Indigenous diaphragm and non-noble BI-functional catalysts based alkaline wastewaters electrolyzer

Abstract

The present invention provides electrolyzer system that comprises of a membrane electrode assembly, and an electrolyte; wherein the membrane electrode assembly comprises of the anode, cathode, and a separator membrane; characterized in that the separator membrane is a hexagonal boron nitride (HBN) coated chitosan-based diaphragm. Further the present invention provides an HBN dispersed chitosan-based indigenous diaphragm membrane and a method of preparation thereof. Furthermore, the present invention provides catalysts and a method of preparation thereof.

Description

[0001] INDIGENOUS DIAPHRAGM AND NON-NOBLE BI-FUNCTIONAL CATALYSTS BASED ALKALINE WASTEWATERS ELECTROLYZER

[0002] FIELD OF INVENTION

[0003] The present invention relates to advancements in the field of hydrogen production, from wastewater, employing electrolyzers. Particularly the present invention relates to employing electrolyzers. More particularly the present invention relates to zero gap alkaline electrolyzer system including an anode, cathode, a indigenous diaphragm membrane and an electrolyte.

[0004] BACKGROUND OF THE INVENTION

[0005] Global energy demand is expected to double by 2050 and triple by the end of the 21st century. Given the severe pollution caused by conventional fossil fuel usage, it is essential to explore renewable energy sources. Despite the intermittent nature of sustainable natural resources, storing energy in molecular bonds like hydrogen has advantages over electrochemical storage methods such as Li-ion batteries, which suffer from selfdischarge during storage. Hydrogen is considered a promising energy carrier for future socio-economic development. However, its current predominant production method, utilizing fossil fuels, contributes to approximately 830 million tons of CO2 emissions annually. Steam methane reforming (SME) is the prevalent method for gray hydrogen production (48%), emitting at least 6.6 tons of CO2 per 1 ton of H2. To meet international carbon neutrality goals, there is an urgent need to boost the market for green hydrogen production.

[0006] To overcome the challenge of green hydrogen production, methods like water electrolysis are being considered as an attractive alternative to fossil-fuel-based techniques. However, a major obstacle to widespread adoption of green hydrogen production is the need for ultrapure water, which puts pressure on freshwater resources. Efforts have been made to explore alternative water sources, such as seawater electrolysis. But the presence of salts in seawater poses challenges, leading to the generation of harmful chlorine gas and corrosion of catalyst and support materials. Water-related issues in many countries are hindering the development of green hydrogen infrastructure. To address this, utilizing treated wastewater has been identified as an effective strategy. Significant waste in agricultural, domestic, and industrial sectors necessitates efficient wastewater treatment methods. Traditional methods are often ineffective, while the organic matter in wastewater, with a potential energy content of 17.8 kJ g-1COD, can be a valuable resource. Biological H2 production offers numerous benefits in contrast to photoelectrochemical or thermochemical processes, given its minimal energy demands and cost-effective nature. Among the array of wastewater biotreatment technologies, the bioelectrochemical method stands out as an effective approach for producing harmless wastewater and utilizing resources efficiently.

[0007] Green hydrogen production from wastewater has significant potential for development. Industries such as distilleries and wastewater treatment plants can use water recycling to create green hydrogen and oxygen. Distilleries are looking to replace fossil fuels in boilers with green hydrogen and sell any excess green hydrogen produced from these processes on the market. The involvement of the wastewater industry in this eco-friendly production process is crucial for meeting decarbonization targets. Given the challenges posed by global warming and climate change due to high greenhouse gas emissions, it is essential to develop low-carbon, clean, and sustainable energy sources for achieving carbon neutrality.

[0008] Wastewater treatment processes also result in significant CCb-equi valent emissions. Additionally, an estimated 5.5 billion liters of pure water are required to produce 3 million tons of H2, equivalent to the annual water consumption of 1.6 million people. Simultaneous degradation and hydrogen production during wastewater treatment provide an opportunity to reduce freshwater consumption and address water shortages in hydrogen production through water splitting.

[0009] Efforts are being made to explore more cost-effective and cleaner methods for hydrogen production, and water treatment is proving to be a promising source of green hydrogen that is attracting increasing interest. Water electrolysis is a suitable, dependable, and scalable solution for converting renewable electricity into the chemical energy of green hydrogen. The proton exchange membrane water electrolyzer (PEMWE), solid oxide electrolysis cell (SOEC), alkaline water electrolyzer (AWE), and anion exchange membrane water electrolyzer (AEMWE) are the main technologies for this purpose. SOEC is suitable for industrial settings with readily available high-temperature streams. The cost of PEMWE is significantly influenced by membrane material expenses, while AEMWE faces maintenance costs due to membrane stability issues.

[0010] Alkaline water electrolysis is a promising method for energy conversion. Developing transition metal-based electrocatalyst materials with low overpotential and fast kinetics is crucial for improving efficiency and reducing costs. Industrial wastewater is a viable solution for sustainable green hydrogen production, providing an environmentally friendly alternative to conventional methods. However, wastewater contains various ions, salts, impurities, and microbes, which can pose risks for the corrosion of electrolyzer components such as the anode, cathode, and diaphragm. Nevertheless, it also presents an opportunity for innovative solutions in electrolyzer design and operation.

[0011] To address these challenges, the inventors have developed a method for producing hydrogen and oxygen from wastewater. The system features a zero-gap alkaline electrolyzer with non-noble catalysts (Ni-NCNT, NiFe-NCNT, and NiFe-ECNT) composed of transition metal nanoparticles encapsulated within carbonaceous structures, specifically nitrogen-doped carbon nanotubes (NCNT) and etched carbon nanotubes (ECNT), which funchon as bifunctional catalysts. These catalysts are applied to carbon cloth substrates, serving as both the anode and cathode components. Additionally, the invention incorporates a chitosan-based indigenous diaphragm membrane as a separator. This membrane is fabricated using a straightforward casting technique, resulting in the production of high-purity gases at the anode and cathode, thereby enhancing the overall efficiency and efficacy of the hydrogen production process.

[0012] SUMMARY OF THE INVENTION The present invention discloses an electrolyzer system for the production of hydrogen and oxygen from wastewater. More particularly the present invention relates to a zerogap alkaline water electrolyzer that comprises an anode, cathode, an indigenous diaphragm membrane and an electrolyte. The anode and the cathode are prepared by using a catalyst comprising transition metal nanoparticles encapsulated in carbonaceous structures. The indigenous diaphragm membrane is chitosan-based indigenous diaphragm membrane that is dispersed with hexagonal boron nitride (HBN) and aged in Cu2+solution.

[0013] Further the present invention relates to a method for preparing the chitosan-based indigenous diaphragm membrane. The HBN coated chitosan-based indigenous diaphragm membrane of the present invention configured as a separator between the anode and cathode prevents crossover and permeation of hydrogen and oxygen gases. The indigenous diaphragm membrane enhances ion transport and provides improved selectivity for the evolved gases during electrolysis.

[0014] BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order that the invention may be readily understood and put into practical effect, reference will now be made to exemplary embodiments as illustrated with reference to the accompanying figures. The figures together with a detailed description below, are incorporated in and form part of the specification, and serve to further illustrate the embodiments and explain various principles and advantages, in accordance with the present invention where:

[0016] Figure 1 illustrates zero-gap alkaline electrolyzer.

[0017] Figure 2 illustrates components of zero-gap alkaline electrolyzer.

[0018] Figure 3 illustrates the setup for hydrogen production from industrial wastewater. Figure 4 illustrates (a) X-Ray diffractogram of the catalysts; (b) X-Ray diffractogram of chitosan-based diaphragm membranes.

[0019] Figure 5 illustrates Raman spectra of the catalysts.

[0020] Figure 6 illustrates (a and b) illustrates SEM image of Ni NCNT, (c) elemental mapping of Ni NCNT

[0021] Figure 7 illustrates (a and b) SEM image of NiFe NCNT and (c) elemental mapping of NiFe NCNT

[0022] Figure 8 illustrates (a, b) SEM image of NiFe ECNT; and (c) Elemental mapping of NiFe ECNT

[0023] Figure 9 illustrates SEM image of Chitosan based diaphragm membranes.

[0024] Figure 10 illustrates (a) OER polarization curve of the catalysts in 3 M KOH + Industrial wastewater; (b) HER polarization curve of the catalysts in 3 M KOH + Industrial wastewater; and (c) Tafel plot of the catalysts in OER; d. Tafel plot of the catalysts in HER

[0025] Figure 11 illustrates long term stability test of the catalysts at 10 mA / cm2 in 3 M KOH + Industrial wastewater.

[0026] Figure 12 illustrates electrochemical performance of the catalysts in 3 M KOH + Industrial Wastewater.

[0027] Figure 13 illustrates electrochemical performance of Ni NCNT with different diaphragm membranes.

[0028] Figure 14 illustrates chlorine test to confirm absence of chlorine evolution.

[0029] DETAILED DESCRIPTION OF THE INVENTION At the very outset of the detailed description, it may be understood that the ensuing description only illustrates a particular form of this invention. However, such a particular form is only an exemplary embodiment, and without intending to imply any limitation on the scope of this invention. Accordingly, the description is to be understood as an exemplary embodiment and teaching of invention and not intended to be taken restrictively.

[0030] Unless defined otherwise, technical, and scientific terms used herein have the same meaning as commonly understood by one of the ordinary skills in the art to which this invention belongs. Further, unless otherwise required by context, singular terms shall include pluralities and plural terms shall include the singular.

[0031] As used herein, the terms "comprise," "comprising," or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a method that comprises a list of acts does not include only those acts but may include other acts not expressly listed or inherent to such method. In other words, one or more acts in a method proceeded by "comprises... a" does not, without more constraints, preclude the existence of other acts or additional acts.

[0032] As used herein, "zero-gap" implies that the distance between the anode and cathode is near to zero. This minimizes the resistance of the overall cell significantly. The zero-gap configuration is achieved by sandwiching the cellulose-based material or a synthetic polymer-based material between the bifunctional anode and cathode in a separator electrode assembly.

[0033] As used herein, electrode means cathode and anode.

[0034] As used herein, the term "fabricated" refers to the construction or assembly of a zero-gap alkaline electrolyzer, typically through a manufacturing process. To fabricate something in this context entails creating or assembling the essential components required for the operation of the electrolyzer. This process encompasses various steps such as designing, engineering, and manufacturing electrodes, separator membranes, and other necessary parts, and subsequently assembling them into a fully functional electrolyzer system. Therefore, a "fabricated zero-gap alkaline electrolyzer" denotes an electrolyzer that has been constructed or manufactured specifically for operation with zero gap between the electrodes. Such electrolyzers likely utilize advanced materials and manufacturing techniques to achieve high efficiency and reliability.

[0035] As used herein, the term "OER "refers to Oxygen evolution reaction .

[0036] As used herein, the term "HER" refers to Hydrogen evolution reaction.

[0037] As used herein, the term "SHE" refers to Standard hydrogen electrode.

[0038] Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limit of that range and any other stated or intervening value in that stated range, is encompassed within the methods. The upper and lower limits of these smaller ranges may independently be included in the smaller ranges and are also encompassed within the methods, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the methods.

[0039] Certain ranges are presented herein with numerical values being preceded by the term "about." The term "about" is used herein to provide literal support for the exact number that it precedes, as well as a number that is near to or approximately the number that the term precedes. In determining whether a number is near to or approximately a specifically recited number, the near or approximating unrecited number may be a number which, in the context in which it is presented, provides the s ubstantial equivalent of the specifically recited number. The articles "a" and "an" are used herein to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article. By way of example, "an element" means one element or more than one element.

[0040] Any discussion of documents, methods, acts, materials, equipment, and the like that has been included in this specification is solely for the purpose of providing a context for the invention. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the invention as it existed anywhere before the priority date of this application.

[0041] The present invention relates to an electrolyzer system for the production of hydrogen and oxygen from wastewater, the electrolyzer system comprising an anode, a cathode, an indigenous diaphragm membrane and an electrolyte.

[0042] In one of the embodiments the electrolyzer system is used in the field of hydrogen production, particularly from wastewater. The electrolyzer system enable the efficient generation of hydrogen and oxygen from treated wastewater, marking a significant leap forward in sustainable hydrogen production technologies.

[0043] The present invention particularly relates to a zero-gap alkaline water electrolyzer assembly comprising of membrane electrode assembly, graphitic conducting blocks with serpentine flow fields for flow of electrolyte, stainless-steel plates for connecting power supply.

[0044] In yet another embodiment the membrane electrode assembly is prepared by configuring together the anode, cathode, and the indigenous diaphragm as separator membrane.

[0045] In a wastewater electrolyzer, both the anode and cathode play integral roles in the electrolysis process. The anode, serving as the positively charged electrode, initiates oxidation reactions essential for breaking down organic pollutants and contaminants present in the wastewater. This oxidation process leads to the conversion of pollutants into simpler compounds or ions, while also facilitating the production of oxygen gas. Conversely, the cathode, functioning as the negatively charged electrode, facilitates reduction reactions. Here, water molecules are reduced to produce hydrogen gas, aiding in the removal of excess hydrogen ions from the solution and maintaining electrical neutrality. Together, these complementary processes at the anode and cathode contribute to the effective treatment and purification of wastewater.

[0046] In one of the embodiments the anode and the cathode are prepared by using a catalyst comprising transition metal nanoparticles encapsulated in carbonaceous structures.

[0047] The catalyst comprising transition metal nanoparticles encapsulated in carbonaceous structures, serves as bifunctional catalyst material for anode and cathode.

[0048] The carbonaceous structures include nitrogen-doped carbon nanotubes (NCNT) and etched carbon nano tubes (ECNT).

[0049] In one of the embodiments the catalysts are selected from Ni- NCNT (Nickel Nitrogen- Doped Carbon Nanotubes) and Ni Fe -NCNT (Nickel-Iron Nitrogen-Doped Carbon Nano tubes).

[0050] In one of the embodiments the anode and cathode are coated with the catalyst on a carbon substrate.

[0051] In one of the preferable embodiments the carbon substrate is a carbon cloth.

[0052] In yet another embodiment the carbon substrate is selected from carbon paper, graphite felt, carbon cloth, carbon mesh, microporous carbon coated carbon cloth or polytetrafluoroethylene coated carbon cloth.

[0053] The anode and cathode are coated with the catalyst on a carbon cloth substrate to enhance non-corrosive properties in wastewater.

[0054] The anode and / or cathode are prepared using catalysts coated on non-corrosive carbon cloth of desired dimensions. The active area of both the anode and cathode measures 6.25cm2 / L.

[0055] In yet another embodiment the active area of both the anode and cathode measures 1 to 100 square centimeters per liter (cm2 / L).

[0056] In yet another embodiment when active area increases, consequently the production of H2 also increases.

[0057] The anode and / or cathode is formed by coating the bifunctional catalyst material on a carbon substrate. Any coating technique, as known to or appreciated by any person skilled in art may be used. Thus, by way of example, the coating is brush coating and spray coating.

[0058] The amount of the catalyst material to be applied on carbon substrate to prepare a cathode and anode is lmg / cm2.

[0059] In one of the embodiments the indigenous diaphragm membrane is a chitosan-based diaphragm membrane that is dispersed with hexagonal boron nitride (HBN) and aged in Cu2+solution.

[0060] The aging of HBN-coated chitosan indigenous diaphragm membranes in Cu+2solution enhances the metal ion separation properties. It improves selectivity by potentially modifying the membrane's surface chemistry, enabling more effective binding of copper ions while allowing other ions to pass through. It enhances the interaction between the chitosan material and copper ions, thereby increasing resistance to degradation from exposure to water or chemicals. Moreover, it boosts adsorption capacity by providing more time for copper ions to interact with the membrane material, potentially leading to higher efficiency in copper ion removal. Additionally, aging in Cu+2solution may alter surface properties like charge and hydrophilicity / hydrophobicity, influencing membrane performance in metal ion separation processes. This alteration reduces fouling, creating a more resistant surface or enhancing the membrane's ability to repel unwanted substances. The aging in Cu+2solution offers a cost-effective approach for enhancing membrane performance compared to developing entirely new materials or technologies.

[0061] In yet another embodiment the HBN-coated chitosan indigenous diaphragm membrane is configured as a separator between the anode and cathode to prevent crossover and permeation of hydrogen and oxygen gases.

[0062] In an embodiment electrolyzer system comprises of an electrolyte. Electrolytes serve vital roles in wastewater electrolyzers, primarily by enhancing the electrical conductivity within the solution. When treating wastewater, which often contains various impurities and ions, electrolytes like sodium chloride or sulfuric acid are added to augment ion concentration and, consequently, conductivity. This elevated conductivity enhances the transmission of electrical current, facilitating more efficient electrolysis. Additionally, electrolytes aid in ion exchange during electrolysis, promoting the breakdown of water molecules into hydrogen and oxygen gases. They also play a crucial role in protecting electrodes from corrosion or degradation, potentially forming a protective layer. Furthermore, electrolytes can help regulate the pH of the electrolyte solution, ensuring optimal conditions for electrolysis.

[0063] In yet another embodiment the electrolyte used is an alkaline solution comprises potassium hydroxide (KOH) and / or sodium hydroxide (NaOH).

[0064] In a preferable embodiment the electrolyte comprises of treated wastewater by adding KOH, preferably by adding 3 M KOH.

[0065] In yet another embodiment sodium hydroxide (NaOH) serves as an alternative electrolyte and is almost interchangeable with potassium hydroxide (KOH). These two compounds, NaOH and KOH, are the most chemically similar among hydroxides. In alkaline water electrolysis, KOH is typically preferred over NaOH to avoid corrosion issues from acidic electrolytes. This preference stems from the higher conductivity of KOH compared to NaOH. KOH solutions are about 5% more conductive than NaOH solutions at equivalent molar concentrations. For instance, KOH exhibits a maximum specific conductivity of 950 mS cm-1at 50°C with a 30 wt.% solution, whereas NaOH reaches 650 mS cm-1under similar conditions with a 20 wt.% solution.

[0066] KOH is recognized as a stronger base compared to NaOH, attributed partly to the weaker K-O bond due to the larger size of potassium (K) compared to sodium (Na), resulting in a more facile release of hydroxide ions (OH-). This characteristic is supported by the ionization energy values, with sodium requiring more energy (495.8 kJ / mol) to ionize compared to potassium (418.8 kj / mol). Consequently, potassium is more electro- positive / reactive than sodium, enhancing the propensity of KOH to lose OH- ions and thus exhibiting stronger basic properties than NaOH.

[0067] In one of the embodiments the chitosan-based indigenous diaphragm membrane is fabricated by dissolving chitosan powder in acetic acid, adding HBN, casting the solution on a petri dish, and aging in Cu2+solution

[0068] The method of preparing HBN-dispersed Chitosan-based indigenous diaphragm membranes involve several sequential steps: i. dissolving chitosan powder in acetic acid at room temperature. The chitosan is stirred overnight to achieve a homogeneous and transparent solution. ii. adding 1 wt.% HBN to the chitosan solution obtained in step (i). The mixture is then cast onto a petri dish and left to air dry, resulting in the formation of a chitosan membrane with dispersed HBN. iii. subjecting the indigenous diaphragm membrane obtained from step (ii) to further aging in a Cu2+ saturated sodium hydroxide (NaOH) solution (Na2Cu (OH)4) (sodium tetr ahy dr oxy cuprate (II) ) for a duration of 4 days. After aging, the membrane is washed with deionized water to remove any excess sodium hydroxide (NaOH), and then dried at room temperature. The HBN-dispersed Chitosan-based indigenous diaphragm membrane is obtained through the previously described process. The aging process in a Cu2+solution serves to enhance the metal ion separation properties of the separator membrane.

[0069] In yet another embodiment, the present invention provides a method for preparing nonnoble catalysts (Ni-NCNT, NiFe-NCNT, and NiFe-ECNT), which involves the following steps:

[0070] For Ni-NCNT: i. Melamine is dissolved in ethanol, and NiCh is added to the solution. The mixture is stirred continuously overnight at 400 rpm to achieve homogeneity. ii. The mixture from step (i) is heated to 800°C to evaporate the solvent, leaving behind a residue. iii. The collected residue is then heated in a tube furnace under a nitrogen atmosphere at a flow rate of 20 ml / min. The temperature is ramped up to 700°C at a rate of 5 °C / min and maintained for two hours. iv. The product obtained from step (iii) is cooled to yield the final product, Ni-NCNT.

[0071] Similarly, for NiFe-NCNT:

[0072] The same procedure as described above is followed, with the addition of Ni(NO,)2 and Fe(NO,)2 as precursors in step (i).

[0073] For NiFe-ECNT: i. Fe(NO,)2 and CNT are mixed using a mortar and pestle, then heated in a box furnace under an air atmosphere at 400°C with a ramp rate of 5 °C / min for two hours. ii. The product from step (i) is refluxed in concentrated HNO3 at 120°C for 24 hours. iii. The residue from step (ii) is washed several times with deionized water and dried at 60°C to obtain ECNT. iv. NiCh, Fe(NO3)2, and ECNT are mixed using a mortar and pestle, loaded into an alumina boat, and heated in a tube furnace under a nitrogen environment at 700°C with a ramp rate of 5 °C / min for two hours. v. The mixture from step (iv) is cooled to ambient temperature to yield NiFe-ECNT.

[0074] In yet another embodiment the method of production of the electrolyzer system for hydrogen production comprises the following steps: i. synthesizing, the catalysts by dissolving melamine in ethanol, adding nickel and iron nitrates, stirring, evaporating the solvent, and heating in a nitrogen environment; ii. coating, the anode and the cathode with the synthesized catalyst on a carbon cloth substrate; iii. fabricating, a chitosan-based indigenous diaphragm membrane by dissolving chitosan powder in acetic acid, adding hBN, casting the solution on a petri dish, drying, and aging in Cu2+ solution; and iv. assembling the electrolyzer system with the prepared anode, cathode, and indigenous diaphragm membrane.

[0075] In yet another embodiment the wastewater, can be selected from industries, agriculture, hospitals, sewage, and seawater.

[0076] The electrolyzer system operates at a voltage of 2.55 V, achieving a current density of 669 mA / cm2with the HBN-coated chitosan indigenous diaphragm and 785 mA / cm2with the chitosan indigenous diaphragm membrane without HBN coating.

[0077] In yet another embodiment increasing the voltage directly increases the current density since voltage and current density are directly proportional to each other.

[0078] Certain specific aspects and embodiments of the present application will be explained in greater detail with reference to the following examples, which are provided only for purposes of illustration and should not be construed as limiting the scope of the application in any manner. While particular aspects of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.

[0079] EXAMPLES

[0080] The following examples are for the purpose of illustration of the invention and are not intended in any way to limit the scope of the invention.

[0081] Experimental Details:

[0082] Synthesis ofnon-noble catalyst:

[0083] Example 1:

[0084] Synthesis ofNi Fe -NCNT and Ni -NCNT

[0085] Nickel (II) nitrate (Ni(NO3)2) and iron(II) nitrate (Fe(NO3)2) were utilized as precursors, while melamine served as a carbon and nitrogen source. Initially, melamine was dissolved in 10 ml of ethanol. Subsequently, a predetermined amount of Ni(NO3)2 (1g) and Fe(NO3)2 (1g) were gently added to this solution under continuous stirring. The resulting mixture was stirred overnight at 400 rpm to achieve homogeneity. Following this, the mixture was heated to 80°C to facilitate solvent evaporation. The residue obtained after evaporation was collected and subjected to further treatment in a tube furnace under a nitrogen environment (N2 flow rate of 20 ml / min) at 700°C, with a ramp rate of 5°C / min, for two hours. After completion of the heating process, the material was allowed to cool to ambient temperature and subsequently ground to produce the final product, denoted as Ni Fe-NCNT. A similar procedure was employed to synthesize Ni- NCNT, omitting the use of Fe(NO3)2. Example 2:

[0086] Synthesis of Nickel Iron - Electrospun Carbon Nanotubes (Ni Fe-ECNT):

[0087] The synthesis process begins with the preparation of ECNT. Initially, 0.5 grams of Fe(NO3)2 were mixed with 0.4 grams of carbon nanotubes (CNT) using a mortar and pestle. The resulting mixture was then heated in a box furnace in an air atmosphere at 400°C, with a ramp rate of 5°C / min, for two hours. Subsequently, the collected sample underwent acid treatment using concentrated HNO3 at 120°C for 24 hours employing a reflux method. The residue obtained after acid treatment was washed multiple times with deionized (DI) water and dried at 60°C. The resulting product was termed ECNT.

[0088] The second step involved the preparation of Ni Fe-ECNT. A mixture comprising NiC13, Fe(NO3)2, and ECNT was thoroughly mixed using a mortar and pestle. This mixture was then loaded into an alumina boat and heated in a tube furnace under a nitrogen environment (N2 flow rate of 20 ml / min) at 700°C, with a ramp rate of 5°C / min, for two hours. After completion of the heating process, the material was allowed to cool to ambient temperature before being ground into a finished product.

[0089] Synthesis of HBN dispersed Chitosan-based diaphragm membranes

[0090] Example 3:

[0091] To synthesize the chitosan-based diaphragm membranes, initially, 1 gram of chitosan powder was dissolved in 200 milliliters of 4 wt.% acetic acid solution at room temperature. The solution was stirred overnight to achieve a homogeneous and transparent chitosan solution. Subsequently, 1 wt.% hexagonal boron nitride (HBN) was added to the solution. The resulting mixture was then cast onto a petri dish and allowed to dry in the air, resulting in the formation of a chitosan membrane. To further enhance the properties of the diaphragm membrane, it underwent an aging process in a 2 wt.% Cu2+ saturated NaOH solution (Na2Cu(OH)4) for a duration of 4 days. Following the aging process, the membrane was washed with deionized water to remove excess NaOH and then dried at room temperature.

[0092] Preparation of working electrode

[0093] Example 4:

[0094] To fabricate the working electrode, a catalyst ink was prepared by dispersing 10 milligrams (mg) of catalyst in a hybrid solvent consisting of 90 microliters (pL) of deionized water, 50 microliters (pL) of ethyl alcohol, and 10 microliters (pL) of 5 wt.% Nation solution. The mixture underwent ultrasonication treatment for 20 minutes to ensure proper dispersion. Subsequently, the ink was coated onto a carbon cloth substrate measuring 1 centimeter (cm) by 1 centimeter (cm). The coated substrate was then dried at 60°C until fully dry.

[0095] Example 5:

[0096] Preparation of anode and cathode

[0097] To fabricate the anode and cathode, catalyst ink was prepared by dispersing 15 milligrams of catalyst in a hybrid solvent consisting of 3 millilitres (ml) of ethyl alcohol and 90 microliters of 5 wt.% Nation solution. The resulting mixture underwent ultrasonication treatment for 20 minutes to ensure proper dispersion. Subsequently, the ink was coated onto carbon cloth substrates measuring 2.5 centimetres by 2.5 centimetres. The coated substrates were then dried at 60°C until fully dry.

[0098] Electrochemical Testing:

[0099] Example 6: The electrochemical performance of Ni NCNT for industrial wastewater splitting was evaluated using a Biologic SP-300 potentiostat. The working electrode underwent preparation and testing in a three-electrode setup employing Ag / AgCl and platinum wire as reference and counter electrodes, respectively. The electrolyte consisted of 3 M KOH in industrial wastewater. Prior to measuring polarization curves, the electrodes were subjected to 15 cycles of cyclic voltammetry (CV) to attain stable polarization.

[0100] The OER and HER polarization curves were determined through linear sweep voltammetry (LSV) with a scan rate of 5 mV / s, with 100% iR correction applied via software in potentistatic electrochemical impedance mode.

[0101] To assess the catalyst's durability, two-electrode measurements were conducted via chronopotentiometry at a current density of 10 mA / cm2. These measurements occurred in an electrolyte composed of 3 M KOH mixed with industrial wastewater at room temperature, following CV activation.

[0102] Assembly of zero-gap alkaline electrolyzer

[0103] Firstly, a membrane electrode assembly was fabricated by pressing together the anode, cathode, and the prepared indigenous diaphragm serving as the separator membrane (refer to Fig. 1). Following this, a zero-gap alkaline electrolyzer was assembled. This assembly included the fabricated membrane electrode assembly, graphitic conducting blocks featuring serpentine flow fields for electrolyte flow, and stainless-steel plates for connecting to the power supply.

[0104] A schematic illustration of the setup for hydrogen production from industrial wastewater is shown in figure 1 and schematic illustration of the components of zero-gap alkaline electrolyzer is shown in figure 2.

[0105] The catalysts performance underwent testing within the setup illustrated in Figure 2, which included an assembled zero-gap alkaline electrolyzer, a peristaltic pump (MICLINS INDIA), and a DC power supply unit (Aplab). The electrolyte, consisting of 3 M KOH and industrial wastewater, was circulated through the zero-gap alkaline electrolyzer using the peristaltic pump. The DC power supply was responsible for providing the necessary potential across the electrolyzer terminals.

[0106] Material Characterization:

[0107] The phase composition of the synthesized samples was analyzed using X-Ray diffraction o

[0108] (Rigaku Supermini flex) with a Cu Ka radiation source (X = 1.5406 A). Raman spectra and morphology were acquired utilizing a Raman spectrometer (Horiba XPLORA-MV2000), while scanning electron microscopy (Apreo S) was employed for further characterization of the samples' morphology.

[0109] Analysis:

[0110] The X-Ray Diffractograms of the three catalysts are presented in Fig. 3a. All catalysts exhibit peaks at 25.93° attributable to carbon (ICDD Reference No. 98-001-7125). Moreover, Ni NCNT displays peaks at 44.41°, 51.77°, and 76.21° corresponding to (111), (002), and (022) planes of Ni (ICDD Reference No. 98-012-3812). In addition, the diffractogram of NiFe NCNT reveals peaks at 35.9°, 43.94°, and 51.24° associated with FeNi3 (ICDD Reference No. 98-007-3210). The diffractogram of NiFe ECNT indicates peaks at 36.91° and 62.75°, indicating the presence of iron (ICDD Reference No. 98-007- 1820), and at 43.44°, attributed to FeNi (ICDD Reference No. 98-006-0276). Furthermore, the X-Ray diffractogram of the Chitosan diaphragm membrane exhibits peaks corresponding to chitosan, HBN, and NaOH, which may be attributed to aging in NaOH solution (Fig. 3b).

[0111] The Raman spectra (Fig. 4) of the catalysts reveal characteristic vibrations of the D and G bands at approximately 1350 cmA-l and 1580 cmA-l, respectively. These bands correspond to the defects and amorphousness of carbon atoms, and the tangential oscillations and vibrations of spA2-hybridized carbon atoms, as documented [2,3]. Typically, the intensity ratio of the D and G bands (ID / IG) is considered a crucial parameter for evaluating the degree of structural disorder in carbon materials. A higher ID / IG ratio signifies a greater degree of defects in the carbon materials [4],

[0112] Specifically, Ni NCNT exhibits an ID / IG ratio of 0.9, NiFe NCNT shows a ratio of 1.04, and NiFe ECNT displays a ratio of 0.81.

[0113] Figures 5a and 5b present the SEM images of Ni NCNT, illustrating an encapsulated structure where Ni particles are confined within N-doped carbon nano tubes, along with small-sized Ni particles adorning the N-doped carbon nanotubes. Elemental mapping of the catalyst reveals a uniform distribution of Ni on the N-doped carbon nanotubes (Fig. 5c). Transitioning to NiFe NCNT, SEM images (Fig. 6a and 6b) exhibit Ni and Fe particles decorating N-doped carbon nanotubes, with elemental mapping indicating a homogeneous distribution of both metals (Fig. 6c). NiFe ECNT displays a rugged morphology with evenly dispersed Ni and Fe nanoparticles, alongside carbon nanotubes on the surface (Fig. 7). Finally, the SEM image of the chitosan diaphragm membrane aged in Cu2+ saturated solution and coated with Cu2+ displays a morphological alteration, resulting in a rough surface post-HBN coating on the chitosan aged in Cu2+ sol u tion (Fig. 8).

[0114] Electrochemical data:

[0115] The electrochemical performance of the synthesized catalysts for industrial wastewater splitring was meticulously evaluated, focusing on their activity in both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) within a solution composed of 3 M KOH + Industrial wastewater. Figures 9a and 9b illustrate the polarization curves of OER and HER, respectively. The Ni NCNT catalyst exhibited an overpotential (qlO) of 410.13 mV to achieve a current density of 10 mA / cm2, showcasing superior performance compared to NiFe NCNT with an r lO of 519.19 mV and NiFe ECNT displaying the lowest r l 0 of 382.41 mV among the three catalysts in OER (Fig. 9a). Conversely, in HER (Fig. 9b), Ni NCNT demonstrated a significantly lower overpotential (qlO) of 86.15 mV at 10 mA / cm2, while NiFe NCNT and NiFe ECNT displayed overpotentials of 149.49 mV and 135.32 mV, respectively.

[0116] The, Tafel slope analysis was employed to assess the kinetic performance of the catalysts, with smaller Tafel slopes indicating better catalytic kinetics and higher catalytic activity. The Tafel slope, calculated from the Tafel equation: 77=a+Mog( / ) ,

[0117] (where b denotes Tafel slope, j denotes current density, and q denotes overpotential)

[0118] In OER (Fig. 9c), NiFe ECNT exhibited the lowest Tafel slope of 92.47 mV / dec among the catalysts, while Ni NCNT and NiFe NCNT displayed Tafel slopes of 120.78 mV / dec and 115.09 mV / dec, respectively. Conversely, in HER (Fig. 9d), NiFe NCNT demonstrated superior kinetics with a smaller Tafel slope of 156.59 mV / dec, whereas Ni NCNT and NiFe ECNT exhibited Tafel slopes of 251.56 mV / dec and 215.93 mV / dec, respectively.

[0119] The overall industrial wastewater splitting performance of the catalysts was investigated utilizing a two-electrode configuration employing bifunctional catalysts in 3 M KOH + Industrial wastewater. The same catalyst served as both the anode and cathode. Chronopotentiometry studies were conducted at a current density of 10 mA / cm2for 30 hours. Figure 10 illustrates the, NiFe ECNT achieved the lowest cell potential of 1.81 V at 10 mA / cm2, whereas Ni NCNT and NiFe NCNT exhibited cell potentials of 2.45 V and 1.93 V, respectively. Importantly, all catalysts demonstrated excellent stability in the electrolyte.

[0120] Further enhancing the study, a zero-gap cell was constructed based on the optimized electrochemical performance of the catalysts in both three-electrode and two-electrode configurations. Utilizing 3 M KOH + Industrial wastewater electrolyte, the cell circulated the electrolyte via a peristaltic pump while a DC power supply provided the necessary potential across the terminals. Figure 11 demonstrated the performance of the catalysts with a butter sheet diaphragm membrane. At a cell voltage of 2V, NiFe ECNT achieved the highest current density of 318.08 mA / cm2, while Ni NCNT and NiFe NCNT exhibited current densities of 164.32 mA / cm2and 100.8 mA / cm2, respectively. Additionally, the performance of the prepared diaphragm membranes was evaluated using Ni NCNT as a bifunctional catalyst (Figure 12). Interestingly, at a voltage of 2.55 V, Ni NCNT demonstrated a current density of 785 mA / cm2with a chitosan (aged in Cu2+) diaphragm membrane, whereas with an HBN- coated chitosan (aged in Cu2+) diaphragm membrane, a current density of 669 mA / cm2was achieved.

[0121] While a slightly lower current density was obtained with the diaphragm membrane coated with HBN, the HBN coating effectively prevented the crossover of oxygen and hydrogen gas, resulting in high-purity gas at both the anode and cathode. A chlorine test conducted post the electrochemical test for Ni NCNT indicated no evolution of chlorine (Figure 13).

[0122] Thus, it is evident that the specially designed diaphragm enhances ion transport and provides improved selectivity for the evolved gases in electrolysis process. A zero-gap alkaline electrolyzer is constructed using the developed anode, cathode, and HBN-coated chitosan-based diaphragm membranes as separators. The catalyst Ni NCNT demonstrates a current density of 669 mA / cm2 at 2.55 V when paired with the HBN- coated chitosan diaphragm membrane treated with Cu2+. Additionally, a higher current density of 785 mA / cm2 is achieved with the chitosan diaphragm membrane without HBN coating. The absence of hypochlorite and chlorine indicates the possibility of generating green hydrogen from industrial wastewater without encountering the constraints observed in alternative media, such as seawater.

[0123] Therefore, the non-noble catalysts and separator membranes developed in this invention work together to enhance electrochemical performance, providing a sustainable approach to hydrogen production from industrial wastewater. Additionally, these catalysts and diaphragm membranes have the potential to be applied to the production of hydrogen and oxygen from various sources of industrial wastewater across different industries.

[0124] While preferred aspects have been shown and described, it is to be understood that various further modifications and additional configurations will be apparent to those skilled in the art. It is intended that the specific embodiments and configurations disclosed herein are illustrative of the preferred nature of the invention and should not be interpreted as limitations on the scope of the invention.

Claims

We Claim:

1. An electrolyzer system for the production of hydrogen and oxygen from wastewater, the electrolyzer system comprising: an anode, a cathode, an indigenous diaphragm membrane and an electrolyte, wherein the anode and the cathode are prepared by using a catalyst comprising transition metal nanoparticles encapsulated in carbonaceous structures, wherein the indigenous diaphragm membrane is chitosan-based indigenous diaphragm membrane that is dispersed with hexagonal boron nitride (HBN) and aged in Cu2+sol u tion.

2. The electrolyzer system as claimed in claim 1, wherein the catalysts are selected from Ni- NCNT (Nickel Nitrogen-Doped Carbon Nanotubes) and Ni Fe -NCNT (Nickel-Iron Nitrogen-Doped Carbon Nanotubes).

3. The electrolyzer system as claimed in claim 1, wherein the anode and cathode are coated with the catalyst on a carbon cloth substrate.

4. The electrolyzer system as claimed in claim 1, wherein the HBN-coated chitosan indigenous diaphragm membrane is configured as a separator between the anode and cathode.

5. The electrolyzer system as claimed in claim 1, wherein the electrolyte used is an alkaline solution comprises potassium hydroxide (KOH), and / or sodium hydroxide (NaOH) .

6. The electrolyzer system as claimed in claim 1, wherein the chitosan-based indigenous diaphragm membrane is fabricated by dissolving chitosan powder in acetic acid, adding HBN, casting the solution on a petri dish, and aging in Cu2+solution.

7. A method of production of the electrolyzer system for hydrogen production as defined in claim 1, the method comprising:synthesizing, the catalysts by dissolving melamine in ethanol, adding nickel and iron nitrates, stirring, evaporating the solvent, and heating in a nitrogen environment; coating, the anode and the cathode with the synthesized catalyst on a carbon cloth substrate; fabricating, a chitosan-based indigenous diaphragm membrane by dissolving chitosan powder in acetic acid, adding HBN, casting the solution on a petri dish, drying, and aging in Cu2+solution; and assembling the electrolyzer system with the prepared anode, cathode, and indigenous diaphragm membrane.

8. The electrolyzer system, as claimed in claim 1, utilized for the production of hydrogen from wastewater, wherein the wastewater can be selected from industries, agriculture, hospitals, sewage, and seawater.

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