Nickel sulphide supported on MOF-based electrocatalyst for larger active area AEM water electrolyser

Abstract

The present disclosure relates to a nickel sulphide supported on MOF-based electrocatalyst for electrochemical water splitting. The present disclosure also relates to a method for the synthesis of nickel sulphide supported on MOF-based electrocatalyst for electrochemical water splitting. The present disclosure has an application in large active surface area AEM electrochemical water splitting. The electrocatalyst of the present disclosure has an excellent performance (>1 Acm-2 of current densities) at larger areas of active electrodes (>10 cm2) and for a longer period of operation (>100h) at elevated temperatures that are attractive to industries.

Description

[0001]PT / 2025 / 13367 NICKEL SULPHIDE SUPPORTED ON MOF-BASED ELECTROCATALYST FOR LARGER ACTIVE AREA AEM WATER ELECTROLYSER FIELD OF THE INVENTION The present disclosure relates to a nickel sulphide supported on MOF-based electrocatalyst for larger active area AEM water electrolyser. More particularly, the present disclosure relates to a non-PGM-based nickel sulfide pair NiS||Ni3S2supported on MIL-53 electrocatalyst (NSMA and rNSMA) and the process for its synthesis and application in larger active surface area AEM water electrolysis. BACKGROUND OF THE INVENTION Depletion of fossil fuels at a rapid rate and, as a consequence, the environmental impacts of their combustion demands alternative sustainable energy sources. Green hydrogen is a sustainable energy source with great potential for use as fuel in the future due to its high energy density and zero carbon footprint. It is required to seek alternative, affordable, and green methods to produce hydrogen to minimize the use of fossil fuels and reduce CO2 emissions. Electrochemical water splitting using renewable electricity is an ideal pathway for green hydrogen production. Although being a potential game changer in the electrolyser industry, Anion Exchange Membrane Water Electrolyser (AEMWE) technology is struggling with poor performance and stability primarily due to the following reasons: 1. Although several promising electrocatalysts based on non-precious metal (non-PGM) oxides and sulfides offer low overpotential, they suffer from poor stability primarily due to catalyst deactivation and leaching. 2. Some of them (e.g., a few metal sulfide-based catalysts), although reported to be performing significantly well in a lab scale (3-electrode mode), suffer from poor performance at the device scale, especially with limited scalability. 3. Metal-sulfide-based electrocatalysts exhibit low stability at industrial operating conditions, such as higher potentials or current densities, at elevated operation temperatures, especially in corrosive (higher pH) conditions. PT / 2025 / 13367 There is a need to enhance the performance of high-performing metal sulfide-based electrocatalysts to ensure long-lasting and stable operation. However, many active sites in metal sulfides are largely buried and unavailable for catalysis. Metal-organic frameworks (MOFs) offer several advantages, such as uniform and ample nanoscale inner space, an electron-conducting carbon network with metal centers, and better binding sites, making them potentially effective catalysts. The challenge lies in achieving the right MOF structure that facilitates higher charge conductivity, improved reaction kinetics, and greater electrochemical stability. Some reports in the literature suggest that using metal-organic frameworks (MOFs) as electrocatalysts has achieved only moderate success, which is not as effective as metal sulfides. Conversely, some studies indicate that MOFs can be used as precursors to create high- surface-area metal oxides, phosphides, and sulfides supported on porous carbon through pyrolysis. However, this pyrolysis process destroys the structural and compositional characteristics of the MOFs, resulting in the loss of active sites and hindering the interaction between the electrode and the electrolyte. The smart strategy is to combine the advantages of these two materials. Retaining the high-surface-area metal-organic frameworks (MOFs) as precursors for electrocatalysts could lead to their optimal utilization. However, MOFs typically exhibit lower catalytic activity due to their inherently low charge transfer capacities. To enhance the electrical conductivity and electrocatalytic performance of MOFs, metal oxide and chalcogenide nanoparticles can be incorporated through a post-synthesis process. Zhao et al., as referred to in the publication, Strong Electronic Interaction Enhanced Electrocatalysis of Metal Sulfide Clusters Embedded Metal-Organic Framework Ultrathin Nanosheets toward Highly Efficient Overall Water Splitting, Advanced Science, 7 (2020) 2001965, synthesized the metal sulfide (MS) clusters embedded ultrathin nanosheets of Fe / Ni metal-organic framework (MOF) catalyst and exhibited decent performance for overall water splitting at a smaller active area of about 1 cm x 1cm. It is known that such materials pose serious scalability issues primarily due to the structure-activity relation translation to a larger scale of production and demonstration. Wu et al. [Nanoscale, 2019, 11, 14785-14792] discloses a preparation of a Ni-S / MIL-53(Fe) / NF hybrid catalyst by a two-step process wherein first MIL-53(Fe) nanosheets were directly grown on nickel foam (NF) via a solvothermal method wherein MIL- 53(Fe) was prepared by the solvothermal reaction of FeCl3·6H2O and 1,4-BDC in DMF, while NF also being present in the reaction medium. Then, Ni-S film was electrodeposited on MIL- 53(Fe) / NF nanosheets using NiCl2 and thiourea as nickel and sulfur sources, respectively, to form Ni-S / MIL-53(Fe) / NF hybrid catalyst through a constant current deposition approach. Loiseau et al. [Chem. Eur. J.2004, 10, 1373-1382] discloses a hydrothermal synthesis of porous PT / 2025 / 13367 aluminum terephthalate (MIL-53(Al)) MOF by heating a mixture of aluminum nitrate, 1,4- benzenedicarboxylic acid (BDC), and water in a Teflon-lined stainless steel Parr bomb under autogenous pressure, for three days at 220 °C. Ren et al. [Nanoscale, 2018, 10, 17347-17353] discloses the fabrication of nickel sulfide (Ni3S2) films on Ni foam (Ni3S2 / NF) as an efficient bifunctional electrode for overall water splitting, through direct dropping of mercaptoethanol solution on nickel foam (NF) followed by annealing at 300 °C for 50 s under N2 atmosphere. CN112264047B discloses a method for preparing a noble metal single-atom catalyst for electrolyzing water to produce oxygen, comprising the steps of mixing a non-noble metal salt such as nickel nitrate and thiourea in water to obtain a stock solution, using a conductive substrate such as nickel foam as a working electrode, depositing a non-noble metal sulfide on the surface of the conductive substrate by an electrochemical reduction method in the stock solution, using the conductive substrate deposited with the non-noble metal sulfide substrate as a working electrode, adsorbing noble metal single atoms on the surface of the non-noble metal sulfide substrate by an electrochemical reduction method in the electrosorption solution, to obtain the noble metal single-atom catalyst. CN116180136A discloses the preparation of nickel hydroxide composite nickel-molybdenum-sulfur nano array (Ni(OH)x / Mo-Ni3S2 / NF) hydrogen evolution electrode catalyst prepared by a process wherein first foamed nickel loaded nickel sulfide nanosheet array (Mo-Ni (OH) 2 / NF) was prepared by the reaction of NH4F, urea, nickel nitrate, sodium molybdate and foamed nickel at 120 °C for 6 hours, followed by the reaction of the prepared Mo-Ni(OH)2 / NF with 2-mercaptoethanol at a temperature of 150 °C for 5 h to afford nickel-molybdenum-sulfur nanosheet array loaded on the foamed nickel (Mo- Ni3S2 / NF) which was further followed by carrying out an in-situ electrochemical reduction on Mo-Ni3S2 / NF under a voltage of -1.5 to-1.6 V for 6-18 hours to obtain the nickel hydroxide composite nickel-molybdenum-sulfur nano array (Ni(OH)x / Mo-Ni3S2 / NF) wherein amorphous nickel hydroxide grows on the nickel foam loaded nickel-molybdenum-sulfur nano array by adopting an in-situ reduction method, an optimized heterostructure generates a synergistic effect on the electro-catalytic reaction to afford a high-efficiency HER electro- catalyst wherein overpotentials of Ni3S2 / Ni(OH)x / NF are 127, 194 and 239mV when the current density reaches 100, 500 and 1000mA / cm2(electrocatalysis under 1M KOH electrolyte test). Srinivas et al. [ACS Sustainable Chem. Eng. 2021, 9, 4, 1920–1931] discloses metal– organic framework (MOF)-derived nickel (Ni) and nickel sulfide (NiS) heteronanoparticle- embedded semi-MOFs (Ni / (α,β)-NiS MOF@CNT (Ni-M@C-temp)) prepared by a partial sulfurization strategy wherein a hydrothermal treatment of Ni-MOF@CNT with a sulfur source (thioacetamide) was carried out at different temperatures (110, 130, 150, and 170 °C) for 6 h PT / 2025 / 13367 followed by annealing at 350 °C for 2 h in a flowing N2gas and the resulting samples were named as Ni-M@C-110, Ni-M@C-130, NiM@C-150, and Ni-M@C-170. To the best of the inventor’s understanding, there are no reports on the demonstration of high electrochemical performance and stability attractive to industrial exploitation, i.e., larger active area electrodes, longer durability of performance at higher current densities, higher operational temperatures, etc. Herein, the present disclosure invents a high-performing electrocatalyst system that can perform both HER and OER at higher current densities (on par with the commercial standard catalysts) at pH nearly 14 and for longer operation hours and higher temperatures that are attractive for industry. The present disclosure reports: (i) the near ambient synthesis of a non-PGM based electrocatalytic system, NiS@MIL-53 / NF (NSMA) with NiS anchored on the MIL-53(Al) / NF microporous substrate; (ii) the means to resolve the active material leaching issue to offer better stability to the electrocatalytic performance; (iii) the understanding of the extraordinary activity and the reasons for its sustenance using various physical and electrochemical means at a molecular level, and (iv) a demonstration of excellent performance (>1 Acm-2of current densities) at larger areas of active electrodes (>10 cm2) and for a longer period of operation (>100h) at elevated temperatures that are attractive to industries. OBJECTIVES OF THE INVENTION The main objective of the present disclosure is to provide a nickel sulphide (NiS||Ni3S2) supported on MOF-based electrocatalyst, a non-PGM metal-based electrocatalyst system capable of catalyzing the HER and OER reactions for a larger active area AEM water electrolyzer stack, wherein the electrocatalyst demonstrates higher current densities (>1 A cm-2) and better stability (>100 h). Another objective of the present disclosure is to provide a process for the synthesis of above said NiS||Ni3S2supported on MIL-53 electrocatalyst. PT / 2025 / 13367 Yet another objective of the present disclosure is to provide a large active surface area AEM water splitting process using the above-mentioned NiS||Ni3S2 supported on MIL-53 electrocatalyst. SUMMARY OF THE INVENTION Accordingly, in order to accomplish an objective, the present disclosure provides a NiS||Ni3S2 supported on MIL-53 electrocatalyst for a larger active area AEM water electrolyser stack, wherein the non-PGM metal-based electrocatalyst system displays higher current densities (>1 A cm-2) and better stability (>100 h). An embodiment of the present disclosure provides a nickel sulphide supported on an MOF- based electrocatalyst for electrochemical water splitting, wherein the electrocatalyst comprises a unique phase of nickel sulphide anchored on the MIL-53(Al) modified porous nickel foam (NSMA) and (rNSMA). In an aspect, the present disclosure provides an electrocatalyst for water splitting, comprising: combination of nickel sulphide and metal organic framework (MOF) supported on a support, wherein the electrocatalyst comprises phase(s) of nickel sulphide anchored on the MOF, and the MOF is coated onto the support; and a surface area of the MOF contained in the electrocatalyst is in the range of 1000 m2 / g to 1500 m2 / g. In an embodiment, the phase(s) of nickel sulphide is represented by the formula: NixSy, wherein x is in the range of 1 to 3 and y is 1 or 2. In an embodiment, the electrocatalyst is unreduced or electrochemically reduced electrocatalyst. In an embodiment, the electrocatalyst comprises phase(s) of nickel sulphide based on millerite nickel sulphide (NiS), and / or trinickel disulfide (Ni3S2). In an embodiment, the electrocatalyst comprises phase(s) of nickel sulphide having crystallite size in the range of 5-6 nm, and are in hexagonal shape. PT / 2025 / 13367 In an embodiment, the electrocatalyst comprises uniform distribution of combination of elements selected from nickel, sulfur, and aluminium. In an embodiment, the MOF is selected from a material of Institut Lavoisier-53 (MIL-53), with a metal selected from group 13 element; and In an embodiment, the support is selected from nickel foam, nickel mesh, nickel felt, stainless steel fiber, and carbon paper. In an embodiment, the group 13 element is selected from a group comprising of boron (B), aluminum (Al), gallium (Ga), indium (In), and thallium (Tl). In specific embodiment, the group 13 element is aluminium. In specific embodiment, the MOF is aluminium metal contained MOF. In an embodiment, the surface area of the MOF contained in the electrocatalyst is in the range of 1050 m2 / g to 1400 m2 / g. In an embodiment, the surface area of the MOF contained in the electrocatalyst is in the range of 1100 m2 / g to 1300 m2 / g. In an embodiment, the surface area of the MOF contained in the electrocatalyst is in the range of 1150 m2 / g to 1200 m2 / g. In an embodiment, the surface area of the MOF contained in the electrocatalyst is in the range of 1160 m2 / g to 1180 m2 / g. In specific embodiment, the surface area of the MOF contained in the electrocatalyst is 1160 m2 / g. In another aspect, the present disclosure provides a process for the synthesis of the electrocatalyst, the process comprising: a) stirring a reaction mixture of precursor of group 13 element, a linker, and a solvent with heating followed by drying to afford MOF; PT / 2025 / 13367 b) coating a support with a slurry comprising the MOF obtained in step a), poly(vinylidene fluoride), carbon black, and N-methyl pyrrolidone, followed by drying to afford MOF coated support; c) taking solution of nickel (Ni) precursor and sulfur precursor in water as electrodeposition bath and carrying out electrodeposition in a three-electrode system, wherein the three- electrode system comprises the MOF coated support as obtained in step b) is used as a working electrode, graphite rod as auxiliary electrode, and standard calomel electrode (SCE) as reference electrode, respectively, for the electrodeposition followed by drying to obtain the unreduced electrocatalyst; and d) reducing the unreduced electrocatalyst as obtained in step c) electrochemically in a three- electrode system, wherein the unreduced electrocatalyst acts as a working electrode, graphite rod as auxiliary electrode, and Hg / HgO as reference electrode, respectively for reduction, followed by drying to afford the reduced electrocatalyst. In an embodiment, the precursor of group 13 element is selected from chloride of group 13 element, nitrate of group 13 element, sulfate of group 13 element, hydroxide of group 13 element, and lactate of group 13 element. In specific embodiment, the group 13 element is selected from selected from a group comprising of boron (B), aluminum (Al), gallium (Ga), indium (In), and thallium (Tl). In specific embodiment, the group 13 element is aluminium. In specific embodiment, the precursor of group 13 element is precursor of aluminium. In specific embodiment, the precursor of aluminium is selected from a group comprising of aluminium chloride (AlCl3), aluminium nitrate nonahydrate, aluminum sulfate (Al₂(SO₄)₃), aluminium hydroxide (Al(OH)3), and aluminium lactate (Al(C₃H₅O₃)₃), or any of combination thereof. In an embodiment, a concentration of the precursor of group 13 element is ranging from 0.1 to 0.5 M. In an embodiment, the linker in step a) is selected from a group comprising of benzene tri-carboxylic acid (BTC), and benzene di-carboxylic acid (BDC), amine substituted benzene di-carboxylic acid, dihydroxy substituted benzene di-carboxylic acid, or combination thereof. PT / 2025 / 13367 In an embodiment, a concentration of the linker is ranging from 0.1 to 0.6 M. In an embodiment, the solvent in step a) is polar solvent selected from a group comprising of dimethylformamide (DMF), dimethyl sulfoxide (DMSO), water (H2O), and ethanol (CH3CH2OH) or any of combination thereof. In an embodiment, the reaction mixture in step a) is heated at a temperature in the range of 160-200°C for a time period in the range of 20-30 h and drying at a temperature in the range of 150-180°C for a time period in the range of 18-24 h. In an embodiment, the drying in step b) is carried out at a temperature ranging from 80-100°C for a time period ranging from 8-10 h in a vacuum. In an embodiment, the Ni precursor in step c) is selected from a group comprising of Ni(NO3)2·6H2O, NiSO4·6H2O, NiCl2·6H2O, and NiC4H6O4·4H2O or any of combination thereof. In an embodiment, a concentration of the Ni precursor is ranging from 0.3 to 0.6 M. In an embodiment, the sulfur precursor in step c) is selected from a group comprising of thiourea, sulfur powder, thioacetamide (TAA), L-cysteine (L-Cys) and combination thereof. In an embodiment, a concentration of the sulfur precursor is ranging from 1.3 to 1.8 M. In an embodiment, the electrodeposition in step c) is carried out at a current density in the range of -60 mA cm-2to -100 mA cm-2for time period in the range of 10-20 minutes and the drying in step c) is carried out at a temperature in the range of 80-100 °C for a time period in the range of 5-10 h in a vacuum. In an embodiment, the reduction in step d) is carried out at a current density in the range of - 200 to -500 mA cm-2for a time period in the range of 1-5 h and drying in step d) is carried out at a temperature in the range of 80-100°C for a time period in the range of 5-10 h under vacuum. In another aspect, the present disclosure provides an electrolyzer for water splitting, comprising: i. the electrocatalyst as claimed in claim 1 as an anode and / or a cathode; ii. anion exchange membrane; and iii. electrolyte. PT / 2025 / 13367 In an embodiment, the anion exchange membrane is selected from sustainion (STN) and aemion (AMN) membrane. In an embodiment, the electrolyte is selected from potassium hydroxide and sodium hydroxide. In an embodiment, the concentration of electrolyte is in the range of 0.5-1.5 M. In an embodiment, the electrolyzer comprises the electrocatalyst in unreduced form (NSMA) as cathode, and the electrocatalyst in electrochemically reduced form (rNSMA) as anode. In another aspect, the present disclosure provides a process for water splitting, comprising treating water with the electrocatalyst as claimed in claim 1 as an anode and / or as a cathode for performing full-cell experiment in 5.5 cm2(10X) and 12.96 cm2(13X) electrolyzer. In an embodiment, the anion exchange membrane is selected from sustainion (STN) and aemion (AMN) membrane. In an embodiment, the electrolyte is selected from potassium hydroxide and sodium hydroxide. In an embodiment, the concentration of electrolyte is in the range of 0.5-1.5 M. In an embodiment, the process additionally comprises soaking of the anion exchange membrane in said electrolyte for time period in the range of 20-40 h. In an embodiment, the process comprises the electrocatalyst in unreduced form (NSMA) as cathode, and the electrocatalyst in electrochemically reduced form (rNSMA) as anode. In an embodiment, the process is done in the electrolyzer at temperature in the range of 55-60 ℃ for time period in the range of 5-10 h. In specific aspect, the present disclosure provides a process for the synthesis of nickel sulphide supported on MOF-based electrocatalyst for electrochemical water splitting, wherein said process comprises the steps of: a) synthesizing MIL-53(Al) MOF by stirring the reaction mixture of an aluminum (Al) precursor, a linker, and a solvent with heating, followed by drying to afford MIL-53(Al) MOF; PT / 2025 / 13367 b) coating the thoroughly cleaned nickel foam (NF) with a slurry containing MIL-53(Al) MOF obtained at step a), poly(vinylidene fluoride), carbon black, and N-methyl pyrrolidone by brush and keeping it for drying to afford MIL-53(Al) / NF; c) synthesizing NS / MIL-53(Al) / NF (NSMA) by taking solution of nickel (Ni) precursor and sulfur precursor in water as electrodeposition bath and carrying out electrodeposition in a three-electrode system, wherein MIL-53(Al) / NF as obtained in step b) is used as a working electrode, and Graphite rod and Standard Calomel electrode (SCE) act as auxiliary and reference electrodes, respectively, for electrodeposition followed by drying blackish nickel sulfide (NiS) deposition to afford NS / MIL-53(Al) / NF (NSMA); and d) reducing the NS / MIL-53(Al) / NF (NSMA) obtained at step c) electrochemically in a three- electrode system, wherein NSMA acts as a working electrode, and Graphite rod and Hg / HgO act as auxiliary and reference electrodes, respectively, for reduction, followed by drying to afford N3S2 / MIL-53(Al) / NF (rNSMA). Yet another embodiment of the present disclosure provides a process for electrochemical water splitting, wherein said process comprises the NSMA as an anode and rNSMA as a cathode are utilized for performing full cell experiments in 10X (5.5 cm2of active area) and 13X (12.96 cm2of active area) electrolyzer systems. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 represents a schematic illustration of the synthesis of NSMA and rNSMA. Figure 2 illustrates a) Comparative Powder XRD pattern of NSMA and rNSMA along with JCPDs file data, b) High-resolution Transmission electron microscopy (HR-TEM) analysis of NSMA with d-spacing (inset image shows the SAED Pattern), c) High-resolution Transmission electron microscopy (HR-TEM) analysis of rNSMA with d-spacing (inset image shows the SAED Pattern), d) HAADF-STEM image of NSMA along with respective elemental mapping of Ni, S, and Al shows uniform distribution of elements, and e) HAADF-STEM image of rNSMA along with respective elemental mapping of Ni, S, and Al shows uniform distribution of elements. Figure 3 illustrates (a) iR-corrected LSV curves at 1mV / s of the NiS, Pt / C, MIL-53(Al), Bare NF, NSMA, and rNSMA for HER in 1M KOH (b) Tafel slope of catalysts for HER (c) IR- PT / 2025 / 13367 corrected LSV curves at 1mV / s of the NiS, Pt / C, MIL-53(Al), Bare NF, and NSMA for OER in 1M KOH (d) Tafel slope of catalysts for OER (e) Polarisation curve for NSMA||rNSMA cell configuration compared with state of art cell configuration Ru / C||Pt / C in open cell for Overall Water Splitting (OWS), (f) Chronopotentiometry curve for 100h in open cell. Figure 4 illustrates (a) Polarisation curve for NSMA || STN || rNSMA 10X cell configuration compared with state-of-the-art cell configuration Ru / C || STN || Pt / C, (b) Chronopotentiometry curve in the form of the staircase from 0.182 A cm-2to 0.909 A cm-2with the duration of 2h for each current at 10X cell (c) Polarisation curve for NSMA || AMN || rNSMA 13X cell configuration at different temperatures in 1M KOH, (d) correlation curve between temperature (RT to 70 ℃) and J2(Current density at 2V) at 13X, (e) 100 h stability at 400 mA cm-2current with on-off cycle at NSMA || AMN || rNSMA 13X cell configuration. DETAILED DESCRIPTION OF THE INVENTION It is to be understood that the figures and descriptions of the present disclosure have been simplified to illustrate relevant elements for a clear understanding of the invention. The detailed description will be provided herein below with reference to the attached drawing. The term “MIL-53(Al)” covers materials of Institut Lavoisier-53 (Al), which is a metal organic framework (MOF) made up of aluminum and oxygen (AlO6) nodes with 1,4-benzodicarboxylic acid struts between the nodes. Sustainion anion exchange membranes are primarily composed of a polymer backbone (often styrene-based) with functionalized ionic liquid groups, typically imidazolium-based, that facilitate anion conductivity. Aemion anion exchange membranes are made from hydrocarbon polymers and feature a unique polymer structure that enhances stability and conductivity. These membranes are designed to facilitate anion transport, specifically hydroxide ions (OH-), in electrochemical applications like fuel cells and water electrolysis. The present disclosure provides a NiS||Ni3S2 supported on MIL-53 electrocatalyst for a larger active area AEM water electrolyser, wherein the electrocatalyst has higher current densities (>1 A cm-2) and better stability (>100 h). PT / 2025 / 13367 An embodiment of the present disclosure provides a nickel sulphide supported on MOF-based electrocatalyst for electrochemical water splitting, wherein the electrocatalyst comprises a unique phase of nickel sulphide anchored on the MIL-53(Al) modified porous nickel foam (NSMA). In another aspect of an embodiment, the millerite nickel sulphide (NiS) phase is reconstructed to the nickel sulphide (Ni3S2) phase through controlled in-situ electroreduction (rNSMA). In some embodiment, the electrocatalyst acts at oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) with ^100 performance of 322 mV with 66 mV dec-1Tafel slope and ^100of 80 mV with 67 mV dec-1Tafel slope, respectively. In some embodiment, the electrocatalyst is further combined with the Sustainion (STN) and Aemion (AMN) membrane to form NSMA||STN||rNSMA and NSMA||AMN||rNSMA, respectively. In some embodiment, the NSMA||STN||rNSMA and NSMA||AMN||rNSMA deliver current densities of 418 mA cm-2(@25 ℃) and 1062 mA cm-2(@70 ℃), respectively, surpassing the standard catalyst pair Pt / C||STN||Ru / C values. Prolonged durability (100 h at 13X with 400 mA cm-2) is noted with 99% and 100% H2purity faradaic efficiencies. In some embodiment, the MOF covered in the electrocatalyst offers a larger surface area in the range of 1000-1500 m2 / g that enhances the dispersion of nickel sulfide and phase(s) thereof. This aids in the localization and delocalization of charge throughout the electrocatalyst. Additionally, the millerite NiS phase of nickel sulfide in the electrocatalyst (NSMA) and the Ni3S2 phase of nickel sulfide in the electrocatalyst (rNSMA) significantly contribute to their effectiveness as electrocatalysts for water splitting. Another embodiment of the present disclosure provides a process for the synthesis of nickel sulphide supported on MOF-based electrocatalyst for electrochemical water splitting, wherein said process comprises the steps of: a) synthesizing MIL-53(Al) MOF by stirring the reaction mixture of an aluminum (Al) precursor, a linker, and a solvent with heating, followed by drying to afford MIL-53(Al) MOF; PT / 2025 / 13367 b) coating the thoroughly cleaned nickel foam (NF) with a slurry containing MIL-53(Al) MOF obtained at step a), poly(vinylidene fluoride), carbon black, and N-methyl pyrrolidone by brush and keeping it for drying to afford MIL-53(Al) / NF; c) synthesizing NS / MIL-53(Al) / NF (NSMA) by taking solution of nickel (Ni) precursor and sulfur precursor in water as electrodeposition bath and carrying out electrodeposition in a three-electrode system, wherein MIL-53(Al) / NF as obtained in step b) is used as a working electrode, and Graphite rod and Standard Calomel electrode (SCE) act as auxiliary and reference electrodes, respectively, for electrodeposition followed by drying blackish nickel sulfide (NiS) deposition to afford NS / MIL-53(Al) / NF (NSMA); and d) reducing the NS / MIL-53(Al) / NF (NSMA) obtained at step c) electrochemically in a three- electrode system, wherein NSMA acts as a working electrode, and Graphite rod and Hg / HgO act as auxiliary and reference electrodes, respectively, for reduction, followed by drying to afford N3S2 / MIL-53(Al) / NF (rNSMA). In some embodiment, the Al precursor in step a) is selected from a group comprising of Aluminium chloride (AlCl3), Aluminium Nitrate Nonahydrate Al (NO3)3.9H2O) and combination thereof and has a concentration ranging from 0.1 to 0.5 M. Preferably, the Al precursor is AlCl3 or Al (NO3)3.9H2O). In some embodiment, the linker in step a) is selected from a group comprising of benzene tri-carboxylic acid (BTC), benzene di-carboxylic acid (BDC), amine substituted benzene di-carboxylic acid, dihydroxy substituted benzene di-carboxylic acid and combination thereof and has a concentration ranging from 0.1 to 0.6 M. Preferably, the linker is BDC. In some embodiment, the solvent in step a) is polar solvent selected from a group comprising of Dimethylformamide (DMF), Dimethyl sulfoxide (DMSO), water (H2O), Ethanol (CH3CH2OH) and combination thereof. Preferably, the solvent is DMF, DMSO, or ethanol. In some embodiment, the reaction mixture in step a) is heated at a temperature in the range of 160-200°C for a time period in the range of 20-30 h and drying at a temperature in the range of 150-180°C for a time period in the range of 18-24 h. In some embodiment, the drying in step b) is carried out at a temperature ranging from 80-100°C for a time period ranging from 8-10 h in vacuum. PT / 2025 / 13367 In some embodiment, the Ni precursor in step c) is selected from a group comprising Ni(NO3)2·6H2O, NiSO4·6H2O, NiCl2·6H2O, NiC4H6O4·4H2O, and a combination thereof, and has a concentration ranging from 0.3 to 0.6 M. In some embodiment, the sulfur precursor in step c) is selected from a group comprising of thiourea, sulfur powder, thioacetamide (TAA), L-cysteine (L-Cys) and a combination thereof, and has a concentration ranging from 1.3 to 1.8 M. In some embodiment, the electrodeposition in step c) is carried out at a current density in the range of -60 to -100mA cm-2for time period in the range of 10-20 minutes and drying in step c) is carried out at a temperature in the range of 80-100 °C for a time period in the range of 5- 10 h in a vacuum. In some embodiment, the reduction in step d) is carried out at a current density in the range of - 200 to -500 mA cm-2for a time period in the range of 1-5 h and drying in step d) is carried out at a temperature in the range of 80-100°C for a time period in the range of 5-10 h under vacuum. Still another embodiment of the present disclosure is to provide a process for electrochemical water splitting, wherein said process comprises the NSMA as an anode and rNSMA as a cathode are utilized for performing full-cell experiments in 10X and 13X electrolyzer systems. In an aspect of an embodiment, reactions 1-3 are involved in forming a nickel sulfide film on the substrate as explained in step c) of the above-said process; Ni2++ 2e → Ni (1) CS(NH2)2 + 2e → S2−+ CN−+ NH4+(2) xNi2++ yS2−→ NixSy(3) During the electrodeposition, Ni2+can be reduced to Ni on the MIL-53(Al) substrate surface (eq-1). The S2-generated by splitting the CS(NH2)2 molecule (eq-2). The final nickel sulfide forms by reaction of Ni2+and S2-(eq-3). Yet another embodiment of the present disclosure is to provide a process for water splitting, wherein the NSMA as anode and rNSMA as a cathode are used for performing full-cell experiments in 10X and 13X electrolyzer systems. PT / 2025 / 13367 EXAMPLES Example 1: Synthesis of MIL-53 MOF Firstly, (Al (NO3)3.9H2O) or AlCl3, BDC or BTC, and DMF or water or DMSO or ethanol was taken in a 250 ml beaker. Afterward, the above solution was stirred for 10-20 min, transferred into a Teflon liner hydrothermal autoclave, and kept at 160-2000C for 20-30 h. After completion of the reaction, the final product washing was carried out under DMF and the ethanol solution and kept for drying at 150-1800C for 18-24 h. Finally, the white color compound was obtained, and Powder X-ray diffraction confirms crystallinity (Fig.1). Example 2: Synthesis of MIL-53 / NF Nickel Foam (NF) was cut into (1 cm x 3 cm) rectangular sheet. The NF was cleaned with deionized water, 3-5 M HCl, deionized water, and ethanol (each for 10-15 minutes respectively with sonication) to remove the oxides and impurities from the surface of NF and then dried at 80-1000C for three hours. The 1 cm x 1 cm area of NF foam was coated by prepared slurry, and the rest was covered by Teflon tape. 89-95% (MIL-53 MOF), 2-5% (Poly(vinylidene fluoride), 2-5% (carbon black), and 70-100 µL (N-Methyl pyrrolidone) were taken for making slurry and coated on NF (1 cm x 1 cm) by brush and kept it for drying at 80-1000C for 8-10 h in vacuum. Finally, MIL-53(Al) / NF is obtained, which is subjected to the next step (Fig.1). Example 3: Synthesis of NS / MIL-53(Al) / NF (NSMA) Typically, a solution consisting of Ni(NO3)2.6H2O or Ni(NO3)2·6H2O or NiSO4·6H2O, NiCl2·6H2O or NiC4H6O4·4H2O and thiourea or sulfur powder or TAA or L-Cys in 50-100 ml of MQ water was taken as the electrodeposition bath. The electrodeposition was carried out in a three-electrode system, where MIL-53(Al) / NF was used as a working electrode, and Graphite rod and Standard Calomel electrode (SCE) were used as auxiliary and reference electrodes, respectively. A current density of -60 to -100mA cm-2is used for 10-20 minutes for electrodeposition. The reactions of Nickel Sulfide (NiS) electrodeposited on MIL-53(Al) / NF. A blackish electrodeposit was obtained and dried at 80-1000C for 5-10 h in a vacuum. Example 4: Synthesis of electrochemically reduced NS / MIL-53(Al) / NF (rNSMA) The electrochemical reduction was carried out in a three-electrode system. NSMA was used as a working electrode, and Graphite rod and Hg / HgO were used as auxiliary and reference PT / 2025 / 13367 electrodes, respectively. A constant current density of -200 to -500 mA cm-2for 1-5 h for reduction is used. A darker black color electrode was obtained and subjected to a drying of 80- 1000C for 5-10 h under a vacuum. Characterization of synthesized electrocatalyst: The phase and crystallinity of the material were appraised through a Rigaku 2D X-ray micro diffractometer (Model MicroMax-007HF) equipped with a high-intensity microfocus rotating anode X-ray generator and PANalytical X’Pert PRO at a scan rate of 1 degree min-1in the 2θ range of 5 to 80 degree. FEI Nova Nano SEM 450 field-emission scanning electron microscopy (FESEM) instrument (operating voltage 0.5kV to 30kV) integrated with Energy Dispersive Spectroscopy (EDS) was used to analyze the morphology and element present in the materials. High-resolution imaging was performed using the JEOL JEM F-200 HRTEM instrument (operating voltage 80kV to 200kV), and RADIUS Desktop 2.0 software was used to measure the fringes. The X-ray photoelectron spectroscopy (XPS) was performed on a Thermo Scientific K ALPHA+ instrument, a fully integrated, monochromatic small-spot X-ray Photoelectron Spectroscopy (XPS) system. A Quantachrome Autosorb iQ2 instrument was used for the BET analysis, and the data was analyzed using ASiQwin Software. Precursors such as Ni(NO3)2.6H2O or Ni(NO3)2·6H2O or NiSO4·6H2O, NiCl2·6H2O or NiC4H6O4·4H2O for nickel and thiourea or sulfur powder or TAA or L-Cys for sulphur with different electrodeposition time period such as 5 or 10 or 15 or 20 min are also tested to achieve better activity for electrodeposited Nickel Sulfide (NiS) on the Bare Nickel Form (NF). However, after achieving better performance, the issue of the catalyst leaching from the NF is raised, and the catalyst's performance is lost. So, to mitigate this issue, a high surface area (BET surface area 1160 m2 / g) MOF is synthesized by tuning the concentration of precursors, temperature, and solvothermal time to modify the NF substrate [Jiang et al., Angewandte Chemie International Edition, 57 (2018) 3916-3921]. Afterward, MIL-53(Al) is decorated onto Nickel Foam (NF) through slurry coating to enhance the surface area of the support and improve the NiS binding to the substrate. Finally, NiS is electrodeposited on MIL-53(Al) / NF using NiCl2and CS(NH2)2as Ni and S sources, respectively. Reactions 1-3 are involved in depositing the Nickel sulfide layer on MIL-53(Al) / NF. The millerite NiS phase formed during electrodeposition and demonstrated the interfacial interaction with MIL-53(Al). Interestingly, the millerite NiS phase reconstructs itself to the Ni3S2phase during the chronoamperometry PT / 2025 / 13367 (CP) and forms rNSMA. The process is explained in the Schematic illustration is given in Figure 1. The NiS is prone to form millerite NiS corresponding to the 0.2-0.3 V v / s RHE at pH 4, depicted in the Pourbaix diagram created by Yan et al. [Catalysis, Joule, 1 (2017) 600-612]. By applying -200 to -500 mA cm-2with pH 4-5, the Pourbaix diagram assumptions and obtain a potential of around 0.2-0.3 V v / s RHE can be reciprocated. Nevertheless, the millerite NiS phase is reduced to Ni3S2by chronoamperometry (CP) under alkaline conditions. So, the above results align with the assumptions of the Pourbaix diagram. To understand the phase purity and crystal phases present in the NSMA, and rNSMA are analyzed by X-ray diffraction (XRD) and compared with the JCPDS file Figure 2a. All catalysts are subjected to X-ray diffraction at a scan rate of 1 degree per minute because it is hard to detect less intense peaks at higher scan rates. NSMA shows the same XRD pattern as NiS because the electrodeposition synthesized sample forms nano-crystalline of millerite NiS. However, after electrochemical reduction, the millerite NiS is wholly transformed into Ni3S2with 5-6 nm crystallite size in the hexagonal shape in Figure 2c. Hence, the XRD diffraction peak in the case of rNSMA, as shown in Figure 2a, can be detected. The main peak match 2θ values of 21.76º, 31.76º, 37.78º, 38.27º, 44.33º, 49.73º, 50.12º, and 55.16º can be well matched with the (101), (110), (003), (021), (202), (113), (211), and (122) planes of the Ni3S2phase (JCPDS No.44-1418) indicated the only Ni3S2 phase is present after the reconstruction. The catalyst is scratched from the Nickel Foam to perform HRTEM because the catalyst is synthesized by electrodeposition on the substrate. Figure 2b shows the distinctive lattice fringes with interplanar spacing of 0.220 nm and 0.174 nm, corresponding to millerite NiS planes (211) and (411) and the selected area electron diffraction (SAED) pattern of NSMA (inset in Figure 2b) indicates the crystalline nature of NSMA. After electrochemical reduction, the lattice fringes with interplanar spacing 0.166 nm, 0.181 nm, and 0.183 nm, which correspond to Ni3S2 planes (122) and (211) and (113), respectively, can be observed in Figure 2c. Crystallinity for the reconstructed phase Ni3S2in rNSMA is confirmed by the selected area electron diffraction (SAED) pattern (inset in Figure 2c). The High-Angle Annular Dark-Field Scanning Transmission Electron Microscopy (HAADF-STEM) image of NSMA and rNSMA is presented in Figure 2d-e, respectively, with the respective elemental mapping analysis data, which confirm the uniform distribution of the Ni, S, and Al. The HRTEM results align well PT / 2025 / 13367 with the XRD data, validating the reconstruction of the millerite NiS phase to Ni3S2after in- situ reduction. Other techniques like FESEM and XPS also support the phase reconstruction. Electrochemical Measurements A Potentiostat (Bio-Logic-SP-300) is used for the electrochemical analysis of the synthesized materials in 1 M KOH solution using a three-electrode setup. The Hg / HgO is used as the reference electrode (RE), graphite rod as the counter electrode (CE), and as prepared self- standing catalysts as the working electrode (WE) with an active area of 1 x 1 cm2. The Hg / HgO electrode is calibrated in an H2-saturated 1 M KOH solution. After the calibration results, the potentials concerning RHE are referenced by adding 0.925 V. The following equation is used to reference the potentials concerning RHE. ERHE= EHg / HgO+ 0.0591pH + 0.098 (4) The electrochemical cyclic voltammetry (CV) analysis is performed in 1 M KOH solution. Before performing the linear sweep voltammetry (LSV) at a scan rate of 1 mVs-1, 25 cycles of CV and LSV are done at 50 mV s-1at room temperature. The overpotential value is calculated using the LSV plot, which is 100 % iR corrected. The Tafel slopes are calculated from the linear sweep voltammograms by the equation. η = a+ b logj (5) Where η is the overpotential at a given current density j, b is the Tafel slope, and a is the intercept. For comparison, the commercial Ru / C and Pt / C catalysts are coated on NF in a 1 x 1 cm2area with a loading of 4 mg cm2, and the analysis is done by keeping a similar condition. For the overall water splitting analysis, 1 x 1 cm2of NSMA as anode and rNSMA as cathode were used. The device-level performance of NSMA is checked on 5.5 cm2(10X) and 13 cm2(13X) active area electrolyzer cells in 1 M KOH. The electrochemical surface area (ECSA) analysis is performed by recording CV in the non-faradic region (0.16 to 0.26 V) at different scan rates. The peak current obtained at 0.21 V is plotted against the corresponding scan rate to get a straight line, where the slope corresponds to the double-layer capacitance (Cdl) value. Using the specific capacitance (Cs) of the elements, the ECSA value can be calculated from the following equation: PT / 2025 / 13367 ECSA = Cdl / Cs(6) The overall water splitting is performed with NSMA and rNSMA as Anode and Cathode, respectively. The water displacement method evaluated the amount of gas that evolved during the OWS at the 5.5 cm2electrolyzer cell. The gas purity is checked using gas chromatography (GC), where a SHIMADZU Nexis GC-2030 gas chromatograph is fitted with a thermal conductivity detector (TCD), and Nitrogen is used as the carrier gas. The carbosphere column is used to detect the gases. The oven temperature is maintained at 50 °C, and the detector temperature is kept at 100 °C during the measurements. A tight syringe injected 500 µL of gas from the headspace into the GC. The HER performance of all prepared electrocatalysts NiS, Pt / C, Al-MOF, Bare NF, NSMA, and rNSMA is assessed in a three-electrode setup in 30 ml of 1M KOH electrolyte. For reference, the same experimental conditions are applied to the Pt / C catalyst. All the Linear Sweep Voltammograms (LSV) curves are recorded with 100% iR drop (ZIR) at a low scan rate of 1 mV / s, as shown in Figure 3a. The standard Pt / C exhibits an overpotential of 34 mV to reach a current density of 100 mA cm-2. The synthesized MIL-53(Al), NS, and bare Nickel foam require an overpotential of 267 mV, 143 mV, and 434 mV to get a current density of 100 mA cm-2,respectively. However, the NSMA catalyst exhibits an overpotential of only 137 mV to generate 100 mA cm-2,significantly lower than electrodeposited NiS for the given experimental condition. After electrochemical reduction, the overpotential decreased considerably from 137 mV to 80 mV for 100 mA cm-2current density due to the phase reconstruction from the millerite NiS phase to the Ni3S2phase. According to several reports, the Ni3S2 secured the most activity among all the NiS phases for HER. Here, a microporous substrate provides better dispersion of the active site of reconstructed Ni3S2 and better charge transfer. Furthermore, to analyze the catalyst performance and the reaction kinetics, the Tafel slope of all the prepared catalysts is calculated in Figure 3b. The NSMA catalyst shows a Tafel value of 83 mV / dec, which is lower than MIL-53(Al) (104 mV / dec) NiS (88 mV / dec). However, the rNSMA catalyst Tafel value improves from 83 mV / dec to 67 mV / dec after electrochemical reduction due to the phase reconstruction and electron transfer channel formation through MIL- 53(Al). The above results suggest that NSMA exhibits better activity than NiS due to the better dispersion of the catalyst on the porous substrate. The NSMA catalyst forms an agglomerated spheres type of morphology, but after electrochemical reduction, the catalyst reconstructs from PT / 2025 / 13367 Millerite NiS to Ni3S2and forms the flower-like morphology. The nanosheets are randomly but densely oriented with enough void space for electrolyte flow, which could promote higher HER performance. OER activity tests are also conducted on synthesized catalysts in a three-electrode system using 1M KOH aqueous solution. The NSMA displayed an impressive performance in OER, achieving a 100 mA cm-2current density value at 322 mV (η100). However, MIL-53(Al) and NiS struggled to reach 100 mA cm-2current density at 422 mV and 337 mV, respectively. Compared with the benchmarked catalyst Ru / C and bare NF, the NSMA catalyst has shown better activity. NF and Ru / C required 467 mV and 347 mV overpotential to get 100 mA cm-2current density Figure 3c. The Tafel slope values for NF, Al-MOF, Ru / C, and NiS are 154 mV dec-1, 150 mV dec-1, 78 mV dec-1and 129 mV dec-1, respectively, which is higher than NSMA (66 mV dec-1). The lower Tafel value indicates the superior kinetics of the NSMA Figure 3d. Ensuring the superior HER and OER performance by rNSMA / NF and NSMA / NF, respectively NSMA as anode and rNSMA as a cathode, is employed for OWS. Primitively, the open cell NSMA || rNSMA with a 1 cm2active electrode area is set up to evaluate the performance for OWS. Then LSV is recorded without iR compensation at a scan rate of 5 mV / s after stabilization, which showed 1.49 V potential to afford the electrolytic current density of 10 mA cm-2by outperforming the state-of-the-art electrocatalyst cell configuration Pt / C || Ru / C (required 1.586 V for attaining 10 mA cm-2current density) Figure 3e. Moreover, NSMA || rNSMA cell configuration shows superb durability as only negligible voltage augment (1 µV / h degradation rate and 99.4% retention) is observed over 100 h continuous electrolysis at a constant current density of 10 mA cm-2. The minimal degradation rate after 100 h shows the robustness of the catalyst for long-term OWS, which makes NSMA and rNSMA suitable candidates for industrial scale. Example 5: AEM electrolyzer level testing (5.5 cm2active electrode area) (10X) Like undivided cell (1 cm2), in 5.5 cm2AEM zero gap electrolyzer systems, NSMA as anode and rNSMA as cathode were used for performing full-cell experiments. The cell was purchased from Dioxide Materials, and the actual active area is 2.35 cm x 2.35 cm, on which the catalyst was coated. Hence, the current densities reported in this work are as per the actual electrode area (5.5 cm2). NSMA as cathode and rNSMA as anode were used for water electrolysis. SustainionTMX37-50 grade 60 with a thickness of approximately 50 µm was used as AEM. PT / 2025 / 13367 The membrane was soaked in 1 M KOH solution for 20-40 h, and then heat treatment was performed for 5-10 h at 55-60 ˚C. The AEMWE performance and durability were evaluated on square-shaped single-cell tests with an active area of 5.5 cm2.1 M KOH solution was used as an electrolyte and was supplied from both sides at a flow rate of 1-5 mL min cm-2with the help of a peristaltic pump. The Membrane Electrode Assembly (MEA) was assembled with a fixed torque of 1.0-5.0 N⋅m. and the cell performance was evaluated via the linear sweep voltammetry method from 0 to 2 V at a scan rate of 5 mV s-1. In addition, impedance measurements (16 kHz–50mHz) were performed at a constant voltage of 1.8 V with an amplitude of 50 mV to measure the ohmic charge transfer and mass transfer resistance of the 5.5 cm2. The durability of the 10X AEMWE was evaluated using a chronoamperometry test at various applied current densities of 182, 364, 545, 727, and 909 mA cm-2. Example 6: AEM electrolyzer level testing (12.96 cm2active electrode area)(13X) AEM electrolyzer cell with a 12.96 cm2active area was fabricated in the laboratory inspired by Symes et al. [ Electrochimica Acta, 2023, 444, 142030]. NSMA as an anode and rNSMA as a cathode were used for the AEM electrolyzer cell. Aemion membrane used a separator thickness of approximately 80-90 µm. Initially, the membrane was soaked in 1M KCL to convert iodide ions with chloride ions for 24-48 h and then immersed in 1 M KOH for 24-48h to convert all the chloride ions into hydroxyl ions. Pre-heated 1 M KOH solution electrolyte feed from both sides (Anode and Cathode) at a flow rate of 2 to 5 mL min cm-2with the help of a peristaltic pump. Hot Plates were used to heat the electrolyte solution. The Membrane Electrode Assembly (MEA) was assembled with a 1 to 5 N⋅m torque. The cell performance was evaluated via the linear sweep voltammetry method from 0 to 2 V at a scan rate of 5 mV s-1. The durability of the AEM electrolyzer cell was assessed using a chronoamperometry test applied to a current density of 400 mA cm-2at 40 ℃ by using a power supply (Itech ITDM / 3900 / D / 10 / 170) with 10V and 170 A). 5.5cm2Zero gap electrolyser cell performance (10X) After accomplishing the excellent performance at 1cm2, the NSMA (anode) and rNSMA (cathode) catalysts were subjected to constructing the cell configuration NSMA || STN || rNSMA at 5.5 cm2electrolyzer cell level to evaluate the potential application at large scale. Before assembling, the STN membrane was activated by keeping it in 1M KOH solution for 24 - 48 h, and before mounting on the electrolyzer cell, the membrane was heated at 55-60 ℃ PT / 2025 / 13367 for 5-10 h in 1M KOH solution. The electrolyzer cell was assembled by following the instructions given above. After cell assembly, the current density at 2V (25 ℃) was used to assess the performance. At the same time, identical conditions were applied to the standard electrocatalysts, namely Pt / C (5 wt%) for HER and Ru / C (5 wt%) for OER, forming Ru / C || STN || Pt / C cell configuration. The NSMA || STN || rNSMA configuration outperformed the standard catalysts configuration Ru / C || STN || Pt / C (322 mA / cm2at 2V) by showing 418 mA / cm2current density at 2V as shown in the polarization curve in Figure 4a. However, in the case of Ru / C || STN || Pt / C, destabilization is observed at the mass transport region due to the leaching of the Ru / C catalyst. The short duration of CP at higher current density is relatable to the long-run CP at lower current density. So, to check the robustness of catalysts NSMA and rNSMA at a larger scale, the durability test was performed by applying the current density in the form of the staircase from 0.182 A cm-2(1A current) to 0.909 A cm-2(5A current) with a duration of 2h for each current Figure 4b. Interestingly, the NSMA || STN || rNSMA configuration outperforms the benchmark configuration Ru / C || STN || Pt / C at lower as well as higher current density, which shows the robustness of the catalysts for AEM technology. Here, in the case of NSMA || STN || rNSMA configuration, MIL-53 porous support helps to sustain the catalyst at a higher current density and electron channels through porous support to enhance the activity of the catalyst. 13cm2Zero gap electrolyser cell performance (13X) The pertinent way to check the catalyst's potential to reach the industrial level. It should go through the same industrial conditions. In industrial water splitting, the operational temperature is 60 to 70 ℃, and the active area of electrodes is more than 10 cm2. In this scenario, 12.96 cm2active area electrodes were coated for a 13 cm2AEM electrolyzer cell. Both electrodes were sandwiched between the monopolar plate using an AMN membrane to separate the anode and cathode. The assembly procedure for the 13 cm2cell is mentioned above. After the 13 cm2cell assembly, the polarization curve of NSMA||AMN||rNSMA assembly was measured over the temperature range. In Figure 4c, as the temperature of the electrolyzer cell gradually increased from Room Temperature (RT) (25 ℃) to 70 ℃ the current density required by NSMA||AMN||rNSMA configuration to achieve 2V also increased from 0.381 A cm-2to 1.062 A cm-2respectively. The correlation graph in Figure 4d between J2 (Current density at 2V) and temperature shows the exponential increase in current density with temperature, proving that the NSMA and rNSMA perform well in harsh conditions like 70 ℃ and 1 M KOH. PT / 2025 / 13367 Furthermore, the assembled NSMA||AMN||rNSMA AEM cell demonstrates remarkable stability for 100 h at 400 mA cm−2at 40 ℃ with an industrially accepted degradation rate of 0.5 mV / h Figure 4e. The low degradation rate due to the robust nature of the NSMA and rNSMA catalysts yields a negligible change in activity after 100 h operation at 40 ℃. Moreover, the electrolyzer was shut down two times for 12h between the stability operations to ensure activity retention after the on-off cycle. Interestingly, there is no change in activity after the on-off cycle. It shows an active site of the NiS nanoparticle over the MIL-53(Al) nanorods and the electronic variables promoting the performance of both OER and HER. ADVANTAGES OF THE INVENTION: • Developing electrocatalysts from cheaper non-PGM precursors in near-ambient conditions significantly contributes to cost-effectiveness and effortless scalability. • To prevent the leaching of the electrocatalyst, the substrate is decorated by the MIL- 53(Al) and the active nickel sulphide instead of using a binder (i.e., Ionomer) • MIL-53(Al) is used for the first time for electrochemical water splitting. • The electrocatalyst shows better performance in HER (80 mV at 100 mA cm-2) as well as OER (322 mV at 100 mA cm-2) activity. • The present disclosure provides MOF between the substrate and catalyst which help to increase the performance and activity of the electrocatalyst surpassing to the state of art catalyst Pt||Ru. • It also provides the performance at 12.96 cm2area more than 1 A cm-2 at 2 V. • It also provides electrocatalyst having 100 h of stability at 12.96 cm2electrolyzer cell, and current density at 2V is >1 A cm-2. • The present disclosure provides a NiS||Ni3S2supported on MIL-53 electrocatalyst, wherein the electrocatalyst comprises a unique phase of NiS anchored on the MIL-53(Al) modified porous nickel foam (NSMA) as an OER catalyst with ^100 performance of 322 mV with 66 mV dec-1Tafel slope. PT / 2025 / 13367 • The millerite NiS phase reconstructed to Ni3S2phase through controlled in-situ electroreduction (rNSMA) is the HER catalyst with ^100 of 80 mV with 67 mV dec-1Tafel slope. • At device levels (10X (5.5 cm2) and 13X (12.96 cm2)), the pair, along with Sustainion or Aemion membrane, NSMA||STN||rNSMA, and NSMA||AMN||rNSMA deliver current densities of 414 mA cm-2(@25 ℃) and 1062 mA cm-2(@70 ℃), respectively, surpassing the standard catalyst pair Pt / C||STN||Ru / C values.

Claims

PT / 2025 / 13367 WE CLAIM:

1. An electrocatalyst for water splitting, comprising: combination of nickel sulphide and metal organic framework (MOF) supported on a support, wherein the electrocatalyst comprises phase(s) of nickel sulphide anchored on the MOF, and the MOF is coated onto the support; and a surface area of the MOF contained in the electrocatalyst is in the range of 1000 m2 / g to 1500 m2 / g.

2. The electrocatalyst as claimed in claim 1, wherein the phase(s) of nickel sulphide is represented by the formula: NixSy, wherein x is in the range of 1 to 3 and y is 1 or 2; the electrocatalyst is unreduced or electrochemically reduced electrocatalyst; the electrocatalyst comprises phase(s) of nickel sulphide based on millerite nickel sulphide (NiS), and / or trinickel disulfide (Ni3S2); the electrocatalyst comprises phase(s) of nickel sulphide having crystallite size in the range of 5-6 nm, and are in hexagonal shape; and the electrocatalyst comprises uniform distribution of combination of elements selected from nickel, sulfur, and aluminium.

3. The electrocatalyst as claimed in claim 1, wherein the MOF is selected from a material of Institut Lavoisier-53 (MIL-53), with a metal selected from group 13 element; and the support is selected from nickel foam, nickel mesh, nickel felt, stainless steel fiber, and carbon paper.

4. A process for the synthesis of the electrocatalyst as claimed in claim 1 or 2, the process comprising:PT / 2025 / 13367 a) stirring a reaction mixture of precursor of group 13 element, a linker, and a solvent with heating followed by drying to afford MOF; b) coating a support with a slurry comprising the MOF obtained in step a), poly(vinylidene fluoride), carbon black, and N-methyl pyrrolidone, followed by drying to afford MOF coated support; c) taking solution of nickel (Ni) precursor and sulfur precursor in water as electrodeposition bath and carrying out electrodeposition in a three-electrode system, wherein the three-electrode system comprises the MOF coated support as obtained in step b) is used as a working electrode, graphite rod as auxiliary electrode, and standard calomel electrode (SCE) as reference electrode, respectively, for the electrodeposition followed by drying to obtain the unreduced electrocatalyst; and d) reducing the unreduced electrocatalyst as obtained in step c) electrochemically in a three-electrode system, wherein the unreduced electrocatalyst acts as a working electrode, graphite rod as auxiliary electrode, and Hg / HgO as reference electrode, respectively for reduction, followed by drying to afford the reduced electrocatalyst.

5. The method as claimed in claim 4, wherein the precursor of group 13 element is selected from chloride of group 13 element, nitrate of group 13 element, sulfate of group 13 element, hydroxide of group 13 element, and lactate of group 13 element; a concentration of the precursor of group 13 element is ranging from 0.1 to 0.5 M; the linker in step a) is selected from a group comprising of benzene tri-carboxylic acid (BTC), and benzene di-carboxylic acid (BDC), amine substituted benzene di-carboxylic acid, dihydroxy substituted benzene di-carboxylic acid, or combination thereof; a concentration of the linker is ranging from 0.1 to 0.6 M; and the solvent in step a) is polar solvent selected from a group comprising of dimethylformamide (DMF), dimethyl sulfoxide (DMSO), water (H2O), and ethanol (CH3CH2OH) or any of combination thereof.

6. The method as claimed in claim 4, whereinPT / 2025 / 13367 the reaction mixture in step a) is heated at a temperature in the range of 160-200°C for a time period in the range of 20-30 h and drying at a temperature in the range of 150- 180°C for a time period in the range of 18-24 h; and the drying in step b) is carried out at a temperature ranging from 80-100°C for a time period ranging from 8-10 h in a vacuum.

7. The method as claimed in claim 4, wherein the Ni precursor in step c) is selected from a group comprising of Ni(NO3)2·6H2O, NiSO4·6H2O, NiCl2·6H2O, and NiC4H6O4·4H2O or any of combination thereof; a concentration of the Ni precursor is ranging from 0.3 to 0.6 M; the sulfur precursor in step c) is selected from a group comprising of thiourea, sulfur powder, thioacetamide (TAA), L-cysteine (L-Cys) and combination thereof; and a concentration of the sulfur precursor is ranging from 1.3 to 1.8 M.

8. The method as claimed in claim 4, wherein the electrodeposition in step c) is carried out at a current density in the range of -60 mA cm-2to -100 mA cm-2for time period in the range of 10-20 minutes and drying in step c) is carried out at a temperature in the range of 80-100 °C for a time period in the range of 5-10 h in a vacuum; and the reduction in step d) is carried out at a current density in the range of -200 to -500 mA cm-2for a time period in the range of 1-5 h and drying in step d) is carried out at a temperature in the range of 80-100°C for a time period in the range of 5-10 h under vacuum.

9. An electrolyzer for water splitting comprising: i. the electrocatalyst as claimed in claim 1 as an anode and / or a cathode; ii. anion exchange membrane; and iii. electrolyte.PT / 2025 / 13367 10. A process for water splitting, comprising treating water with the electrocatalyst as claimed in claim 1 as an anode and / or as a cathode for performing full-cell experiment in 5.5 cm2(10X) and 12.96 cm2(13X) electrolyzer.

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