阅读说明：本技术 一种泡沫镍负载作尿素电解辅助制氢双功能催化剂电极 (Dual-function catalyst electrode for urea electrolysis-assisted hydrogen production by foam nickel load ) 是由 温新竹 秦少平 刘明真 杨雪婷 彭玉颜 于 2019-11-20 设计创作，主要内容包括：本发明是一种泡沫镍负载作尿素电解辅助制氢双功能催化剂电极,属于物理化学领域。本发明采用简单、低成本的方法合成了泡沫镍负载的非贵金属多孔氮化镍电催化剂(Co<Sub>5.47</Sub>N NS/NF),用于高效尿素电解辅助制氢,在1.345V电流密度为10mA/cm<Sup>2</Sup>时表现出优异的UOR性能。Co<Sub>5.47</Sub>N NS/NF对HER也表现出很高的活性,在10mA/cm<Sup>2</Sup>时仅需116mV,这表明Co<Sub>5.47</Sub>N NS/NF是一种优良的UOR和HER双功能催化剂。此外,相应的双电极电解槽只需要1.348V来驱动10mA/cm<Sup>2</Sup>,比水电解低0.2V,并且可以保持高电流密度(100mA/cm<Sup>2</Sup>)电解20小时。Co<Sub>5.47</Sub>N NS/NF电极在完整的尿素电解过程中具有优异的性能,比水分解制氢效率更高,而Co<Sub>5.47</Sub>N NS/NF电极具有很高的活性和稳定性,在替代贵金属和有效处理含尿素工业废水方面具有很大的潜力。(The invention relates to a foam nickel loaded bifunctional catalyst electrode for urea electrolysis-assisted hydrogen production, belonging to the field of physical chemistry. The invention adopts a simple and low-cost method to synthesize the foamed nickel-supported non-noble metal porous nickel nitride electrocatalyst (Co) 5.47 N NS/NF) for high-efficiency urea electrolysis-assisted hydrogen production with current density of 10mA/cm at 1.345V 2 Exhibit excellent UOR performance. Co 5.47 N NS/NF also showed very high activity on HER at 10mA/cm 2 Only 116mV is needed, which indicates that Co is present 5.47 N NS/NF is an excellent dual-function catalyst of UOR and HER. In addition, the corresponding two-electrode electrolytic cell only needs 1.348V to drive 10mA/cm 2 0.2V lower than water electrolysis and can maintain high current density (100 mA/cm) 2 ) And electrolyzing for 20 hours. Co 5.47 The N NS/NF electrode has excellent performance in the complete urea electrolysis process, has higher hydrogen production efficiency than water decomposition, and Co 5.47 The N NS/NF electrode has high activity and stability, and has great potential in the aspects of replacing noble metals and effectively treating industrial wastewater containing urea.)

1. A dual-function catalyst electrode for preparing hydrogen by urea electrolysis under the load of foamed nickel is prepared through synthesizing Co on foamed nickel by hydrothermal method (COO NS/NF)₂O₃Nanosheets; the second process is Co_5.47Synthesizing N NS/NF; then placing the prepared CoO NS/NF in a ceramic crucible by a calcination method; due to the unique nanostructure, UOR has high activity, with a potential of only 1.431V and 100mA/cm²(ii) a More importantly, Co_5.47N can be used as a bifunctional catalyst of UOR and HER for large-scale hydrogen production, and realizes 10mA/cm²Only 1.348V is needed; as shown in fig. 1, the prepared catalyst is used as an electrode, and is a nanosheet array grown on a foam nickel substrate; during the electrolysis process, nitrogen and carbon dioxide are released when urea is absorbed and diffused;

the raw material adopts cobalt (II) chloride hexahydrate (CoCl)₂.6H₂O), potassium hydroxide (KOH), urea and hexamethylenetetramine, all chemicals of nickel foam are used as purchased without further purification, Pt/C and IrO₂The purity is 99.9 percent, and the mixture ratio is 20 percent respectively;

the first step is to synthesize cobalt oxide nanosheets (CoO NS/NF) on foamed nickel; 4mmol of CoCl₂·6H₂Dissolving O and 12mmol of hexamethylenetetramine in 50ml of ultrapure water, and continuously stirring; then, the suspension and the pre-treated bubbles are mixedThe nickel foam was transferred to a 100ml teflon lined autoclave and heated at 100 ℃ for 10 hours; the second step is the synthesis of Co_5.47N NS/NF; the CoO NS/NF prepared above was placed in a ceramic crucible and calcined at 350 ℃ for 2 hours (1 ℃/min)^-1) At NH₃In the environment, the obtained product is used for the next physical characterization and electrochemical experiment;

scanning Electron Microscope (SEM) images were taken from a JEOL 7001SEM instrument at a voltage of 3kV, Transmission Electron Microscope (TEM) images were obtained from Feitecnan aig2t20 at 200kV, sample preparation was carried out by scraping off nickel foam directly and then dropping ethanol solution onto a porous carbon-copper grid, X-ray diffraction patterns were obtained in the range of 25-70 θ using copper K α radiation (. lamda.0.15418 nm) on Bruker D8 advanced ECO powder X-ray equipment with a scanning step of 0.01, X-ray photoelectron spectroscopy (XPS) measurements were carried out using an electron spectrometer, electrochemical measurements were carried out on a CHI 660E electrochemical workstation using a standard three-electrode system, the electrode material prepared was used directly as the working electrode, the reference electrode was HGO/Hg (MOE), the electrode was a bar, the graphite electrode was converted to reversible hydrogen potential at an electrochemical scanning rate of 1000000 mV, electrochemical impedance compensation was carried out at 1000000 mV/M.H.H. eHG/HGO +0.098+ 0.059;

Co_5.47XRD of N NS/NF is shown in FIG. 2A; diffraction peaks at 43.62 °, 50.77 ° and 74.86 ° correspond to the (111), (200) and (220) crystal planes of Co5.47N (JCPDS 41-0943), respectively; the peaks at 44.47 °, 51.79 ° and 76.59 ° correspond to Ni (JCPDS 04-0850), which is associated with the matrix, and no additional peaks are found, which means high purity co5.47n NS/NF; the standard cards in the figure may also index the peak value of COO NS/NF well; characterization of Co by XPS_5.47The surface composition and electron binding energy of the N NS/NF; FIG. 2B shows CO₂Two characteristic peaks at 779.5eV and 795.1eV, which can be designated Co2p3/2 and Co2p 1/2 [ 10 ]; the peak of N1 is shown in fig. 2C; clearly, the peaks at 397.5 and 399.9eV are associated with cobalt and nitrogen oxides [ 11, 12 ];

the morphology of the catalyst is observed by a scanning electron microscope; co shown in FIG. 3_5.47The low-power and high-power scanning electron microscope images of N NS/NF show that the morphology and the overall performance of the nanosheet array grow well on the foamed nickel substrate (FIGS. 3A and B), and the scanning electron microscope images of CoO NS/NF show that the CoO nanosheet array in the images completely covers the foamed nickel;

FIGS. 3C-D show high definition TEM images of N-NiZnCu LDH/rGO monoliths, while observing their loose porous morphology, Co_5.47High Resolution Transmission Electron Microscopy (HRTEM) of N NS/NF showed the plane spacing. High resolution lattice fringes at 0.18 and 0.21nm, corresponding to Co_5.47N NS/NF (200) and (111), this characterization is consistent with the conclusions drawn by XRD;

co is determined by electrochemical experiments_5.47N NS/NF (load: 0.23 mg/cm)²) Catalytic UOR activity and the most suitable urea concentration (0.5M) was selected by the concentration gradient polarization curve; co_5.47LSV of N NS/NF was tested in different electrolytes as shown in FIG. 4; at 100mA/cm²When the voltage is over-potential of 1.431V, 100mA/cm can be driven²Current density of (d); but less than OER (1.763V), indicating that uranium ore reduction activity is superior to OER activity; at 10mA/cm²When is Co_5.47N NS/NF，CoO NS/NF，IrO₂And NF at 1.345, 1.366, 1.576 and 1.602V, respectively, as shown in fig. 4B; obviously, Co_5.47The potential of N NS/NF was lowest, indicating that Co_5.47The UOR activity of N NS/NF is superior to other substances; the Tafel curve can be used to explain the catalytic kinetics of the electrode, Co_5.47N NS/NF, CoO NS/NF and IrO₂The Tafel slopes of (A) were 47, 60 and 78mV/dec (FIG. 4C), respectively; obviously, Co_5.47The Tafel slope of N NS/NF is lowest, which means that it has fast kinetics and excellent UOR catalytic activity; at the same time, the present study is also on Co_5.47The stability of N NS/NF was evaluated; obtain Co_5.47Multistep chronopotentiometric curve of N NS/NF (FIG. 4D); in Co_5.47Applying a step potential from 1.35V to 1.46V to the N NS/NF electrode, wherein the increase is 11mV every 2 hours; at the starting current value, the potential immediately tends to stabilize and remains unchanged for the remaining 2 hours, in particular at higher currents; quick timing electric soundShould mean excellent quality transmission; these results show that Co_5.47N NS/NF has good mass transport, conductivity and mechanical stability (inward diffusion of OH and outward diffusion of bubbles and rapid response to current density in each potential change step), with a current density after 3000CV cycles of 93.8% of the original; meanwhile, the peak value of XRD is substantially the same as the peak value before 3000CV cycles, still agreeing well with the standard card (fig. 1); these results show that it has good stability.

Technical Field

The invention relates to a foam nickel loaded bifunctional catalyst electrode for urea electrolysis-assisted hydrogen production, belonging to the field of physical chemistry.

Background

The rapid depletion of fossil fuel resources has created a tremendous demand for clean and renewable energy sources [ 1 ]. As a green energy source (high energy without secondary pollution), hydrogen energy is widely considered as an ideal energy source for replacing fossil energy [ 2 ]. Recently, the electrocatalytic Hydrogen Evolution Reaction (HER) of water splitting is almost considered to be the most efficient method of producing hydrogen. However, Oxygen Evolution Reactions (OERs), as anodes for water decomposition, have a higher theoretical oxidation potential, which greatly limits the production of hydrogen [ 3 ]. Therefore, the selection of a Urea Oxidation Reaction (UOR) with a lower potential theoretically has important implications for hydrogen economy [ 4 ]. Meanwhile, water contamination by urine has become a challenging environmental problem [ 5 ]. Urine contains urea, which can be converted to ammonia and nitrogen compounds, which can contaminate the atmosphere, theoretically, urea has a standard potential of 0.37V on the anode and water is reduced at 0V at the cathode in an alkaline medium relative to a reversible hydrogen electrode (reversible hydrogen electrochemical rhe). Then obtaining the lower theoretical potential of 0.37V of urea electrolysis under the standard condition, and effectively solving the problem of waste water-urea pollution [ 6-8 ] through electrolysis. Therefore, urea electrolysis has recently become a focus of attention, not only to treat wastewater, but also to contribute to efficient hydrogen generation [ 9 ]. The reaction process is

CO(NH₂)₂(aq)+6OH-→N₂(g)+5H₂O(l)+CO₂(aq)+6e^-(1)

6H₂O(l)+6e^-→3H₂(g)+6OH^-(2)

CO(NH₂)₂(aq)+H₂O(l)→N₂(g)+3H₂(g)+CO₂(aq)(3)

The substitution of the low theoretical potential of the Urea Oxidation Reaction (UOR) for the high theoretical potential of the anodic water splitting (OER oxygen evolution reaction) is an urgent need for hydrogen energy storage and conversion. Adopts hydrothermal and roasting method to synthesize foamFoamed nickel (Co)_5.47N NS/NF) loaded high-performance bifunctional catalyst cobalt nitride nanosheet (Co)_5.47N NS/NF). The morphology and composition of the catalyst were studied by XRD, XPS, SEM, TEM, HRTEM and elemental analysis. For electrochemical performance and stability, Co-based alloy is constructed_5.47Bipolar electrode cell (Co) with NNS/NF as anode and cathode material_5.47N NS/NF|Co_5.47N NS/NF). Drive 100mA/cm²Only 1.687V is needed, which is much lower than Pt/C IrO₂And the density can now be maintained for at least 20 hours, indicating that its excellent activity and stability are commercially advantageous.

Disclosure of Invention

Aiming at the defects in the prior art, the invention aims to achieve the effect and provides the dual-function catalyst electrode for urea electrolysis-assisted hydrogen production by using the nickel foam as the load, and the preparation process comprises the first step of synthesizing Co on the nickel foam by a hydrothermal method (COO NS/NF)₂O₃Nanosheets; the second process is Co_5.47Synthesizing N NS/NF; then placing the prepared CoO NS/NF in a ceramic crucible by a calcination method; due to the unique nanostructure, UOR has high activity, with a potential of only 1.431V and 100mA/cm²(ii) a More importantly, Co_5.47N can be used as a bifunctional catalyst of UOR and HER for large-scale hydrogen production, and realizes 10mA/cm²Only 1.348V is needed; as shown in fig. 1, the prepared catalyst is used as an electrode, and is a nanosheet array grown on a foam nickel substrate; during the electrolysis process, nitrogen and carbon dioxide are released when urea is absorbed and diffused;

the raw material adopts cobalt (II) chloride hexahydrate (CoCl)₂.6H₂O), potassium hydroxide (KOH), urea and hexamethylenetetramine, all chemicals of nickel foam are used as purchased without further purification, Pt/C and IrO₂The purity is 99.9 percent, and the mixture ratio is 20 percent respectively;

the first step is to synthesize cobalt oxide nanosheets (CoO NS/NF) on foamed nickel; 4mmol of CoCl₂·6H₂Dissolving O and 12mmol of hexamethylenetetramine in 50ml of ultrapure water, and continuously stirring;the suspension and pretreated nickel foam were then transferred to a 100ml teflon lined autoclave and heated at 100 ℃ for 10 hours; the second step is the synthesis of Co_5.47NNS/NF; the CoO NS/NF prepared above was placed in a ceramic crucible and calcined at 350 ℃ for 2 hours (1 ℃/min)^-1) At NH₃In the environment, the obtained product is used for the next physical characterization and electrochemical experiment;

scanning Electron Microscope (SEM) images were taken from a JEOL 7001SEM instrument at a voltage of 3kV, Transmission Electron Microscope (TEM) images were obtained from Feitecnan aig2t20 at 200kV, sample preparation was carried out by scraping off nickel foam directly and then dropping ethanol solution onto a porous carbon-copper grid, X-ray diffraction patterns were obtained in the range of 25-70 θ using copper K α radiation (. lamda.0.15418 nm) on Bruker D8 advanced ECO powder X-ray equipment with a scanning step of 0.01, X-ray photoelectron spectroscopy (XPS) measurements were carried out using an electron spectrometer, electrochemical measurements were carried out on a CHI 660E electrochemical workstation using a standard three-electrode system, the electrode material prepared was used directly as the working electrode, the reference electrode was HGO/Hg (MOE), the electrode was a bar, the graphite electrode was converted to reversible hydrogen potential at an electrochemical scanning rate of 1000000 mV, electrochemical impedance compensation was carried out at 1000000 mV/M.H.H. eHG/HGO +0.098+ 0.059;

Co_5.47XRD of N NS/NF is shown in FIG. 2A; diffraction peaks at 43.62 °, 50.77 ° and 74.86 ° correspond to the (111), (200) and (220) crystal planes of Co5.47N (JCPDS 41-0943), respectively; the peaks at 44.47 °, 51.79 ° and 76.59 ° correspond to Ni (JCPDS 04-0850), which is associated with the matrix, and no additional peaks are found, which means high purity co5.47n NS/NF; the standard cards in the figure may also index the peak value of COO NS/NF well; characterization of Co by XPS_5.47The surface composition and electron binding energy of the N NS/NF; FIG. 2B shows CO₂Two characteristic peaks at 779.5eV and 795.1eV, which can be designated Co2p3/2 and Co2p 1/2 [ 10 ]; the peak of N1 is shown in fig. 2C; clearly, the peaks at 397.5 and 399.9eV are associated with cobalt and nitrogen oxides [ 11, 12 ];

observe with scanning electron microscopeThe morphology of the agent; co shown in FIG. 3_5.47The low-power and high-power scanning electron microscope images of N NS/NF show that the morphology and the overall performance of the nanosheet array grow well on the foamed nickel substrate (FIGS. 3A and B), and the scanning electron microscope images of CoO NS/NF show that the CoO nanosheet array in the images completely covers the foamed nickel;

FIGS. 3C-D show high definition TEM images of N-NiZnCu LDH/rGO monoliths, while observing their loose porous morphology, Co_5.47High Resolution Transmission Electron Microscopy (HRTEM) of N NS/NF showed the plane spacing. High resolution lattice fringes at 0.18 and 0.21nm, corresponding to Co_5.47N NS/NF (200) and (111), this characterization is consistent with the conclusions drawn by XRD;

co is determined by electrochemical experiments_5.47N NS/NF (load: 0.23 mg/cm)²) Catalytic UOR activity and the most suitable urea concentration (0.5M) was selected by the concentration gradient polarization curve; co_5.47LSV of N NS/NF was tested in different electrolytes as shown in FIG. 4; at 100mA/cm²When the voltage is over-potential of 1.431V, 100mA/cm can be driven²Current density of (d); but less than OER (1.763V), indicating that uranium ore reduction activity is superior to OER activity; at 10mA/cm²When is Co_5.47N NS/NF，CoO NS/NF，IrO₂And NF at 1.345, 1.366, 1.576 and 1.602V, respectively, as shown in fig. 4B; obviously, Co_5.47The potential of N NS/NF was lowest, indicating that Co_5.47The UOR activity of N NS/NF is superior to other substances; the Tafel curve can be used to explain the catalytic kinetics of the electrode, Co_5.47N NS/NF, CoO NS/NF and IrO₂The Tafel slopes of (A) were 47, 60 and 78mV/dec (FIG. 4C), respectively; obviously, Co_5.47The Tafel slope of N NS/NF is lowest, which means that it has fast kinetics and excellent UOR catalytic activity; at the same time, the present study is also on Co_5.47The stability of N NS/NF was evaluated; obtain Co_5.47Multistep chronopotentiometric curve of N NS/NF (FIG. 4D); in Co_5.47Applying a step potential from 1.35V to 1.46V to the N NS/NF electrode, wherein the increase is 11mV every 2 hours; at the initial current value, the potential immediately stabilizes and remains unchanged for the remaining 2 hoursParticularly at higher currents; fast chronopotentiometric response means excellent quality transmission; these results show that Co_5.47N NS/NF has good mass transport, conductivity and mechanical stability (inward diffusion of OH and outward diffusion of bubbles and fast response to current density in each potential change step), with current density after 3000CV cycles being 93.8% of the original; at the same time, the peak value of XRD was substantially the same as the peak value before 3000CV cycles, still in good agreement with the standard card (fig. 1); these results show that it has good stability.

The invention has the beneficial effects that: the invention adopts a simple and low-cost method to synthesize the foamed nickel-supported non-noble metal porous nickel nitride electrocatalyst (Co)_5.47N NS/NF) for high-efficiency urea electrolysis-assisted hydrogen production with current density of 10mA/cm at 1.345V²Exhibit excellent UOR performance. Co_5.47N NS/NF also showed very high activity on HER at 10mA/cm²Only 116mV is needed, which indicates that Co is present_5.47N NS/NF is an excellent dual-function catalyst of UOR and HER. In addition, the corresponding two-electrode electrolytic cell only needs 1.348V to drive 10mA/cm²0.2V lower than water electrolysis and can maintain high current density (100 mA/cm)²) And electrolyzing for 20 hours. Co_5.47The N NS/NF electrode has excellent performance in the complete urea electrolysis process, has higher hydrogen production efficiency than water decomposition, and Co_5.47The N NS/NF electrode has high activity and stability, and has great potential in replacing noble metal and treating industrial waste water containing urea effectively to reach the aim of ① synthesizing foamed nickel (Co)_5.47NNS/NF) loaded high-performance bifunctional catalyst cobalt nitride nanosheet (Co)_5.47N NS/NF). Synthetic foamed nickel (Co)_5.47N NS/NF) loaded high-performance bifunctional catalyst cobalt nitride nanosheet (Co)_5.47N NS/NF), ② analyzing the appearance and composition of the cobalt nitride nanosheet catalyst by XRD, XPS, SEM, TEM, HRTEM and elements, ③ synthesizing the cobalt nitride nanosheet catalyst with the driving voltage of 100mA/cm²Only 1.687V is needed, compared with the current most effective catalyst Pt/C I IrO₂The required voltage (1.816V) is greatly reduced, ④ synthesized cobalt nitride sodiumThe rice flake catalyst can maintain high current density (100 mA/cm)²) The electrolysis time is 20 hours, and the activity and the stability are excellent.

Drawings

Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments with reference to the following drawings:

fig. 1 is a nanosheet array electrode pattern on a foamed nickel substrate of the present invention.

FIG. 2 shows the invention of Co_5.47XRD and XPS characterization patterns of N NS/NF.

FIG. 3 shows the invention of Co_5.47SEM images of N NS/NF and HRTEM images.

FIG. 4 shows (A) Co of the present invention_5.47LSV (B) LSV (C) Co of N NS/NF in different electrolytes_5.47N NS/NF，CoONS/NF，IrO₂And Tafel slope (D) Co of NF_5.47N NS/NF multistep chronopotentiometric curves.

Detailed Description

In order to make the technical means, the creation characteristics, the achievement purposes and the effects of the invention easy to understand, the invention is further described with the specific embodiments.

Referring to fig. 1-4, the present invention provides a dual-function catalyst electrode for urea electrolysis assisted hydrogen production with nickel foam supported thereon, which is prepared by synthesizing Co on nickel foam by hydrothermal method (COO NS/NF)₂O₃Nanosheets; the second process is Co_5.47Synthesizing N NS/NF; then placing the prepared CoO NS/NF in a ceramic crucible by a calcination method; due to the unique nanostructure, UOR has high activity, with a potential of only 1.431V and 100mA/cm²(ii) a More importantly, Co_5.47N can be used as a bifunctional catalyst of UOR and HER for large-scale hydrogen production, and realizes 10mA/cm²Only 1.348V is needed; as shown in fig. 1, the prepared catalyst is used as an electrode, and is a nanosheet array grown on a foam nickel substrate; during the electrolysis process, nitrogen and carbon dioxide are released when urea is absorbed and diffused;

the raw material adopts cobalt (II) chloride hexahydrate (CoCl)₂.6H₂O), potassium hydroxide (KOH), urea and hexamethylenetetramine, all chemicals of nickel foam are used as purchased without further purification, Pt/C and IrO₂The purity is 99.9 percent, and the mixture ratio is 20 percent respectively;

the first step is to synthesize cobalt oxide nanosheets (CoO NS/NF) on foamed nickel; 4mmol of CoCl₂·6H₂Dissolving O and 12mmol of hexamethylenetetramine in 50ml of ultrapure water, and continuously stirring; the suspension and pretreated nickel foam were then transferred to a 100ml teflon lined autoclave and heated at 100 ℃ for 10 hours; the second step is the synthesis of Co_5.47NNS/NF; the CoO NS/NF prepared above was placed in a ceramic crucible and calcined at 350 ℃ for 2 hours (1 ℃/min)^-1) At NH₃In the environment, the obtained product is used for the next physical characterization and electrochemical experiment;

scanning Electron Microscope (SEM) images were taken from a JEOL 7001SEM instrument at a voltage of 3kV, Transmission Electron Microscope (TEM) images were obtained from Feitecnan aig2t20 at 200kV, sample preparation was carried out by scraping off nickel foam directly and then dropping ethanol solution onto a porous carbon-copper grid, X-ray diffraction patterns were obtained in the range of 25-70 θ using copper K α radiation (. lamda.0.15418 nm) on Bruker D8 advanced ECO powder X-ray equipment with a scanning step of 0.01, X-ray photoelectron spectroscopy (XPS) measurements were carried out using an electron spectrometer, electrochemical measurements were carried out on a CHI 660E electrochemical workstation using a standard three-electrode system, the electrode material prepared was used directly as the working electrode, the reference electrode was HGO/Hg (MOE), the electrode was a bar, the graphite electrode was converted to reversible hydrogen potential at an electrochemical scanning rate of 1000000 mV, electrochemical impedance compensation was carried out at 1000000 mV/M.H.H. eHG/HGO +0.098+ 0.059;

Co_5.47XRD of N NS/NF is shown in FIG. 2A; diffraction peaks at 43.62 °, 50.77 ° and 74.86 ° correspond to the (111), (200) and (220) crystal planes of Co5.47N (JCPDS 41-0943), respectively; the peaks at 44.47 °, 51.79 ° and 76.59 ° correspond to Ni (JCPDS 04-0850), which is associated with the matrix, and no additional peaks are found, which means high purity co5.47n NS/NF;the standard cards in the figure may also index the peak value of COO NS/NF well; characterization of Co by XPS_5.47The surface composition and electron binding energy of the N NS/NF; FIG. 2B shows CO₂Two characteristic peaks at 779.5eV and 795.1eV, which can be designated Co2p3/2 and Co2p 1/2 [ 10 ]; the peak of N1 is shown in fig. 2C; clearly, the peaks at 397.5 and 399.9eV are associated with cobalt and nitrogen oxides [ 11, 12 ];

the morphology of the catalyst is observed by a scanning electron microscope; co shown in FIG. 3_5.47The low-power and high-power scanning electron microscope images of N NS/NF show that the morphology and the overall performance of the nanosheet array grow well on the foamed nickel substrate (FIGS. 3A and B), and the scanning electron microscope images of CoO NS/NF show that the CoO nanosheet array in the images completely covers the foamed nickel;

FIGS. 3C-D show high definition TEM images of N-NiZnCu LDH/rGO monoliths, while observing their loose porous morphology, Co_5.47High Resolution Transmission Electron Microscopy (HRTEM) of N NS/NF showed the plane spacing. High resolution lattice fringes at 0.18 and 0.21nm, corresponding to Co_5.47N NS/NF (200) and (111), this characterization is consistent with the conclusions drawn by XRD;

co is determined by electrochemical experiments_5.47N NS/NF (load: 0.23 mg/cm)²) Catalytic UOR activity and the most suitable urea concentration (0.5M) was selected by the concentration gradient polarization curve; co_5.47LSV of N NS/NF was tested in different electrolytes as shown in FIG. 4; at 100mA/cm²When the voltage is over-potential of 1.431V, 100mA/cm can be driven²Current density of (d); but less than OER (1.763V), indicating that uranium ore reduction activity is superior to OER activity; at 10mA/cm²When is Co_5.47N NS/NF，CoO NS/NF，IrO₂And NF at 1.345, 1.366, 1.576 and 1.602V, respectively, as shown in fig. 4B; obviously, Co_5.47The potential of N NS/NF was lowest, indicating that Co_5.47The UOR activity of N NS/NF is superior to other substances; the Tafel curve can be used to explain the catalytic kinetics of the electrode, Co_5.47N NS/NF, CoO NS/NF and IrO₂The Tafel slopes of (A) were 47, 60 and 78mV/dec (FIG. 4C), respectively; obviously, Co_5.47T of N NS/NFThe afel slope is lowest, which means that it has fast kinetics and excellent UOR catalytic activity; at the same time, the present study is also on Co_5.47The stability of N NS/NF was evaluated; obtain Co_5.47Multistep chronopotentiometric curve of N NS/NF (FIG. 4D); in Co_5.47Applying a step potential from 1.35V to 1.46V to the N NS/NF electrode, wherein the increase is 11mV every 2 hours; at the starting current value, the potential immediately tends to stabilize and remains unchanged for the remaining 2 hours, in particular at higher currents; fast chronopotentiometric response means excellent quality transmission; these results show that Co_5.47N NS/NF has good mass transport, conductivity and mechanical stability (inward diffusion of OH and outward diffusion of bubbles and fast response to current density in each potential change step), with current density after 3000CV cycles being 93.8% of the original; at the same time, the peak value of XRD was substantially the same as the peak value before 3000CV cycles, still in good agreement with the standard card (fig. 1); these results show that it has good stability.

Cited documents:

【1】H.Du,L.Xia,S.Zhu,F.Qu,F.Qu,Al-doped Ni2P nanosheet array:asuperior and durable electrocatalyst for alkaline hydrogen evolution,Chem.Commun.54(2018)2894– 2897.

【2】Y.Y.Chen,Y.Zhang,X.Zhang,T.Tang,H.Luo, S.Niu,Z.H.Dai,L.J.Wan,J.S.Hu,Self-Templated fabrication of MoNi4/MoO3-x nanorod arrays with dualactive components for highly efficient hydrogen evolution,Adv.Mater. 29(2017)17 03 311.

【3】J.Gwak,M.Choun,J.Lee,Alkaline ammonia electrolysis onelectrodeposited platinum for controllable hydrogen production,ChemSus Chem 9(2016)403–408.

【4】M.A.Khan,H.Zhao,W.Zou,Recent progresses in electrocatalysts forwater electrolysis,Electrochem.Energy Rev.4(2018)483–530.

【5】F.Guo,K.Ye,M.Du,Electrochemical impedance analysis of urea

electro-oxidation mechanism on nickel catalyst in alkaline medium,Electrochim.Acta 210(2016)474-482.

【6】C.Xiao,S.Li,X.Zhang,MnO2/MnCo2O4/Ni heterostructure with quadruplehierarchy:a bifunctional electrode architecture for overall urea oxidation,J.Mater. Chem.A 5(2017)7825-7832.

【7】G.Wang,Y.Ling,X.Lu,H.Wang,F.Qian,Y.Tong, Y.Li,Solar drivenhydrogen releasing from urea and human urine,Energy Environ.Sci.5(2012)8215-8219.

【8】M.S.Wu,R.Y.Ji,Y.R.Zheng,Nickel hydroxide electrode with amonolayer of nanocup arrays as an effective electrocatalyst for enhancedelectrolysis of urea, Electrochim.Acta 144(2014)194-199.

【9】L.Wang,L.Ren,X.Wang,Multivariate MOF-Templated pomegranate-likeNi/C as efficient bifunctional electrocatalyst for hydrogen evolution andurea oxidation,Acs Appl.Mater.Inter.10(2018)4750-4756.

【10】Tong Y,Chen P,Zhou T,Xu K,Chu W,Wu C and Xie Y 2017 ABifunctional Hybrid Electrocatalyst for Oxygen Reduction and Evolution:CobaltOxide Nanoparticles Strongly Coupled to B,N-Decorated Graphene AngewChem.Int.Ed.129 7227.

【11】Liu T,Li M,Dong P,Zhang Y and Guo L 2018 Design and facilesynthesis of mesoporous cobalt nitride nanosheets modified by pyrolyticcarbon for the nonenzymatic glucose detection Sensor.Actuat.B:Chem.255 1983.

【12】Gao D,Zhang J,Wang T,Xiao W and Tao K 2016 Metallic Ni3NNanosheets with Exposed Active Surface Sites for Efficient Hydrogen EvolutionJ.Mater.Chem.A 4 17363.

while there have been shown and described what are at present considered the fundamental principles and essential features of the invention and its advantages, it will be apparent to those skilled in the art that the invention is not limited to the details of the foregoing exemplary embodiments, but is capable of other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim concerned.

Furthermore, it should be understood that although the present description refers to embodiments, not every embodiment may contain only a single embodiment, and such description is for clarity only, and those skilled in the art should integrate the description, and the embodiments may be combined as appropriate to form other embodiments understood by those skilled in the art.