Electrocatalysis SOR assisted seawater electrolysis hydrogen production material and preparation method and system thereof

Abstract

The invention discloses a material for electrocatalytic SOR assisted electrolysis of seawater for hydrogen production and a preparation method and system thereof, and belongs to the field of electrocatalytic hydrogen evolution, the method comprises the following steps: S1, dissolving Ni (NO3) 2.6 H2O, Co (NO3) 2.6 H2O, CO (NH2) 2 and NH4F in deionized water, and carrying out ultrasonic treatment until powder is completely dissolved; s2, transferring the obtained solution and foamed nickel into a high-pressure reaction kettle, and putting the high-pressure reaction kettle into a drying oven for heating reaction; s3, after the solution is naturally cooled, the obtained electrode is washed with deionized water and then placed in a vacuum oven to be dried, and the obtained electrode is recorded as CoNi / NF; s4, placing the prepared CoNi / NF and sodium hypophosphite on different side surfaces in a porcelain crucible; then, putting the porcelain crucible into a tubular furnace, enabling one side containing the sodium hypophosphite to face an argon inlet of the tubular furnace, heating the tubular furnace from room temperature to 350 DEG C in an argon atmosphere, and preserving heat; the material CoNiP / NF for hydrogen production through seawater electrolysis assisted by electro-catalysis SOR is obtained, and the problems of low catalytic activity, poor stability and toxic sulfide recovery in the prior art are solved.

Description

Technical Field

[0001] The present invention relates to the field of electrocatalytic hydrogen evolution, and particularly to materials for electrocatalytic SOR-assisted electrolysis of seawater to produce hydrogen, a preparation method thereof, and a system thereof. Background Art

[0002] In view of the increasingly serious environmental and energy problems with the overuse of non-renewable fossil fuels, the development of hydrogen energy with high calorific value and zero carbon emissions is one of the keys to laying out the future energy structure. The electrolytic water technology can be driven by electrical energy converted from renewable energy, and the whole process is clean and pollution-free, which is an important method for efficient and sustainable hydrogen production. However, two major challenges hinder the development of hydrogen production by water electrolysis. One is the dependence on scarce fresh water for electrolysis, which limits its large-scale and continuous commercial application. The other is that the anode OER with a complex and slow four-electron transfer process shows a high oxidation potential (>1.23V vs. RHE), resulting in a large amount of energy consumption. Compared with fresh water resources, seawater accounts for 96.5% of the world's total water reserves and is an abundant and sustainable water resource. At the same time, coastal areas are rich in renewable solar and wind energy resources, and these intermittent energy sources can be used to power the electrolysis system, further improving the energy conversion efficiency and reducing the cost. However, seawater electrolysis is affected by the anodic competitive reaction - chloride oxidation reaction (ClOR), which greatly reduces the efficiency of the electrolysis system. The ClOR reaction involving two single-electron transfer processes shows better kinetic advantages than the oxygen evolution reaction, indicating that the ClOR reaction will occur preferentially when the applied voltage reaches the same interval required for the two reactions, producing by-products such as free chlorine, hypochlorous acid, and chlorine gas, corroding the anode, reducing the stability of the catalyst, and even polluting the environment. Generally, it is inhibited by controlling the overpotential of the anodic reaction at 490 mV or by preparing a selective catalyst through interface regulation. However, the former is difficult to achieve a large current density, and the latter increases the complexity of the catalyst preparation process, and neither has achieved good results.

[0003] Using the sulfur ion oxidation reaction (SOR) with a lower theoretical potential to replace the oxygen evolution reaction and coupling it with the hydrogen evolution reaction to prepare a unique hydrogen production system of sulfur ion oxidation reaction - hydrogen evolution reaction can greatly reduce the energy consumption caused by the high potential of the oxygen evolution reaction. At the same time, the low theoretical potential of this electrolysis system can further inhibit ClOR and recover sulfur in an environmentally friendly electrochemical manner at the anode, achieving a "double win" effect. However, since sulfur ions have a certain corrosiveness to metal catalysts, if noble metal catalysts are used, the cost is too high, and sulfur ions cannot be recovered. Therefore, it is necessary to prepare low-cost, sulfur corrosion-resistant, and efficient catalysts to further improve the efficiency and stability of the electrolysis system. Summary of the Invention

[0004] The present invention provides a material for electrocatalytic SOR-assisted electrolysis of seawater to produce hydrogen, a preparation method thereof, and a system, which solve the problems of low catalytic activity, poor stability, and recovery of toxic sulfides existing in the prior art.

[0005] To solve this technical problem, the present invention provides the following technical solutions:

[0006] A preparation method of a material for electrocatalytic SOR-assisted electrolysis of seawater to produce hydrogen, comprising the following steps:

[0007] S1. Dissolve Ni(NO3)2·6H2O, Co(NO3)2·6H2O, CO(NH2)2, and NH4F in deionized water, and ultrasonically treat until the powder is completely dissolved;

[0008] S2. Then transfer the obtained solution and nickel foam to a high-pressure reaction kettle, and place it in an oven for heating reaction;

[0009] S3. After the solution is naturally cooled, wash the obtained electrode with deionized water, and then place it in a vacuum oven for drying. The obtained electrode is recorded as CoNi / NF;

[0010] S4. Place the prepared CoNi / NF and sodium hypophosphite on different sides in a porcelain crucible; subsequently, place the porcelain crucible in a tubular furnace, with the side containing sodium hypophosphite facing the argon inlet of the tubular furnace, and then raise the temperature of the tubular furnace from room temperature to 350 °C and keep it warm in an argon atmosphere; obtain the material CoNiP / NF for electrocatalytic SOR-assisted electrolysis of seawater to produce hydrogen.

[0011] An electrode of nickel foam-supported bimetallic phosphide nanosheet array (CoNiP / NF) is successfully prepared through a one-step hydrothermal and one-step phosphating process. The CoNiP / NF electrode exhibits efficient catalytic performance for SOR and HER, and only requires an applied potential of 0.27 V vs. RHE (SOR) and 0.18 V vs. RHE (HER) respectively to reach a current density of 100 mA cm -2 At the same time, it shows strong catalytic durability, which is due to the bimetallic synergistic effect of Co and Ni improving the electronic configuration of the catalytic active sites. Meanwhile, during the SOR process, the phosphorus-containing part in CoNiP / NF overflows to form a rich porous structure and unsaturated sites. The increase in the number of active sites and the intrinsic activity of the active sites for SOR are also improved. Therefore, the CoNiP / NF electrode exhibits excellent catalytic performance.

[0012] Preferably, in step S1, the molar ratio of Ni(NO3)2·6H2O, Co(NO3)2·6H2O, CO(NH2)2, and NH4F is 1:1:10:5.

[0013] Preferably, the concentration of Ni(NO3)2·6H2O is 0.025 mmol / mL; the concentration of Co(NO3)2·6H2O is 0.025 mmol / mL; the concentration of CO(NH2)2 is 0.25 mmol / mL; the concentration of NH4F is 0.125 mmol / mL.

[0014] Preferably, the heating reaction temperature in step S2 is 120 °C and the reaction time is 6 h.

[0015] Preferably, the oven drying temperature in step S3 is 60 °C and the oven drying time is 12 h.

[0016] Preferably, the heating rate in step S3 is 5 °C / min; the heat preservation time is 1 h.

[0017] This solution provides an electrocatalytic SOR-assisted electrolytic seawater hydrogen production material prepared by the above-mentioned preparation method of the electrocatalytic SOR-assisted electrolytic seawater hydrogen production material.

[0018] This solution also provides an electrocatalytic SOR-assisted electrolytic seawater hydrogen production system, including a cathode electrolyte and an anode electrolyte. A cation exchange membrane is used to separate the anode mass and the cathode mass to establish an asymmetric coupling electrolytic cell. An anode catalytic electrode and a cathode catalytic electrode are respectively arranged in the anode electrolyte and the cathode electrolyte. The anode catalytic electrode and the cathode catalytic electrode use the electrocatalytic SOR-assisted electrolytic seawater hydrogen production material prepared by the above method or the above-mentioned electrocatalytic SOR-assisted electrolytic seawater hydrogen production material.

[0019] The innovative coupling system (SOR-HER) can achieve a current density of 100 mA cm -2 only with a relatively low voltage of 0.71 V. Compared with traditional seawater electrolysis (HER-OER, 2.27 V), the power consumption is reduced by 69%. An innovative method is introduced for the rapid development of energy-saving and chlorine-free seawater electrolysis technology, and the problem of recycling toxic sulfide waste is also solved.

[0020] Preferably, the cathode electrolyte is 1 M NaOH and 0.5 M NaCl, and the anode electrolyte is 1 M NaOH and 0.5 M NaCl containing 0.5 M Na2S.

[0021] Furthermore, the cathode electrolyte is alkaline seawater, and the anode electrolyte is alkaline seawater containing 0.5 M Na2S.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] The nickel foam-supported bimetallic phosphide nanosheet array (CoNiP / NF) electrode was successfully prepared through a one-step hydrothermal and one-step phosphidation process. The CoNiP nanosheets grown on nickel foam were used as an efficient bifunctional catalyst for HER and SOR. The CoNiP / NF catalytic electrode achieved a current density of 100 mA cm -2 only requires 0.27 V vs. RHE in SOR, and the anodic potential is greatly reduced compared to OER (1.57 V vs. RHE). In addition, the CoNiP / NF catalytic electrode also exhibited excellent HER performance, achieving a current density of 100 mA cm -2 only requires 0.18 V vs. RHE. Therefore, Co- and Ni-based materials showed high catalytic performance towards the sulfide ion oxidation reaction, and the bimetallic synergistic effect can induce the redistribution of electrons to enhance the electrocatalytic activity.

[0024] Using CoNiP / NF as the catalytic electrode, a unique seawater electrolysis device based on the coupling of SOR and HER was constructed. This unique coupling system (SOR-HER) showed strong stability and excellent electrochemical performance, only requiring a low voltage of 0.71 V at 100 mA cm -2 . This voltage value is much lower than that of traditional water electrolysis methods (OER-HER, 2.27 V), which can save about 69% of energy consumption. At the same time, the problem of recycling toxic sulfide waste was also solved. Therefore, an innovative method for developing an energy-saving and chlorine-free seawater electrolysis hydrogen production technology proposed in this scheme provides an effective reference for realizing low-energy-consuming electrolysis of seawater for hydrogen production. Description of the Drawings

[0025] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, form a part of this application, and do not limit the embodiments of the present invention. In the drawings:

[0026] Figure 1 is the XRD pattern of the sample;

[0027] Figure 2 are the SEM images of CoP / NF and NiP / NF;

[0028] Figure 3 are the SEM, TEM, and EDS images of CoNiP / NF;

[0029] Figure 4 are the Co 2p, NiP / NF Ni 2p, Co 2p, and Ni 2p XPS spectra of CoNiP / NF;

[0030] Figure 5 are the P 2p XPS spectra of CoNiP / N, CoP / NF, and NiP / NF;

[0031] Figure 6 are the polarization curves and the corresponding Tafel slopes;

[0032] Figure 7 is the impedance test chart of the catalyst;

[0033] Figure 8 are the CV test chart and the linear relationship between the scan rate and the current density;

[0034] Figure 9 are the polarization current density and stability test charts of CoNiP / NF normalized to the electrochemically active area and the loading amount;

[0035] Figure 10 is the XPS spectrum of CoNiP-S / NF;

[0036] Figure 11 are the SEM and TEM images of CoNiP-S / NF;

[0037] Figure 12 is the elemental mapping of CoNiP-S / NF;

[0038] Figure 13 are the UV-Vis spectra of electrolyte samples at different reaction times and the XRD patterns of the samples;

[0039] Figure 14 are the polarization curves of the electrode, the potentials corresponding to different current densities, and the corresponding Tafel slopes;

[0040] Figure 15 is the current density of the catalytic electrode normalized to the electrochemically active area and the loading amount;

[0041] Figure 16 are the impedance test chart of the catalytic electrode and the hydrogen evolution stability test chart of CoNiP / NF;

[0042] Figure 17 are the polarization curves, stability tests of the coupled system, and the electrical energy required to produce 1 Kg of H2; Specific Embodiments

[0043] In order to make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with embodiments. The illustrative embodiments and descriptions thereof of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0044] Embodiment 1

[0045] As Figure 1As shown, the purchased nickel foam (NF) was washed several times with hydrochloric acid, deionized water, and ethanol to remove the surface oxides and oil film, and then dried in an oven. Subsequently, 0.75 mmol of Ni(NO3)2·6H2O, 0.75 mmol of Co(NO3)2·6H2O, 7.5 mmol of CO(NH2)2, and 3.75 mmol of NH4F were dissolved in 30 mL of deionized water and sonicated for 10 minutes until the powder was completely dissolved. Then the obtained solution and the treated nickel foam were transferred to a high-pressure reactor, placed in an oven, heated from room temperature to 120 °C and maintained for 6 h. After the solution was naturally cooled, the obtained electrode was further washed several times with deionized water and then placed in a vacuum oven at 60 °C for 12 h. The finally obtained electrode was recorded as CoNi / NF.

[0046] The prepared CoNi / NF electrode and 2 g of sodium hypophosphite (NaH2PO2) were placed on different sides in a porcelain crucible. Subsequently, the porcelain crucible was placed in a tube furnace, and the side containing sodium hypophosphite was oriented towards the argon inlet of the tube furnace. Then, in an argon atmosphere, the tube furnace was heated from room temperature to 350 °C at a heating rate of 5 °C / min and held for 1 h. The obtained electrode was named CoNiP / NF.

[0047] Comparative Example 1

[0048] The purchased nickel foam (NF) was washed several times with hydrochloric acid, deionized water, and ethanol to remove the surface oxides and oil film, and then dried in an oven. Subsequently, 0.75 mmol of Co(NO3)2·6H2O, 7.5 mmol of CO(NH2)2, and 3.75 mmol of NH4F were dissolved in 30 mL of deionized water and sonicated for 10 minutes until the powder was completely dissolved. Then the obtained solution and the treated nickel foam were transferred to a high-pressure reactor, placed in an oven, heated from room temperature to 120 °C and maintained for 6 h. After the solution was naturally cooled, the obtained electrode was further washed several times with deionized water and then placed in a vacuum oven at 60 °C for 12 h. The finally obtained electrode was recorded as Co / NF.

[0049] The prepared Co / NF electrode and 2 g of sodium hypophosphite (NaH2PO2) were placed on different sides in a porcelain crucible. Subsequently, the porcelain crucible was placed in a tube furnace, and the side containing sodium hypophosphite was oriented towards the argon inlet of the tube furnace. Then, in an argon atmosphere, the tube furnace was heated from room temperature to 350 °C at a heating rate of 5 °C / min and held for 1 h. The obtained electrode was named CoP / NF electrode.

[0050] Comparative Example 2

[0051] The purchased nickel foam (NF) was washed several times with hydrochloric acid, deionized water, and ethanol to remove the surface oxides and oil film, and then dried in an oven. Subsequently, 0.75 mmol of Ni(NO3)2·6H2O, 7.5 mmol of CO(NH2)2, and 3.75 mmol of NH4F were dissolved in 30 mL of deionized water and sonicated for 10 minutes until the powder was completely dissolved. Then, the obtained solution and the treated nickel foam were transferred to a high-pressure reactor, placed in an oven, heated from room temperature to 120 °C, and maintained for 6 h. After the solution cooled naturally, the obtained electrode was further washed several times with deionized water and then placed in a vacuum oven at 60 °C for 12 h. The finally obtained electrode was recorded as Ni / NF.

[0052] The prepared Ni / NF electrode and 2 g of sodium hypophosphite (NaH2PO2) were placed on different sides in a porcelain crucible. Subsequently, the porcelain crucible was placed in a tubular furnace, with the side containing sodium hypophosphite facing the argon inlet of the tubular furnace, and then the tubular furnace was heated from room temperature to 350 °C at a heating rate of 5 °C / min in an argon atmosphere and held for 1 h. The obtained electrode was named NiP / NF.

[0053] Example 2

[0054] The catalysts prepared in Example 1 and Comparative Examples 1-2 and nickel foam were used as the working electrode, a carbon rod as the counter electrode, and Hg / HgO as the reference electrode to construct a three-electrode system. All measured potential values were converted to those relative to the reversible hydrogen electrode (RHE). 1 mol L -1 NaOH and 0.5 mol L -1 NaCl solutions were used to simulate alkaline seawater. Linear sweep voltammetry was carried out in the three-electrode system in alkaline seawater at a rate of 10 mV s -1 for the OER and HER reactions respectively; linear sweep voltammetry was carried out in the three-electrode system in simulated alkaline seawater containing 1 mol L -1 Na2S at a rate of 10 mV s -1 for the SOR reaction. Cyclic voltammetry (CV) was carried out in an acetonitrile solution containing 0.15 mol L -1 potassium hexafluorophosphate at scan rates of 10, 20, 30, 50, and 100 mV s -1 respectively. Electrochemical impedance spectroscopy (EIS) was carried out in a simulated alkaline seawater electrolyte containing 1 mol L -1 Na2S, with a frequency range of 10 -2 -10 5 Hz. Chronopotentiometry was used to evaluate the stability of the catalyst in a simulated alkaline seawater electrolyte containing 1 mol L -1 Na2S.

[0055] Example 3

[0056] A two - electrode system for water electrolysis was constructed with the CoNiP / NF prepared in Example 1 as both the anode and the cathode. Simulated alkaline seawater (1M NaOH and 0.5M NaCl) was used as the cathode electrolyte, and simulated alkaline seawater containing 0.5M Na2S was used as the anode electrolyte. A cation - exchange membrane made of polyethylene was used to connect the cathode and the anode, and the polarization curve was measured.

[0057] Example 4

[0058] In simulated alkaline seawater (1M NaOH and 0.5M NaCl), a traditional seawater electrolysis system coupling OER and HER was constructed with the same catalytic electrode (CoNiP / NF prepared in Example 1) as both the anode and the cathode. A cation - exchange membrane made of polyethylene was used to connect the cathode and the anode, and the polarization curve was measured.

[0059] Example 5

[0060] On the basis of Example 3, in this example, a two - electrode system for seawater electrolysis was constructed with the CoNiP / NF prepared in Example 1 as both the anode and the cathode. Real seawater was used as the cathode electrolyte, and seawater containing 0.5M Na2S was used as the anode electrolyte. A cation - exchange membrane made of polyethylene was used to connect the cathode and the anode, and the obtained application effect was the same as the test effect of Example 3.

[0061] Example 6

[0062] To study the SOR mechanism, the catalyst prepared in Example 1 was used as the working electrode, a carbon rod as the counter electrode, and Hg / HgO as the reference electrode to form a three - electrode system. All the measured potential values were converted to those relative to the reversible hydrogen electrode (RHE). 1mol L -1 NaOH and 0.5mol L -1 NaCl solution was used to simulate alkaline seawater. Linear sweep voltammetry in the three - electrode system was carried out at a rate of 10mV s -1 in simulated alkaline seawater containing 1mol L -1 Na2S, scanning 4 times in the range from - 1V to 0V vs. Hg / HgO. The CoNiP / NF after SOR was denoted as the CoNiP - S / NF electrode.

[0063] The X-ray diffractometer (CX-2700, Dandong, China) was used to analyze the phase and crystal structure of the materials prepared in the examples and comparative examples. The surface morphology of the materials was analyzed by a scanning electron microscope (SEM, S4800, Hitachi, Japan). The transmission electron microscope (TEM, FEI Tecnai G2 F20, USA) was used to characterize the microstructure. Elemental composition analysis was carried out by X-ray photoelectron spectroscopy (XPS, Kratos, UK).

[0064] According to Figure 1 the XRD patterns in, strong and sharp peak signals were detected at 44.5°, 51.8°, and 76.4° in the XRD patterns of both the bimetallic phosphide and monometallic phosphide samples, corresponding to the NF substrate (PDF#04-0850). Meanwhile, in the XRD patterns of the monometallic phosphides, the additional diffraction peaks of CoP / NF and NiP / NF corresponded to Co2P (PDF#32-0306) and Ni5P4 (PDF#18-0883), respectively. The XRD pattern of CoNiP / NF was quite different from that of the monometallic phosphides, showing three weak diffraction peaks corresponding to the (111), (210), and (300) planes of CoNiP (PDF#71-2336) at 40.9°, 47.5°, and 54.4°, confirming the formation of CoNiP on the NF surface. In the XRD pattern of CoNiP-S / NF, in addition to the diffraction peaks attributed to CoNiP, some new diffraction peaks corresponding to the (311), (422), and (822) planes of Co2NiS4 (PDF#20-0782) were observed at 31.5°, 47.4°, and 88.3°. The results indicate that metal sulfide will be in-situ formed on the CoNiP-S / NF electrode during the SOR process.

[0065] The surface morphologies of the mono- and bimetallic phosphides were analyzed by SEM as Figure 2 shown, as Figure 2 shown in a of, after phosphating treatment, the surface of CoP / NF presented a vertically grown nanowire structure, while NiP / NF presented a cluster structure of stacked petal-like nanosheets, as Figure 2 shown in b of. Compared with the monometallic phosphides, the microstructure of the bimetallic phosphides was significantly changed by the bimetallic synergistic effect. As Figure 3 shown in a of, CoNiP / NF exhibited a cross-linked nanosheet array vertically grown on NF, presenting a dense structure. Compared with the monometallic phosphides, the interlaced nanosheet structure of CoNiP / NF could provide a larger surface area, which could promote the full contact between the electrolyte and the electrode. Figure 3 The TEM image of CoNiP / NF shown in b of further showed the structure and width of the nanosheets as The lattice fringes correspond to the (210) crystal plane of CoNiP (PDF#71-2336). At the same time, according to the elemental mapping images, Co, Ni, and P elements show a uniform distribution on CoNiP / NF, as shown in Figure 3 c of. The reason for the significant difference in the surface morphology of single and double metal phosphides may be due to the synergistic effect between Co and Ni metals to regulate the growth state of metal compounds on NF.

[0066] The elemental composition and corresponding chemical valence states of the electrodes were further analyzed by XPS. As shown in Figure 4 a of, signals corresponding to two peaks of the Co-P bond were detected in the high-resolution XPS spectrum of Co2p of CoP / NF, located at binding energies of 776.8 eV and 791.3 eV. In addition, due to the inevitable oxidation of the material during preparation or storage, two signals corresponding to the oxides of Co were detected at binding energies of 781.2 and 797.1 eV. Figure 4 b of shows the XPS spectrum of Ni 2p of NiP / NF. Two characteristic peaks corresponding to the Ni-P bond were observed at 853.5 eV and 870.2 eV, while the XPS peaks at binding energies of 857.1 eV and 874.9 eV are related to the Ni-O bond. The Co 2p XPS spectrum of CoNiP / NF is shown in Figure 4 c of. Peaks belonging to the Co-P bond were observed at binding energies of 777.4 eV and 791.7 eV, and peaks belonging to the Co-O bond were observed at binding energies of 781.7 eV and 797.4 eV. At the same time, as shown in Figure 4 d of, in the Ni 2p XPS spectrum of CoNiP / NF, characteristic peak signals corresponding to the Ni-P bond were detected at binding energies of 869.8 eV and 853.1 eV, and two significant peaks at 856.5 eV and 874.4 eV correspond to Ni-O.

[0067] The P 2p XPS spectra of CoNiP / NF, CoP / NF, and NiP / NF are shown in Figure 5As shown in a, b, and c, the P 2p XPS spectra of the single and double metal phosphides are extremely similar. The peaks at binding energies of 129.9 eV and 134.4 eV correspond to the metal phosphide and the oxidized state of P, respectively, indicating that the P species in the catalyst exist in the form of P-metal bonds and P-O bonds. It is worth noting that compared with the corresponding XPS peaks of CoP / NF and NiP / NF, the XPS peaks of Co and Ni species in the XPS spectrum of CoNiP / NF show positive and negative shifts in binding energy, respectively. This result is due to the electronegativity difference between Co (1.88) and Ni (1.91), resulting in the transfer of some electrons from Co to Ni. The redistribution of electrons can improve the adsorption state of reactants and intermediates at the active center, causing the adsorption energy and desorption energy of the reaction intermediates to be in a moderate position, thereby obtaining better catalytic performance. The above characterization results indicate the successful preparation of Co, Ni double metal phosphide nanosheets supported on NF.

[0068] Under the same test conditions, the electrochemical performance of the CoNiP / NF electrode in simulated alkaline seawater solution with or without 1 M Na2S was compared (i.e., the comparison of SOR and OER under the same conditions). As Figure 6 obviously shown in a, when the same current density is reached, the applied potential of SOR is significantly lower than that of OER. At the same time, to catalyze a current density of 100 mA cm -2 for SOR, only 0.28 V vs. RHE is required, which is much lower than that for OER (1.58 V vs. RHE) based on the same catalytic electrode (CoNiP / NF). The results show that compared with OER, the thermodynamic advantage of SOR can reduce the reaction potential and show the advantage of low energy consumption, further indicating the feasibility of SOR-assisted low-energy electrolytic water hydrogen production. In addition, the SOR catalytic activities of CoNiP / NF, CoP / NF, NiP / NF, and NF were further evaluated, Figure 6 and the test data are intuitively shown in b. The CoNiP / NF electrode obtained the highest polarization current density at the same applied potential, showing the best SOR catalytic performance. The applied potentials for CoNiP / NF to achieve current densities of 10 and 100 mA cm -2 are only 0.21 V and 0.28 V vs. RHE, which are better than those of single metal materials (CoP / NF (0.26 V and 0.32 V vs. RHE), NiP / NF (0.31 V and 0.45 V vs. RHE), NF substrate (0.53 V and 0.70 V vs. RHE)) and most previously reported electrocatalysts for SOR, as shown in Table 1. This result further indicates that the synergistic effect of Co and Ni can improve the catalytic activity of SOR. At the same time, with the increase of the applied potential, this advantage becomes more obvious. According to Figure 6Tafel plots in c, the Tafel slopes of CoNiP / NF, CoP / NF, NiP / NF, and NF are 48.2, 141.2, 150.8, and 163.5 mV dec -1 . CoNiP / NF exhibits a smaller Tafel slope, indicating that compared with CoP / NF, NiP / NF, and NF electrodes, CoNiP / NF can achieve a larger current density increment under the same given applied potential increment.

[0069] Table 1

[0070]

[0071] According to Figure 7 , the charge transfer resistance (Rct) of CoNiP / NF is 0.75 Ω, lower than that of CoP / NF (1.31 Ω), NiP / NF (16.20 Ω), and NF (212.31 Ω). This result indicates that CoNiP / NF can exhibit more efficient electron transfer efficiency during the SOR catalytic process. The lower potential, smaller Tafel slope, and higher electron transfer efficiency all indicate that CoNiP / NF has strong SOR catalytic performance.

[0072] According to Figure 8 , the double-layer capacitance curves of the samples are obtained through cyclic voltammetry tests (CV), as shown in Figure 8 a, b, c of , the catalytic electrodes are scanned at different scan rates in the range of 0 V - 0.1 V vs. Hg / HgO, and the corresponding current density is observed and recorded. And the double-layer capacitance curves and electrochemically active surface areas of the samples are obtained according to the CV results. In addition, in previous studies, the specific capacitance value of a smooth standard with an actual surface area of 1 cm -2 is 16 uF cm -2 . Therefore, the ECSA of the catalytic materials is calculated, and the results are shown in Table 2. It can be directly seen from it that the electrochemically active surface area (ECSA) of the CoNiP / NF electrode is 45.63 cm -2 , higher than that of CoP / NF (27.50 cm -2 ) and NiP / NF (35.00 cm -2 ), further indicating that the high-density cross-linked nanosheet array structure improves the ECSA of CoNiP / NF, which is beneficial to increasing the interfacial contact efficiency between the active sites and the electrolyte, thus showing higher electrochemical performance. Figure 8 d of shows the linear relationship between the scan rate and the current density at 0.05 V vs. Hg / HgO.

[0073] Although the current density normalized to the geometric area is considered an accurate indicator for evaluating the overall catalytic performance of an electrode, this indicator ignores the influence of the electrode microstructure. The electrochemically active surface area (ECSA) can accurately describe the actual contact area between the electrolyte and the catalyst. Therefore, the polarization curve with the current density normalized to the ECSA is a more accurate indicator than the GA-based normalized current density for evaluating the intrinsic activity of the electrode. In addition, the current density normalized based on the mass loading can also reflect to a certain extent the utilization efficiency of the metal material. Therefore, in order to further accurately describe the intrinsic SOR activity of the electrocatalyst, the polarization curves with the current density further normalized to the ECSA (Table 2) and the mass loading (as shown in Table 3) are respectively as Figure 9 a of Figure 9 and Figure 9 a of Figure 9 and Figure 9 b of -2 shown in b. It can be clearly seen from the figure that whether based on the ECSA or the mass loading, the normalized current density of the CoNiP / NF electrode is higher than that of other catalytic electrodes. These results indicate that the CoNiP / NF electrode exhibits a more efficient metal utilization rate, and its active sites show more excellent intrinsic catalytic activity towards SOR compared with CoP / NF and NiP / NF. According to the results of the ECSA (Table 2) and the normalized current density (such as

[0074] Table 2

[0075]

[0076] Table 3

[0077] CoNiP CoP / NF NiP / NF <![CDATA[Load mass (mgcm -2 )]]> 8.26 10.6 7.06

[0078]

[0074] Table 2

[0075]

[0076] Table 3

[0077] CoNiP CoP / NF NiP / NF <![CDATA[Load mass (mgcm -2 )]]> 8.26 10.6 7.06

[0078] Figure 9 a of Figure 9 and Figure 9 b of -2 ), it can be known that the synergistic effect between Co, Ni, and P in CoNiP / NF not only increases the exposed area and number of active sites in the electrolyte but also improves the intrinsic catalytic activity of each active site towards SOR. Therefore, CoNiP / NF shows the most efficient apparent catalytic performance towards SOR. In addition to performance, a good catalyst also needs to have good stability. The durability of the CoNiP / NF electrode in a sulfur-rich alkaline seawater environment was tested by chronopotentiometry, as

[0074] Table 2

[0075]

[0076] Table 3

[0077] CoNiP CoP / NF NiP / NF <![CDATA[Load mass (mgcm -2 )]]> 8.26 10.6 7.06

[0078]

[0074] Table 2

[0075]

[0076] Table 3

[0077] CoNiP CoP / NF NiP / NF <![CDATA[Load mass (mgcm -2 )]]> 8.26 10.6 7.06

[0078] Figure 9 c of -2 shown. Since the S species in the electrolyte is continuously converted into polysulfides and accumulates on the electrode surface around the electrode, a magnetic stirrer was used in the experiment to continuously stir to prevent the polysulfides from accumulating on the electrode surface and blocking the active sites. Therefore, the collected data fluctuates slightly, which is a normal phenomenon. Generally speaking, at a constant 100 mA cm -2 , CoNiP / NF only shows very small fluctuations during the long-term test (35 h), and the potential remains stable, indicating good durability in a sulfur-rich environment.

[0074] Table 2

[0075]

[0076] Table 3

[0077] CoNiP CoP / NF NiP / NF <![CDATA[Load mass (mgcm -2 )]]> 8.26 10.6 7.06

[0078] To determine the mechanism for enhancing the SOR catalytic performance of CoNiP / NF, the composition and morphology of the catalyst after SOR (CoNiP-S / NF in Example 6 above) were further analyzed in detail. Figure 10 a of Figure 10 and b of 2+ show the high-resolution XPS spectra of Co 2p and Ni 2p of the CoNiP / NF electrode after SOR testing, respectively. According to the XPS spectrum of Co 2p, the XPS peak signals corresponding to Co 2+ were detected, which were similar to the corresponding Co Figure 4 signals in CoNiP / NF ( 3+ c). In addition, the additional peaks located at binding energies of 779.1 eV and 794.3 eV corresponded to Co 3 / 2 2p 1 / 2 and 2p Figure 10 respectively, indicating that the valence state of some Co substances in the catalyst increased after undergoing SOR. As shown in 2+ b of 3 / 2 the XPS peaks located at 856.8 eV and 874.6 eV were assigned to Ni 1 / 2 2p Figure 10 and 2p Figure 10 respectively. It should be particularly noted that, as shown in Figure 10 b of 3 / 2 compared with CoNiP / NF, the XPS peak of Ni 2p showed an obvious positive shift. These results indicate that during the SOR process, the chemical valence states of some Co and Ni substances increased, and the catalyst with a higher valence state was beneficial to the oxidation reaction and was an effective active site for the oxidation reaction. In addition, as shown in 1 / 2 c of Figure 1 compared with the initial CoNiP / NF, the peak intensity of the P 2p XPS peak of the P substance in CoNiP-S / NF decreased significantly, and the corresponding P content decreased from 14.6% to 4.41% (Table 4), indicating that some P ions overflowed during the SOR process. As shown in

[0079] Table 4

[0080] d of Figure 10 the S2p XPS spectrum of CoNiP-S / NF presented three peaks. The peaks located at 162.0 eV and 163.2 eV corresponded to S2p 3 / 2 and 2p 1 / 2 of the S-metal bond, and another peak located at 168.7 eV was due to the formation of sulfate. In summary, during the SOR process, the phosphide on the catalyst surface was in-situ transformed into sulfide, Figure 1 and the XRD pattern of

[0079] also confirmed this. In the XRD pattern of CoNiP-S / NF, in addition to the strong peaks belonging to NF, the additional peaks corresponded to Co2NiS4 (PDF#20-0782), which proved the formation of sulfide on the electrode surface during the SOR process.

[0079] Table 4

[0080] Sample P (at.%) S (at.%) CoNiP / NF 14.6 - CoNiP-S / NF 4.41 4.93

[0081] As shown by a in Figure 11 , CoNiP-S / NF inherits the basic skeleton of the initial CoNiP / NF, but the surface of the nanosheets in CoNiP-S / NF becomes significantly rougher. In addition, as Figure 11 shown by b in Figure 12 , a pore structure can be clearly observed in the TEM image of the nanosheets in CoNiP-S / NF. This structure is attributed to the partial spillover of P in CoNiP / NF during the SOR reaction process, which leads to the formation of a large number of defect structures and unsaturated sites. These structural features can increase the exposure area and the number of active sites, while improving the adsorption and activation energy of reactants at the active sites, thus obtaining high intrinsic activity. At the same time, as

[0082] shown by Figure 13 , the evolution process of the electrolyte at different time intervals was monitored during the entire long-term SOR process. As Figure 13 shown by a in 2 —S n 2- , the color of the electrolyte changes from transparent to yellow and further deepens, which corresponds to the continuous accumulation of polysulfide during the reaction process. In addition, the changes in the electrolyte at different reaction times were further analyzed by a UV-Vis spectrophotometer (UV-Vis). Figure 13 As shown by b in

[0083] , the formation of S8 was proven by XRD analysis, indicating that the recovery of sulfur pollutants based on SOR was achieved in this work. Figure 14 As shown by a in Figure 14 and b in -2 , when further evaluating the HER catalytic performance of CoNiP / NF, CoP / NF, NiP / NF, and NF, the best CoNiP / NF electrode only requires an applied voltage of 0.18 V vs. RHE to reach 100 mA cmThe current density exhibits excellent HER catalytic activity, lower than that of CoP / NF (0.20 V vs. RHE), NiP / NF (0.26 V vs. RHE), and NF (0.35 V vs. RHE), and is comparable to or even close to some noble metal catalysts reported previously (Table 5). Compared with single-metal phosphides, the bimetallic phosphide shows better catalytic performance, which is due to the synergistic effect between Co and Ni improving the HER activity, consistent with previous studies. In addition, the Tafel slope of CoNiP / NF Figure 14 in c) is 82.9 mV dec -1 , significantly higher than that of CoP / NF (122.0 mV dec -1 ), NiP / NF (107.4 mV dec -1 ), and NF (131.0 mV dec -1 ), indicating that CoNiP / NF can achieve a greater enhancement of the cathodic current density at the same potential increment.

[0084] Table 5

[0085]

[0086] According to Tables 2 and 3, the hydrogen evolution polarization current densities of the catalytic electrodes were normalized to the electrochemically active area and the loading amount, respectively, and the obtained data are as Figure 15 shown. It can be intuitively seen from Figure 15 a and Figure 15 b that, whether it is the normalized current density based on ECSA and mass loading, CoNiP / NF is superior to other electrocatalysts in this work, indicating that the catalytic sites in CoNiP / NF have high intrinsic HER activity.

[0087] Meanwhile, as shown in Figure 16 a, the CoNiP / NF electrode shows a lower electrochemical transfer impedance in the electrochemical impedance test, indicating that the electrode also exhibits a higher electron transfer efficiency during the HER catalytic process. In addition, the durability of the CoNiP / NF electrode at 100 mA cm -2 was evaluated by chronopotentiometry. Since bubbles (H2) are continuously generated near the catalyst and loaded on the catalyst surface, the data of the stability test will show some fluctuations, which is a normal phenomenon. As shown in Figure 16 b, during the long-term HER, the potential of CoNiP / NF only shows a small change, indicating that the CoNiP / NF electrode has high HER catalytic durability. The high catalytic activity and stability indicate that CoNiP / NF is a good HER catalyst.

[0088] Typically, traditional seawater electrolysis limits the overpotential to below 0.48 V to avoid the influence of harmful ClOR, but this limits the current density. Apparently, seawater electrolysis devices based on SOR and HER can avoid this obstacle. Since the oxidation potential of SOR is much lower than that of ClOR. Therefore, chlorine-free and low-energy-consuming electrolysis of seawater for hydrogen production can be achieved through an SOR-coupled HER electrolysis device, but there is less research in this area. According to the above three-electrode electrochemical tests, as Figure 6 and Figure 14 shown, the CoNiP / NF electrode exhibits high catalytic performance for both SOR and HER, laying a solid foundation for the construction of an efficient hydrogen production device based on the efficient coupling of HER and SOR. To further confirm that CoNiP / NF is an efficient bifunctional catalyst and has lower energy consumption in practical applications, a two-electrode coupled seawater electrolysis device based on HER and SOR was established using two CoNiP / NF electrodes as catalytic electrodes for hydrogen production. In this novel coupling system, simulated alkaline seawater (1 M NaOH and 0.5 M NaCl) was used as the cathode electrolyte, and simulated alkaline seawater containing 0.5 M Na2S was used as the anode electrolyte. The cathode and anode were connected by a cation exchange membrane (Example 5 above). At the same time, in simulated alkaline seawater (1 M NaOH and 0.5 M NaCl), a traditional seawater electrolysis system coupling OER and HER was constructed based on the same catalytic electrode (CoNiP / NF) (Example 4 above).

[0089] As Figure 17 shown in a of -2 , compared with traditional seawater electrolysis (HER + OER), the unique HER-SOR coupling system shows a significant reduction in the applied potential. The HER-SOR coupling system only requires a low voltage of 0.71 V to reach 100 mA cm -2 , which is superior to the traditional seawater electrolysis system (2.27 V) and the coupling systems of the prior art. In addition, the power consumption for producing 1 kg of H2 by the two hydrogen production systems at 100 mA cm -2 was further calculated, as Figure 17 shown in c of Figure 17 . The HER-SOR coupling system only requires 18.875 kWh, which is significantly lower than that of the HER-OER coupling system (60.349 kWh). In addition, Figure 17 shown in b of -2 shows the stability test of the HER-SOR coupling system at 100 mA cm -2 . It can be directly seen from this that the potential remains stable during the long-term test (35 hours), showing only very small fluctuations, indicating that the HER-SOR coupling system has excellent stability in hydrogen production. These results confirm the realization of low-energy-consuming electrolysis of seawater for hydrogen production based on this unique HER-SOR coupling system and the recovery of sulfur-containing pollutants in an environmentally friendly manner.

[0090] The specific embodiments described above further elaborate on the object, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only the specific embodiments of the present invention and is not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. Preparation method of materials for electrocatalytic SOR-assisted electrolysis of seawater to produce hydrogen, characterized in that It includes the following steps: S1. Dissolve Ni(NO3)2·6H2O, Co(NO3)2·6H2O, CO(NH2)2 and NH4F in deionized water, and ultrasonically treat until the powder is completely dissolved; S2. Then transfer the obtained solution and nickel foam into a high-pressure reactor, and place it in an oven for heating reaction; S3. After the solution is naturally cooled, wash the obtained electrode with deionized water, and then place it in a vacuum oven for drying. The obtained electrode is recorded as CoNi / NF; S4. Place the prepared CoNi / NF and sodium hypophosphite on different sides in a porcelain crucible; subsequently, put the porcelain crucible into a tubular furnace, with the side containing sodium hypophosphite facing the argon inlet of the tubular furnace, and then heat the tubular furnace from room temperature to 350 °C and keep it warm in an argon atmosphere; obtain the material CoNiP / NF for electrocatalytic SOR-assisted electrolysis of seawater to produce hydrogen.

2. The preparation method of the material for electrocatalytic SOR-assisted electrolysis of seawater to produce hydrogen according to claim 1, characterized in that, In step S1, the molar ratio of Ni(NO3)2·6H2O, Co(NO3)2·6H2O, CO(NH2)2 and NH4F is 1:1:10:

5.

3. The preparation method of the material for electrocatalytic SOR-assisted electrolysis of seawater to produce hydrogen according to claim 2, characterized in that, The concentration of Ni(NO3)2·6H2O is 0.025 mmol / mL; the concentration of Co(NO3)2·6H2O is 0.025 mmol / mL; the concentration of CO(NH2)2 is 0.25 mmol / mL; the concentration of NH4F is 0.125 mmol / mL.

4. The preparation method of the material for electrocatalytic SOR-assisted electrolysis of seawater to produce hydrogen according to claim 1, characterized in that, The heating reaction temperature in step S2 is 120 °C, and the reaction time is 6 h.

5. The preparation method of the material for electrocatalytic SOR-assisted electrolysis of seawater to produce hydrogen according to claim 1, characterized in that, The drying temperature of the oven in step S3 is 60 °C, and the drying time of the oven is 12 h.

6. The preparation method of the material for electrocatalytic SOR-assisted electrolysis of seawater to produce hydrogen according to claim 1, characterized in that, The heating rate in step S3 is 5 °C / min; the holding time is 1 h.

7. The material for electrocatalytic SOR-assisted electrolysis of seawater to produce hydrogen prepared by the preparation method of the material for electrocatalytic SOR-assisted electrolysis of seawater to produce hydrogen according to any one of claims 1-6.

8. The system for electrocatalytic SOR-assisted electrolysis of seawater to produce hydrogen is characterized in that, It includes a cathode electrolyte and an anode electrolyte. A cation exchange membrane is used to separate the anode mass and the cathode mass to establish an asymmetric coupled electrolytic cell. An anode catalytic electrode and a cathode catalytic electrode are respectively arranged in the anode electrolyte and the cathode electrolyte. The anode catalytic electrode and the cathode catalytic electrode use the material for electrocatalytic SOR-assisted electrolysis of seawater to produce hydrogen prepared by the method according to any one of claims 1-6 or the material for electrocatalytic SOR-assisted electrolysis of seawater to produce hydrogen according to claim 7.

9. The system for electrocatalytic SOR-assisted electrolysis of seawater for hydrogen production according to claim 8, characterized in that, The cathode electrolyte is 1M NaOH and 0.5M NaCl, and the anode electrolyte is 1M NaOH and 0.5M NaCl containing 0.5M Na2S.

10. The system for electrocatalytic SOR-assisted electrolysis of seawater for hydrogen production according to claim 9, wherein The cathode electrolyte is alkaline seawater, and the anode electrolyte is alkaline seawater containing 0.5M Na2S.

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