Description:FIELD OF THE INVENTION
The present disclosure pertains to the field of relates to hydrogen gas and oxygen gas generation device. In particular, the invention relates to a device and method for continuous in situ separation of hydrogen and oxygen from water.

BACKGROUND OF THE INVENTION
Hydrogen energy is now more practical thanks to recent technological advances. As sustainable energy, it has potential applications in construction, transportation, mobile devices, automobiles, and even space travel. It is a chemical that is used in the making of ammonia, methanol, and gasoline. Green H2 produced using water electrolysis is a promising and practical option for meeting the world's growing energy demand. Hydrogen can be produced from diverse domestic resources with the potential for near-zero greenhouse gas emissions. Once produced, hydrogen generates electrical power in a fuel cell, emitting only water vapor and warm air. It holds promise for growth in both the stationary and transportation energy sectors. Throughout the world, hydrogen is used widely in petroleum refining, chemical synthesis, and metal refining, and in recent years it can be used in many fields such as in hydrogen stations for fuel cell vehicles and hydrogen power plants.
Methods of producing hydrogen can be primarily divided into those using fossil fuels as raw materials and those through decomposition of water (water electrolysis). Of these, water electrolysis is regarded as one of the most promising because of no unwanted emissions, large-scale availability, and inexpensiveness. Industrially, gases such as oxygen and hydrogen are generated by disassociating a chemical compound into its constituent elements. Conventionally, several devices utilize electrolytic cells for disassociating such compounds and generating gas. Such electrolytic cells take a variety of forms, but generally include a catalytic anode, a catalytic cathode and an adjacent electrolyte which is in electrical contact with both the anode and the cathode. A voltage is applied across the catalytic electrodes to drive the reaction. When reactants contact an electrode, they are dissociated into their constituent ionic forms, and the evolved gas is collected.
U.S. Patent No. 3870616, describes a hydrogen generator having a main water tank supplying water to the anode of an electrolytic cell for dissociation. However, not all the water supplied to the anode is dissociated. In fact, the bulk of the water supplied to the anode is transported with the dissociated hydrogen ions across the ion-exchange membrane into the cathode chamber. Part of this water returns to the anode chamber by diffusion back across the ion-exchange membrane; however, when gas is being actively generated, the rate of protonic pumping by the hydrogen ions is much greater than the diffusion rate of the water back across the membrane so that eventually a build-up of water takes place in a accumulator chamber disposed above the cathode chamber. Whenever the water in the accumulator chamber rises above a predetermined level, a solenoid valve is closed to shut off the water supply from the main tank to the anode chamber. In order to continue the reaction, and the production of gas, water must be supplied to the anode. However, the only water supplied to the anode chamber comes from the diffusion of water from the cathode chamber back across the ion-exchange membrane. During this period, the dissociation of the water is rate limited by the rate of water diffusing lack across the membrane.
The development of a micro channel embedded water electrolyzer (MEWE) was prompted by the need for economically viable production of green H2. Conventional water electrolyzers are heavy, expensive, and have enormous losses, limiting scalability. The present invention focuses on fabricating the MEWE by 3D printing which is inexpensive, user-friendly, efficient, with minimal losses, and highly scalable. The current density was directly proportional to channel width and electrolyte flow rate. The MEWE produced 34 mL/hour of hydrogen and 17 mL/hour of oxygen at a voltage of 2.5 volts. In addition, a stack was constructed and demonstrated a stacking efficiency of 95%.

SUMMARY OF THE INVENTION
Accordingly, the present invention in one aspect provides a water-splitting device (100) for continuous in situ separation of hydrogen and oxygen from water. The device comprises at least one micro channel embedded micro fluidic reactor, a housing with at least one electricity source, a reservoir for storing electrolytes, at least one pair of electrodes and at least 2 in situ separate transport channels. The at least one micro channel embedded micro fluidic reactor comprises a water inlet at one end and a product outlet at the other end. Further, the at least one pair of electrodes, constitutes an anode and a cathode, operatively connected to the at least one electricity source. The electrodes comprise at least one operative end and are positioned within the embedded micro channel in fluidic communication with water to attain pre-determined electric field thereby generating oxygen and hydrogen via electrolysis of the water. The device also comprises at least 2 in situ separate transport channels for transporting generated oxygen to a first outlet (11) and a second fluidic transport channel for transporting generated hydrogen to a second outlet (10) such that the at least 2 in situ separate transport channels prevent any mixing of the generated oxygen and the generated hydrogen.

BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated in and constitute a part of this disclosure, illustrate exemplary embodiments and, together with the description, serve to explain the disclosed principles:
FIG.1 illustrates an exemplary schematic diagram of the serpentine micro channels embedded in the cell with a Channel Width of 0.46 mm, in accordance with some embodiments of the present disclosure.
FIG.2 illustrates an exemplary schematic diagram for the assembly of micro channel embedded water electrolyzer (MEWE), in accordance with some embodiments of the present disclosure.
FIG.3 illustrates an exemplary schematic diagram for the assembly of micro channel embedded water electrolyzer (MEWE) stack, in accordance with some embodiments of the present disclosure.
FIG.4a and FIG. 4b. illustrates the linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) of 3D Printed MEWE at 5 different flow rates, in accordance with some embodiments of the present disclosure.
FIG.5 illustrates the LSV of MEWE and Conventional electrolyser at flow rate of 2 ml min-1, in accordance with some embodiments of the present disclosure.
FIG.6 illustrates the chronoamperometry of MEWE at 2.5 Volts and a flow rate of 2 ml min-1 for 24 hours, in accordance with some embodiments of the present disclosure.
FIG.7 illustrates the relation between no. of cells with current /density and stacking efficiency of MEWE Stack, in accordance with some embodiments of the present disclosure.
DETAILED DESCRIPTION OF THE INVENTION
The following is a detailed description of embodiments of the present disclosure. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
Unless the context requires otherwise, throughout the specification which follow, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense that is as “including, but not limited to.”
Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.
As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
In some embodiments, the numbers expressing quantities of ingredients, properties such as concentration, and so forth, used to describe and claim certain embodiments of the invention are to be understood as being modified in some instances by the term “about.” Accordingly, in some embodiments, the numerical parameters set forth in the written description are approximations that can vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable.
The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein.
All methods described herein can be performed in suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.
The headings and abstract of the invention provided herein are for convenience only and do not interpret the scope or meaning of the embodiments.
Various terms are used herein. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.
The present invention discloses a device and a method for continuous in situ separation of hydrogen and oxygen from water. In one aspect of the present invention, disclosed is a device for continuous in situ separation of hydrogen and oxygen from water. The device is a water-spitting device. Figure 2 is a preferred embodiment of the present invention illustrating the schematic diagram for the assembly of micro channel embedded water electrolyzer (MEWE), in accordance with some embodiments of the present disclosure. In accordance with Figure 1, the water-splitting device (100) for continuous in situ separation of hydrogen and oxygen from water comprises at least one micro channel embedded micro fluidic reactor, a housing with at least one electricity source, a reservoir for storing electrolytes, at least one pair of electrodes and at least 2 in situ separate transport channels. The at least one micro channel embedded micro fluidic reactor comprises a water inlet at one end and a product outlet at the other end. Further, the at least one pair of electrodes, constitutes an anode and a cathode, operatively connected to the at least one electricity source. The electrodes comprise at least one operative end and are positioned within the embedded micro channel in fluidic communication with water to attain pre-determined electric field thereby generating oxygen and hydrogen via electrolysis of the water. The device also comprises at least two in situ separate transport channels for transporting generated oxygen to a first outlet (11) and a second fluidic transport channel for transporting generated hydrogen to a second outlet (10) such that the at least two in situ separate transport channels prevent any mixing of the generated oxygen and the generated hydrogen. All the components of the water-splitting device are housed in an enclosure (not shown in the figure).
Typically, in an exemplary embodiment, the cell has an overall size of 55 mm x 55 mm x 6 mm, and an area measuring 25 mm x 25 mm has micro channels embedded in it. Inlets and outlets that measured 3.54 mm in diameter controlled the electrolyte flow through the MEWE. Micro channels were engraved to a depth of 1 mm, the width of the channels was 0.47 mm. The active area of the MEWE was 6.25 cm2. To make the assembly of each cell easier, eight screw holes measuring 3 mm in diameter were made into each cell.
In an embodiment of the present invention, the micro channel embedded micro fluidic reactor causes the electrolyte to flow in the micro channels to adhere to a laminar regime thereby providing more control over the flow.
In a preferred embodiment of the present invention, the micro channels are serpentine.
In another embodiment of the present invention, the micro channel embedded micro fluidic reactor provides a narrow residence-time distribution and an increase in heat and mass transport thereby enhancing electrolyte flow through the electrodes and providing a wide surface area for the reaction.
Typically, the micro channel embedded micro fluidic reactor is positioned downstream of the reservoir.
In yet another embodiment of the present invention, the product outlet separately receives any secondary product produced during water-splitting.
The water-splitting device (100), further comprises a renewable electricity generating source disposed over the micro fluidic reactor and having electrical connectivity with the anode and the cathode of the micro fluidic reactor. Typically, the at least one electricity source is selected from solar panels and proton exchange membrane (PEM) electrolysis. Typically, the anode is a porous nickel foam treated first with 1M hydrochloric acid followed with isopropyl alcohol and the cathode is a platinum sputtered nickel foam such that a sacrificial layer of titanium with a pre-determined thickness is sputtered followed by platinum.
In an exemplary embodiment of the present invention, a solar panel is positioned over the enclosure. The solar panel generates electricity which create high intensity electric field inside the micro channel embedded micro fluidic reactors though the anode and the cathode assembly.
In another preferred embodiment of the present invention, the device comprises a stack of micro channel embedded micro fluidic reactors connected in series with respective water inlet at one end and respective product outlet at the other end.
In an exemplary embodiment of the present invention, the MEWE is 3D printed and the micro fluidic channels are etched on the electrodes with much better details. The MEWE comprises an electrolyte inlet micro channel and a gas product exit micro channel. The micro channel surrounds the electrodes, providing a large surface area-to-volume ratio for rapid electrochemical reactions. The electrodes are sandwiched between the flow plates embedded with the micro channel, which is supplied with electrolytes. When a voltage is applied, gas products form on the electrode surface and cause a two-phase flow in the micro channel. Micro fluidic electrolyzers do not use membranes, and instead, achieve gas product separation in the micro channel by generating a regulated electrolyte flow. This 3D printing and embedding the channels in the cell up to the micro fluidic details, improved the cell's performance, and the 3D-printed electrodes reduced the cell's ohmic losses. The current density generated was approximately eight times greater than the conventional water electrolyzer. The scalability of the 3D-printed micro fluidic device was depicted by preparing a stack resulting in 95% stack efficiency. In another exemplary embodiment of the present invention, the 3D model of the MEWE was prepared using Free CAD (version 0.19 ). The designs were then exported in the STL format to the Preform Software (version- 3.24.2), which is a powerful and flexible slicing software for Formlabs 3D printers. The appropriate orientation was determined with the help of the Preform software, and support structures were included in the design so that it could be successfully printed. After that, the designs were sent to the Formlabs Form 3 Printer for printing. The prints were constructed one layer at a time by the Formlabs printer using a technique called low-force stereolithography. To print the devices, a transparent v4 resin was purchased and used. The 3D model of the MEWE was printed at a speed of 100 microns per layer. The flow channels were 1mm deep and had a width of 0.47mm. According to the calculations, the area of the cell that is electrochemically active is 6.25 cm2.
In yet another embodiment of the present invention, the MEWE was assembled from two 3D printed parts encompassing the micro channels, a Pt-sputtered Ni foam that served as the cathode [8], and a nickel foam that served as the anode [6], as depicted in Figure 2. Two gaskets [5] measuring 35 mm x 35 mm, each having a cut-out of 25 mm x 25 mm in the center was used to help prevent leaking. For ion separation, a Nafion 117 membrane [7] was used (35 mm x 35 mm). The MEWE was assembled by tightening it with 3mm screws and bolts. The connection between the electrodes and the Potentiostat was accomplished by using titanium wires and a Biologic SP 150 Potentiostat was employed for taking the readings. The electrolyte consisted of a 30 wt% solution of KOH. Peristaltic pumps were used to pump the electrolyte through the device at different flow rates.
The results of linear sweep voltammetry (LSV) conducted in the voltage range 0 to 4 V on the MEWE at five different flow rates are depicted in Figure 4a. It is evident that, for a given voltage, the current density increases with the flow rate. For the MEWE, the current density at 4 volts was 72.51 mA/cm2, 75.92 mA/cm2, 80.447 mA/cm2, 83.88 mA/cm2, and 90.559 mA/cm2 for flow rates of 0.1 mL/min, 0.25 mL/min 0.5 mL/min, 1 mL/min, and 2 mL/min, respectively. It could be observed that the current density increases as the flow rate increases. The MEWE was subjected to galvanostatic electrochemical impedance spectroscopy (GEIS) at five different flow rates and a current of 50 mA. Comparing the EIS plots of the MEWE at five different flow rates, as shown in Fig 4b, the x-intercept of the curve reveals the ohmic resistance. It is evident from the graph that the x-intercept of the curve decreases as flow rates increase. Hence the Ohmic resistance of the MEWE comes out to be 4.45 O, 4.17O, 4.09O, 4.01O, 3.92O at the flow rates of 0.1 mL/min, 0.25 mL/min, 0.5 mL/min, 1 mL/min and 2 mL/min, respectively. Also, the charge transfer resistance for the MEWE which is the resistance against the process of electron transfer from one phase to another comes out to be 1.616O, 1.527O, 1.504O, 1.501O, and 1.34O at the flow rates of 0.1 mL/min, 0.25 mL/min, 0.5 mL/min, 1 mL/min and 2 mL/min, respectively. It was observed that the ohmic resistance and the charge transfer resistance of the MEWE reduce as the flow rate increases.
It is evident from Figure 4 that in the MEWE, when the electrolyte flow rate increases, the current density increases, and the resistance decreases. Huge ohmic losses through the gold plates were a shortcoming of the conventional micro fluidic system, which may be resolved by boosting the flow rates to the ideal levels.
MEWE's increased current density and lower ohmic and charge transfer resistance may be due to the following factors:(i) as a result of the increased mass transfer - as the flow rate is greater, more mass passes through the electrolyzer per unit of time, resulting in a greater current density. (ii) As a result of the pressure caused by the rapid flow rate, the bubbles on the catalyst detach extremely quickly, providing a new surface for the electrolyte to react with. At low flow rates, these bubbles become entrapped on the catalyst, resulting in a reduction in the electrochemically active surface.
Since it is obvious that the MEWE operate more efficiently at higher flow rates, as this increases their current density and decreases their ohmic resistances, higher flow rates should be preferred.
The Conventional electrolyser and the MEWE were both operated at a flow rate of 2 ml min-1, and their performance was evaluated. Figure 5 compares the Current densities of the MEWE and the conventional electrolyser when operated at a Flow rate of 2 ml min-1. The conventional electrolyser exhibited a current density of 11.95 mA cm-2 at 4 Volts, whereas the MEWE exhibited a current density of 90.55 mA cm-2 at the same voltage, which is approximately eight times that of the conventional electrolyser. The low current density and higher ohmic resistance in the conventional electrolyzer may be attributed to the Graphite plates used in conventional cells, which generate enormous losses, resulting in a fall in current density and an increase in ohmic resistance. In addition, the difference in current density and ohmic resistance between the MEWE and conventional electrolyzer may be due to the superior flow dispersion of the MEWE. In addition, since the MEWE was 3D printed using resins and we employed titanium wires for the connections, they exhibit far lower ohmic losses than the conventional electrolyzer, which employs graphite for its connections.
The Chronoamperometry of MEWE (depicted in Fig 6) was carried out for 24 h at a voltage of 2.5 volts, and the results showed that the device remained stable throughout the entire experiment. Throughout the course of the test, the device produced a current with a nearly constant value of 80 mA/cm2. The overall area of the graph depicting current density vs time is calculated to be nearly 7100 C. The device generated an average of 34 mL/h of hydrogen and 17 mL/h of oxygen. The apparatus was shown to be very reliable and effective in its operation.
A stack of the MEWE was created, and then water electrolysis was carried out on the Stack in the same manner as performed previously on the MEWE. It was determined through testing that the stack had an efficiency of 95%, 94%, 93%, and 90%, as well as a current density of 258 mA/cm2, 343 mA/cm2, 510 mA/cm2, and 980 mA/cm2 for stacks containing 3, 4, 6, and 2 cells, respectively (depicted in Figure 7).
The functionality of the MEWE that was manufactured using 3D printing was demonstrated. The MEWE performed PEM water electrolysis using Ni Foam as the anode and a Pt-sputtered cathode, with no electrolyte flow on the cathode side. The performance of the micro fluidic device that was manufactured using a 3D printer was significantly higher than that of the conventional electrolyzer that is utilized in the laboratory. When operating at a flow rate of 2 ml min-1 and 4 volts, the MEWE demonstrated a current density of 90.55 mA cm-2, which was about eight times that of a conventional electrolyzer. The laboratory-produced MEWE proved to be very stable and efficient in producing hydrogen via the electrolysis of water. A stack of MEWE was created. Testing of the stack proved that the MEWE is extremely scalable and efficient at high voltage. At 4 volts, a stack of 3 MEWEs exhibited an efficiency of 95% and a current density of 258 mA cm-2.
While the foregoing description discloses various embodiments of the disclosure, other and further embodiments of the invention may be devised without departing from the basic scope of the disclosure. , Claims:WE CLAIM:

1.) A water-splitting device (100) for continuous in situ separation of hydrogen and oxygen from water, said device comprising:
- at least one micro channel embedded micro fluidic reactor comprising a water inlet at one end and a product outlet at the other end;
- a housing with at least one electricity source;
- a reservoir for storing electrolytes;
- at least one pair of electrodes, constituting an anode and a cathode, operatively connected to said at least one electricity source;
wherein said electrodes comprise at least one operative end and positioned within said embedded micro channel in fluidic communication with water to attain pre-determined electric field thereby generating oxygen and hydrogen via electrolysis of the water; and
- at least 2 in situ separate transport channels for transporting generated oxygen to a first outlet (11) and a second fluidic transport channel for transporting generated hydrogen to a second outlet (10);
wherein said at least 2 in situ separate transport channels prevent any mixing of said generated oxygen and said generated hydrogen.

2.) The water-splitting device (100) as claimed in claim 1, wherein said micro channel embedded micro fluidic reactor causes said electrolyte to flowing in said micro channels to adhere to a laminar regime thereby providing more control over the flow.
3.) The water-splitting device (100) as claimed in claim 1, wherein said micro channels are serpentine.
4.) The water-splitting device (100) as claimed in claim 1, wherein said micro channel embedded micro fluidic reactor provides a narrow residence-time distribution and an increase in heat and mass transport thereby enhancing electrolyte flow through the electrodes and providing a wide surface area for the reaction.
5.) The water-splitting device (100) as claimed in claim 1, wherein said micro channel embedded micro fluidic reactor is positioned downstream of said reservoir.
6.) The water-splitting device (100) as claimed in claim 1, wherein said product outlet separately receives any secondary product produced during water-splitting.
7.) The water-splitting device (100) as claimed in claim 1, further comprising a renewable electricity generating source disposed over said micro fluidic reactor and having electrical connectivity with said anode and said cathode of said micro fluidic reactor.
8.) The water-splitting device (100) as claimed in claim 1, wherein said at least one electricity source is selected from solar panels and proton exchange membrane (PEM) electrolysis.
9.) The water-splitting device (100) as claimed in claim 1, wherein said anode is a porous nickel foam treated first with 1M hydrochloric acid followed with isopropyl alcohol.
10.) The water-splitting device (100) as claimed in claim 1, wherein said cathode is a platinum sputtered nickel foam;
wherein a sacrificial layer of titanium with a pre-determined thickness is sputtered followed by platinum.

11.) The water-splitting device (100) as claimed in claim 1, wherein said device comprises a stack of micro channel embedded micro fluidic reactors connected in series with respective water inlet at one end and respective product outlet at the other end.