Bipolar green hydrogen production from electroreforming of biomass derivatives using silver-based electrocatalyst

Abstract

The present disclosure relates to a bipolar hydrogen production system and a method for producing hydrogen gas from the bipolar hydrogen production system. The system comprises a silver-based anodic catalyst deposited on an anode electrode, a cathode electrode, and an alkaline electrolyte containing an organic compound with aldehyde functional group extracted from lignocellulosic biomass waste or an aldehyde-containing chemical compound extracted from chemical waste.

Description

BIPOLAR GREEN HYDROGEN PRODUCTION FROM ELECTROREFORMINGOF BIOMASS DERIVATIVES USING SILVER-BASED ELECTROCATALYSTCROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority to the Singapore patent application no. 10202400024P filed on 4 January 2024, the contents of which are hereby incorporated by reference in its entirety for all purposes.TECHNICAL FIELD

[0002] This application relates to a bipolar hydrogen production system and a method of producing hydrogen gas from the bipolar hydrogen system. In particular, the application relates to a bipolar hydrogen production system comprising a silver-based electrocatalyst for the electroreforming of biomass derivatives.BACKGROUND

[0003] Green hydrogen production: Hydrogen is not only a vital feedstock for various industrial applications (such as petroleum refining, reducing metallic ores, ammonia synthesis from the Haber-Bosch process, and processing foods, etc.) but also acts as a promising clean fuel to replace fossil fuel. Currently, most of the industrial hydrogen production (approximately 95%) comes from fossil fuels by steam reforming of methane or other light hydrocarbon, partial oxidation of heavier hydrocarbons, and coal gasification, owing to their advantages of low cost (1.4-4.4 USD / kg) and high industrial maturity. Nevertheless, these methods are neither sustainable nor environmentally friendly due to the massive emissions of toxic chemicals and greenhouse gases during their processes. Therefore, it is of great importance to seek for green methods for hydrogen production (so called “green hydrogen” production). Nowadays, there two methods to produce “green hydrogen”, one is to use Power-to-gas (often abbreviated P2G), in which the hydrogen is produced through electrolysis of water powered by renewable energysuch as wind, solar or fuel cells, another is by reforming landfill gas / biogas. Methane and carbon dioxide are the main constituents of landfill gas, which is thus able to be used for producing hydrogen by conventional dry reforming method. However, high temperature and pressure are still required in this process. In addition, a great amount of carbon dioxide will also be emitted. In consequence, the P2G has gradually emerged as a more promising method for “green hydrogen” production and has drawn worldwide attention recent years due to its ability to achieve high-purity hydrogen production in ambient environments (i.e., room temperature and pressure) and in the absence of greenhouse gases emission.

[0004] However, despite the aforementioned advantages, the high cost (about 4.2-12.4 USD / kg) resulting from the required high-voltage input (1.6-2.0 V) due to the sluggish and less- valued oxygen evolution reaction (OER) restricts the commercial scalability of this process. Moreover, gas crossover may occur owing to the potential lower production rates of hydrogen and oxygen in water electrolysis than their permeating rates when low power is applied, which may result in the accumulation of explosive oxygen-hydrogen mixtures posing severe safety hazards. In addition, the reactive oxygen species (ROS) generated by the coexistence of H2 / O2 mixtures and active catalysts may cause degradation of the membrane in between the electrolyzer.

[0005] Therefore, to address the above issues, there has aroused growing interest in exploring alternative oxidation reactions that are more thermodynamically favorable and can improve the efficiency and sustainability of the hydrogen production process.

[0006] It is therefore desirable to provide a system and a method that seeks to address at least one of the problems described hereinabove, or at least to provide an alternative.SUMMARY

[0007] According to a first aspect of the present disclosure, a bipolar hydrogen production system is provided. The system comprises a silver-based anodic catalyst deposited on an anode electrode, a cathode electrode, and an alkaline electrolyte containing an organic compound withaldehyde functional group extracted from lignocellulosic biomass waste or an aldehyde- containing chemical compound extracted from chemical waste.

[0008] In some embodiments, the silver-based anodic catalyst is silver chloride (AgCl).

[0009] In some embodiments, the silver-based anodic catalyst is a silver-copper (Ag-Cu) bimetallic catalyst co-deposited directly onto an oxide-derived copper foam, denoted as Ag@OD-Cu.

[0010] In some embodiments, the silver-based anodic catalyst is a silver-copper (Ag-Cu) bimetallic catalyst in powder form, coated onto a conductive support or on the anode electrode.

[0011] According to a second aspect of the present disclosure, a method for producing hydrogen gas from a bipolar hydrogen production system is provided, The method comprises depositing a silver-based anodic catalyst on an anode electrode, providing a cathode electrode; and introducing an alkaline electrolyte containing an organic compound with aldehyde functional group extracted from lignocellulosic biomass waste or an aldehyde-containing chemical compound extracted from chemical waste into the bipolar hydrogen production system, allowing electrooxidation of the organic compound with the aldehyde functional group or the aldehyde-containing chemical compound, at the anode electrode of the bipolar hydrogen production system to facilitate hydrogen production.

[0012] In some embodiments, hydrogen gas is produced at both the anode electrode and the cathode electrode.

[0013] In some embodiments, the electrooxidation of the organic compound with the aldehyde functional group or the aldehyde-containing chemical compound at the anode electrode occurs at a reduced onset voltage ranging from 0.0 V to 0.2 V (vs RHE).BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Various embodiments of the present disclosure are described hereinbelow in the detailed description with reference to the following drawings:FTG. l is a schematic drawing of an example of an electrolyzer employed in accordance with some embodiments of the present disclosure.FIG. 2A shows the linear sweep voltammetry (LSV) curves of AgCl electrode in 1 M KOH, with and without adding furfural.FIG. 2B shows the LSV curves of silver chloride (AgCl) electrode in 1 M KOH with lOOmM, 200mM, and 300mM 5 -hydroxymethyl furfural (HMF).FIG. 3A shows the comparison of furfural electrooxidized reactions (FOR) and oxygen evolution reaction (OER) for water electrolysis using AgCl catalyst.FIG. 3B shows the comparison of 2-furoic acid electrooxidized reactions (FOR) and oxygen evolution reaction (OER) for water electrolysis using AgCl catalyst.FIG. 4 shows the comparison of electrooxidized reactions for furfural from empty fruit bunch fiber (EFBF) using different catalysts.FIG. 5A shows the gas chromatograph (GC) spectrum for collected gaseous products.FIG. 5B shows the total hydrogen amount collected for different samples.FIG. 6 shows the LSV curves of copper (Cu), silver (Ag) and silver-copper (Ag-Cu) bimetallic catalysts for furfural electrooxidation. The catalyst support is carbon fiber (CF).DETAILED DESCRIPTION

[0015] The following detailed description is made with reference to the accompanying drawings, showing details and embodiments of the present disclosure for the purposes of illustration. Features that are described in the context of an embodiment may correspondingly be applicable to the same or similar features in the other embodiments, even if not explicitly described in these other embodiments. Additions and / or combinations and / or alternatives as described for a feature in the context of an embodiment may correspondingly be applicable to the same or similar feature in the other embodiments.

[0016] Tn the context of various embodiments, the articles “a”, “an” and “the” as used with regard to a feature or element include a reference to one or more of the features or elements.

[0017] In the context of various embodiments, the term “about” or “approximately” as applied to a numeric value encompasses the exact value and a reasonable variance as generally understood in the relevant technical field, e.g., within 10% of the specified value.

[0018] As used herein, the term “and / or” includes any, and all combinations of one or more of the associated listed items.

[0019] As used herein, “comprising” means including, but not limited to, whatever follows the word “comprising”. Thus, use of the term “comprising” indicates that the listed elements are required or mandatory, but that other elements are optional and may or may not be present.

[0020] As used herein, “consisting of’ means including, and limited to, whatever follows the phrase “consisting of’. Thus, use of the phrase “consisting of’ indicates that the listed elements are required or mandatory, and that no other elements may be present.

[0021] A detailed description of various embodiments will be described below with reference to the drawings.

[0022] Tn the present disclosure, it has been found that silver-based catalysts, such as silver chloride (AgCl), silver-copper (Ag-Cu) bimetallic catalyst and other silver-containing binary or ternary metallic alloy systems can enhance hydrogen production rate for anodic electrooxidation of organic compounds with aldehyde functional group or aldehyde-containing chemical compound. Such compounds with aldehyde functional group includes organic compounds extracted from lignocellulosic biomass waste or aldehyde-containing chemical compounds extracted from chemical waste. It was found that silver exhibits electrocatalytic properties similar to copper, resulting in a significant synergistic effect of the silver-based catalyst in the electrooxidation of the organic compounds with the aldehyde functional group or the aldehyde-containing chemical compounds.

[0023] Tn accordance with a first aspect of the present disclosure, a bipolar hydrogen production system is provided. The bipolar hydrogen production system comprises a silverbased anodic catalyst deposited on an anode electrode; a cathode electrode; and an alkaline electrolyte containing an organic compound with aldehyde functional group extracted from lignocellulosic biomass waste or an aldehyde-containing chemical compound extracted from chemical waste.

[0024] The lignocellulosic biomass waste can be any lignocellulosic biomass waste including, but not limited to, empty fruit bunch fiber (EFBF), sugarcane bagasse, corn stover, agriculture waste, woody waste, paper waste and food waste.

[0025] As used herein, “agriculture waste” refers to byproducts or waste generated during the cultivation, harvesting, processing and storage of crops that contain lignocellulose. Such waste includes, but is not limited to, straw (e.g., wheat straw, rice straw, barley straw), cotton stalks, soybean stover, etc.

[0026] As used herein, “woody waste” refers to byproducts or waste generated from wood products or processes that contain lignocellulose. Such waste includes, but is not limited to, wood chips, sawdust, bark from shredded trees and shrubs, stumps and roots from tree remains, pulpwood residues, etc.

[0027] As used herein, “paper waste” refers to discarded paper products that contain lignocellulose. Such waste includes, but is not limited to, cardboard, printer paper, newspaper, etc.

[0028] As used herein, “food waste” refers to any edible food that is discarded and contains lignocellulose. Such waste includes, but is not limited to, fruit and vegetable peels, stems and leaves, cores and seeds of fruits, shells of nuts, etc.

[0029] The chemical waste can be any aldehyde-containing chemical waste including, but not limited to, formaldehyde.

[0030] Tn some embodiments, the silver-based anodic catalyst is selected from the group consisting of silver chloride (AgCl), silver-copper (Ag-Cu) bimetallic catalyst and other silver- containing binary or ternary metallic alloy systems.

[0031] In some embodiments, the silver-based anodic catalyst is silver chloride (AgCl). In these embodiments, the anodic oxidation reaction exhibits a significantly reduced onset voltage of 0.2V (vs RHE) as compared to OER. The silver chloride (AgCl) can be deposited or coated onto the anode electrode. The anode electrode in this case is made of silver.

[0032] In other embodiments, the silver-based anodic catalyst is a silver-copper (Ag-Cu) bimetallic catalyst co-deposited directly onto an oxide-derived copper foam, denoted as Ag@OD-Cu. In these embodiments, the Ag-Cu bimetallic catalyst and the oxide-derived copper foam form the anode electrode The Ag-Cu bimetallic catalyst demonstrates a significantly enhanced electrooxidation performance of the organic compound with the aldehyde functional group, compared to known copper catalyst. The onset potential of this Ag- Cu bimetallic catalyst is further reduced to near 0 V (vs RHE).

[0033] In some embodiments, the Ag-Cu bimetallic catalyst is co-deposited in the form of a film directly onto the oxide-derived copper foam Compared to other electrode such as those comprising silver foils, the foam presents a three-dimensional hierarchical porous structure that results in a much larger surface area, allowing the exposure of more active sites, thereby enhancing catalytic performances.

[0034] In some embodiments, the silver-based anodic catalyst is a silver-copper (Ag-Cu) bimetallic catalyst in powder form, coated onto a conductive support or an anode electrode. The conductive support or the anode electrode can be made of a variety of materials including, but not limited to, carbon black, carbon paper and metal electrode.

[0035] In various embodiments, the organic compound with the aldehyde functional group is furfural. The furfural employed for electrolysis is directly derived from lignocellulosic biomass waste. In some embodiments, the furfural is extracted from the lignocellulosic biomasswaste in an aqueous solution through hydrothermal treatment or microwave hydrothermal treatment to obtain a furfural-containing solution. The furfural-containing solution is subjected to azeotropic distillation to obtain a furfural-water mixture. The furfural -water mixture is then transferred to an electrolyzer for bipolar hydrogen production. The process for extracting the organic compound such as furfural from lignocellulosic biomass waste can be powered by renewable energy sources, such as solar power, offering an accessible means to drive this hybrid electrolysis process.

[0036] The present disclosure demonstrates the successful implementation of AgCl catalyst and Ag@OD-Cu foam catalyst as anode material, respectively, enabling high current density and substantial hydrogen production yields through the anodic electrooxidation of the organic compound with the aldehyde functional group, such as furfural, at extremely low voltage, ranging from near 0.0 to 0.2 V (vs RHE).

[0037] By employing a stable and efficient AgCl or Ag@OD-Cu foam anodic catalyst to replace the unstable copper catalyst reported in existing literature, the potential for achieving large-scale bipolar green hydrogen production through anodic electrooxidation of the organic compound with the aldehyde functional group (such as furfural), coupled with HER, has been significantly enhanced.

[0038] Since the electrooxidation of the organic compound with the aldehyde functional group occurs at a much lower potential than OER, oxygen production is fully suppressed. As a result, the operation is much safer than that of conventional water electrolyzers, as it eliminates issues such as H2-O2 gas mixing and reactive oxygen species (ROS) formation. In addition, the anodic products, such as hydrogen and 2-furoic acid, are significantly more useful than those produced in conventional water electrolyzers, which typically produce oxygen gas.

[0039] In accordance with a second aspect of the present disclosure, a method for producing hydrogen gas from a bipolar hydrogen production system is provided. The method comprises depositing a silver-based anodic catalyst on an anode electrode; providing a cathode electrode;and introducing an alkaline electrolyte containing an organic compound with aldehyde functional group extracted from lignocellulosic biomass waste or an aldehyde-containing chemical compound extracted from chemical waste into the bipolar hydrogen production system, allowing electrooxidation of the organic compound with the aldehyde functional group or the aldehyde-containing chemical compound, at the anode electrode of the bipolar hydrogen production system to facilitate hydrogen production.

[0040] In some embodiments, the organic compound with the aldehyde functional group is furfural.

[0041] In some embodiments, the alkaline electrolyte containing the furfural is prepared by: extracting furfural from the lignocellulosic biomass waste in an aqueous solution through hydrothermal treatment to obtain a furfural-containing solution; subjecting the furfural- containing solution to azeotropic distillation to obtain a furfural -water mixture; and adjusting the pH of the furfural -water mixture to form the alkaline electrolyte.

[0042] In some embodiments, the pH of the furfural -water mixture is adjusted to be above 7, preferably in the range of 8 to 14, 11 to 14 or 13 to 14.

[0043] In some embodiments, the silver-based anodic catalyst is selected from the group consisting of silver chloride (AgCl), silver-copper (Ag-Cu) bimetallic catalyst and other silver- containing binary or ternary metallic alloy systems.

[0044] In some embodiments, the silver-based anodic catalyst is silver chloride (AgCl).

[0045] In some embodiments, the silver-based anodic catalyst is a silver-copper (Ag-Cu) bimetallic catalyst co-deposited directly onto an oxide-derived copper foam, denoted as Ag@OD-Cu.

[0046] The silver-based anodic catalyst can be deposited on the anode electrode using any suitable method including, but not limited to electrodeposition, electrodeless depostion, physical vapor depostion etc.

[0047] Tn other embodiments, the silver-based anodic catalyst is a silver-copper (Ag-Cu) bimetallic catalyst in powder form, coated onto a conductive support or on the anode electrode. Any suitable method of coating may be employed including, but not limited to spray coating, electrodepostion etc.

[0048] In some embodiments, the lignocellulosic biomass waste is selected from the group consisting of empty fruit bunch fiber, sugarcane bagasse, com stover, agriculture waste, woody waste, paper waste and food waste.

[0049] In the present disclosure, the hydrogen gas is produced at both the anode electrode and the cathode electrode.

[0050] In some embodiments, the electrooxidation of the organic compound with the aldehyde functional group or the aldehyde-containing chemical compound at the anode electrode occurs at a reduced onset voltage ranging from 0.0 V to 0.2 V (vs RHE).

[0051] In some embodiments, the cathode catalyst is made of platinum or it is platinum / carbon (Pt / C) in powder form. The hydrogen evolution reaction (HER) occurs at the cathode electrode under catalysis of the platinum.

[0052] The system and method of the present disclosure can be safely and efficiently coupled with photovoltaics, or other renewable power such as wind, for power-to-hydrogen fuel / chemical conversion, owing to the suppression of the OER and the low potential required. This advancement contributes to a more sustainable system and method for producing green hydrogen with high efficiency and supporting the transition to cleaner energy sources.

[0053] The bipolar hydrogen production system of the present disclosure offers several advantages, including increased energy efficiency, effectiveness, and environmental friendliness compared to state-of-the-art green hydrogen production system and method. Solar energy or other renewable energy sources can be used to drive the bipolar hydrogen production process. In contrast to most existing devices, which produce green hydrogen only at the cathode, this electrolyzer system enables bipolar green hydrogen production with high current densityand yield The electrolysis process operates at ambient temperature and low pressure, making it less energy-intensive than existing commercial hydrogen production methods, such as steam- methane reforming, which requires elevated temperature and pressure.

[0054] Other advantages include the fact that silver-based electrocatalyst demonstrates significantly higher performances than known electrocatalysts for similar reactions.

[0055] n the embodiments where microwave heating is used in the process for treating the biomass waste, microwave heating achieves a higher heating rate, which helps mitigate the formation of by-products such as humins. Additionally, the overall energy consumption during the furfural production process can be greatly reduced compared to the traditional hydrothermal method.

[0056] Furthermore, no additional purification process for the organic compound or furfural is required. The resulting furfural -water mixture can be directly fed into an electrolyzer for use. This enables the streamlined production of green hydrogen directly from biomass waste in industrial furfural production lines.

[0057] The bipolar hydrogen production from direct biomass-derived organic compound or furfural electrolysis using the catalysts described hereinabove has several commercial applications, including but not limited to a new scalable process to convert biomass waste into value-added chemicals and hydrogen, which is in combination with HER to achieve bipolar hydrogen production through electrolysis. This approach not only presents a more environmentally friendly alternative to burning of waste biomass for heat recovery that produces air pollution, but also substantially enhances hydrogen yield compared to any other water electrolysis.

[0058] The system and method of the present disclosure are also new techniques that can be deployed at waste biomass management site to upcycle biomass waste into value-added chemicals as well as to produce green hydrogen, which can significantly lower the carbon emission and landfilled waste.

[0059] The bipolar hydrogen production technology of the present disclosure can also be employed to upgrade waste / contaminated furfural product, where the furfural-water azeotrope can be directly fed into the electrolyzer, enabling bipolar hydrogen production. Concurrently, furfural undergoes electrooxidation into value-added organic compounds. This process eliminates the need for further furfural purification, leading to decreased energy consumption.

[0060] The bipolar hydrogen production system allows a new hybrid electrolyzer to be developed by replacing the water oxidation reaction with biomass derived furfural aqueous solution oxidation reaction. This not only improves the hydrogen production energy efficiency but also ensures safe operation and prolongs the life of the electrolyzer with suppressed OER.

[0061] The method and system of the present disclosure also provide a new safe and dynamic approach that capitalizes renewable energy such as solar or hydroelectric power for green hydrogen production. These intermittent excessive energy from renewable sources could thus be harnessed and stored as green hydrogen fuel.

[0062] To facilitate a better understanding of the invention, the following examples of specific embodiments are given. In no way should the following examples be read to limit or define the entire scope of the invention One skilled in the art will recognize that the examples set out hereinbelow are not an exhaustive list of the embodiments of this invention.EXAMPLESExample 1

[0063] Furfural production from biomass waste

[0064] This example illustatres a process of extracting furfural-containing solution from biomass waste. The biomass waste used in this example was empty fruit bunch fiber (EFBF).

[0065] Firstly, the collected EFBF underwent simple size reduction process to 3-5 cm using cutting. The smaller EFBF pieces were then fed into a ball mill, equipped with zirconia balls, to reduce them further into sub-millimeter-sized particles. Afterward, 3g of the ball-milled EFBF was introduced into a pressure vessel, where 20 ml of a mixed solution comprisingsulphuric acid (H2SO4) (lOOmM) and iron (TTI) sulfate (Fez(SO4)3) (20mM) was added for microwave-assisted reaction. Following the microwave treatment, the resulting solid-liquid mixture was transferred to a rotary evaporator for azeotropic distillation, yielding a mixture of furfural and water. The furfural-water mixture can then be directly utilized for electrolysis, after adding a specific amount of KOH pellets to create a furfural-containing alkaline electrolyte.Example 2

[0066] Bipolar hydrogen production through hybrid electrolysis

[0067] A hybrid electrolyzer with alkaline electrolyte, i.e., alkaline hybrid electrolysis (AHE) at lab scale using an electrochemical cell combined with gas collection setup was set up. FIG. 1 is a schematic drawing illustrating the structure of an example of an electrolyzer 100 employed in the present disclosure. The electrolyzer comprises a cathode compartment 101 and an anode compartment 102, separated by a membrane or separator 103. The cathode compartment 101 includes a cathode 104 and an outlet 105 for green hydrogen. The anode compartment 102 contains an anode 106, with an outlet 107 for green hydrogen and an additional outlet 108 for green furoic acid. The electrolyzer may also include a supplementary outlet 109 for green hydrogen, as shown in FIG. 1. Both the cathode 104 and the anode 106 are connected to a power source (such as battery) 110.

[0068] Silver foils and copper foams were purchased from Kesirui new materials Co., Ltd. Potassium chloride, hydrochloric acid, sulfuric acid, iron (III) sulfate, silver nitrite, ammonia solution, potassium hydroxide, HMF, furfural and 2-furoic acid were purchased from Sigma- Aldrich. All chemicals were used as received without further purification. The reference electrode (Hg / HgO / lM KOH) and Counter electrode (Pt mesh) were purchased from Shanghai LEDONLAB electrochemistry Co., Ltd.

[0069] The anode 106 consists of an AgCl catalyst, which was prepared using a facile template-free anodic electrodeposition method. This method involved depositing AgCl onto asilver (Ag) foil (with dimensions of 1 cm X 1 cm and a thickness of 0.1 cm). In general, the electrodeposition was conducted in a standard two-electrode configuration at room temperature with an electrolyte of IM KC1 solution. Silve (Ag) foil and platinum (Pt) wire were utilized as the working electrode and counter electrode, respectively. A constant current of 15 mA- cm'2for 600 s was applied for the electrodeposition to obtain the anodic AgCl catalyst.

[0070] In other embodiments, the anode may comprise Ag@OD-Cu foam catalyst. The Ag@OD-Cu foam catalyst was prepared by co-electroreduction of copper (II) oxide (CuO) in a silver-ammonia solution. In details, CuO nanosheets were first grown on pretreated copper foams using a modified wet-chemical oxidation method. Then, the obtained CuO foams were calcinated at 550 °C for 3 h in Ar gas to obtain a Cu2O / Cu foam. The Cu2O / Cu foam was subsequently immersed in a silver-ammonia solution and subjected to electroreduction at a voltage of -1.4 V (vs. RHE) for 600 s. The obtained Ag-Cu bimetallic foam was washed in ethanol and deionised water three times and dried in air for further used.

[0071] A certain amount of pure furfural was added to 30ml IM KOH solution to obtain a mixed solution with lOOmM, 200mM, 300mM and 400mM furfural, respectively. For the furfural -water mixture from distillation, KOH pellets were added directly into 30ml solution to get IM concentration. For comparative purposes, 100 mM, 200 mM, and 300 mM HMF- containing solution with IM KOH were also prepared

[0072] The furfural-containing alkaline electrolyte was subjected to electrooxidation at the anode, using AgCl or Ag@OD-Cu foam catalyst as the anodic catalyst. The electrooxidation procedure was implemented using Gamry (Reference 600) potentiostat with a configuration of three-electrode cell. The synthesized AgCl or Ag-Cu bimetallic catalyst was employed as the working electrode, the Hg / HgO / lM KOH electrode as the reference electrode, and Pt mesh as the counter electrode. All the recorded potentials in this study are referenced in relation to RHE. Conversion from the Ag / AgCl reference electrode to RHE was accomplished by E (versus RHE) = E (versus Ag / AgCl) + 0.0591 x pH + 0.1976. LSV experiment was conducted usingthe three-electrode cell with a scan rate of 5 mV / s from 0 V to 0 8 V Controlled potential electrolysis was performed at 0.6 V for furfural and 0.65 V for HMF for 30 mins.

[0073] The method produced 2-furoic acid, along with the generation of green hydrogen. The anodic oxidation reaction occurred at extremely low potentials, such as 0-0. IN (vs RHE), effectively suppressing the oxygen evolution reaction (OER). Meanwhile, the hydrogen evolution reaction (HER) took place at the cathode under the catalysis of a platinum (Pt) mesh electrode. The combination of the anodic and cathodic reactions resulted in a bipolar hydrogen production.

[0074] The gaseous products produced in both the anode and cathode half-cell were collected in a syringe by a simple water replacement method for further analysis. iR compensation (current times parasitic resistance) was implemented across all electrochemical experiments to remove influence of Ohmic loss.

[0075] The reaction LSV curves of solutions containing different concentrations of furfural and EIMF in 30 mL of 1 M KOH, as well as the furfural-water solution produced from distillation and those pure 1 M KOH are shown in FIGs. 2A and 2B. In the absence of furfural addition to a 1M KOH electrolyte, anodic current is negligible within the voltage range of 0- 0.8V on both Ag and AgCl catalysts. Nevertheless, the introduction of a certain quantity of furfural and HMF into the IM KOH solution initiates anodic current density at voltages greater than 0.2V and greater than 0.3 V, respectively, which increases rapidly as the voltage rises. With the addition of lOOmM furfural, the increase in current density peaked at approximately 0.65V, followed by a subsequent decrease. However, when furfural concentration exceeds 1 OOmM, the current density maintains an upward trend throughout the entire voltage range. This phenomenon may be due to the competition of concurrent AgCl oxidation reaction. For the electrolyte with lower furfural concentration, the competing AgCl oxidation reaction dominates at lower potential, resulting in the earlier occurrence of the current density peak corresponding to AgCl oxidation. Similar trend also appears in HMF oxidation reaction (shown in FIG. 2B),with the peak shifting to higher voltage region. Additionally, the furfural and HMF concentration also significantly affects current density where higher furfural concentration leads to larger current density. As the furfural and HMF concentration increases from lOOrnM to 300mM, the maximum current density within the voltage range rises from 57.4 mA / cm2and 36.2 mA / cm2to 174.5 mA / cm2and 106 mA / cm2, respectively. However, further elevating the furfural concentration to 400mM no longer increases the maximum current density, comparing the case of 300mM with 400 mM due to the limit of mass transport. For the furfural-water solution produced from EFBF, the obtained LSV curve trend closely resembles that of lOOrnM pure furfural addition, except for a notably higher maximum current density of 89.5 mA / cm2. These results suggest that the furfural concentration of the produced solution lies between lOOrnM and 200mM. These results were verified using high-performance liquid chromatography (HPLC).

[0076] HPLC was employed to quantify the concentrations of HMF and furfural in the solutions after microwave treatment and subsequent azeotropic distillation. Based on the analysis, approximately 120 mM of furfural were detected in the microwave-treated solution, and its concentration remained unaffected by the subsequent rotary evaporation This demonstrates the formation of furfural-water azeotrope during distillation. Nevertheless, the HMF concentration in the obtained solution was quite limited (around 10 mM) and decreased to 0 after rotary evaporation. This indicates that HMF cannot be evaporated under the azeotropic temperature of furfural and water. Therefore, the resulting solution after rotary evaporation was a mixture of furfural and water, accompanied by trace amounts of low-boiling-point organic acids such as formic acid and acetic acid as detected by HPLC. Moreover, the onset potential for positive anodic current in the EFBF sample appears to lag slightly behind that of other pure furfural samples, which is attributed to the presence of other larger molecules from EFBF. In addition, the color of the solution with pure furfural addition was yellow tone (before electrooxidation) and gradually changed to dark brown tone after 30 mins electrolysis.However, for the EFBF sample, the solution gradually turned turbid after the addition of KOH pellets, which is attributed to the precipitation of remaining contaminants (ash and extractives) from the EFBF under alkaline conditions. Similar to the pure furfural samples, the color of the EFBF-derived furfural sample changed from light-yellow to dark brown with the progression of electrolysis.

[0077] FIG. 3A elucidates that the furfural electrooxidation reaction is more thermodynamically favorable than OER, with the onset voltage about 1.5V and 1.45V lower than the latter, for pure furfural samples and the furfural from EFBF waste, respectively. This observation indicates the suitability of furfural electrooxidation as a viable alternative for the sluggish OER. Furthermore, FIG. 3B illustrates that the electrooxidation of 2-furoic acid, the main product of furfural oxidation, initiates at the potential close to OER without the formation of Hz. Therefore, the Hz produced on the anode was totally from the low potential electrooxidation of furfural. The results show that AgCl catalyst is capable of achieving a current density of about 89.5 mA / cm2while Ag@OD-Cu foam catalyst is capable of achieving a current density of about 203 mA / cm2, even at a lower potential, as shown in FIG. 4. Additionally, the onset current for Ag@OD-Cu foam is nearly 0 V, which is 0.2 V lower than that of AgCl catalyst. The substantial improvement in catalytic performance can be explained by the enhanced electrochemical active surface area and the strong synergistic effect between silver and copper in the electrooxidation of furfural.Example 3

[0078] Qualitative and quantitative analysis of gaseous products

[0079] The qualitative and quantitative analysis of gaseous products collected from different samples were conducted by GC-FID. As shown in FIG. 5A, hydrogen gas was the exclusive product generated across all samples, with a remarkable purity of up to 99%. FIG. 5B depicts the quantities of Hz produced by various samples after 30 minutes of electrolysis. It can be observed that as the introduced furfural concentration increases from lOOmM to 300mM, theresultant hydrogen gas volume rises from 1.12 mL to 2.5 mL. Nevertheless, further enhancing the furfural concentration no longer contributes to increased hydrogen production. In the case of the EFBF-derived furfural, the hydrogen content reached 1.38 mL after 30-mins electrolysis, between that of the lOOmM furfural and that of the 200mM furfural, which corresponds well with the previous results of current density and furfural concentration obtained by HPLC (approximately 120mM).

[0080] Example 4

[0081] FIG. 6 shows the LSV curves of Cu, Ag and Ag-Cu bimetallic catalysts for furfural electrooxidation. The catalyst support is carbon fiber (CF). The figure shows the LSV curves of various Ag-Cu bimetallic catalysts with controlled atomic ratio between Ag and Cu. It shows that the atomic ratio indeed influences the activity of the catalyst, but the difference is small. Overall, the activities are very good. Notably, higher Ag content will endow the catalyst better stability.

[0082] According to one aspect, the present disclosure describes various embodiments of a bipolar hydrogen production system. The system includes: a silver-based anodic catalyst deposited on an anode electrode; a cathode electrode; and an alkaline electrolyte containing an organic compound with aldehyde functional group extracted from lignocellulosic biomass waste or an aldehyde-containing chemical compound extracted from chemical waste.

[0083] In some embodiments, the silver-based anodic catalyst is silver chloride (AgCl).

[0084] In some embodiments, the silver-based anodic catalyst is a silver-copper (Ag-Cu) bimetallic catalyst co-deposited directly onto an oxide-derived copper foam, denoted as Ag@OD-Cu.

[0085] In some embodiments, the silver-based anodic catalyst is a silver-copper (Ag-Cu) bimetallic catalyst in powder form, coated onto a conductive support or on the anode electrode.

[0086] In some embodiments, the organic compound is furfural.

[0087] Tn some embodiments, the lignocellulosic biomass waste is selected from the group consisting of empty fruit bunch fiber, sugarcane bagasse, com stover, agriculture waste, woody waste, paper waste and food waste.

[0088] According to another aspect, the present disclosure describes various embodiments of a method for producing hydrogen gas from a bipolar hydrogen production system. The method includes: depositing a silver-based anodic catalyst on an anode electrode; providing a cathode electrode; and introducing an alkaline electrolyte containing an organic compound with aldehyde functional group extracted from lignocellulosic biomass waste or the aldehyde- containing chemical compound extracted from chemical waste into the bipolar hydrogen production system, allowing electrooxidation of the organic compound with the aldehyde functional group or the aldehyde-containing chemical compound, at the anode electrode of the bipolar hydrogen production system to facilitate hydrogen production.

[0089] In some embodiments, the organic compound with the aldehyde functional group is furfural.

[0090] In some embodiments, the alkaline electrolyte containing the furfural is prepared by: extracting furfural from the lignocellulosic biomass waste in an aqueous solution through hydrothermal treatment to obtain a furfural-containing solution; subjecting the furfural - containing solution to azeotropic distillation to obtain a furfural -water mixture; and adjusting the pH of the furfural -water mixture to form the alkaline electrolyte.

[0091] In some embodiments, the silver-based anodic catalyst is silver chloride (AgCl).

[0092] In some embodiments, the silver-based anodic catalyst is a silver-copper (Ag-Cu) bimetallic catalyst co-deposited directly onto an oxide-derived copper foam, denoted as Ag@OD-Cu.

[0093] In some embodiments, the silver-based anodic catalyst is a silver-copper (Ag-Cu) bimetallic catalyst in powder form, coated onto a conductive support or on the anode electrode.

[0094] Tn some embodiments, the lignocellulosic biomass waste is selected from the group consisting of empty fruit bunch fiber, sugarcane bagasse, com stover, agriculture waste, woody waste, paper waste and food waste.

[0095] In some embodiments, the hydrogen gas is produced at both the anode electrode and the cathode electrode.

[0096] Tn some embodiments, the electrooxidation of the organic compound with the aldehyde functional group or the aldehyde-containing chemical compound at the anode electrode occurs at a reduced onset voltage ranging from 0.0 V to 0.2 V (vs RHE).

[0097] In some embodiments, the cathode electrode comprises platinum as a catalyst. In some embodiments, hydrogen evolution reaction (HER) occurs at the cathode electrode under catalysis of the platinum. In some embodiments, the cathode electrode comprises platinum and carbon in powder form.

[0098] All examples described herein, whether of apparatus, methods, materials, or products, are presented for the purpose of illustration and to aid understanding, and are not intended to be limiting or exhaustive. Modifications may be made by one of ordinary skill in the art without departing from the scope of the claimed invention

Claims

Claims1. A bipolar hydrogen production system, comprising: a silver-based anodic catalyst deposited on an anode electrode; a cathode electrode; and an alkaline electrolyte containing an organic compound with aldehyde functional group extracted from lignocellulosic biomass waste or an aldehyde-containing chemical compound extracted from chemical waste.

2. The bipolar hydrogen production system according to claim 1, wherein the silver-based anodic catalyst is silver chloride (AgCl).

3. The bipolar hydrogen production system according to claim 1, wherein the silver-based anodic catalyst is a silver-copper (Ag-Cu) bimetallic catalyst co-deposited directly onto an oxide-derived copper foam, denoted as Ag@OD-Cu.

4. The bipolar hydrogen production system according to claim 1 , wherein the silver-based anodic catalyst is a silver-copper (Ag-Cu) bimetallic catalyst in powder form, coated onto a conductive support or on the anode electrode.

5. The bipolar hydrogen production system according to claim 1, wherein the organic compound is furfural.

6. The bipolar hydrogen production system according to claim 1, wherein the lignocellulosic biomass waste is selected from the group consisting of empty fruit bunch fiber, sugarcane bagasse, com stover, agriculture waste, woody waste, paper waste and food waste.

7. A method for producing hydrogen gas from a bipolar hydrogen production system, comprising: depositing a silver-based anodic catalyst on an anode electrode; providing a cathode electrode; and introducing an alkaline electrolyte containing an organic compound with aldehyde functional group extracted from lignocellulosic biomass waste or the aldehyde-containing chemical compound extracted from chemical waste into the bipolar hydrogen production system, allowing electrooxidation of the organic compound with the aldehyde functional group or the aldehyde-containing chemical compound, at the anode electrode of the bipolar hydrogen production system to facilitate hydrogen production.

8. The method according to claim 7, wherein the organic compound with the aldehyde functional group is furfural.

9. The method according to claim 8, wherein the alkaline electrolyte containing furfural is prepared by: extracting furfural from the lignocellulosic biomass waste in an aqueous solution through hydrothermal treatment to obtain a furfural-containing solution; subjecting the furfural-containing solution to azeotropic distillation to obtain a furfural- water mixture; and adjusting the pH of the furfural-water mixture to form the alkaline electrolyte.

10. The method according to claim 7, wherein the silver-based anodic catalyst is silver chloride (AgCl).1 1 . The method according to claim 7, wherein the silver-based anodic catalyst is a silvercopper (Ag-Cu) bimetallic catalyst co-deposited directly onto an oxide-derived copper foam, denoted as Ag@OD-Cu.

12. The method according to claim 7, wherein the silver-based anodic catalyst is a silvercopper (Ag-Cu) bimetallic catalyst in powder form, coated onto a conductive support or on the anode electrode.

13. The method according to claim 7, wherein the lignocellulosic biomass waste is selected from the group consisting of empty fruit bunch fiber, sugarcane bagasse, corn stover, agriculture waste, woody waste, paper waste and food waste.

14. The method according to claim 7, wherein hydrogen gas is produced at both the anode electrode and the cathode electrode.

15. The method according to claim 7, wherein the electrooxidation of the organic compound with the aldehyde functional group or the aldehyde-containing chemical compound at the anode electrode occurs at a reduced onset voltage ranging from 0.0 V to 0.2 V (vs RHE).

16. The method according to claim 7, wherein the cathode electrode comprises platinum as a catalyst.

17. The method according to claim 16, wherein hydrogen evolution reaction (TIER) occurs at the cathode electrode under catalysis of the platinum.

18. The method according to claim 16, wherein the cathode electrode comprises platinum and carbon in powder form.

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