Nickel-based cathode capable of enhancing hydrogen production of microbial electrolysis cell and preparation method of nickel-based cathode

Abstract

The invention relates to the technical field of microbial electrolysis cell cathode preparation, and particularly discloses a nickel-based cathode capable of enhancing hydrogen production of a microbial electrolysis cell and a preparation method of the nickel-based cathode. The method comprises the following steps: adding nickel nitrate hexahydrate into water, and mixing to obtain a nickel nitrate solution; adding urea into the nickel nitrate solution, and stirring until the urea is dissolved to obtain a first mixed solution; and foamed nickel is pretreated and then added into the first mixed solution to be subjected to a heating reaction, the foamed nickel is taken out to be calcined after the heating reaction is finished, and then the nickel-based cathode capable of enhancing hydrogen production of the microbial electrolysis cell is obtained through post-treatment. The foamed nickel is used as a carrier, the urea is used as a precipitator, the nickel nitrate hexahydrate is used as a nickel source, and the nickel base is loaded on the surface of the foamed nickel, so that the overpotential of the hydrogen evolution reaction is further reduced, and the hydrogen evolution efficiency of the microbial electrolytic tank is greatly improved.

Description

Technical Field

[0001] The present invention relates to the technical field of cathode preparation of microbial electrolysis cells, and in particular to a nickel-based cathode capable of enhancing hydrogen production in a microbial electrolysis cell and a preparation method thereof. Background Art

[0002] The cathode of a microbial electrolysis cell (MEC) generally consists of two parts: a support that provides active sites for the hydrogen evolution reaction and a catalyst that reduces the overpotential of the hydrogen evolution reaction. Common supports include carbon-based materials (carbon cloth, carbon felt, asbestos mesh), stainless steel mesh, iron mesh, and titanium. However, the HER catalytic activity of these materials is poor, and it is often necessary to adhere catalysts such as platinum to the surface to reduce the HER overpotential in order to enhance the hydrogen production performance of the MEC. For example, Call et al.

[25] adhered platinum catalysts on carbon cloth as a single-chamber MEC cathode, achieving a cathode hydrogen recovery rate of 78% to 96% and an overall energy efficiency of 78%. Similarly, Rozendal et al. used a Pt-loaded titanium mesh cathode in single-chamber and double-chamber MECs, with a hydrogen production rate of up to 0.3 m / s at an applied voltage of 1 V. 3 H2 / m 3 d. Therefore, platinum has become the most commonly used catalyst due to its low HER overpotential and strong catalytic activity. However, its high price significantly limits its large-scale application in practical engineering. Furthermore, platinum is susceptible to poisoning by chemicals such as sulfide or phosphate anions. Therefore, the search for affordable and efficient alternative non-precious metal HER catalysts is urgent.

[0003] In recent years, various transition metal materials, such as nickel and molybdenum, have been frequently used as cathode catalysts in MECs to improve hydrogen evolution efficiency due to their high electrochemical activity, stable chemical properties, abundant raw materials, and low cost. For example, the nickel particles contained in stainless steel electrodes can act as a hydrogen evolution catalyst, enabling relatively high hydrogen production efficiency. Transition metal nickel, due to its low HER overpotential, is widely used as a cathode support and catalyst. For example, nickel foam (NF) is more stable than other precious metals under alkaline conditions.

[0004] Nickel foam has better mechanical properties and electrical conductivity than carbon-based materials. In addition, the three-dimensional network structure of NF can effectively promote electron transport and accelerate the electron transfer rate. At the same time, it provides more active sites for catalyst particle fixation and hydrogen evolution reaction. Its 3D network structure provides a larger electroactive surface area to produce more hydrogen. Lu et al. reported the performance of two cathodes: nickel foam loaded with platinum (Pt / NF) and carbon cloth loaded with platinum (Pt / CC), and explained the difference between the two cathodes through electrochemical characterization. The results showed that the Pt / NF cathode performed better in terms of hydrogen production rate, with a value ranging from 2.01 to 2.12 m 3 H2 / m 3·d, slightly better than Pt / CC.

[0005] However, as mentioned above, the hydrogen production rate of existing nickel-based cathode materials is only slightly better than that of traditional carbon-based cathodes. Although the existing nickel-based cathodes are low in cost, their hydrogen production efficiency is not much different from that of traditional carbon-based cathodes.

[0006] Therefore, it is necessary to design a nickel-based cathode that can enhance hydrogen production in microbial electrolysis cells to solve the problem of low hydrogen production efficiency of traditional nickel-based cathodes. Summary of the Invention

[0007] In view of this, the present invention proposes a nickel-based cathode that can enhance hydrogen production in a microbial electrolysis cell, so as to solve the problem of low hydrogen production efficiency of traditional nickel-based cathodes.

[0008] In one aspect, the present invention provides a method for preparing a nickel-based cathode capable of enhancing hydrogen production in a microbial electrolysis cell, comprising the following steps:

[0009] Add nickel nitrate hexahydrate to water and mix to obtain a nickel nitrate solution;

[0010] adding urea to the nickel nitrate solution and stirring until dissolved to obtain a first mixed solution;

[0011] The nickel foam is pretreated and then added to the first mixed solution for heating reaction. After the reaction, the nickel foam is taken out and calcined, and then post-treated to obtain a nickel-based cathode that can enhance hydrogen production in the microbial electrolysis cell.

[0012] Furthermore, the concentration of the nickel nitrate solution is 0.02 mol / L.

[0013] Furthermore, the molar ratio of nickel nitrate to urea in the first mixed solution is 1:(1-20).

[0014] Furthermore, the pretreatment is specifically as follows: cutting the nickel foam, placing the cut nickel foam in a hydrochloric acid solution for ultrasonic cleaning, then placing the cut nickel foam in ethanol for ultrasonic cleaning, and then rinsing with water and drying.

[0015] Furthermore, the ultrasonic cleaning time is 15 minutes, and the drying temperature is 60°C.

[0016] Furthermore, the temperature of the heating reaction is 105° C. and the reaction time is 10 hours.

[0017] Furthermore, the calcination temperature is 300° C. and the calcination time is 2 hours.

[0018] Furthermore, the post-treatment specifically includes cooling the calcined nickel foam to room temperature, then rinsing with water, and drying naturally.

[0019] On the other hand, the present invention also provides a nickel-based cathode that can enhance hydrogen production in a microbial electrolysis cell.

[0020] Compared with the prior art, the present invention has the following beneficial effects: the present invention uses nickel foam as a carrier, urea as a precipitant, and nickel nitrate hexahydrate as a nickel source. The nickel base loaded on the surface of the nickel foam further reduces the overpotential of the hydrogen evolution reaction, thereby significantly improving the hydrogen evolution efficiency of the microbial electrolysis cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiment below. The accompanying drawings are for illustration purposes only and are not to be considered as limiting the present invention. The same reference symbols are used throughout the drawings to represent the same components. In the drawings:

[0022] Figure 1 A flow chart of a method for preparing a nickel-based cathode capable of enhancing hydrogen production in a microbial electrolysis cell provided in an embodiment of the present invention;

[0023] Figure 2 The LSV test results and Tafel slope graph of NF / 1:1, NF / 1:5, NF / 1:10, NF / 1:20 and NF in the embodiment of the present invention are shown;

[0024] Figure 3 These are the EIS graphs of NF, NF / 1:5, and NF / 1:20 in the examples of the present invention;

[0025] Figure 4 This is the XPS high-resolution full spectrum of NF / 1:20 in the embodiment of the present invention;

[0026] Figure 5 This is a fine spectrum of Ni2p with NF / 1:20 in an embodiment of the present invention;

[0027] Figure 6 This is the fine spectrum of O1s at NF / 1:20 in the embodiment of the present invention;

[0028] Figure 7 This is an electron microscope micrograph of NF / 1:20 in the embodiment of the present invention;

[0029] Figure 8 This is the XRD analysis result diagram of NF / 1:20 in the embodiment of the present invention;

[0030] Figure 9 This is a physical picture of the microbial electrolysis cell used in the effect test of the present invention;

[0031] Figure 10 This is a physical picture of the MEC system used in the effect test of the present invention;

[0032] Figure 11 1 is a graph showing the current density of the reactor when NF / 1:20 and NF are used as cathode in MEC according to an embodiment of the present invention;

[0033] Figure 12 Graphs showing the COD degradation and coulombic efficiency of MEC when NF / 1:20 and NF are used as cathodes in an embodiment of the present invention;

[0034] Figure 13 Graphs showing the gas production and gas concentration of MEC when NF / 1:20 and NF are used as cathodes in an embodiment of the present invention;

[0035] Figure 14 Graphs showing the hydrogen production rate and electron recovery efficiency of MEC when NF / 1:20 and NF are used as cathodes in an embodiment of the present invention;

[0036] Figure 15 Graphs showing the hydrogen production rate and electrical energy recovery rate of MEC when NF / 1:20 and NF are used as cathodes in an embodiment of the present invention. DETAILED DESCRIPTION

[0037] Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art. It should be noted that, unless there is a conflict, the embodiments of the present disclosure and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments.

[0038] In recent years, various transition metal materials, such as nickel and molybdenum, have been frequently used as cathode catalysts in MECs to improve hydrogen evolution efficiency due to their high electrochemical activity, stable chemical properties, abundant raw materials, and low cost. For example, the nickel particles contained in stainless steel electrodes can act as a hydrogen evolution catalyst, enabling relatively high hydrogen production efficiency. Transition metal nickel, due to its low HER overpotential, is widely used as a cathode support and catalyst. For example, nickel foam (NF) is more stable than other precious metals under alkaline conditions.

[0039] Nickel foam has better mechanical properties and electrical conductivity than carbon-based materials. In addition, the three-dimensional network structure of NF can effectively promote electron transport and accelerate the electron transfer rate. At the same time, it provides more active sites for catalyst particle fixation and hydrogen evolution reaction. Its 3D network structure provides a larger electroactive surface area to produce more hydrogen. Lu et al. reported the performance of two cathodes: nickel foam loaded with platinum (Pt / NF) and carbon cloth loaded with platinum (Pt / CC), and explained the difference between the two cathodes through electrochemical characterization. The results showed that the Pt / NF cathode performed better in terms of hydrogen production rate, with a value ranging from 2.01 to 2.12 m 3 H2 / m 3 d, slightly better than Pt / CC. However, as mentioned above, the hydrogen production rate of existing nickel-based cathode materials is only slightly better than that of traditional carbon-based cathodes. Although existing nickel-based cathodes are low-cost, their hydrogen production efficiency is not much different from that of traditional carbon-based cathodes. Therefore, it is necessary to design a nickel-based cathode that can enhance hydrogen production in microbial electrolysis cells to solve the problem of low hydrogen production efficiency of traditional nickel-based cathodes.

[0040] On the one hand, if Figure 1 As shown, in some embodiments of the present application, a method for preparing a nickel-based cathode capable of enhancing hydrogen production in a microbial electrolysis cell comprises the following preparation steps:

[0041] Add nickel nitrate hexahydrate to water and mix to obtain a nickel nitrate solution;

[0042] adding urea to the nickel nitrate solution and stirring until dissolved to obtain a first mixed solution;

[0043] The nickel foam is pretreated and then added to the first mixed solution for heating reaction. After the reaction, the nickel foam is taken out and calcined, and then post-treated to obtain a nickel-based cathode that can enhance hydrogen production in the microbial electrolysis cell.

[0044] Specifically, the water is ultrapure water.

[0045] It can be understood that the present invention uses nickel foam as a carrier, urea as a precipitant, and nickel nitrate hexahydrate as a nickel source. The nickel base is loaded on the surface of the nickel foam to further reduce the overpotential of the hydrogen evolution reaction, thereby greatly improving the hydrogen evolution efficiency of the microbial electrolysis cell.

[0046] In some embodiments of the present application, the concentration of the nickel nitrate solution is 0.02 mol / L.

[0047] In some embodiments of the present application, the molar ratio of nickel nitrate to urea in the first mixed solution is 1:(1-20), preferably 1.

[0048] In some embodiments of the present application, the pretreatment is specifically: cutting the nickel foam, placing the cut nickel foam in a hydrochloric acid solution for ultrasonic cleaning, and then placing it in ethanol for ultrasonic cleaning, followed by rinsing with water and drying.

[0049] In some embodiments of the present application, the ultrasonic cleaning time is 15 minutes, and the drying temperature is 60°C.

[0050] Specifically, nickel foam (NF) was cut into a size of 8 cm in length and 1.5 cm in width using sterile scissors. The cut NF was ultrasonically cleaned in 3M hydrochloric acid for 15 minutes, then ultrasonically cleaned in anhydrous ethanol for 15 minutes, then repeatedly rinsed with ultrapure water, and dried at 60°C for later use.

[0051] It is understandable that the purpose of ultrasonic cleaning in 3M hydrochloric acid is to remove the oxide film and dust on the surface and increase the surface area, and the purpose of ultrasonic cleaning in anhydrous ethanol is to remove excess hydrochloric acid and impurities.

[0052] In some embodiments of the present application, the temperature of the heating reaction is 105° C., and the reaction time is 10 hours.

[0053] Specifically, the first mixed solution and the nickel foam were added into a reactor, which was then sealed and placed in an oven for heating at 105° C. for 10 hours.

[0054] In some embodiments of the present application, the calcination temperature is 300° C. and the calcination time is 2 hours.

[0055] Specifically, the nickel foam after the reaction was placed in a tube furnace and calcined at 300° C. for 2 hours under an N 2 atmosphere.

[0056] In some embodiments of the present application, the post-treatment is specifically to cool the calcined nickel foam to room temperature, then rinse with water, and dry naturally.

[0057] Specifically, the water is pure water.

[0058] On the other hand, in some embodiments of the present application, a nickel-based cathode capable of enhancing hydrogen production in a microbial electrolysis cell is prepared by the method for preparing a nickel-based cathode capable of enhancing hydrogen production in a microbial electrolysis cell.

[0059] Example 1

[0060] S1. Add 0.406 g of nickel nitrate hexahydrate and 70 ml of purified water into a beaker and stir until completely dissolved to obtain a nickel nitrate solution with a concentration of 0.02 mol / L;

[0061] S2. Add 0.084 g of urea to the nickel nitrate solution and stir until completely dissolved to obtain a first mixed solution;

[0062] S3. Use sterile scissors to cut nickel foam (NF) into pieces of 8 cm in length and 1.5 cm in width. Place the cut NF in 3M hydrochloric acid for ultrasonic cleaning for 15 minutes, then place it in anhydrous ethanol for ultrasonic cleaning for 15 minutes, then rinse it repeatedly with ultrapure water, and dry it at 60°C for use to obtain pretreated nickel foam.

[0063] S4. Add the first mixed solution and the pretreated nickel foam into the reactor, then place the sealed reactor in an oven at 105°C for 10 hours. After the reaction is completed, take out the nickel foam, place it in a tube furnace, and calcine it at 300°C for 2 hours under N2 atmosphere. When the inner wall of the tube furnace cools to room temperature, take out the sample, rinse it with a slow stream of ultrapure water, and dry it naturally to obtain a nickel-based cathode that can enhance hydrogen production in a microbial electrolysis cell.

[0064] Example 2

[0065] S1. Add 0.406 g of nickel nitrate hexahydrate and 70 ml of purified water into a beaker and stir until completely dissolved to obtain a nickel nitrate solution with a concentration of 0.02 mol / L;

[0066] S2. Add 0.42 g of urea to the nickel nitrate solution and stir until completely dissolved to obtain a first mixed solution;

[0067] S3. Use sterile scissors to cut nickel foam (NF) into pieces of 8 cm in length and 1.5 cm in width. Place the cut NF in 3M hydrochloric acid for ultrasonic cleaning for 15 minutes, then place it in anhydrous ethanol for ultrasonic cleaning for 15 minutes, then rinse it repeatedly with ultrapure water, and dry it at 60°C for use to obtain pretreated nickel foam.

[0068] S4. Add the first mixed solution and the pretreated nickel foam into the reactor, then place the sealed reactor in an oven at 105°C for 10 hours. After the reaction is completed, take out the nickel foam, place it in a tube furnace, and calcine it at 300°C for 2 hours under N2 atmosphere. When the inner wall of the tube furnace cools to room temperature, take out the sample, rinse it with a slow stream of ultrapure water, and dry it naturally to obtain a nickel-based cathode that can enhance hydrogen production in a microbial electrolysis cell.

[0069] Example 3

[0070] S1. Add 0.406 g of nickel nitrate hexahydrate and 70 ml of purified water into a beaker and stir until completely dissolved to obtain a nickel nitrate solution with a concentration of 0.02 mol / L;

[0071] S2. Add 0.84 g of urea to the nickel nitrate solution and stir until completely dissolved to obtain a first mixed solution;

[0072] S3. Use sterile scissors to cut nickel foam (NF) into pieces of 8 cm in length and 1.5 cm in width. Place the cut NF in 3M hydrochloric acid for ultrasonic cleaning for 15 minutes, then place it in anhydrous ethanol for ultrasonic cleaning for 15 minutes, then rinse it repeatedly with ultrapure water, and dry it at 60°C for use to obtain pretreated nickel foam.

[0073] S4. Add the first mixed solution and the pretreated nickel foam into the reactor, then place the sealed reactor in an oven at 105°C for 10 hours. After the reaction is completed, take out the nickel foam, place it in a tube furnace, and calcine it at 300°C for 2 hours under N2 atmosphere. When the inner wall of the tube furnace cools to room temperature, take out the sample, rinse it with a slow stream of ultrapure water, and dry it naturally to obtain a nickel-based cathode that can enhance hydrogen production in a microbial electrolysis cell.

[0074] Example 4

[0075] S1. Add 0.406 g of nickel nitrate hexahydrate and 70 ml of purified water into a beaker and stir until completely dissolved to obtain a nickel nitrate solution with a concentration of 0.02 mol / L;

[0076] S2. Add 1.62 g of urea to the nickel nitrate solution and stir until completely dissolved to obtain a first mixed solution;

[0077] S3. Use sterile scissors to cut nickel foam (NF) into pieces of 8 cm in length and 1.5 cm in width. Place the cut NF in 3M hydrochloric acid for ultrasonic cleaning for 15 minutes, then place it in anhydrous ethanol for ultrasonic cleaning for 15 minutes, then rinse it repeatedly with ultrapure water, and dry it at 60°C for use to obtain pretreated nickel foam.

[0078] S4. Add the first mixed solution and the pretreated nickel foam into the reactor, then place the sealed reactor in an oven at 105°C for 10 hours. After the reaction is completed, take out the nickel foam, place it in a tube furnace, and calcine it at 300°C for 2 hours under N2 atmosphere. When the inner wall of the tube furnace cools to room temperature, take out the sample, rinse it with a slow stream of ultrapure water, and dry it naturally to obtain a nickel-based cathode that can enhance hydrogen production in a microbial electrolysis cell.

[0079] Effect test:

[0080] The nickel-based cathodes prepared in Examples 1-4 for enhancing hydrogen production in microbial electrolysis cells and conventional unmodified nickel foam were tested for their effectiveness.

[0081] Among them, the molar ratio of nickel nitrate to urea in Example 1 is 1:1, so the nickel-based cathode for enhancing hydrogen production in the microbial electrolysis cell prepared in Example 1 is named NF / 1:1; the molar ratio of nickel nitrate to urea in Example 2 is 1:5, so the nickel-based cathode for enhancing hydrogen production in the microbial electrolysis cell prepared in Example 2 is named NF / 1:5; the molar ratio of nickel nitrate to urea in Example 3 is 1:10, so the nickel-based cathode for enhancing hydrogen production in the microbial electrolysis cell prepared in Example 3 is named NF / 1:10; the molar ratio of nickel nitrate to urea in Example 4 is 1:20, so the nickel-based cathode for enhancing hydrogen production in the microbial electrolysis cell prepared in Example 4 is named NF / 1:20; conventional unmodified nickel foam is named NF.

[0082] 1. LSV and EIS tests were performed on the modified and unmodified nickel foams using a conventional three-electrode system. The electrolyte was purged with nitrogen before the test to eliminate the interference of oxygen. The electrolyte was a 1 mol / L phosphate buffer solution with a pH of 7.

[0083] The results are as follows Figure 2 As shown, where:

[0084] Part a shows the LSV test results of NF / 1:1, NF / 1:5, NF / 1:10, NF / 1:20, and NF. The results show that within -0.6 to 0 V vs. RHE, the current density of NF / 1:20 is higher overall, with the maximum current density reaching 96.92 mA cm -2 , higher than NF's 62.68mAcm -2 and NF / 1:5 at 68.18 mA cm -2 , while the maximum current density that NF / 1:1 and NF / 1:5 can achieve is only 55mAcm -2 and 52.64 mA cm -2 , which shows that NF / 1:20 has the best hydrogen evolution performance. When the current density is 10mAcm -2 When the overpotential of NF / 1:20 is 316 mV, which is better than 347 mV of NF. The overpotentials of NF / 1:10, NF / 1:1 and NF / 1:5 are 344 mV, 360 mV and 372 mV respectively, which shows that the hydrogen evolution performance of NF / 1:20 is improved compared with that of unmodified nickel foam, while the hydrogen evolution performance of NF / 1:10 is close to that of unmodified nickel foam, and the hydrogen evolution performance of NF / 1:1 and NF / 1:5 are not as good as that of unmodified nickel foam.

[0085] Part b is the Tafel slope calculated from the linear region of the LSV graph for the corresponding material, which reflects the kinetics of the hydrogen evolution process. A lower Tafel slope generally indicates that the material has better reaction rate and catalytic activity at a lower overpotential. As can be seen from the figure, NF / 1:20 has a lower Tafel slope of 152.6mVdec compared to NF, NF / 1:10, NF / 1:1, and NF / 1:5. -1 The other Tafel slopes are 194mVdec -1 、186.1mVdec -1 、253.7mVdec -1 、275mVdec -1 It can be seen that the catalytic hydrogen evolution reaction kinetics of NF / 1:20 prepared with different material ratios during the synthesis process has the fastest rate, which is consistent with the LSV test results. This shows that when urea is added in a large amount as a precipitant, nickel-based compounds begin to precipitate on the surface of nickel foam. During the subsequent calcination process, the nickel-based compounds on the surface of nickel foam lose water molecules and become nickel oxides. Nickel oxides have good catalytic performance.

[0086] AC impedance test was conducted on NF, NF / 1:5 and NF / 1:20. The results are as follows: Figure 3 As shown in the figure, the semicircle diameter corresponds to the charge transfer resistance, which reflects the difficulty of charge transfer in the electrochemical reaction. NF / 1:20 has the smallest semicircle diameter, indicating the lowest impedance, the easiest charge transfer process, and the best electrochemical reaction kinetics. NF / 1:5 has the largest semicircle diameter, the highest impedance, and the greatest charge transfer resistance. The charge transfer capacity of NF is between the two. NF / 1:20 exhibits superior electrocatalytic performance compared to unmodified nickel foam.

[0087] 2. Perform physical characterization tests on NF / 1:20.

[0088] First, XPS technology was used to investigate the elemental composition and valence state of the NF / 1:20 surface. Figure 4 The high-resolution XPS full spectrum of the sample is displayed, confirming the presence of Ni, O, and C elements. The presence of C is caused by the exposure of NF / 1:20 to air.

[0089] Figure 5 The fine spectrum of Ni2p is shown, with four peaks appearing at 856.2eV, 861.85eV, 873.8eV, and 879.86eV. The peaks with binding energies of 856.2eV and 861.85eV correspond to Ni2p. 3 / 2 The main peak and its satellite peaks are fitted with peaks at 873.8eV and 879.86eV corresponding to Ni2p 1 / 2 The main peak and its satellite peaks, two split peaks caused by spin-orbit coupling Ni2p3 / 2 and Ni2p 1 / 2 The energy difference of 17.6 eV between the two groups proves that Ni in the oxide form 2+ The clear symmetry indicates the presence of NiO. The satellite peaks at 861.85 eV and 879.86 eV at higher energy levels also confirm the presence of Ni in its divalent oxidized form.

[0090] Figure 6 The O1s spectrum is shown in detail. A strong peak at 530.9 eV is observed, which is consistent with the characteristic signal of lattice oxygen in NiO, indicating the presence and stability of lattice oxygen in NiO. The weaker peak at 532.85 eV is likely the oxygen present in the hydroxyl groups on the surface of NF / 1:20, confirming the presence of negative divalent oxygen. XPS results indicate that the nickel matrix supported on the surface of the NF / 1:20 sample exists in the form of NiO.

[0091] like Figure 7 The electron microscope micrographs of NF / 1:20 are shown. The magnifications of Figures (a), (b), (c), and (d) are 2000 times, 10000 times, 20000 times, and 50000 times, respectively. It can be clearly seen that NiO grows evenly on the surface of the nickel foam substrate. NiO is in the form of thin flakes with clear edges and wrinkles. The flakes are stacked and interwoven to form a three-dimensional structure similar to a "flower cluster". This flake stacking structure greatly increases the specific surface area of ​​the material and provides abundant surface active sites, which is beneficial to the adsorption and activation of reactants in catalytic reactions. In addition, the pores between the clusters may form material transfer channels, which can improve the diffusion efficiency of ions / molecules in the catalytic reaction and reduce mass transfer resistance. In addition, studies have shown that nickel foam loaded NiO may undergo in-situ reduction to form Ni in alkaline electrolyte. 0 / NiO heterostructure, thereby adjusting the hydrogen adsorption free energy (ΔG_H*) and optimizing the reaction path of the Volmer step. In the alkaline hydrogen evolution reaction, the Volmer step (H2O+e - →H*+OH-) is usually the rate-determining step, NiO / Ni 0 The interface can simultaneously promote water decomposition and the adsorption and desorption of hydrogen intermediates, improving the overall catalytic efficiency.

[0092] The XRD analysis results of NF / 1:20 are as follows Figure 8As shown in the figure, there are three diffraction peaks at 2θ = 44.5°, 51.8° and 76.4°, which correspond to the (111), (200) and (220) crystal planes of Ni (JCPDS, No. 65-2865), respectively. No diffraction peak of NiO was observed. It may be that the NiO layer is very thin and the signal is masked by the Ni element of the foam substrate. The diffraction peak of NF loaded with NiO is very similar to that of bare NF, indicating that the diffraction peak of Ni in the NF / 1:20 synthesized in a series of ways is very strong, which makes the diffraction peaks of other compounds not obvious.

[0093] 3. The hydrogen evolution catalytic ability of NF / 1:20 and NF as cathodes in the MEC system was analyzed. NF was used as the control group and NF / 1:20 as the experimental group to explore the stability and hydrogen evolution catalytic ability of nickel foam after loading nickel oxide in the microbial electrolysis cell system.

[0094] (1) Construction of MEC device

[0095] Devices such as Figure 9 As shown, the main body is a headspace bottle with an effective volume of 100ml. It is made of high-borosilicate glass, which has the characteristics of high temperature resistance, low expansion rate, and chemical stability. The top is equipped with a silicone plug for a good seal, which can be inserted with needles and wires. Two titanium wires pass through the silicone plug at the top of the reactor. One connects the anode carbon brush at the bottom of the reactor to the positive terminal of the power supply, and the other connects the cathode nickel foam at the top of the reactor to the negative terminal of the power supply. The distance between the anode and cathode is 3cm. The DC power supply (ITEX IT6302) applies a voltage of 0.8V to the reactor. A 5ml syringe needle is inserted into the rubber plug at the top of the reactor. The other end of the needle is connected to a 6cm section of peristaltic pump tubing. The connection is sealed with glue. The other end of the pump tubing is equipped with an air bag to collect gas. A sealable opening is also left on each side of the reactor to facilitate the replacement of culture medium.

[0096] It is important to avoid contact between the titanium wire connected to the anode and the titanium wire connected to the cathode in the reactor, or between the titanium wire connected to the anode and the cathode nickel foam on the top of the reactor, to prevent short circuits.

[0097] In this experiment, the titanium wires in the reactor were all inserted into the PTFE capillary tube, and the insulation property of the PTFE capillary tube was used to prevent the above situation from happening.

[0098] The entire MEC system is sealed before operation. The screw hole on the top of the reactor is tightened with a hole cover to make the silicone plug more tightly connected to the reactor. Vaseline is applied to the place where the two titanium wires and the needle pass through the silicone plug to prevent air leakage.

[0099] (2) MEC startup

[0100] The microorganisms inoculated in the reactor of this experiment come from the effluent of the MEC reactor that has been operating stably in the laboratory of the School of Environmental Science and Engineering of Sun Yat-sen University. The culture medium is a 50mM phosphate buffer solution with a substrate of 2g / L sodium acetate and rich in nutrients. At the start-up, the MEC effluent rich in microorganisms is mixed with PBS and added to the reactor, and then a nitrogen needle is used to aerate the reactor for 10 minutes to remove oxygen. The DC power supply (IT6302) applies a constant voltage of 0.8V to the reactor. The positive pole of the power supply is connected to the anode and the negative pole of the power supply is connected to the cathode. The current can be directly measured through the DC power supply and fed back to the computer. The current data is recorded every 2 minutes. The inoculum is only put in during the first cycle of the reaction. After waiting for four to five days, the gas is collected in the air bag, and when the current monitored in the circuit is stable, the reactor can be considered to have started successfully. After the current in the measured circuit is less than 0.5mA, it is determined that the substrate in the reactor has been consumed, the reaction cycle is over, and the culture medium needs to be replaced. The entire MEC system is as follows: Figure 10 shown.

[0101] (3) Take two reactors that have been successfully started and run stably for two months. Replace the cathode with NF / 1:20 and NF respectively. The culture medium is 50mM phosphate buffer and the substrate is 2g / L sodium acetate. The hydraulic retention time is 48 hours per cycle. Run for 7 cycles at a constant voltage of 0.8V to observe the current density and gas production. The gas composition is analyzed by gas chromatography. The results are as follows: Figure 11-15 shown.

[0102] As shown in the figure, Figure 11 (a) shows the current of the reactor when NF / 1:20 is used as the cathode in the MEC for seven days, with an average current density of 87.82 A / m 3 , the maximum current density reached 106A / m in the first cycle 3 Then the current density gradually decreased in the 2nd to 7th cycles, and the overall current density dropped to 72A / m 3 3-7(b) is the current density diagram when NF is used as cathode, with an average current of 87.43A / m 3 , the maximum current density reached 97.89A / m in the fourth cycle 3 At the end of the third, fourth and fifth cycles, the current density dropped to 40A / m 3 Below, it can be considered that the substrate is basically degraded, and then the current density drops to 77A / m in the seventh cycle. 3When the two materials are used as cathodes, the average current density is similar, and the maximum current density NF / 1:20 is higher than NF. However, without considering the complete degradation of the substrate within seven cycles, the current density of NF / 1:20 decreases more overall. It can be concluded from the figure that nickel foam can operate stably in a neutral MEC after being loaded with nickel oxide, and the maximum hydrogen evolution current density is higher. Long-term immersion in the electrolyte to produce hydrogen does not lead to a rapid decrease in current, and there is no inactivation of anode microorganisms. This proves that the prepared nickel foam loaded with nickel oxide has sufficient stability.

[0103] As shown in the figure, Figure 12 (a) shows the COD degradation of MEC when the two materials are used as cathodes. It can be seen that the COD degradation rates of MEC are very high. The overall degradation rate of NF / 1:20 is between 80-90%, and the overall degradation rate of NF is between 85-95%. In addition, except for the first cycle, the COD degradation rate of NF / 1:20 is higher than that of NF, and the COD degradation rate of NF is higher in the remaining cycles. (b) shows the coulomb efficiency of MEC when the two materials are used as cathodes. Coulomb efficiency refers to the ratio of the total coulombs generated in the circuit to the total theoretical amount of coulombs generated based on COD removal. The coulomb efficiency of NF / 1:20 reaches a maximum of 108%, and the coulomb efficiency of NF reaches a maximum of 102%. The overall coulomb efficiency of the two curves exceeds 80%, indicating that most of the coulombs generated by the added substrate during removal can enter the circuit, but both curves have parts exceeding 100%.

[0104] This indicates that an internal H2 cycle occurs within the reactor, and the homoacetogenic bacteria consume the hydrogen in the reactor to produce acetate. This cycle seriously damages the hydrogen production and energy efficiency through the internal recovery of hydrogen, threatening the practical application of MEC in hydrogen production

[31] . The overall coulombic efficiency of NF / 1:20 is greater than that of NF. Considering the previous current density situation, the average current density generated by the two is similar, indicating that the substrate degradation rate of NF / 1:20 is lower than that of NF. Except for the first cycle, the rest are consistent with the COD degradation rate.

[0105] As shown in the figure, Figure 13 (a) and (b) show the gas production of MEC when NF / 1:20 and NF were used as cathodes, respectively. During the entire experiment, the total gas production and hydrogen production of the two groups showed a downward trend. Except for the sixth cycle, the total gas production and hydrogen production of the NF / 1:20 group were greater than those of the NF group. It was observed that in the first cycle, both groups reached the maximum hydrogen production, which was 110.6ml and 81.16ml respectively, with a hydrogen production rate of 0.55m 3 H2 / m 3 d and 0.4m 3 H2 / m 3d. The first cycle represents the initial hydrogen evolution cycle after cathode replacement, assuming minimal microbial contamination. During this period, the cathode surface is primarily dominated by the hydrogen evolution reaction, indicating that the NF / 1:20 cathode exhibits a higher maximum hydrogen evolution catalytic capacity in the MEC than the NF. Subsequently, hydrogen production in the NF / 1:20 group slowly decreased from the first to fifth cycles. From the fifth to sixth cycles, total gas production and hydrogen production rapidly decreased, from 111 ml and 84 ml to 49.5 ml and 28.5 ml, respectively, and to 39.5 ml and 17.2 ml in the seventh cycle. Total gas production and hydrogen production in the NF group steadily decreased from 99.5 ml and 81.2 ml in the first cycle to 36.5 ml and 14 ml in the seventh cycle. Changes in total gas production coincided with changes in hydrogen production, indicating that the hydrogen evolution reaction dominated. Overall, the NF / 1:20 group produced more hydrogen, indicating that nickel foam-supported nickel oxide exhibits a stronger hydrogen evolution catalytic capacity than unmodified nickel foam, consistent with the electrochemical analysis results previously reported.

[0106] (c) and (d) show the gas concentrations produced by the MEC when NF / 1:20 and NF were used as cathodes, respectively. Hydrogen concentrations reached their highest level in the first cycle for both groups, reaching 84.4% in the NF / 1:20 group and 81.58% in the NF group. Subsequently, hydrogen concentrations decreased steadily, reaching 43.55% in the NF / 1:20 group and 38.42% in the NF group by the seventh cycle. During this decrease in hydrogen concentration, methane concentrations were observed to increase, rising from 7.65% in the NF / 1:20 group to 51.6% in the seventh cycle, and from 10.08% in the NF group to 51.22% in the seventh cycle. This decrease in hydrogen concentration and increase in methane concentration is typical of hydrogenotrophic methanogens, which metabolize hydrogen and convert it into methane. In connection with the methane production in (a) and (b), methane production was observed in the first cycle after replacing the cathode. The methane volume of the NF / 1:20 group was 10 ml, and the methane volume of the NF group was 10 ml, indicating that methanogens existed in the anode and the electrolyte. Then the methane volume slowly increased. The methane volume of the NF / 1:20 group reached a maximum of 21 ml in the fifth cycle, and the methane volume of the NF group reached a maximum of 24 ml in the fourth cycle. During the seven cycles, the methane volume did not increase by one-fourth of the decrease in the hydrogen volume, indicating that in addition to hydrogenotrophic methanogens that consume hydrogen, there are other anaerobic microorganisms competing for hydrogen consumption.

[0107] As shown in the figure, Figure 14 (a) shows the hydrogen production rate of MEC when NF / 1:20 and NF are used as cathodes. From the figure, it can be seen that from the first to the fifth cycle, the hydrogen production rates of the NF / 1:20 group are 0.553, 0.512, 0.445, 0.423, and 0.419 m3 H2 / m 3 ·d, the hydrogen production rates of the NF group were 0.406, 0.330, 0.361, 0.245, and 0.237 m 3 H2 / m 3 d. The hydrogen production rate of the NF / 1:20 group was greater than that of the NF group. Then, from the fifth to the sixth cycle, the hydrogen production rate of the NF / 1:20 group dropped rapidly from 0.419 to 0.143 m 3 H2 / m 3 d. The hydrogen production rates in the sixth and seventh cycles were similar to those in the NF group. The NF / 1:20 group produced faster hydrogen in the first five cycles, indicating that NiO / NF had a stronger catalytic hydrogen evolution ability than NF. However, the hydrogen production rates and catalytic hydrogen evolution abilities of the two groups were essentially identical in the sixth and seventh cycles. This may be due to the dissolution of nickel oxide in the nickel foam-loaded nickel oxide cathode in the NF / 1:20 group, significantly reducing its catalytic hydrogen evolution ability. The nickel ion concentrations in the MEC effluents of the NF / 1:20 group and the NF group after seven cycles were detected using an inductively coupled plasma spectrometer. The results showed that the nickel ion concentration in the MEC effluent of the NF / 1:20 group was maintained at around 5 mg / L, while the nickel ion concentration in the MEC effluent of the NF group was lower than that of the NF / 1:20 group, indicating that NF itself would dissolve nickel ions. At the same time, more nickel ions dissolved into the water from the NiO / NF cathode in the electrolyte than from the NF cathode. The source of more nickel in the NiO / NF cathode than in the NF cathode was nickel oxide on the surface. The dissolution of nickel oxide resulted in a higher nickel ion concentration in the solution. When nickel oxide dissolved to a certain extent, the hydrogen evolution catalytic ability of NiO / NF decreased significantly, so that the hydrogen production rate decreased rapidly from the fifth cycle to the sixth cycle.

[0108] The cathode electron recovery rate refers to the ratio between the actual amount of hydrogen collected and the maximum hydrogen production that can be recovered theoretically based on the circuit current, reflecting the electron recovery efficiency of the cathode of the MEC system. Figure 14Figure (b) shows the electron recovery of the MEC cathode using NF / 1:20 and NF as cathodes. The figure shows that the cathode electron recovery rates of the NF / 1:20 group in cycles 1 to 5 are 55.57%, 48.45%, 44.39%, 40.61%, and 40.88%, respectively, while those of the NF group are 42.65%, 30.28%, 32.88%, 21.32%, and 21.77%, respectively. The electron recovery rates of the NF / 1:20 group are higher than those of the NF group in the first five cycles, indicating that the actual electron utilization rate of the NiO / NF cathode is higher than that of the NF electrode. This is due to the low hydrogen evolution overpotential and strong hydrogen evolution catalytic ability of the NiO / NF cathode, which results in fewer electrons lost at the cathode. The cathode electron recovery rate of the NF / 1:20 group drops rapidly from 40.88% to 15.97% from the fifth to sixth cycles, and then approaches that of the NF group in cycles 6 and 7. The downward trend in the cathode electron recovery rate mirrors the downward trend in the hydrogen production rate. This phenomenon, combined with the gas composition analysis previously reported, suggests that a significant amount of electrons are lost in the circuit, ultimately failing to be converted into hydrogen. This is due to competitive consumption of hydrogen by methanogens, homoacetogens, and anaerobic bacteria at the cathode. Furthermore, the prolonged reaction time and microbial contamination of the cathode reduce the electrochemical activity of the cathode surface, hindering electron transfer and reducing hydrogen evolution performance.

[0109] As shown in the figure, Figure 15(a) shows the hydrogen yield of the MEC when NF / 1:20 and NF were used as cathodes. The hydrogen yield of both groups showed a downward trend, similar to the hydrogen generation rate. The hydrogen yield of the NF / 1:20 group was higher in the first to fifth cycles, at 2.22, 1.94, 1.78, 1.62, and 1.64 molH2 / molacetate, respectively, compared to the 1.71, 1.21, 1.32, 0.85, and 0.7 molH2 / molacetate of the NF group. This indicates that when NiO / NF is used as the cathode, more hydrogen is produced per molar volume of sodium acetate than when NF is used as the cathode, resulting in higher substrate utilization and more electrons being used for hydrogen generation. This is due to the low hydrogen evolution overpotential of NiO / NF, which is consistent with the electrochemical detection results mentioned above. Subsequently, the hydrogen yield of the NiO / NF group decreased significantly in the sixth cycle, and the hydrogen yields in the sixth and seventh cycles were similar to those of the NF group. This phenomenon is similar to the hydrogen generation rate, cathode electron utilization, and hydrogen production generation mentioned above. (b) is the energy recovery rate of MEC when NF / 1:20 and NF are used as cathodes. It can be seen that both groups can maintain fluctuations above 100% in the first five cycles, indicating that the energy recovery is high and the MEC system can effectively convert electricity into hydrogen and methane. Subsequently, the energy recovery rates of both groups fell below 100% in the sixth and seventh cycles, indicating that the operating capacity of the MEC system declined, the hydrogen production efficiency decreased, and the energy waste increased. The energy recovery rate of the NF / 1:20 group in the first five cycles was greater than that of the NF group, which also shows that the hydrogen evolution efficiency of NiO / NF is greater than that of NF, and less electricity is wasted. Comprehensively evaluating the two cathodes, NiO / NF is more energy-efficient and more practical when used as a MEC cathode.

[0110] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing a nickel-based cathode capable of enhancing hydrogen production in a microbial electrolytic cell, characterized in that: The method comprises the following preparation steps: Add nickel nitrate hexahydrate to water and mix to obtain a nickel nitrate solution; adding urea to the nickel nitrate solution and stirring until dissolved to obtain a first mixed solution; The nickel foam is pretreated and then added to the first mixed solution for heating reaction. After the reaction, the nickel foam is taken out and calcined, and then post-treated to obtain a nickel-based cathode that can enhance hydrogen production in the microbial electrolysis cell.

2. The method for preparing a nickel-based cathode capable of enhancing hydrogen production in a microbial electrolytic cell according to claim 1, characterized in that: The concentration of the nickel nitrate solution is 0.02 mol / L.

3. The method for preparing a nickel-based cathode capable of enhancing hydrogen production in a microbial electrolytic cell according to claim 2, wherein: The molar ratio of nickel nitrate to urea in the first mixed solution is 1:(1-20).

4. The method for preparing a nickel-based cathode capable of enhancing hydrogen production in a microbial electrolytic cell according to claim 3, wherein: The pretreatment specifically includes: cutting the nickel foam, placing the cut nickel foam in a hydrochloric acid solution for ultrasonic cleaning, placing the cut nickel foam in ethanol for ultrasonic cleaning, and then washing with water and drying.

5. The method for preparing a nickel-based cathode capable of enhancing hydrogen production in a microbial electrolytic cell according to claim 4, characterized in that: The ultrasonic cleaning time is 15 minutes, and the drying temperature is 60°C.

6. The method for preparing a nickel-based cathode capable of enhancing hydrogen production in a microbial electrolytic cell according to claim 5, characterized in that: The temperature of the heating reaction is 105° C., and the reaction time is 10 hours.

7. The method for preparing a nickel-based cathode capable of enhancing hydrogen production in a microbial electrolytic cell according to claim 6, characterized in that: The calcination temperature is 300° C. and the calcination time is 2 hours.

8. The method for preparing a nickel-based cathode capable of enhancing hydrogen production in a microbial electrolytic cell according to claim 7, characterized in that: The post-treatment specifically includes cooling the calcined nickel foam to room temperature, then rinsing with water, and naturally drying.

9. A nickel-based cathode capable of enhancing hydrogen production in a microbial electrolysis cell, characterized in that: The nickel-based cathode capable of enhancing hydrogen production in a microbial electrolysis cell is prepared by the preparation method of any one of claims 1 to 8.

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