was obtained by adding 85 µl of palladium chloride solution, 5 µl of potassium tetrachloroplatinate solution, 30 µl of potassium chloride solution, 60 µl of acidic ethanol and 60 µl of deionised water.
4. Once the aluminium-polyimide assembly was affixed to the double-sided tape, a specific volume of the solution was drop-cast right next to the clearance between the aluminium and the base. Due to capillary action, the whole clearance was filled with the precursor solution. After around 4-5 minutes, the reaction between the precursor and the aluminium was completed. The precursor solution was washed away with deionized water. The aluminium polyimide assembly was removed from the double-sided tape, and the aluminium tape was removed from the polyimide-aluminium assembly. The electrically conductive metal nanoparticle deposit obtained on the polyimide was washed by squirting deionized water on it for 5-10 seconds. Subsequently, the polyimide was kept on a Kimwipe to absorb the remaining water from the deposit.
VI. Post Treatment Step:
Once the electrically conductive metal nanoparticle deposit was fabricated, it underwent a “post-treatment” step. Here, fresh precursor solution was dropped on the electrically conductive metal nanoparticle deposit and remained there for typically one minute (unless stated otherwise). The volume of precursor solution was not explicitly estimated here, but the minimum volume that would cover the entire deposit was used. e.g., For the 3 cm long electrically conductive metal nanoparticle deposit, 50 µL of the precursor solution was used for post-treatment.
Upright assembly approach:
1. An aluminium tape with a cello tape backing was stuck on a piece of polyimide.
2. A one-piece “container-frame” was cut from an electrical tape and stuck around the aluminium tape.
3. A specific volume of the same precursor solution was dropped inside the container frame, and the reaction was allowed to proceed for 4-5 minutes. Once the reaction was complete, the precursor was washed away with deionized water. Both the container frame and the residual aluminium tape were removed. The electrically conductive metal nanoparticle deposit was again washed with deionized water, and the excess water was absorbed on a Kimwipe tissue.
By following these steps, the flexible hydrogen detection sensor was fabricated.
Modifications to embodiments of the present disclosure described in the foregoing are possible without departing from the scope of the present disclosure as defined by the accompanying claims. Expressions such as "including", "comprising", "incorporating", "have", "is" used to describe, and claim the present disclosure are intended to be construed in a non-exclusive manner, namely allowing for items, components or elements not explicitly described also to be present. Reference to the singular is also to be construed to relate to the plural. The word "exemplary" is used herein to mean "serving as an example, instance or illustration". Any embodiment described as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments and/or to exclude the incorporation of features from other embodiments. The word "optionally" is used herein to mean "is provided in some embodiments and not provided in other embodiments". It is appreciated that certain features of the present disclosure, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the present disclosure, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable combination or as suitable in any other described embodiment of the disclosure.

, Claims:We claim:
1. A method (100) for fabrication of a flexible hydrogen detection sensor, comprising:
preparing a polyimide-substrate assembly;
pre-treating the polyimide-substrate assembly with an alkaline solution;
creating an aluminium-polyimide assembly by affixing an aluminium tape (204B) to the pre-treated polyimide-substrate assembly;
preparing a precursor solution comprising palladium and platinum compounds;
applying the precursor solution to the aluminium-polyimide assembly (200B), allowing the precursor solution to contact the aluminium tape (204B);
allowing a reaction between the precursor solution and the aluminium tape (204B) to proceed for a first predetermined time period;
removing the precursor solution and separating the aluminium tape (204B) from the polyimide-substrate assembly to reveal an electrically conductive metal nanoparticle deposit on a surface of the polyimide-substrate assembly; and
performing a post-treatment step by applying a fresh batch of the precursor solution to the electrically conductive metal nanoparticle deposit for a second predetermined time period, wherein the electrically conductive metal nanoparticle deposit forms an electrically conductive network on the polyimide-substrate assembly, and wherein the electrically conductive network formed by the electrically conductive metal nanoparticle deposit exhibits a measurable change in electrical resistance upon exposure to hydrogen, said change being correlatable to hydrogen concentration.
2. The method (100) as claimed in claim 1, further comprising washing the electrically conductive metal nanoparticle deposit with deionized water after removing the precursor solution and before performing the post-treatment step.
3. The method (100) as claimed in claim 1, wherein the alkaline solution is a potassium hydroxide solution.
4. The method (100) as claimed in claim 1, wherein the first predetermined time period is between 60 to 1200 seconds.
5. The method (100) as claimed in claim 1, wherein the second predetermined time period is 10 to 1000 seconds.
6. The method (100) as claimed in claim 1, wherein the preparing the polyimide-substrate assembly comprises adhering a polyimide tape (202B) to a polyester sheet (206B).
7. The method (100) as claimed in claim 1, wherein the precursor solution comprises 35.4 volume/volume percentage (%v/v) of palladium chloride and 2.1 %v/v of potassium tetrachloroplatinate.
8. The method (100) as claimed in claim 1, further comprising applying a molecular sieve coating to the electrically conductive metal nanoparticle deposit after the post-treatment step to enhance selectivity for hydrogen detection.
9. The method (100) as claimed in claim 1, wherein the aluminium-polyimide assembly (200B) is placed in an upright orientation with an aluminium side of the aluminium tape (204B) facing downward during the application of the precursor solution.
10. The method (100) as claimed in claim 9, wherein the applying the precursor solution to the aluminium-polyimide assembly (200B) comprises: creating a container-frame (402B) around the aluminium tape on the polyimide-substrate assembly; filling the container-frame (402B) with the precursor solution; and allowing the precursor solution to react with the aluminium tape in the upright orientation.
11. The method (100) as claimed in claim 1, wherein the aluminium-polyimide assembly (200B) is placed in an inverted orientation with an aluminium side of the aluminium tape (204B) facing upward during the application of the precursor solution.
12. The method (100) as claimed in claim 11, wherein the applying the precursor solution to the aluminium-polyimide assembly (200B) comprises: securing the aluminium-polyimide assembly (200B) in an inverted orientation with the aluminium side of the aluminium tape (204B) facing upward; creating the clearance (304) between the aluminium tape and the supporting surface; applying the precursor solution to fill the clearance (304); and allowing the precursor solution to react with the aluminium tape in the inverted orientation.
13. The method (100) as claimed in claim 1, further comprising attaching electrical contacts to the electrically conductive metal nanoparticle deposit for measuring the change in electrical resistance.
14. The method (100) as claimed in claim 1, wherein the concentration of the precursor solution used in the post-treatment step is the same as the concentration used when initially applying the precursor solution to the aluminium-polyimide assembly (200B).
15. The method (100) as claimed in claim 1, wherein the volume of precursor solution applied is proportional to the length of the aluminium tape used in the aluminium-polyimide assembly (200B).