Foam nickel-based transition metal nitride microrod Co x MoN y O z H w Method for preparing MRs@NF and use thereof

Abstract

The application discloses transition metal nitride microrods Co x MoN y O z H w MRs@NF, first, foam nickel (NF) is sliced, and then, the sliced foam nickel is put into a mixed solution of ammonium molybdate (AHM) and Co(NO3)2·6H2O with deionized water as a solvent to obtain a precursor cobalt molybdate microrod CoMoO4 MRs@NF. The precursor is calcined and nitridated at high temperature to obtain transition metal nitride microrods Co x MoN y O z H w MRs@NF electrocatalyst. The method has the advantages that the product NF has single morphology and high purity, and the product NF has excellent stability and extremely small overpotential and Tafel slope in HER performance testing at a high current density (200-280 mA / cm 2 ). The product has a large specific surface area, many active sites and good stability, and has excellent electrocatalytic activity.

Description

Technical Field

[0001] This invention relates to methods for preparing transition metal nitrides and their applications, particularly to Co-based transition metal nitrides using nickel foam. x MoN y O z H w Preparation method and applications of MRs@NF. Background Technology

[0002] With the increasing depletion of traditional fossil fuels and the growing environmental pollution caused by their consumption, there is an urgent need for clean, efficient, and sustainable new energy sources. Therefore, energy conversion, especially energy storage, will become a crucial pillar for collecting energy when and where it is needed. Hydrogen, with its advantages of being clean, recyclable, having high energy density, being feasible to transport and store, and having high energy conversion efficiency, is considered the most promising energy carrier. Furthermore, hydrogen is used to produce ammonia fertilizer, helping to feed the growing global population; since the mid-20th century, hydrogen has been an indispensable part of the refining energy industry. The demand for pure hydrogen has more than tripled since 1975 and continues to rise to 70 million tons per year. Green hydrogen can be easily obtained through water electrolysis using clean energy sources such as solar power. Therefore, hydrogen production through water electrolysis has become a rapidly emerging research hotspot. However, electrolysis only provides 2% of global hydrogen production. Currently, most commercial green hydrogen projects involve the installation of proton exchange membrane electrolyzers (PEMWEs) and alkaline electrolyzers (AWEs), which are relatively mature technologies. Commercial AWE technologies primarily use nickel-based materials, with some systems also using platinum (and cobalt). The International Renewable Energy Agency (IRENA) emphasizes the need for further research and development of AWE materials to significantly improve performance and durability. To achieve large-scale hydrogen production through industrial water electrolysis, exploring low-cost, stable electrocatalysts capable of electrolyzing water at high current densities is crucial. However, most current research on HER and OER in water electrolysis focuses primarily on the material-synthesis-activity correlation of HER / OER catalysts, with limited research on catalyst design under high current density operating conditions.

[0003] Among these transition metal electrocatalysts, transition metal nitrides (TMNs) exhibit high catalytic activity due to their unique physical and chemical properties. In TMNs, small-radius nitrogen atoms tend to occupy the voids in the densely packed metal atom lattice, forming interstitial alloys. The lattice structure is close to that of pure metal catalysts, resulting in high metal abundance and good conductivity, which is beneficial for electrocatalytic reactions. Different research groups have conducted NH3 thermal nitridation reactions on CoMoO4. Due to different nitridation conditions, the products obtained also differ. However, these products have all been found to be effective electrocatalysts for OER and HER. However, few studies have investigated current densities greater than 100 mA / cm². -2 HER performance at 100 mA / cm. -2 Below, the overpotential of HER is 132 mV, and the Tafel slope is 77.5 mVdec. -1 It is one of the best-performing non-precious metal HER electrocatalysts in alkaline solutions, but research on it under higher current density operating conditions is still limited. Summary of the Invention

[0004] Objective of the invention: This invention provides a transition metal nitride Co based on nickel foam. x MoN y O z H w Preparation method of MRs@NF.

[0005] Specifically, it is a transition metal nitride Co based on Nifoam (NF) that possesses ultra-stable and ultra-low overpotential characteristics. x MoN y O z H w Microrods - Co x MoN y O z H w Preparation method of MRs@NT.

[0006] Technical solution: The present invention relates to a transition metal nitride Co based on nickel foam. x MoN y O z H w The method for preparing MRs@N is characterized by comprising the following steps:

[0007] (1) Nickel foam (NF) was sliced ​​and placed in a mixed solution of ammonium molybdate (AHM) and Co(NO3)2·6H2O using deionized water as solvent. The precursor CoMoO4MRs@NF was obtained by high temperature and high pressure hydrothermal synthesis.

[0008] (2) The precursor is subjected to high-temperature calcination and nitriding to obtain the Co with ultra-stable and ultra-low overpotential. x MoN y O z H w MRs@NF electrocatalyst.

[0009] Furthermore, the temperature of the high-temperature calcination nitriding is 300-600°C.

[0010] Furthermore, the high-temperature calcination nitriding temperature is 300, 400, 500, 550, or 600.

[0011] Furthermore, nitriding is performed in an NH3 atmosphere.

[0012] Furthermore, the precursor synthesis temperature and time are 160℃ and 6h.

[0013] Furthermore, the area of ​​the NF is 4.0 × 3.8 cm. 2 The sample was washed beforehand with ethanol and hydrochloric acid solution (1.0 M). The molar ratio of AHM (0.010 M) and Co(NO3)2·6H2O (0.050 M) was 1:5. The hydrothermal synthesis temperature was 160℃, and the holding time was 6 h. The precursor CoMoO4MRs@NF was dried under vacuum for 12 h. x MoN y O z H w The precursor of MRs@NF is CoMoO4MRs@NF.

[0014] The high-temperature calcination involves calcining the precursor in an ammonia atmosphere (flow rate of 1.0-1.5 mL / s) from room temperature at a rate of 5 °C / min. -1 The temperature is increased to 300-600℃ at a rate of 0.5 mL / s, calcined for 3 hours, and then naturally cooled to 200℃. NH3 is then switched to Ar (flow rate 0.5 mL / s), and the mixture is allowed to cool naturally to room temperature for 12 hours. The ammonia tail gas is absorbed by water. Note that the explosion limit of ammonia in air at normal pressure and temperature is 16-28%. Also note the ultra-stable, ultra-low overpotential Co... x MoN y O z H w Application of MRs@NF electrocatalysts for efficient water electrolysis and hydrogen evolution.

[0015] In this invention, Co(NO3)2·6H2O and AHM are used as metal sources, and deionized water is used as a solvent. The mixture is synthesized via hydrothermal synthesis. The precursor CoMoO4MRs@NF is then synthesized via hydrothermal synthesis, and finally, Co is obtained by high-temperature nitridation. x MoN y Oz H w MRs@NF-T (T is the nitriding temperature of the application). This catalyst has a relatively regular shape and uniform coverage, with Co... x MoN y O z H w MRs have an ultrafine particle size and are uniformly grown in situ on a nickel foam framework. Furthermore, the nickel foam has numerous pores, which are Co-like. x MoN y O z H w MRs provide ample growth sites, and the resulting catalysts exhibit ultra-high electrocatalytic activity and stability.

[0016] This paper describes the preparation of Co using the CoMoO4MRs@NF thermonitriding method. x MoN y O z H w MRs@NF-T (T = 300-600) electrodes. A portion of these (T = 400-600) exhibited PXRD spectra similar to γ-Mo₂N. The HER of these materials in alkaline medium (1.0 M KOH) was investigated, in which Co... x MoN y O z H w The MRs@NF-550 electrode showed the best performance. Its surface composition was identified based on various characterization results, revealing a rather complex heterostructure. This electrode performed well in 1.0 M KOH solution at 200 and 280 mA·cm⁻¹. -2 The overpotentials at these times were 33 and 41 mV, respectively, significantly lower than those of the Pt / C@NF electrode (134 and 172 mV). Its Tafel slope was only 15.7 mV dec. -1 Much smaller than Pt / C@NF(28.7mV·dec) -1 This indicates that it exhibits rapid HER kinetics. The aforementioned performance is among the best of all existing electrocatalysts. Finally, the HER stability of the electrode was investigated. Although its surface composition changes significantly due to oxidation during the HER process, its HER activity improves with use in terms of overpotential.

[0017] This invention Co x MoN y O z H w In-situ growth of Co on nickel foam by MRs x MoN y O z H wThe MRs@NF electrocatalyst exhibits extremely high stability; the porous nickel foam framework structure facilitates electron transport and diffusion, thereby effectively enhancing electrocatalytic activity; during high-temperature calcination, the nitrogen element in the support interacts with the metal microrods, altering the hybridization of the metal d orbitals and thus improving the catalyst's catalytic performance; Co x MoN y O z H w The MRs@NF electrocatalyst has an ultra-low overpotential, which is the lowest among existing catalysts used for hydrogen evolution in water electrolysis.

[0018] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0019] This method prepares Co with ultra-low overpotential and ultra-stable properties via hydrothermal synthesis and tubular furnace nitriding. x MoN y O z H w MRs@NF-550 is not only simple and quick to operate, and easy to scale up for production, but also produces Co x MoN y O z H w MRs@NF has advantages such as ultra-stability, ultra-low overpotential, ultra-low Tafel slope, large specific surface area, and many active sites. Attached Figure Description

[0020] Figure 1 Here are low-magnification SEM images of the catalyst prepared according to the method of the present invention: (a, b) CoMoO4 MR s @NF;(c,d)Co x MoN y O z H w MRs@NF-300、(e,f)Co x MoN y O z H w MRs@NF-400、(g,h)Co x MoN y O z H w MRs@NF-500、(i,j)Co x MoN y O z H w MRs@NF-550;

[0021] Figure 2These are high-magnification SEM images of the CoMoO4MRs@NF catalyst prepared according to the method of the present invention: (a) overall view and (b) regional view.

[0022] Figure 3 CoMoO4MRs@NF prepared according to the method of the present invention is a CoMoO4MRs@NF-oriented Co x MoN y O z H w Schematic diagram of MRs@NF catalyst conversion;

[0023] Figure 4 CoMoO4MRs@NF and Co were prepared according to the method of the present invention. x MoN y O z H w XRD pattern of MRs@NF-550 compared with standard card;

[0024] Figure 5 Co prepared according to the method of the present invention x MoN y O z H w XRD patterns of MRs@NF-T(300-600) compared with standard cards;

[0025] Figure 6 Co prepared according to the method of the present invention x MoN y O z H w MRs@NF-550 and Co x MoN y O z H w XRD pattern of MRs@NF-600 compared with standard card;

[0026] Figure 7 These are XPS spectra of CoMoO4MRs@NF prepared according to the method of the present invention: (a) Co2p, (b) Mo3d, (c) O1s, (d) Cls.

[0027] Figure 8 This is an EDS image of Co, Mo, O, and N in CoMoO4MRs@NF prepared according to the method of the present invention;

[0028] Figure 9 CoMoO4MRs@NF and Co were prepared according to the method of the present invention. x MoN y O z H w Spectral data from MRs@NF-550;

[0029] Figure 10 The XPS spectra of CoxMoNyOzHw MRs@NF-550 prepared according to the method of the present invention are: (a) Co2p, (b) Mo3d, (c) Mo3p+N1s, (d) O1s, (e) C1s.

[0030] Figure 11 Co prepared according to the method of the present invention x MoN y O z H w EDS plot of MRs@NF-550;

[0031] Figure 12 CoMoO4MRs@NF and Co were prepared according to the method of the present invention. x MoN y O z H w Comparison of the hydrogen evolution activity of MRs@NF-T and commercial Pt / C catalysts in water electrolysis: (a) LSV, (b) overpotential comparison data bar chart, (c) EIS, (d) Rs and Rct data comparison bar chart, (e) C dl (f) Stability test, (h, g) Tafel slope

[0032] Figure 13 Co prepared according to the method of the present invention x MoN y O z H w MRs@NF-500 at 200mAcm -2 Stability test results at (a) 50h and (b) 130h. Detailed Implementation

[0033] Example 1

[0034] A type of Co with ultra-stable, ultra-low overpotential x MoN y O z H w The preparation method of CoMoO4MRs@NF catalyst precursor includes the following steps:

[0035] 1) Preparation of reaction solution: Measure 80 mL of deionized water as solvent into 100 mL of polytetrafluoroethylene liner, add 1.1641 g of Co(NO3)2·6H2O and 0.9880 g of AHM as metal source, stir magnetically for about 20 min, and mix evenly.

[0036] 2) CoMoO4MRs@NF: 4.0 x 3.8 cm pre-washed and dried 2 The NF samples of different sizes were vertically placed in a polytetrafluoroethylene liner, and the prepared reactor was placed in an oven at 160°C for 6 hours. After the reaction was completed, the purplish-black flaky product was washed three times with ethanol and water, and then vacuum dried at 60°C for 6 hours to obtain CoMoO4MRs@NF.

[0037] Example 2

[0038] A type of Co with ultra-stable, ultra-low overpotential x MoN y O z H w The preparation method of MRs@NF-300 catalyst includes the following steps:

[0039] 1) Preparation of reaction solution: Measure 80 mL of deionized water as solvent into 100 mL of polytetrafluoroethylene liner, add 1.1641 g of Co(NO3)2·6H2O and 0.9880 g of AHM as metal source, stir magnetically for about 20 min, and mix evenly.

[0040] 2) Preparation of CoMoO4MRs@NF precursor: 4.0 x 3.8 cm 2 The NF samples of different sizes were vertically placed in a polytetrafluoroethylene liner, and the prepared reactor was placed in an oven at 160°C for 6 hours. After the reaction was completed, the purplish-black flaky product was washed three times with ethanol and water, and then vacuum dried at 60°C for 6 hours to obtain CoMoO4MRs@NF.

[0041] 3) Co x MoN y O z H w Preparation of MRs@NF-300: The obtained CoMoO4 MRs@NF was placed in a 4.0 x 3.8 cm container. 2 The container was placed in a magnetic boat and heated to 300°C in an ammonia atmosphere at a heating rate of 5°C / min. -1 The product was pre-nitrided at this temperature for 3 hours, then cooled to 200 degrees Celsius and the ammonia gas was turned off. The product was then cooled in an argon atmosphere for 12 hours and then cooled to room temperature to obtain the product.

[0042] Example 3

[0043] A type of Co with ultra-stable, ultra-low overpotential x MoN y O z H w The preparation method of MRs@NF-400 catalyst includes the following steps:

[0044] 1) Preparation of reaction solution: Measure 80 mL of deionized water as solvent into 100 mL of polytetrafluoroethylene liner, add 1.1641 g of Co(NO3)2·6H2O and 0.9880 g of AHM as metal source, stir magnetically for about 20 min, and mix evenly.

[0045] 2) Preparation of CoMoO4MRs@NF precursor: 4.0 x 3.8 cm 2 The NF samples of different sizes were vertically placed in a polytetrafluoroethylene liner, and the prepared reactor was placed in an oven at 160°C for 6 hours. After the reaction was completed, the purplish-black flaky product was washed three times with ethanol and water, and then vacuum dried at 60°C for 6 hours to obtain CoMoO4MRs@NF.

[0046] 3) Co x MoN y O z H w Preparation of MRs@NF-400: The prepared CoMoO4 MRs@NF was used to prepare a 4.0 x 3.8 cm² area sample. 2 Nickel foam was placed in a magnetic boat and heated to 400°C in an ammonia atmosphere at a heating rate of 5°C / min. -1 The product was pre-nitrided at this temperature for 3 hours, then cooled to 200 degrees Celsius and the ammonia gas was turned off. The product was then cooled in an argon atmosphere for 12 hours and then cooled to room temperature to obtain the product.

[0047] Example 4

[0048] A type of Co with ultra-stable, ultra-low overpotential x MoN y O z H w The preparation method of MRs@NF-500 catalyst includes the following steps:

[0049] 1) Preparation of reaction solution: Measure 80 mL of deionized water as solvent into 100 mL of polytetrafluoroethylene liner, add 1.1641 g of Co(NO3)2·6H2O and 0.9880 g of AHM as metal source, stir magnetically for about 20 min, and mix evenly.

[0050] 2) Preparation of CoMoO4MRs@NF precursor: A 4.0 x 3.8 cm² substrate was prepared. 2 NF was vertically placed in a polytetrafluoroethylene-lined reactor, and the prepared reactor was placed in an oven at 160°C for 6 hours. After the reaction was completed, the purplish-black flaky product was washed three times with ethanol and water, and then vacuum dried at 60°C for 6 hours to obtain CoMoO4MRs@NF.

[0051] 3) Co x MoN y Oz H w Preparation of MRs@NF-500: The obtained CoMoO4 MRs@NF was placed in a 4.0 x 3.8 cm container. 2 cm -2 The container was placed in a magnetic boat and heated to 500°C in an ammonia atmosphere at a heating rate of 5°C / min. -1 The product was pre-nitrided at this temperature for 3 hours, then cooled to 200 degrees Celsius and the ammonia gas was turned off. The product was then cooled in an argon atmosphere for 12 hours and then cooled to room temperature to obtain the product.

[0052] Example 5

[0053] A type of Co with ultra-stable, ultra-low overpotential x MoN y O z H w The preparation method of MRs@NF-550 catalyst includes the following steps:

[0054] 1) Preparation of reaction solution: Measure 80 mL of deionized water as solvent into 100 mL of polytetrafluoroethylene liner, add 1.1641 g of Co(NO3)2·6H2O and 0.9880 g of AHM as metal source, stir magnetically for about 20 min, and mix evenly.

[0055] 2) Preparation of CoMoO4MRs@NF precursor: 4.0 x 3.8 cm 2 The NF samples of different sizes were vertically placed in a polytetrafluoroethylene liner, and the prepared reactor was placed in an oven at 160°C for 6 hours. After the reaction was completed, the purplish-black flaky product was washed three times with ethanol and water, and then vacuum dried at 60°C for 6 hours to obtain CoMoO4MRs@NF.

[0056] 3) Co x MoN y O z H w Preparation of MRs@NF-550: The obtained CoMoO4 MRs@NF was placed in a 4.0 x 3.8 cm container. 2 The container was placed in a magnetic boat and heated to 550°C under an ammonia atmosphere at a heating rate of 5°C / min. -1 The product was pre-nitrided at this temperature for 3 hours, then cooled to 200 degrees Celsius and the ammonia gas was turned off. The product was then cooled in an argon atmosphere for 12 hours and then cooled to room temperature to obtain the product.

[0057] Example 6

[0058] A type of Co with ultra-stable, ultra-low overpotential x MoN y O z H wThe preparation method of MRs@NF-600 catalyst includes the following steps:

[0059] 1) Preparation of reaction solution: Measure 80 mL of deionized water as solvent into 100 mL of polytetrafluoroethylene liner, add 1.1641 g of Co(NO3)2·6H2O and 0.9880 g of AHM as metal source, stir magnetically for about 20 min, and mix evenly.

[0060] 2) Preparation of CoMoO4MRs@NF precursor: 4.0 x 3.8 cm 2 cm -2 The NF samples of different sizes were vertically placed in a polytetrafluoroethylene liner, and the prepared reactor was placed in an oven at 160°C for 6 hours. After the reaction was completed, the purplish-black flaky product was washed three times with ethanol and water, and then vacuum dried at 60°C for 6 hours to obtain CoMoO4MRs@NF.

[0061] 3) Co x MoN y O z H w Preparation of MRs@NF-600: The prepared CoMoO4 MRs@NF was placed in a 4.0 x 3.8 cm container. 2 cm -2 The container was placed in a magnetic boat and heated to 600°C in an ammonia atmosphere at a heating rate of 5°C / min. -1 The product was pre-nitrided at this temperature for 3 hours, then cooled to 200 degrees Celsius and the ammonia gas was turned off. The product was then cooled in an argon atmosphere for 12 hours and then cooled to room temperature to obtain the product.

[0062] Composition Description

[0063] The Co prepared in the above examples was analyzed using SEM, XRD, mapping, EDS, XPS, and ICP methods. x MoN y O z H w The MRs@NF catalyst was physically characterized using scanning electron microscopy (SEM). Figure 1 ) Observation, CoMoO4 MRs and Co x MoN y O z H w The uniform coverage of MRs-T on the NF surface indicates that the resulting product is predominantly a microrod structure, uniformly grown on nickel foam. The average size of each CoMoO4 MR is (1.4-2.4) x (1.4-2.6) x 27 μm. 3 ( Figure 2a) In some regions, smaller rod-shaped particles (0.3 x 0.3 x 1.2 μm) form clusters on the surface of larger rod-shaped particles. Figure 2 b). SEM image ( Figure 2 The obtained Co is displayed x MoN y O z H w MRs@NF-T retains its microrod cluster structure. NF turns lilac-colored after hydrothermal reaction and black after nitridation, indicating the transformation from CoMoO4MRs to Co. x MoN y O z H w MRs( Figure 3 ).

[0064] Surface XRD patterns of CoMoO4MRs@NF ( Figure 4 h) indicates that CoMoO4MRs@NF is composed of CoMoO4·nH2O and Ni metal, and has a high degree of crystallinity. ICP-MS results of nanorods scraped from the surface show that the Co:Mo ratio is 0.933:1, which is consistent with the molecular formula of CoMoO4·nH2O.

[0065] Co x MoN y O z H w MRs@NF-T(T=400-550)( Figure 4 , Figure 5 The PXRD pattern of the surface shows the presence of metallic nickel (based on nickel foam). From Figure 5 It can be seen that when the ammonolysis temperature increases from 400℃ to 600℃, the particle size of the product increases because the peak broadening is relatively small. CoMoO4 can be considered as a close mixture of CoO and MoO3, at 400℃ ( Figure 5 The reaction also involved nitriding, similar to the nitriding of MoO3 by NH3, indicating that CoMoO4MRs@NF was successfully nitrided at 550℃. Co prepared at 300-600℃... x MoN y O z H w MRs@NF( Figure 5 PXRD analysis showed that CoMoO4 did not undergo ammonolysis at 300 °C. x MoN y O z H w MRs@NF-300 is essentially still CoMoO4·nH2O MRs@NF. For example... Figure 5As shown, the XRD pattern of the product obtained at 550℃ has a small bulge on the left, which corresponds exactly to the crystal peak of CoMoO4 at this point. Therefore, Co... x MoN y O z H w MRs@NF-550 actually retains ultrafine CoMoO4 components. Therefore, the products prepared at 400-550℃ are similar, and are Co... x MoN y O z H w MRs and CoMoN x O 4-x (x≈0). After detailed analysis, it was found that Co x MoN y O z H w The XRD data of MRs-550 are very similar to those of γ-Mo2N, but due to high-temperature desalination and reduction, the final Co obtained is different. x MoN y O z H w MRs@NF-550 is actually a crystal composed of Co(0) single atoms and other elements such as Mo. Because there are single-atom Co(0) in the crystal, it has high catalytic activity.

[0066] In addition, we investigated the precursors CoMoO4@NF and Co x MoN y O z H w The MRs@NF-550 electrode underwent a series of characterizations, including XPS and XRD.

[0067] XPS of CoMoO4MRs@NF Figure 7 Studies have shown that the oxidation states of Co, Mo, and O are mainly 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 ... + 6 + and 2 - This is consistent with the expected CoMoO4. XPS analysis determined the atomic percentages of Co, Mo, and O on the sample surface to be 7.4%, 15.8%, and 76.8%, respectively (Co:Mo = 0.47:1), consistent with X-ray energy dispersive spectroscopy (EDS). Figure 9 The results (Co:Mo:O:N = 0.69:13.41:85.11:0.79) were consistent. In fact, the precursor CoMoO4MRs@NF contains trace amounts of nitrogen on its surface. Due to the effect of Mo3p3 / 2, the nitrogen peak is buried within the peak, making it undetectable by XPS spectroscopy. The small amount of nitrogen may be due to NH4 adsorbed on the precursor surface. +The EDS element mapping also captured the presence of the N element. Figure 8 EDS revealed that the low concentration of Co was due to the low energy of the applied electron beam (10 kV). XPS spectroscopy also revealed that 7.3% of the Mo was Mo(V).

[0068] Co x MoN y O z H w XPS MRs@NF-550 ( Figure 10 The presence of Co metal, Co(II), and Mo(VI, V, and IV) was revealed. The intensity of the N1s peak was calculated from the area of ​​the Mo3p3 / 2 / N1s peak, as the N1s peak was enclosed by Mo3p3 / 2. CoMoO4MRs@NF and Co x MoN y O z H w After 50 hours of IT testing, MRs@NF-550 samples all contained trace amounts of N ( Figure 11 Co was calculated using XPS peak fitting data. x MoN y O z H w The percentage ratios of Co, Mo, O, and N atoms in MRs@NF-550 are 7.8 / 21.2 / 52.0 / 19.0, consistent with the EDS data spectral results (1.2 / 20.3 / 58.7 / 19.9). Figure 9 Due to the low electron energy (10 keV), the Co content in EDS is low. The ICP-Mass results of the surface-scraped powder show a high Co:Mo ratio, indicating that the surface Co content is lower than that in the bulk phase. Mo metals include Mo3d5 / 2, MoO, MoO2, and Mo4O. 11 The peak XPS values ​​of MoO3 were 227.60–228.20, 228.30, 229.10–229.70, 231.83, and 232.50–232.80 eV, respectively. 3+ The mo3d5 / 2 and mo3d3 / 2 values ​​in MoN were 228.66 and 231.70 eV, respectively. Meanwhile, trace amounts of NH4 were detected in XPS tests. + Its peak value is 401.9 eV. NH4 +The molar ratio of Mo to Mo is 0.093:1. Mo(VI)3d² / 3 and 3d² / 5 were detected at 235.77 and 232.68 eV (0.4 eV higher than CoMoO4); Mo(V)3d² / 3 and 3d² / 5 were detected at 234.16 and 230.69 eV (similar to 234.09 and 231.16 eV for CoMoO4). The molar ratio of Mo(V) to Mo(IV) was 16.3%, less than the 7.3% of CoMoO4 MRs@NF, which is due to the reduction of NH3 during nitriding. Therefore, based on the XPS results, the surface composition of the electrode can be more accurately represented as Co. 0.37 MoN 0.9 O 2.5 MRs@NF-550.

[0069] Subsequently, we conducted detailed tests on its hydrogen evolution performance in water electrolysis. Under 1.0 M KOH conditions, a graphite rod was used as the counter electrode, and a Hg / HgO electrode was used as the reference electrode, with an area of ​​1 x 1 cm². 2 The electrocatalyst was used as the working electrode, and the Co content was determined using a three-electrode system. x MoN y O z H w Electrocatalytic HER performance of MRs@NF-550 and other electrocatalysts. Figure 12 a represents the linear sweep voltammetry (LSV) curves of different electrodes after ir reduction correction. Figure 12 b. The overpotentials of these electrodes at different current densities were compared (the smaller the overpotential, the better the performance of catalytic hydrogen evolution in water electrolysis). The comparisons were made at current densities of 10 and 100 mA·cm⁻¹. -2 At that time, Co x MoN y O z H w The overpotentials of the MRs@NF-550 electrode were 12 and 31 mV, respectively, which are much lower than those of commercial Pt / C (49 and 99 mV), CoMoO4 MRs@NF (219 and 311 mV), and Co x MoN y O z H w MRs@NF-300 (128 and 241mV), Co x MoN y O z H w MRs@NF-400 (23 and 87mV), Co x MoN y O z H w MRs@NF-500 (25 and 44 mV). The electrode is used at 200 and 280 mA cm⁻¹.-2 They also exhibited minimum overpotentials of 33 and 41 mV, respectively; the overpotentials of commercial Pt / C@NF electrodes were 134 and 172 mV, respectively.

[0070] Furthermore, the mechanism of HER was determined by the slope of Tafe1. Figure 12 As shown in g, Co x MoN y O z H w The MRs / NF-550 exhibits the smallest Tafel slope, at 15.7 mV dec. -1 Much smaller than Pt / C@NF(28.7mV·dec) -1 This indicates a rapid HER dynamic. x MoN y O z H w The relatively small Tafel slope of MRs / NF-550 indicates that the first step (Volmer step) is rapid. 15.7 mV·dec -1 The value is closer to the theoretical value of the rate-determining Tafel reaction (29 mV·dec). -1 ), rather than the rate-determining Heyrovsky reaction (38 mV·dec). -1 Pt / C@NF and Co x MoN y O z H w The HER mechanism of MRs@NF-T (T=400-600) is most likely the Tafel step-restricted mechanism, while Co x MoN y O z H w The HER mechanism of MRs@NF-300 and CoMoO4MRs@NF electrodes is most likely a Volmer step-restricted mechanism. Notably and uniquely, this mechanism occurs at 1.90 < logj < 2.35 (j: 79-224 mA·cm⁻¹). -2 Within this range, the Tafel slope is close to 0, such as... Figure 12 As shown in h. Extrapolating the linear portion of the Tafel plot in the range -1 < logj < 1.2 to the logj axis yields the properties of the electrochemical system, namely the exchange current density (j0). An ideal catalyst exhibits a low Tafel slope and a high exchange current density. Co x MoN y O z H w MRs@NF-550 has 1.63 mA·cm -2j0 is much greater than Pt / C@NF(0.24mA·cm). -2 In fact, CoMoO4MRs@NF and Co x MoN y O z H w The exchange current densities of MRs@NF-T (T=300-600) are 0.26 and 0.95-2.05, respectively, both higher than those of commercial Pt / C@NF (0.24mA·cm). -2 To further understand the kinetics of the prepared electrocatalyst, electrical impedance spectroscopy (EIS) was measured. The high-frequency range of the Nyquist plot can be attributed to the charge transfer resistance (Ro) at the catalyst-electrolyte interface. et (R) ct The smaller the value, the faster the electron transport on the catalyst surface. For example... Figure 12 As shown in c and d, Co x MoN y O z H w MRs@NF-550 only R ct The Ω is 7.1 Ω, compared to CoMoO4MRs@NF (27.0 Ω). x MoN y O z H w MRs@NF-300 (20.1Ω), Co x MoN y O z H w MRs@NF-400 (12.3Ω), Co x MoN y O z H w MRs@NF-500 (17.6Ω) and Co x MoN y O z H w MRs@NF-600 (14.4Ω) These electrodes' R ct Much smaller. Co x MoN y O z H w The Rct of MRs@NF-550 indicates that faster electron transport occurs at the interface between the electrocatalyst and the electrolyte during the HER process, thereby improving catalytic performance.

[0071] To further clarify Co x MoN y O z H wGiven the high activity of MRs@NF-550, we investigated the electrochemical activity and electrochemically active surface area (ECSA) of the aforementioned material. s The relationship between ) . For example Figure 12 As shown in e, C of the above material is obtained. dl The value order is: Co x MoN y O z H w MRs@NF-550 (11.38mF·cm) -2 )>Co x MoN y O z H w MRs@NF-400 (9.77mF·cm) -2 )>Co x MoN y O z H w MRs@NF-500 (2.00mF·cm) -2 > CoMoO4MRs@NF(1.13mF·cm) -2 )>Co x MoN y O z H w MRs@NF-300 (0.99mF·cm) -2 Co x MoN y O z H w MRs@NF-550 has the largest C a1 This indicates the largest ECSAs, consistent with HER experimental results. By comparing the C values ​​between the tested materials... d1 Based on the C values ​​and their correlation with electrocatalytic activity, the following inferences can be drawn: First, the oxygen nitride electrode has a higher C value than the corresponding non-oxygen nitride electrode. d1 The high values ​​and electrochemical activity indicate that the nitridation of metal oxides leads to an increase in ECSA, thereby enhancing electrocatalytic activity. The increase in ECSA may be due to the N modification of the metal band in the metal oxynitride compound, making it more favorable for water splitting. Secondly, Co... x MoN y O z H w Electrochemical activity of Co in MRs@NF microrods x MoN y O z H w MRs, small Co(0) clusters and unreacted ultrafine CoMoN x O 4-xThe tight interconnections between (x≈0) allow for rapid electron and mass transport, thereby promoting the breaking of MH bonds and the formation of HH bonds during the HER process, further enhancing electrocatalytic activity.

[0072] Co x MoN y O z H w The MRs@NF-550 electrode operates at a current density of 10 mA·cm⁻¹ -2 It exhibited excellent HER stability in the 24-hour stability test, and the linear scan of the electrode remained unchanged after the test. Figure 12 f). To test its industrial-scale hydrogen evolution performance in water electrolysis, we tested Co. x MoN y O z H w MRs@NF-550 electrode at 200 mA·cm -2 Stability.

[0073] Because of Co x MoN y O z H w MRs@NF-550 maintained excellent catalytic water electrolysis performance after a 50-hour stability test, so its composition was investigated. Co x MoN y O z H w MRs@NF-550 electrode after 50h HER ( Figure 6 The PXRD spectrum of the previous surface material A and the ultrafine CoMo showed that... x O 4-x It disappeared, and Co(OH)2 and possibly Mo appeared. 3-x (OH) x The peaks were observed. XPS analysis revealed that surface Co(0) was oxidized. The area percentage of Co in the satellite peaks also decreased from 36.6% to 33.9%, and the average peak position of Co (781.0 eV) was smaller than the previous (781.5 eV), indicating that some Co(II) was oxidized to Co(III). The XPS spectrum of Mo3d showed that after 50 h HER, product A was oxidized, and the surface N atom percentage decreased from 15.65% to 1.0%. Mo(VI) increased from 54.5% to 87.9%, while Mo(V) and Mo(IV) decreased from 16.2% and 29.2% to 2.7% and 4.2%, respectively. x MoN y O z H wThe atomic percentage of Co in the MRs increased from 5.83% to 12.95%, while the atomic percentage of Mo decreased from 15.82% to 5.93%. Within 50 hours, we observed particles detaching from the electrode. Therefore, more Mo detached from the electrode than Co. Surprisingly, after this significant compositional change, the electrode's performance was even better than the original electrode, such as... Figure 13 As shown in b.

[0074] Therefore, in terms of HER performance, test data from LSV, TafelSlope, etc., indicate that the Co synthesized by this method is superior. x MoN y O z H w MRs@NF-550 exhibits better electrocatalytic performance than commercial Pt / C, and therefore can be used as a commercial electrocatalyst for hydrogen evolution through water electrolysis.

Claims

1. A transition metal nitride Co based on nickel foam x MoN y O z H w The preparation method of MRs@NF is characterized by, Includes the following steps: (1) Nickel foam slices were placed in a mixed solution of ammonium molybdate and Co(NO3)2·6H2O using deionized water as solvent, and the precursor CoMoO4MRs@NF was obtained by high temperature and high pressure hydrothermal synthesis. The molar ratio of ammonium molybdate and Co(NO3)2·6H2O was 1:

5. (2) The precursor was calcined at 500, 550 or 600 °C in an ammonia atmosphere and pre-nitrided at the calcination temperature for 3 h. The ammonia was turned off when the temperature was cooled to 200 °C, and the precursor was cooled in an argon atmosphere for 12 h. The precursor was then cooled to room temperature to obtain Co with ultra-stable and ultra-low overpotential. x MoN y O z H w MRs@NF electrocatalyst.

2. The Co transition metal nitride based on nickel foam according to claim 1 x MoN y O z H w The preparation method of MRs@NF is characterized by, The precursor synthesis temperature and time were 160℃ and 6h, respectively.

3. The transition metal nitride Co based on nickel foam prepared by the method of claim 1 or 2. x MoN y O z H w MRs@NF is used for hydrogen evolution in water electrolysis.

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