Field of the invention:

[0001] The present disclosure generally relates to a process or method for fabrication of a suitable electrode for supercapacitors, and in specific, relates to the preparation of binder-free 3D-carbon doped metal nitride porous architecture via vapour phase growth method over various 3D-conducting networks.
Background of the invention:
[0002] Among the energy storage devices, supercapacitors are considered to be very attractive energy storage systems for their high electrochemical performances, such as higher power density than batteries and higher energy density than conventional dielectric capacitors. Therefore, great attention is focused on the development of supercapacitors with high performances.

[0003] The preparation of the electrode material is the fundamental component for energy storage devices, as it determines the electrochemical performance. Various materials such as carbon materials, metal oxides, and conducting polymers have been widely used as electrode materials for energy storage devices.

[0004] Each electrode materials have its own merits and demerits in energy storage application. For example, porous carbon has a higher specific surface area and good conductivity and structural stability. However, it shows low discharge capacity. Metal oxides and conducting polymer-based electrode material price are cheaper and have high specific capacitance, but their structural stability and cyclic stability are poor.

[0005] The use of metal nitrides/sulphides/phosphides as electrode materials for supercapacitors has attracted a lot of interest due to their outstanding electrochemical properties, high structural stability, and standard technological approach fundamental importance. The metal nitrides/sulphides/phosphides are prepared via a two-step process such as chemical process followed by nitridation, sulfurization (oxide formation then nitride conversion) or phosphorization, which is a time-consuming process and the structure obtained from a chemical method is not stable.

[0006] However, current existing materials used for the fabrication of negative electrodes for supercapacitors are quite limited and most of them are confined to carbon-based materials. A carbon-based negative electrode material exhibits poor specific capacitance and energy density values. In earlier research, iron nitride is used as a negative electrode for supercapacitor, which includes deposition of iron nitride over metal substrates using iron chloride by placing metal substrates over a boat containing iron chloride under ammonia (NH3) gas and hydrogen (H2) gas. Herein, the use of two different types of gases adds extra cost to the experiment.

[0007] Recently, some novel materials like metal-organic frameworks (MOFs) and MXenes are being used to fabricate negative electrodes for supercapacitor. However, they need sophisticated reaction conditions and expensive chemicals. Most of the accomplished research based on negative electrodes for supercapacitors is comprised of the binder method. These binders add extra weight, non-conducting nature, and increases the size of the device.

[0008] Therefore, there is a need for a method for fabricating a suitable negative electrode for supercapacitors. Further, need for a method for the synthesis of binder-free 3D-carbon doped metal nitride, metal sulphide and metal phosphide porous architecture as electrodes for supercapacitor is required. Further, also there is a need for a method that reduces time and cost for fabricating electrodes for supercapacitors.
Objectives of the invention:
[0009] The primary objective of the invention is to develop a method for the synthesis of binder-free 3D-carbon doped metal nitride porous architecture electrodes for supercapacitors and thereof.

[0010] Another objective of the invention is to develop a metal nitride electrode using a mixture of metal chloride (metal precursor) and melamine (active precursor) in a single ceramic boat.

[0011] Another objective of the invention is introducing an interfacial layer between metal nitride and a 3D-conducting network in the 3D-carbon doped metal nitride porous architecture electrode.

[0012] Another objective of the invention is to develop a metal sulphide electrode using a mixture of metal chloride (metal precursor) and thiourea (active precursor) in a single ceramic boat.

[0013] Another objective of the invention is to develop metal phosphide electrode using a mixture of metal chloride (metal precursor) and sodium hypophosphite (active precursor) in a single ceramic boat.

[0014] Another objective of the invention is to provide a method for synthesizing binder-free 3D-carbon doped metal nitride porous architecture on various 3D-conductive network electrodes (Ni, NiCu, NiCo and thereof) via vapour phase growth method for supercapacitor.

[0015] Another objective of the invention is to provide a binder-free 3D-carbon doped iron nitride porous architecture that efficiently produces electrodes utilizing 3D-metal networks on various current collectors (Cu, SS, Ti and thereof).

[0016] Another objective of the invention is to develop various negative electrode materials using a simple method of synthesis.

[0017] Another objective of the invention is to develop various positive electrode materials by using the same method of synthesis as for the negative one.

[0018] Another objective of the invention is to develop a binder-free electrode, and thereby to avoid the usage of binder and additives for electrode preparation.

[0019] Another objective of the invention is to develop a 3D-porous architecture with appreciable electrical conductivity, high surface area, ample porosity and good stability.

[0020] Another objective of the invention is to utilize inert atmosphere (N2 or Ar) throughout the method as a carrier gas to avoid the oxidization of the 3D-metal networks.

[0021] Yet another objective of the invention is to provide a method that reduces time and cost for fabricating an electrode for supercapacitors.

[0022] Another objective of the invention is to design the binder-free 3D-porous architecture electrodes via vapour phase growth.

[0023] Yet another objective of the invention is to utilize moderate operating temperature to avoid high temperature sophisticated experimental conditions.

[0024] Another objective of the invention is to designed electrodes that are binder-free and eliminates the usage of binder and conductive additives.
Summary of the invention:
[0025] The present disclosure proposes a method for vapour phase growth of binder-free 3D-carbon doped metal nitride porous architecture electrode for supercapacitor and thereof. The following presents a simplified summary in order to provide a basic understanding of some aspects of the claimed subject matter. This summary is not an extensive overview. It is not intended to identify key/critical elements or to delineate the scope of the claimed subject matter. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is presented later.

[0026] In order to overcome the above deficiencies of the prior art, the present disclosure is to solve the technical problem to provide a preparation method of electrode material in vapour phase growth binder-free 3D-carbon doped metal nitride porous architecture over various 3D-conducting networks.

[0027] According to an aspect, the invention provides a method for synthesis of vapour phase growth of binder-free 3D carbon-doped metal nitride porous architecture electrode for supercapacitor. First, 3D-porous conductive network is prepared via dynamic hydrogen bubble template method. Then, a calculated amount of metal precursor is kept inside a mortar and heated at 120°C for 30 minutes, and then the metal precursor is taken out from oven. Next, a calculated amount of active precursor is added in the metal precursor and a mixture of the metal precursor and the active precursor is prepared using the mortar and pestle. In specific, the mixture of metal precursor and active precursor is prepared considering their mass ratio as 4:1 and then, the mixture is transferred into a first ceramic boat. Further, the 3D-porous conductive network is placed inside a second ceramic boat.

[0028] Next, the first ceramic boat and the second ceramic boat are placed at the upstream and downstream of a single heating zone tubular furnace, respectively. Both the ceramic boats are subjected to heating at 550 to 600 °C for 1 hour at a ramping rate of 10°C per minute in the single heating zone tubular furnace. The heating of the first and the second ceramic boats is done simultaneously under an inert (N2 or Ar gas) atmosphere to obtain 3D-carbon doped metal nitride porous architecture over 3D-metal networks. Finally, both the ceramic boats are allowed to cool down to room temperature to obtain the binder free 3D-carbon doped metal nitride porous architecture over a 3D-metal network for supercapacitor.

[0029] Further, to introduce an interfacial layer between metal nitride and 3D-conducting networks, following steps are followed. First, the 3D-porous conducting network is +immersed in a solution of 20 ml tri-ethylene glycol (TEG) and 75µL of 0.35M NaOH for 12 hours at 180°C. Later, the 3D-porous conducting network is taken out of the solution and dried at 120°C for 30 minutes to obtain dried 3D-porous conducting network. Consequently, the above mentioned procedure is followed to introduce an interfacial layer between metal nitride and 3D-conducting networks and to form an interfacial layer between metal nitride and 3D-conducting networks.

[0030] The vapour phase growth method is used to design multiple types of electrodes such as metal nitride, metal sulphide, and metal phosphide and thereof. The active precursors include melamine, thiourea, sodium hypophosphite, cellulose and thereof. Further, the 3D-conducting network includes 3D-Ni, 3D-NiCu, 3D-NiCo, and thereof that are prepared using dynamic hydrogen bubble template method. The 3D-conducting networks is deposited on multiple metal substrates of Cu, Ti, stainless steel (SS) sheets and thereof. The metal porous architecture electrode includes metal nitride, metal sulphide, metal phosphide and thereof. The designed electrodes are binder-free and thereby eliminate the usage of binder and conductive additives.

[0031] Further, objects and advantages of the present invention will be apparent from a study of the following portion of the specification, the claims, and the attached drawings.
Detailed description of drawings:
[0032] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention and, together with the description, explain the principles of the invention.

[0033] FIG. 1 illustrates a schematic diagram of method for vapour phase growth of binder-free 3D-carbon doped metal nitride porous architecture electrode for supercapacitor and thereof in accordance with an exemplary embodiment of the invention.

[0034] FIG. 2 illustrates a method for vapour phase growth of binder-free 3D-carbon doped metal nitride porous architecture electrode for supercapacitor and thereof in accordance with an exemplary embodiment of the invention.

[0035] FIG. 3A illustrates a XRD pattern of 3D-carbon doped iron nitride coated over 3D-NiCo conducting network on SS substrate (3D Fe4N-C@NiCo/SS) and 3D-carbon doped iron nitride coated over 3D Ni conducting network on SS substrate (3D Fe4N-C@Ni/SS) electrodes in accordance with an exemplary embodiment of the invention.

[0036] FIG. 3B illustrates a XRD pattern of 3D-carbon doped iron nitride coated over 3D-NiCu conducting network on Cu substrate (3D Fe4N-C@NiCu/Cu) electrode in accordance with an exemplary embodiment of the invention.

[0037] FIG. 3C illustrates a XRD pattern of 3D-carbon doped iron nitride coated over 3D-NiCu conducting network on SS substrate (3D Fe4N-C@NiCu/SS) electrode in accordance with an exemplary embodiment of the invention.

[0038] FIG. 3D illustrates a XRD pattern of 3D-carbon doped iron nitride coated over 3D-NiCu conducting network on Ti substrate (3D Fe4N-C@NiCu/Ti) electrode in accordance with an exemplary embodiment of the invention.

[0039] FIG. 3E illustrates a XRD pattern of 3D-carbon doped iron sulphide coated over 3D-NiCo conducting network on SS substrate (3D Fe3S4-C@NiCo/SS) and 3D-carbon doped iron sulphide coated over 3D-Ni conducting network on SS substrate (3D Fe3S4-C@Ni/SS) electrode in accordance with an exemplary embodiment of the invention.

[0040] FIG. 4A depicts Raman spectroscopy of 3D-carbon doped iron nitride coated over 3D-Ni conducting network on SS substrate (3D Fe4N-C@Ni/SS) electrode in accordance with an exemplary embodiment of the invention.

[0041] FIG. 4B depicts Raman spectroscopy of 3D-carbon doped iron nitride coated over 3D-NiCu conducting network on Cu substrate (3D Fe4N-C@NiCu/Cu)electrode in accordance with an exemplary embodiment of the invention.

[0042] FIG. 4C depicts Raman spectroscopy of 3D-carbon doped iron nitride coated over 3D-NiCu conducting network on SS substrate (3D Fe4N-C@NiCu/SS) electrode in accordance with an exemplary embodiment of the invention.

[0043] FIG. 4D depicts Raman spectroscopy of 3D-carbon doped iron nitride coated over 3D-NiCu conducting network on Ti substrate (3D Fe4N-C@NiCu/Ti) electrode in accordance with an exemplary embodiment of the invention.

[0044] FIG. 5 depicts field emission scanning electron microscopy (FESEM) micrographs of all the prepared electrodes in accordance with an exemplary embodiment of the invention.

[0045] FIG. 6A depicts energy dispersive X-ray (EDX) spectrum of 3D-carbon doped iron nitride coated over 3D-Ni conducting network on SS substrate (3D Fe4N-C@Ni/SS) electrode in accordance with an exemplary embodiment of the invention.

[0046] FIG. 6B depicts the energy dispersive X-ray (EDX) spectrum of 3D-carbon doped iron sulphide coated over the 3D-NiCo conducting network on the SS substrate (3D Fe3S4-C@NiCo/SS) electrode in accordance with an exemplary embodiment of the invention.

[0047] FIG. 7A depicts cyclic voltammetry (CV) curve of 3D-carbon doped iron nitride coated over 3D-Ni conducting network on SS substrate (3D Fe4N-C@Ni/SS) and 3D-carbon doped iron nitride coated over 3D-NiCo conducting network on SS substrate (3D Fe4N-C@NiCo/SS) electrodes at a scan rate of 50 mV s-1 in accordance with an exemplary embodiment of the invention.

[0048] FIG. 7B depicts galvanostatic charge-discharge (GDC) curve of 3D-carbon doped iron nitride coated over 3D-Ni conducting network on SS substrate (3D Fe4N-C@Ni/SS) and 3D-carbon doped iron nitride coated over 3D-NiCo conducting network on SS substrate (3D Fe4N-C@NiCo/SS electrodes at 1 A g-1 current density in accordance with an exemplary embodiment of the invention.

[0049] FIG. 7C depicts specific capacitance of 3D-carbon doped iron nitride coated over 3D-Ni conducting network on SS substrate (3D Fe4N-C@Ni/SS) and 3D-carbon doped iron nitride coated over 3D-NiCo conducting network on SS substrate (3D Fe4N-C@NiCo/SS) electrodes at 1 A g-1 current density in accordance with an exemplary embodiment of the invention.

[0050] FIG. 7D depicts cyclic voltammetry (CV) curve for 3D-carbon doped iron nitride coated over 3D-NiCu conducting network on Cu substrate (3D Fe4N-C@NiCu/Cu), 3D-carbon doped iron nitride coated over 3D-NiCu conducting network on SS substrate (3D Fe4N-C@NiCu/SS) and 3D-carbon doped iron nitride coated over 3D-NiCu conducting network on Ti substrate (3D Fe4N-C@NiCu/Ti) electrodes at a scan rate of 50 mV s-1 in accordance with an exemplary embodiment of the invention.

[0051] FIG. 7E depicts galvanostatic charge-discharge (GDC) curve of 3D-carbon doped iron nitride coated over 3D-NiCu conducting network on Cu substrate (3D Fe4N-C@NiCu/Cu) electrode, 3D-carbon doped iron nitride coated over 3D-NiCu conducting network on SS substrate (3D Fe4N-C@NiCu/SS) and 3D-carbon doped iron nitride coated over 3D-NiCu conducting network on Ti substrate (3D Fe4N-C@NiCu/Ti) electrodes at 5 mA cm-2 current density in accordance with an exemplary embodiment of the invention.

[0052] FIG. 7F depicts specific capacitance of 3D-carbon doped iron nitride coated over 3D-NiCu conducting network on Cu substrate (3D Fe4N-C@NiCu/Cu)electrode, 3D-carbon doped iron nitride coated over 3D-NiCu conducting network on SS substrate (3D Fe4N-C@NiCu/SS) and 3D-carbon doped iron nitride coated over 3D-NiCu conducting network on Ti substrate (3D Fe4N-C@NiCu/Ti) electrodes at 5 mA cm-2 current density in accordance with an exemplary embodiment of the invention.

[0053] FIG. 7G depicts cyclic voltammetry (CV) curve for 3D-carbon doped iron sulphide coated over 3D-Ni conducting network on SS substrate (3D Fe3S4-C@Ni/SS) and 3D-carbon doped iron sulphide coated over 3D-NiCo conducting network on SS substrate (3D Fe3S4-C@NiCo/SS) electrodes at a scan rate of 50 mV s-1 in accordance with an exemplary embodiment of the invention.

[0054] FIG. 7H depicts galvanostatic charge-discharge (GDC) curve of 3D-carbon doped iron sulphide coated over 3D-Ni conducting network on SS substrate (3D Fe3S4-C@Ni/SS) and 3D-carbon doped iron sulphide coated over 3D-NiCo conducting network on SS substrate (3D Fe3S4-C@NiCo/SS) electrodes at 1 A g-1 current density in accordance with an exemplary embodiment of the invention.

[0055] FIG. 7I depicts specific capacitance of 3D-carbon doped iron sulphide coated over 3D-Ni conducting network on SS substrate (3D Fe3S4-C@Ni/SS) and 3D-carbon doped iron sulphide coated over 3D-NiCo conducting network on SS substrate (3D Fe3S4-C@NiCo/SS) electrodes at 1 A g-1 current density in accordance with an exemplary embodiment of the invention.

[0056] FIG. 8A depicts cyclic voltammetry (CV) curves of C-NiCo2O4/Ni and 3D Fe3S4-C@NiCo/SS electrodes of an exemplary supercapacitor at scan rate value 50 mV s-1 in accordance to an exemplary embodiment with the invention.

[0057] FIG. 8B depicts cyclic voltammetry (CV) curves of C-NiCo2O4/Ni and 3D Fe3S4-C@NiCo/SS electrodes of an exemplary supercapacitor at various scan rates in accordance with an exemplary embodiment of the invention.

[0058] FIG. 8C depicts galvanostatic charge-discharge (GDC) curve of C-NiCo2O4/Ni and 3D Fe3S4-C@NiCo/SS electrodes of an exemplary supercapacitor at various current densities in accordance with an exemplary embodiment of the invention.

[0059] FIG. 8D depicts Ragone plot for an exemplary supercapacitor of C-NiCo2O4/Ni and 3D Fe3S4-C@NiCo/SS electrodes of an exemplary supercapacitor in accordance with an exemplary embodiment of the invention.
Detailed invention disclosure:
[0060] Various embodiments of the present invention will be described in reference to the accompanying drawings. Wherever possible, same or similar reference numerals are used in the drawings and the description to refer to the same or like parts or steps.

[0061] The present disclosure has been made with a view towards solving the problem with the prior art described above, and it is an object of the present invention to provide a preparation method of electrode material in binder-free 3D-carbon doped metal nitride/sulphide/phosphide porous architecture over various 3D-conducting networks via vapour phase growth method.

[0062] According to an exemplary embodiment of the invention, FIG. 1 refers to a schematic diagram of vapour phase growth 100 of binder free electrode. A calculated amount of active precursor is mixed with a calculated amount metal precursor (ferric chloride) in a mortar 101 and grounded using a pestle in this scenario as an exemplary means mortar and pestle are used for better understanding but any other means to hold and grind required quantities of active precursor and metal precursor, can be used. The active precursor can be melamine, thiourea, sodium hypophosphite, cellulose and thereof.

[0063] The prepared or grounded mixture is transferred into a first ceramic boat 103 and 3D-metal substrate is transferred or placed inside a second ceramic boat 104. Both ceramic boats are placed at the centre of single heating zone tubular furnace 102. The first and second ceramic boats are situated at the upstream and downstream of the tubular furnace, respectively. Atmosphere in the single heating zone tubular furnace 102 is filled with inert gas (N2 or Ar) to maintain the environment suitable for process.

[0064] Further, both ceramic boats 103 and 104 are placed in the single heating zone tubular furnace 102 and are heated through annealing at 550 to 600 °C for 1 hour under inert atmosphere (N2 or Ar gas) at a ramping rate of 10 °C per minute. The metal precursor reacts with active precursor to form metal nitride in the presence of an inert atmosphere. Thus, N2 or Ar act as a just carrier gas, the active precursor act as the source of carbon/nitrogen/sulphur/phosphorous and metal precursor as the source of metals.

[0065] During the process of annealing binder free 3D-carbon doped metal nitride/sulphide/phosphide porous architecture coated over 3D-conducting network as supercapacitor electrode is obtained. Then the electrode is allowed to cool down in the single heating zone tubular furnace 102 to room temperature and then removed from the single heating zone tubular furnace 102.

[0066] According to another exemplary embodiment of the invention, FIG. 2 refers to a method 200 for synthesis of binder-free 3D-carbon doped metal nitride/sulphide/phosphide porous architecture over various 3D-conducting networks via vapour phase growth method. At step 201, 3D-porous conducting network is prepared using dynamic hydrogen bubble template method. The 3D-porous conducting network includes Ni, NiCo, NiCu and thereof. At step 202, considering as prepared 3D-conducting networks for further process. At step 204, the prepared 3D-conducting networks (Ni, NiCo, NiCu and thereof) are placed into the second ceramic boat. At step 205, a mixture of metal precursor (metal chloride) and active precursor (melamine/thiourea/sodium hypophosphite) is prepared. To obtain the metal nitride/sulphide/phosphide, a calculated amount of the metal chloride is kept at 120 °C for 30 minutes and later it is mixed with a calculated amount of the active precursor (melamine/ thiourea/sodium hypophosphite). The metal precursor and active precursor mixtures are considered with mass ratio of 4:1. Then, the prepared mixture is transferred into the first ceramic boat.

[0067] At step 203, to provide good stability and rate capability an interfacial layer is introduced between the metal nitride and 3D-conducting networks. For this the 3D-conducting networks (NiCu and thereof) are immersed in a solution of 20 ml tri-ethylene glycol (TEG) and 75 µL of 0.35M NaOH for 12 hours at 180°C. At step 203, the 3D-metal substrate is taken out of the solution and dried at 100°C for 30 minutes. Then, the dried 3D-metal substrate is placed into the second ceramic boat and followed the same procedure of step 204, and 205.

[0068] At step 206, the first and the second ceramic boats are subjected to annealing process in a single heating zone tubular furnace under an inert atmosphere (N2 or Ar gases). The first ceramic boat and second ceramic boats are kept at the centre of single heating zone tubular furnace. The first and second ceramic boats are situated at upstream and downstream of the tubular furnace, respectively. The first ceramic boat and the second ceramic boats are heated at 550 to 600 °C in the presence of inert atmosphere (Ar or N2) during the process of annealing for 1 hour at a ramping rate of 10°C per minute to obtain 3D-carbon doped iron nitride/sulphide/phosphide porous architecture over a 3D-conducting network. At step 207, the first ceramic boat and the second ceramic boat are allowed to cool down to room temperature to obtain binder free 3D-carbon doped iron nitride/sulphide/phosphide porous architecture over a 3D-conducting network. The designed electrode is 3D-porous architecture which provides high surface area and huge porosity.

[0069] Further, the three-dimensional microporous metal networks include 3D-Ni, 3D-NiCu, and 3D-NiCo are prepared using dynamic hydrogen bubble template method over multiple substrates of Cu sheet, Ti sheet, stainless steel (SS) sheet and thereof. The vapour phase growth method is used to design multiple types of negative electrodes such as metal nitride, metal sulphide, and metal phosphide, and thereof. The solution TEG and NaOH is prepared with 20 ml TEG and 75 µL of 0.35M NaOH or any other suitable quantities maintaining the ratios.

[0070] According to another exemplary embodiment of the invention, the vapour phase growth method is used to design multiple types of negative electrodes and multiple types of positive electrodes for supercapacitor such as nickel nitride, manganese nitride and cobalt nitride and thereof by using metal precursors nickel chloride, manganese chloride, cobalt chloride respectively. Further, the designed electrodes are binder-free and thereby eliminate the usage of binder and conductive additives. The 3D-carbon doped metal nitride porous architecture electrode is not only confined to the application of supercapacitors but also extendable to versatile applications such as photocatalysis, gas sensing, hydrogen evolution, sensor, battery and thereof due to their 3D structure with huge surface area, appreciable porosity, electrical conductivity, structural stability etc.

[0071] According to another exemplary embodiment of the invention, a total of 7 electrode samples are prepared and analysed. The electrode samples include 3D-carbon doped iron nitride coated over 3D-NiCo conducting network on SS substrate (3D Fe4N-C@NiCo/SS), 3D-carbon doped iron nitride coated over 3D Ni conducting network on SS substrate (3D Fe4N-C@Ni/SS), 3D-carbon doped iron nitride coated over 3D-NiCu conducting network on Cu substrate (3D Fe4N-C@NiCu/Cu), 3D-carbon doped iron nitride coated over 3D-NiCu conducting network on SS substrate (3D Fe4N-C@NiCu/SS), 3D-carbon doped iron nitride coated over 3D-NiCu conducting network on Ti substrate (3D Fe4N-C@NiCu/Ti), 3D-carbon doped iron sulphide coated over 3D-NiCo conducting network on SS substrate (3D Fe3S4-C@NiCo/SS) and 3D-carbon doped iron sulphide coated over 3D-Ni conducting network on SS substrate (3D Fe3S4-C@Ni/SS) electrode.

[0072] According to another exemplary embodiment of the invention, FIG. 3A depicts a XRD pattern of 3D Fe4N-C@NiCo/SS and 3D Fe4N-C@Ni/SS electrodes. Both the electrodes are fabricated using a mixture of 2 gram of FeCl3 and 0.5 gram of melamine. The XRD pattern of the 3D Fe4N-C@NiCo/SS electrode exhibits a broad diffraction peak at 2? = 44.4°, 51.9° and 76.5° that is ascribed to (111), (200) and (220) planes of Ni phase. The peaks related to the 3D-carbon doped Fe4N-Ni electrode is obtained at 41.24°, 47.96° and 75.14° and related to the (111), (200) and (300) planes of ?-Fe4N phase.

[0073] The electrodes 3D Fe4N-C@NiCu/Cu, 3D Fe4N-C@NiCu/SS and 3D Fe4N-C@NiCu/Ti are fabricated using a mixture of 1 gram of FeCl3 and 0.25 gram of melamine. It is observed that the XRD profiles of the three samples depicted peaks corresponding to Ni and Cu due to the presence of higher loading of 3D-NiCu template in the electrodes. This concludes that the percentage of iron nitride (Fe4N) and carbon is very less. Again, samples of the three electrodes are taken and fabricated using a mixture of 3 grams of FeCl3 and 0.75 grams of melamine, while maintaining mass ratio of 4:1.

[0074] According to another exemplary embodiment of the invention, FIG. 3B depicts stacked XRD plots for 3D NiCu-C@Fe4N/Cu. The plots show that, the samples prepared by using low mass of FeCl3-Melamine i.e. 1 gm-0.25 gm do not show any Fe4N peaks. However, the samples prepared using FeCl3-Melamine = 3 gm-0.75 gm clearly shows the diffraction peaks related to ?-Fe4N and additional Ni and Cu peaks are observed.

[0075] According to another exemplary embodiment of the invention, FIG. 3C depicts XRD plots for 3D Fe4N-C@NiCu/SS electrodes. The plots depicts high intensity peaks at 2 theta value 41.5° and 48.3° which corresponds to (111) and (200) planes respectively belongs to ?-Fe4N, and additional peaks belong to Ni and Cu metals.

[0076] According to another exemplary embodiment of the invention, FIG. 3D depicts XRD profiles of the 3D Fe4N-C@NiCu/Ti electrodes. The 3D Fe4N-C@NiCu/Ti electrodes are analyzed in the 2? range from 5 ° to 70 °. The highest intensity peak is appeared at 27.48 ° that belongs to (110) of TiO2. Additionally, the peaks is observed at 41.22° and 48.4° that belongs to (111) and (200) planes of ?-Fe4N, respectively.

[0077] According to another exemplary embodiment of the invention, FIG. 3E depicts XRD plots for the 3D Fe3S4-C@Ni/SS and 3D Fe3S4-C@NiCo/SS electrodes. All the electrodes are fabricated using a mixture of 2 gram of FeCl3 and 0.5 gram of thiourea. The XRD pattern of the 3D Fe3S4-C@NiCo/SS electrode exhibits a broad diffraction peak at 2? = 44.4°, 51.9° and 76.5° that is ascribed to (111), (200) and (220) planes of Ni phase. Further, the cubic phase of Fe3S4 is observed at 15.18°, 25.22°, 29.62°, 31°, 36.3°, 39.26° 47.18°, 62.52°, and 64.9° and related to the (111), (220) and (311), (222), (400), (331), (511), (622) and (444) planes of Fe3S4 phase. The XRD characterization of all the samples of electrodes proves the successful fabrication of iron sulphide incorporated 3D-conducting networks.

[0078] According to another exemplary embodiment of the invention, FIG. 4A, FIG. 4B, FIG. 4C, and FIG. 4D depict Raman spectroscopy of the 3D Fe4N-C@Ni/SS, the 3D Fe4N-C@NiCu/Ti, and the 3D Fe3S4-C@NiCo/SS electrodes. From the XRD pattern, it is observed that, the carbon peak is not observed in case of any electrodes. This is due to the high percentage of Fe4N in the electrodes compared to carbon. The presence of carbon in the electrodes is confirmed by Raman analysis. In FIG. 4A the deposited 3D Fe4N-C@Ni/SS is further characterized by a Raman spectroscopy. The modes obtained at 1353.49 cm-1 and 1593.89 cm-1 indicate D band and G band of carbon. In FIG. 4B, the 3D Fe4N-C@NiCu/Cu electrode, the high intensity peaks are observed at Raman shift positions, which are 1345.2 cm-1 and 1601.9 cm-1, corresponds to D-band and G-band respectively. The high intensity of G-band compared to D-band refers to the high crystallinity of the prepared electrode.

[0079] In FIG. 4C, the 3D Fe4N-C@NiCu/SS shows the high intensity peaks at Raman shift values, which are 1345.2 cm-1 and 1597.9 cm-1, related to D-band and G-band respectively. In FIG. 4D, the deposited 3D Fe3S4-C@NiCo/SS is further characterized by Raman spectroscopy. Further, the obtained vibrational modes at 1353.49 cm-1 and 1593.89 cm-1 indicate D band and G band of carbon.

[0080] According to another exemplary embodiment of the invention, FIG. 5 depicts field emission scanning electron microscopy (FESEM) micrographs of all the prepared electrodes. The samples of the prepared electrode possess microporous structure with variable porosity due to the presence of 3D metal networks. After carbon doped iron nitride/sulfide deposition over the 3D metal networks, particles are seen to be deposited.

[0081] According to another exemplary embodiment of the invention, FIG. 6A and FIG. 6B depict energy dispersive X-ray (EDX) spectrum of the 3D Fe4N-C@Ni/SS electrode and 3D-carbon doped Fe3S4-NiCo/SS electrode. The EDX spectrum of 3D Fe4N-C@Ni/SS electrode confirms the presence of Ni, Fe, C and N. The EDX spectrum of 3D Fe3S4-C@NiCo/SS electrode confirms the presence of Ni, Fe, S, C and Co.

[0082] According to another exemplary embodiment of the invention, FIG. 7A, FIG. 7B, FIG. 7C, FIG. 7D, FIG. 7E, FIG. 7F, FIG. 7G, FIG. 7H and FIG. 7I depict cyclic voltammetry (CV) curve, galvanostatic charge-discharge (GDC) curve, and specific capacitance of the 3D Fe4N-C@Ni/SS, 3D Fe4N-C@NiCo/SS, 3D Fe4N-C@NiCu/Cu, 3D Fe4N-C@NiCu/SS, 3D Fe4N-C@NiCu/Ti, 3D Fe3S4-C@Ni/SS, 3D Fe3S4-C@NiCo/SS electrodes. The electrochemical properties of the prepared electrodes are scrutinized through multiple analyses that include cyclic voltammetry (CV) and galvanostatic charge/discharge (GCD). The analyses are conducted in a three-electrode system in 2M KOH electrolyte, wherein the prepared electrodes act as negative electrodes for a supercapacitor. The negative electrodes exhibit a pseudocapacitive behaviour as the curves are non-rectangular in nature.

[0083] The CV analysis is performed at a scan rate of 50 mV s-1 on the 3D Fe4N-C@Ni/SS, 3D Fe4N-C@NiCo/SS, 3D Fe4N-C@NiCu/SS, 3D Fe4N-C@NiCu/Ti, 3D Fe3S4-C@Ni/SS, 3D Fe3S4-C@NiCo/SS electrodes. The CV curves or profiles exhibit redox peaks, which is a signature of the faradaic oxidation-reduction property of the prepared electrodes as depicted in FIG. 7A, FIG. 7D and FIG. 7G. The GCD analysis is performed at the current density value of 5 mA cm-2 in FIG. 7E and at 1 A g-1 in FIG. 7B and FIG. 7H is performed to evaluate the electrochemical efficiency of the prepared electrodes. The same pseudo-capacitive behaviour is revealed by the prepared electrodes, which matches the result obtained from CV curves depicted in FIG. 7A, FIG. 7D and FIG. 7G.

[0084] Considering discharge time, the specific capacitance values are calculated at a 5 mA cm-2 in FIG. 7E and at 1 A g-1 in FIG. 7B and FIG. 7H and depicted in FIG. 7C, FIG. 7F and FIG. 7I. The 3D Fe4N-C@Ni/SS electrode and 3D Fe4N-C@NiCo/SS electrodes deliver specific capacitance values of 110.6 F g-1, 193.03 F g-1, respectively, at current density value 1 A g-1. The 3D Fe4N-C@NiCu/Cu electrode, 3D Fe4N-C@NiCu/SS electrode, and 3D Fe4N-C@NiCu/Ti electrode, deliver specific capacitance values of 2600 mF cm-2, 570 mF cm-2 and 100 mF cm-2 respectively at current density value 5 mA cm-2. Similarly, 3D Fe3S4-C@Ni/SS electrode and 3D Fe3S4-C@NiCo/SS electrode deliver specific capacitance values 107.26 F g-1 and 822.82 F g-1, respectively, at current density value 1 A g-1.

[0085] According to another exemplary embodiment of the invention, FIG. 8A, FIG. 8B, FIG. 8C and FIG. 8D depicts cyclic voltammetry (CV) curves, galvanostatic charge-discharge (GDC) curve, and Ragone plot for an exemplary supercapacitor. The exemplary supercapacitor is assembled with C-NiCo2O4/Ni as a positive electrode and 3D Fe3S4-C@NiCo/SS as a negative electrode. FIG. 8A depicts the CV curves of both positive electrodes, and a negative electrodes are studied from the three-electrode system at a scan rate of 50 mV s-1. The CV curves have no obvious polarization that signifies the stable working potential window is drawn-output to 1.6 V and the GCD is optimized as up to 1.55 V.

[0086] FIG. 8B and FIG. 8C depicts the CV curves and GCD curves of C-NiCo2O4/Ni electrode and 3D Fe3S4-C@NiCo/SS electrode at various scan rates and current density, respectively. It is observed that the quasi-symmetric shape with distinct redox peaks corresponds to the hybrid characteristics of the battery-like and the capacitive charge storage mechanism. The Ragone plot is used to describe the relationship between power density and energy density. Based on the supercapacitor performance, the obtained maximum energy density is 64 Wh kg-1 at a power density of 755 W kg-1 as depicted FIG. 8D.

[0087] According to another exemplary embodiment of the invention, In previous literatures metal nitride/sulphide/phosphide consist of two step or three step syntheses, i.e. formation of metal oxide followed by nitridation/sulphidation/phosphorization etc. Single step synthesis in the present work reduces the time and cost of experiment and furnishes stable architecture. The vapour phase growth method is used to design multiple types of negative electrodes can be extended to design multiple types of positive electrodes for supercapacitor such as nickel nitride, manganese nitride and cobalt nitride and thereof by using metal precursors nickel chloride, manganese chloride, cobalt chloride respectively. The 3D-carbon doped metal nitride porous architecture electrode is not only confined to the application of supercapacitors but also extendable to versatile applications such as photocatalysis, gas sensing, hydrogen evolution, sensor, battery and thereof due to their 3D structure with huge surface area, appreciable porosity, electrical conductivity, structural stability etc.

[0088] Numerous advantages of the present disclosure may be apparent from the discussion above. In accordance with the present disclosure, a preparation method of an electrode material in vapour phase growth binder-free 3D-carbon doped metal nitride/sulphide/phosphide porous architecture over various 3D-conducting networks.

[0089] The proposed method is suitable for fabricating electrodes for supercapacitors. The proposed method can synthesise a binder-free 3D-carbon doped metal nitride/sulphide/phosphide porous architecture over various 3D-conducting networks and hence eliminates the usage of binder and conductive additives for the preparation of electrode. The proposed method takes less time and less cost for fabrication of electrodes for supercapacitors. The proposed method uses inert gas (N2 or Ar) throughout the process as a carrier gas to avoid the oxidization of the 3D-conducting networks. The proposed method is applicable for fabricating 3D-carbon doped metal nitride/sulphide/phosphide porous architecture over various 3D-conducting networks. The proposed method for synthesis is cost-effective and time saving as it does not employ high-cost chemicals, reactive gases such as ammonia, methane and thereof, sophisticated instruments, high operating temperature and thereof.

[0090] It will readily be apparent that numerous modifications and alterations can be made to the processes described in the foregoing examples without departing from the principles underlying the invention, and all such modifications and alterations are intended to be embraced by this application.

We Claim:

1. A method for vapour phase growth of binder-free 3D-carbon doped metal nitride porous architecture electrode for supercapacitor, comprising:
preparing 3D-porous conductive network via dynamic hydrogen bubble method;
keeping calculated amount of metal precursor inside a mortar and heating at 120°C for 30 minutes;
taking out said metal precursor from oven;
adding a calculated amount of active precursor in said metal precursor and preparing a mixture of said metal precursor and said active precursor using said mortar and pestle;
transferring said mixture into a first ceramic boat;
placing said 3D-porous conductive network into a second ceramic boat;
placing said first ceramic boat and said second ceramic boat at the centre of a single heating zone tubular furnace, said first ceramic boat and said second ceramic boat are situated at said upstream and downstream of said tubular furnace respectively;
heating said first ceramic boat and said second ceramic boat at a range of 500 to 600°C for 1 hour in said tubular furnace under inert atmosphere (N2 or Ar gas) at a ramping rate of 10°C per minute to obtain 3D-carbon doped metal nitride porous architecture over 3D-metal networks, and
cooling down said first ceramic boat and said second ceramic boat to room temperature, whereby electrode of binder free 3D-carbon doped metal nitride porous architecture over a 3D-metal network is obtained.
2. The method for vapour phase growth of binder-free 3D-carbon doped metal nitride porous architecture electrode for supercapacitor as claimed in claim 1, wherein preparing of carbon interfacial layer comprising:
immersing said 3D-porous conducting network in a solution of 20 ml tri-ethylene glycol (TEG) and 75 µL of 0.35M NaOH for 12 hours at 180 °C, and drying said 3D-porous conducting network at 120 °C for 30 minutes after taking out said 3D-porous conducting network from said solution of TEG and NaOH to obtain dried 3D-porous conducting network.
3. The method for vapour phase growth of binder-free 3D-carbon doped metal nitride porous architecture electrode for supercapacitor as claimed in claim 1, wherein said active precursors include melamine, thiourea, sodium hypophosphite, cellulose and thereof.
4. The method for vapour phase growth of binder-free 3D-carbon doped metal nitride porous architecture electrode for supercapacitor as claimed in claim 1, wherein said 3D-porous conducting network includes 3D-Ni, 3D-NiCu, and 3D-NiCo and thereof that are prepared using dynamic hydrogen bubble template method.
5. The method for vapour phase growth of binder-free 3D-carbon doped metal nitride porous architecture electrode for supercapacitor as claimed in claim 1, wherein said 3D-porous conducting network is deposited on multiple substrates of Cu sheet, Ti sheet, stainless steel (SS) sheet and thereof.
6. The method for vapour phase growth of binder-free 3D-carbon doped metal nitride porous architecture electrode for supercapacitor as claimed in claim 1, wherein said metal porous architecture electrode includes metal nitride, metal sulphide, metal phosphide, metal carbide and thereof.
7. The method for vapour phase growth of binder-free 3D-carbon doped metal nitride porous architecture electrode for supercapacitor as claimed in claim 1, wherein said metal precursor and active precursor mixture are considered with mass ratio of 4:1.