A RhNi composite electrocatalyst for electrocatalytic hydrogen evolution and its preparation method

Abstract

A RhNi composite electrocatalyst for electrocatalytic hydrogen evolution and its preparation method belong to the technical field of energy catalytic conversion. In the present invention, Ni(OH)2 nanosheet precursors are prepared by a hydrothermal method, and electrostatically adsorbed Rh 3+ -Ni(OH)2 composites are prepared by a one-step solution impregnation method; subsequently, Rh 3+ -Ni Ni(OH)2 is heat-treated under a reducing atmosphere (H2 / Ar) to obtain a Ni-based RhNi composite electrocatalyst (3D-RhNi) doped with trace Rh; the 3D-RhNi exhibits high electrocatalytic hydrogen evolution reaction activity and excellent stability under acidic and alkaline conditions. The method proposed in the present invention realizes the precise preparation of a Ni-based metal electrocatalyst doped with trace Rh on the surface, effectively reduces the usage amount of precious metals, avoids traditional bulk doping, realizes surface trace metal doping, simplifies the cumbersome preparation process, and reduces the trial-and-error cost of large-scale production.

Description

Technical Field

[0001] The present invention belongs to the technical field of energy catalytic conversion, and particularly relates to a RhNi composite electrocatalyst for electrocatalytic hydrogen evolution and a preparation method thereof. Background Art

[0002] The excessive consumption of fossil resources and the accompanying environmental pollution problems force us to urgently develop and utilize renewable clean energy that can replace fossil fuels. Since hydrogen has great environmental friendliness and a high energy density capacity, hydrogen energy is considered one of the most attractive alternatives to limited storage fossil fuels in the 21st century. Electrolytic water hydrogen production is an effective way to solve the current dilemma. However, the high overpotential during the electrolytic water process results in high energy consumption for electrolytic water. Therefore, we need to develop highly active hydrogen evolution reaction catalysts to reduce the overpotential of the water decomposition reaction, thereby improving the efficiency of electrocatalytic water decomposition. The ideal electrolytic water should produce hydrogen at low cost and high yield. Currently, the most efficient hydrogen-producing electrocatalysts are still mainly based on scarce and expensive noble metal Pt-based materials. However, the extremely scarce resources and poor stability seriously hinder the large-scale industrial application of Pt-based materials. Therefore, there is an urgent need to develop electrolytic water catalysts with low overpotential and abundant reserves on Earth to accelerate the reaction kinetics and improve the efficiency of electrolytic water. Among them, Ni-based materials with abundant reserves have good plasticity and chemical properties and exhibit certain electrocatalytic activity towards the hydrogen evolution reaction. Compared with noble metal-based catalysts, Ni metal with a regular crystal structure (i.e., regular electron structure arrangement) has an unsatisfactory hydrogen binding strength and poor water molecule dissociation ability, which hinders nickel metal from becoming a potential candidate for the hydrogen evolution reaction electrocatalyst in the whole pH range. From the above research inference, regulating the electronic configuration of Ni metal may be the key to optimizing the binding energy between the intermediate and the Ni site and enhancing the intrinsic activity of the electrocatalytic hydrogen evolution reaction (HER).

[0003] In recent years, researchers have explored various methods for regulating electronic structures, including morphology modulation, defect engineering, single-atom modification, and dual-metal structure strategies (DMCs). Among them, heteroatom doping in DMCs has been widely applied due to the advantages of simple synthesis routes and controllable doping amounts. Different from non-noble metals, noble metals have received increasing attention in the regulation of the electronic structure of active sites due to their flexible coordination structures. Surprisingly, Rh atoms can not only generate strong electronic interactions with other metal sites, but also endow Rh-based catalysts with high hydrogen evolution reaction activity due to their near-zero hydrogen binding free energy. Currently, the Rh element in the reported Rh-based catalysts is almost distributed throughout the material, resulting in a very high usage amount of the Rh element. As is well known, catalytic reactions generally occur on the material surface, but the proportion of surface Rh participating in the hydrogen evolution reaction is very small, causing serious waste of resources and low atomic utilization efficiency. Therefore, reducing the usage amount of Rh and designing a surface-concentrated distribution of Rh are of great significance for future commercial applications. However, how to reduce the usage of Rh and simultaneously design a catalyst with surface Rh doping remains a huge challenge in regulating the electronic configuration of Ni metal. Summary of the Invention

[0004] In order to improve the utilization efficiency of noble metal atoms and enhance the catalytic performance of the catalyst, the present invention prepares a trace Rh surface-doped Ni-based electrocatalytic hydrogen evolution RhNi composite electrocatalyst for efficient hydrogen evolution reaction in acidic and alkaline electrolytes and its preparation method, so as to ensure the rapid and efficient production of hydrogen by electrolyzing water.

[0005] The present invention prepares a Ni(OH)2 nanosheet precursor by a hydrothermal method and prepares electrostatically adsorbed Rh 3+ -Ni(OH)2 composite material by a one-step solution impregnation method; subsequently, Rh 3+ -Ni Ni(OH)2 is heat-treated under a reducing atmosphere (H2 / Ar) to obtain a trace Rh-doped Ni-based metal electrocatalyst (3D-RhNi); the 3D-RhNi exhibits high hydrogen evolution reaction activity and excellent stability under acidic and alkaline conditions. This unique catalyst structure provides a new design idea for constructing surface noble metal-doped to activate inert non-noble metal sites, while improving the utilization efficiency of noble metal atoms in surface catalysis.

[0006] The preparation method of a RhNi composite electrocatalyst for electrocatalytic hydrogen evolution according to the present invention comprises the following steps:

[0007] (1) Pretreatment of the carbon cloth (CC) substrate:

[0008] Place carbon in a mixed solution of concentrated nitric acid (mass fraction 35%) and concentrated sulfuric acid (mass fraction 98%) with a volume ratio of 1:3, and treat it at 85 - 95 °C for 4 - 8 h to remove impurities and pollutants on the surface of the carbon cloth; after cooling to room temperature, wash the carbon cloth with H2O and C2H5OH multiple times, and dry it at room temperature to obtain a clean carbon cloth substrate;

[0009] (2) Preparation of a carbon cloth substrate with Ni(OH)2 grown on the surface:

[0010] Add 0.5 - 0.7 g of Ni(NO3)2·6H2O, 0.2 - 0.3 g of NH4F, and 0.6 - 0.8 g of (NH2)2CO to 30 - 40 mL of H2O, and continuously stir for 20 - 40 min to obtain a clear light green solution; then immerse the clean carbon cloth substrate from step (1) into this light green solution, and react at 110 - 130 °C for 4 - 8 h; after cooling to room temperature, take out the carbon cloth substrate and wash it with H2O and C2H5OH multiple times to obtain a carbon cloth substrate with Ni(OH)2 grown on the surface;

[0011] (3) Preparation of a carbon cloth substrate with Ru 3+ -Ni(OH)2 or Rh 3+ -Ni(OH)2 grown on the surface:

[0012] Ultrasonically dissolve 0.02 g of RuCl3·xH2O in 8 - 15 mL of C2H5OH to obtain a solution containing Ru 3+ ; immerse the carbon cloth substrate with Ni(OH)2 grown on the surface into this solution containing Ru 3+ , and let it stand for 1.5 - 3.0 h to obtain a carbon cloth substrate with a Ru 3+ -Ni(OH)2 precursor grown on the surface; take out this carbon cloth substrate and wash it with C2H5OH multiple times, then dry it at room temperature to obtain a carbon cloth substrate with Ru 3+ -Ni(OH)2 grown on the surface;

[0013] Ultrasonically dissolve 0.02 g of RhCl3·xH2O in 8 - 15 mL of C2H5OH to obtain a solution containing Rh 3+ ; immerse the carbon cloth substrate with Ni(OH)2 grown on the surface into this solution containing Rh 3+ , and let it stand for 1.5 - 3.0 h to obtain a carbon cloth substrate with a Rh 3+ -Ni(OH)2 precursor grown on the surface; take out this carbon cloth substrate and wash it with C2H5OH multiple times, then dry it at room temperature to obtain a carbon cloth substrate with Rh 3 + -Ni(OH)2 grown on the surface;

[0014] (4) Preparation of 3D-Ni, 3D-RuNi and 3D-RhNi electrocatalysts:

[0015] Under the condition that the reducing atmosphere is 5% H2 and 95% Ar (the unit of percentage is volume), place the carbon cloth substrate with Ni(OH)2 grown on the surface obtained in step (2) at the center of the tubular furnace. The tubular furnace is heated to 380 - 420 °C at a rate of 1.5 - 3.0 °C / min and kept for 1.5 - 3.0 h for annealing treatment; then it is cooled to room temperature to obtain the 3D-Ni electrocatalyst, and the 3D-Ni loading is 2 - 3 mg / cm 2 ;

[0016] Under the condition that the reducing atmosphere is 5% H2 and 95% Ar (the unit of percentage is volume), place the carbon cloth substrate with Ru 3+ -Ni(OH)2 grown on the surface obtained in step (3) at the center of the tubular furnace. The tubular furnace is heated to 380 - 420 °C at a rate of 1.5 - 3.0 °C / min and kept for 1.5 - 3.0 h for annealing treatment; then it is cooled to room temperature to obtain the 3D-RuNi composite electrocatalyst, and the 3D-RuNi loading is 2 - 3 mg / cm 2 ;

[0017] Under the condition that the reducing atmosphere is 5% H2 and 95% Ar (the unit of percentage is volume), place the carbon cloth substrate with Rh 3+ -Ni(OH)2 grown on the surface obtained in step (3) at the center of the tubular furnace. The tubular furnace is heated to 380 - 420 °C at a rate of 1.5 - 3.0 °C / min and kept for 1.5 - 3.0 h for annealing treatment; then it is cooled to room temperature to obtain the 3D-RhNi composite electrocatalyst, and the 3D-RhNi loading is about 2 - 3 mg / cm 2 。

[0018] Based on different cation adsorption, the present invention prepares Ni-based metal electrocatalysts with trace Rh doping on the surface through hydrogen reduction treatment, and evaluates the effects of different metal trace doping on the crystal structure, electronic structure and electrocatalytic hydrogen evolution performance of the obtained Ni-based metals. Under the condition of ensuring the same doping amount and other experimental conditions, electrochemical performance tests are carried out in different electrolytes (1.0 M KOH and 0.5 M H2SO4). The electrochemical test results show that the synthesized 3D-RhNi composite electrocatalyst exhibits more excellent electrocatalytic hydrogen evolution performance than pure 3D-Ni and 3D-RuNi electrocatalysts. The proposal of the present invention will lay a solid foundation for the large-scale commercial preparation of low-cost, high-activity and high-stability electrocatalytic hydrogen evolution in the future.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] The method proposed by the present invention realizes the precise preparation of a Ni-based metal electrocatalyst with trace surface Rh doping, effectively reducing the usage amount of precious metals, avoiding traditional bulk doping, achieving surface trace metal doping, simplifying the cumbersome preparation process, and reducing the trial-and-error cost of large-scale production. On the other hand, the doping of trace surface Rh optimizes the electronic structure of Ni, endows fast mass transfer and charge transfer capabilities, and enables it to exhibit excellent electrocatalytic hydrogen evolution activity and stability in both alkaline and acidic electrolytes. Description of the Drawings

[0021] Figure 1 : Rh 3+ -Ni(OH)2, Ru 3+ XRD spectra of Ru

[0022] Figure 2 : Ni(OH)2, Ru 3+ -Ni(OH)2, Rh 3+ SEM images of Rh

[0023] Figure 3 : TEM images of 3D-Ni, 3D-RuNi and 3D-RhNi (corresponding to Figures a, b, c respectively); HRTEM images of 3D-Ni, 3D-RuNi and 3D-RhNi (corresponding to Figures d, e, f respectively);

[0024] Figure 4 : Ni 2p XPS spectra of 3D-Ni, 3D-RuNi and 3D-RhNi;

[0025] Figure 5 : Ru 3+ -Ni(OH)2 and Ru 3d XPS spectra of 3D-RuNi (a); Rh 3+ -Ni(OH)2 and Rh3d XPS spectra of 3D-RhNi (b);

[0026] Figure 6 : LSV polarization curves (a) and corresponding Tafel slope plots (b) of blank CC, Ni(OH)2, 3D-Ni, 3D-RuNi and 3D-RhNi in 1.0 M KOH solution;

[0027] Figure 7: LSV polarization curves (a) and corresponding Tafel slope plots (b) of blank CC, Ni(OH)2, 3D-Ni, 3D-RuNi, and 3D-RhNi in 0.5 M H2SO4 solution;

[0028] Figure 8 : Chronoamperometry test curves (I-T) of 3D-RhNi in 1.0 M KOH solution (a) and 0.5 M H2SO4 solution (b).

[0029] Figure 1 Peaks of the precursor obtained by hydrothermal synthesis and the electrocatalyst obtained after hydrogenation treatment are shown. As Figure 1 shown in a, the XRD diffraction peaks of the precursor obtained by hydrothermal synthesis can be attributed to the characteristic peaks of Ni(OH)2. After immersing Ni(OH)2 in Rh 3 + / Ru 3+ solution, the structure of Ni(OH)2 does not change, indicating that Ni(OH)2 and Rh 3+ / Ru 3+ are only surface electrostatic adsorption. After hydrogenation reduction of the Ni(OH)2 precursor, all the XRD peaks of Ni(OH)2 disappear, and only the characteristic peaks of metallic Ni are observed, without any characteristic peaks of Ru / Rh, probably because the content of Ru / Rh is too low. In Figure 1 b, the three peaks at 2θ positions of 44.5°, 51.8°, and 76.4° are attributed to the (111), (200), and (220) crystal planes of metallic Ni. Magnifying Figure 1 b (right figure) shows that, compared with the pure 3D-Ni sample, the 44.5° peak of 3D-RhNi and 3D-RuNi shifts to a lower angle. This is because the atomic radius of Rh / Ru is larger than that of Ni atoms, and Rh / Ru atoms enter the Ni lattice, causing the Ni lattice to expand. The XRD spectrum shows that hydrogenation treatment enables Rh / Ru atoms to successfully enter the Ni lattice.

[0030] The morphology of the synthesized materials was observed using SEM technology. As Figure 2 shown in a, the Ni(OH)2 synthesized by the hydrothermal method is a two-dimensional nanosheet morphology with a smooth surface, interlaced with each other, and uniformly vertically growing on the carbon cloth substrate. After immersing Ni(OH)2 in ethanol solution, Rh 3+ -Ni(OH)2 and Ru 3+ -Ni(OH)2 do not change in morphology and still maintain the original nanosheet morphology of Ni(OH)2 ( Figure 2 b, Figure 2 c). However, Rh 3+ -Ni(OH)2 and Ru 3+Slight wrinkles appeared at the edges of the nano-sheets of -Ni(OH)2. As Figure 2 shown in 3+ d, after hydrogenation treatment, 3D-Ni maintained the nano-sheet skeleton structure. However, due to the departure of surface H2O molecules and -OH, the nano-sheets began to agglomerate and even form lumps. After the ion adsorption of Rh 3+ / Ru Figure 2 on Ni(OH)2, 3D-RhNi and 3D-RuNi also maintained a similar 3D-Ni morphology structure ( Figure 2 e,

[0031] Figure 3 f). Different from the massive morphology of 3D-Ni, 3D-RhNi and 3D-RuNi showed a loose and porous sheet-like morphology structure. This is mainly because the infiltration of Rh / Ru atoms inhibited the agglomeration trend of Ni(OH)2 nano-sheets during the heat treatment process, effectively increasing the surface area of the material. Figure 3 Figures Figure 3 a and Figure 3 b show the TEM and HRTEM image analyses of the samples annealed in a hydrogen atmosphere. As Figure 3 shown in Figure 3 a, 3D-Ni presented irregular particles with non-uniform sizes. While 3D-RuNi and 3D-RhNi were composed of hundreds of uniformly sized nanoparticles interconnected to form a clear three-dimensional network structure framework ( Figure 3 b,

[0032] Figure 4 c). In addition, in the HRTEM image of 3D-Ni ( 0 d), lattice fringes with d = 0.203 nm were observed, corresponding to the (111) crystal plane of metallic Ni. As 2+ shown in 2+ e, after introducing the second metal element Ru, it was found that the d value increased (0.206 nm). When introducing the Rh element, the interplanar spacing increased significantly, d = 0.210 nm ( Figure 3 f). Consistent with the XRD results, it further demonstrated that during the heat treatment process, Ru / Rh with a larger atomic radius entered the lattice of Ni, causing the lattice of Ni to expand, and at the same time proving the successful preparation of this composite electrocatalyst.

[0032] Figure 4 is the Ni 2p XPS spectrum of 3D-Ni: The two peaks at 853.3 and 855.0 eV are attributed to metallic Ni (Ni 0 ) and Ni 2+ peaks respectively, where Ni 2+It may be derived from NiO formed by air oxidation. Compared with the pure 3D-Ni sample, the Ni 2p peak of 3D-RhNi shifts 0.3 eV to a lower binding energy, indicating a strong charge transfer effect between Rh and Ni, that is, Rh changes the local electron environment of Ni and enriches the electrons around Ni. The electron-rich Ni sites of this material can change the adsorption / desorption behavior of the reaction to intermediates, thereby changing the HER activity.

[0033] In Figure 5 Ru 3+ -Ni(OH)2, the Ru 3d peak at 282.0 eV can be attributed to Ru 3+ ( Figure 5 a). Similarly, the Rh 3d (310.3 eV) peak in Rh 3+ -Ni(OH)2 originates from surface-adsorbed Rh 3+ ( Figure 5 b). For the 3D-RuNi and 3D-RhNi catalysts, the Ru / Rh elements mainly exist in the form of metallic Ru 0 / Rh 0 , but there is a weak signal peak of Rh 3+ , further verifying that the electrons of Rh are transferred to the surrounding Ni atoms, resulting in the appearance of Rh 3+ .

[0034] To study the electrocatalytic performance of the catalyst materials, we carried out a series of electrochemical tests on the synthesized catalyst materials in 1.0 M KOH and 0.5 M H2SO4 respectively. As Figure 6 shown in a, compared with other electrode materials, 3D-RhNi requires a lower overpotential of 37 mV to drive a current density of 10 mA / cm 2 in 1.0 M KOH. The alkaline HER overpotential (η 10 = 37 mV) of 3D-RhNi is less than that of 3D-RuNi (η 10 = 47 mV), 3D-Ni (η 10 = 151 mV), Ni(OH)2 (η 10 = 447 mV) and CC (η 10 = 535 mV). Compared with pure 3D-Ni, after the introduction of Rh, the alkaline HER activity of 3D-RhNi is greatly improved, mainly due to the fact that the introduction of Rh causes a large number of electrons to accumulate around Ni, activating the inert Ni atoms around. The size of the Tafel slope value obtained from the LSV curve is used to evaluate the speed of the HER reaction kinetics. As Figure 6As shown in Fig. b, the Tafel slopes of blank CC, Ni(OH)2, 3D-Ni, 3D-RuNi, and 3D-RhNi are 259, 170, 114, 68, and 44 mV / dec, respectively. 3D-RhNi has the smallest Tafel slope, indicating that 3D-RhNi has the fastest HER reaction kinetics in alkaline solution, demonstrating that 3D-RhNi has excellent hydrogen evolution ability.

[0035] As Figure 7 shown in Fig. a, electrochemical tests were carried out in 0.5 M H2SO4 electrolyte. 3D-RhNi exhibited the highest acidic HER activity, and only an overpotential of 18 mV was required to reach a current density of 10 mA / cm 2 . The HER overpotential (η 10 = 18 mV) in this acidic condition is much lower than that of 3D-RuNi (η 10 = 31 mV), 3D-Ni (η 10 = 210 mV), Ni(OH)2 (η 10 = 540 mV), and blank CC (η 10 = 540 mV). As Figure 7 shown in Fig. b, compared with other comparative samples, 3D-RhNi has the smallest Tafel slope (19 mV / dec), that is, the fastest acidic HER kinetics, and 3D-RhNi shows excellent hydrogen evolution ability. The Tafel slopes of blank CC, Ni(OH)2, 3D-Ni, and 3D-RuNi are 144, 222, 141, and 30 mV / dec, respectively.

[0036] In practical applications, in addition to electrochemical activity, the long-term stability of the catalyst is another important indicator for evaluating the electrocatalytic performance of the catalyst. We used the chronoamperometry technique (CA) to test the alkaline and acidic HER stabilities of this composite electrocatalyst in alkaline electrolyte and acidic electrolyte, respectively. As Figure 8 shown in Fig. a, in alkaline electrolyte, after 100 h of stability test, the current density of 3D-RhNi remained relatively stable and did not show a significant decay. At the same time, as Figure 8 shown in Fig. b, in acidic electrolyte, after nearly 60 h of stability test, the current density of 3D-RhNi fluctuated up and down to a certain extent, showing a slight decay. Specific Embodiments

[0037] Example 1: Preparation and electrocatalytic hydrogen evolution performance study of Ni-based composite electrocatalyst with trace Ru doping on the surface:

[0038] It includes the following steps:

[0039] (1) Pretreatment of CC:

[0040] Place a carbon cloth substrate of 2.0×3.0 cm 2 in a mixed solution with a volume ratio of 1:3 of concentrated nitric acid (mass fraction 35%) and concentrated sulfuric acid (mass fraction 98%), and treat it at 90 °C for 6 h to remove surface impurities and contaminants of CC. After cooling to room temperature, wash it repeatedly with H2O and C2H5OH, and dry it at room temperature to obtain a clean carbon cloth substrate.

[0041] (2) Preparation of a carbon cloth substrate with Ni(OH)2 grown on the surface:

[0042] Add 0.697 g of Ni(NO3)2·6H2O, 0.225 g of NH4F, and 0.714 g of (NH2)2CO to 35 mL of H2O, and continuously stir for 30 min to obtain a clear light green solution. Transfer the obtained clear light green solution to a reaction kettle, and then immerse the clean carbon cloth substrate obtained in step (1) into it. Heat it to 120 °C and keep the reaction for 6 h. After the reaction is completed, cool it to room temperature, take out the carbon cloth substrate and wash it repeatedly with H2O and C2H5OH to obtain a carbon cloth substrate with Ni(OH)2 grown on the surface.

[0043] (3) Preparation of a carbon cloth substrate with Ru 3+ -Ni(OH)2 grown on the surface:

[0044] Weigh 0.02 g of RuCl3·xH2O and dissolve it in 10 mL of C2H5OH by ultrasonic wave. Immerse the carbon cloth substrate with Ni(OH)2 grown on the surface into the solution containing Ru 3+ . Let it stand for 2 h. Subsequently, take out the carbon cloth substrate with Ni(OH)2 grown on the surface adsorbed with Ru 3+ and wash it repeatedly with C2H5OH. After drying at room temperature, obtain a carbon cloth substrate with Ru 3+ -Ni(OH)2 grown on the surface.

[0045] (4) Preparation of the 3D-RuNi electrocatalyst:

[0046] Under the condition that the reducing atmosphere is 5% volume of H2 and 95% volume of Ar, place the carbon cloth substrate with Ru 3+ -Ni(OH)2 grown on the surface (2.0×3.0 cm 2 ) at the center of a tube furnace for annealing treatment. After the tube furnace is heated to 400 °C at a rate of 2 °C / min, keep it for 2 h, and then cool it to room temperature at a rate of 2 °C / min to obtain a black product, that is, a composite electrocatalyst, with a loading amount of 2.5 mg / cm 2 , named 3D-RuNi composite electrocatalyst.

[0047] (5) Hydrogen evolution performance test:

[0048] All electrochemical tests were performed using a CHI 760e electrochemical workstation configured with a standard three - electrode system. A 3D - RuNi composite electrocatalyst (2.0×3.0 cm 2 ) was used as the working electrode, and a graphite rod was used as the counter electrode. In an alkaline solution (1.0 M KOH), Hg / HgO was selected as the reference electrode; in an acidic solution (0.5 M H2SO4), a Ag / AgCl saturated with KCl was selected as the reference electrode. At room temperature, polarization curves were collected using the LSV program with a scan rate of 2.0 mV / s.

[0049] In 1.0 M KOH, the potential can be calibrated to the reversible hydrogen electrode according to the following formula:

[0050] E RHE =E Hg / Hgo +0.059×pH + 0.098 (1)

[0051] In 0.5 M H2SO4, the potential can be calibrated to the reversible hydrogen electrode according to the following formula:

[0052] E RHE =E Ag / AgCl +0.059×pH + 0.198 (2)

[0053] In this invention, all the obtained LSV curves of the hydrogen evolution reaction were IR - calibrated in this work.

[0054] Table 1: ICP test results of 3D - RhNi and 3D - RuNi samples

[0055] Elements 3D-RuNi 3D-RhNi Ru:Ni 0.0011:1 - Rh:Ni - 0.0010:1

[0056] Table 1 shows the ICP test results of the samples. From the ICP results of the 3D - RuNi sample, the atomic ratio of Ru / Ni is close to 0.1%, which confirms that the content of Ru is extremely low and is trace doping.

[0057] As Figure 1 shown in 3+ b, after hydrogen reduction, we only observed the diffraction peaks of metallic Ni, and no peaks of Ru or RuNi alloy. It may be that the content of Ru element is too low to be detected by XRD. At the same time, the diffraction peaks of Ni shifted significantly negatively, from which it is inferred that Ru Figure 3 might enter the lattice of Ni. Figure 5 Figure b is a high - magnification transmission image of 3D - RuNi. It can be seen that the interplanar spacing has increased, further indicating that Ru doping causes the lattice of Ni to expand.It can be seen from a that Ru in 3D-RuNi exists in a zero-valent state. In the subsequent LSV electrochemical test, it was obtained that in 1.0 M KOH, 3D-RuNi requires an overpotential of 47 mV to reach a current density of 10 mA / cm 2 2. Figure 6 As shown in b, the Tafel slope value of 3D-RuNi is 68 mV / dec. Figure 7 As shown in b, in a 0.5 M H2SO4 solution, 3D-RuNi requires an overpotential of 31 mV to reach a current density of 10 mA / cm 2 2, and the Tafel slope value of 3D-RuNi is 30 mV / dec.

[0058] Example 2: Preparation of Ni-based composite electrocatalyst doped with trace Rh on the surface and study of electrocatalytic hydrogen evolution performance:

[0059] The specific process is as follows:

[0060] (1) Pretreatment of CC:

[0061] Place the carbon cloth substrate (2.0×3.0 cm 2 ) in a mixed solution of concentrated nitric acid (mass fraction 35%) and concentrated sulfuric acid (mass fraction 98%) with a volume ratio of 1:3, and treat it at 90 °C for 6 h to remove surface impurities and contaminants of CC. After cooling to room temperature, wash it with H2O and C2H5OH multiple times and dry it at room temperature to obtain a clean carbon cloth substrate.

[0062] (2) Preparation of carbon cloth substrate with Ni(OH)2 grown on the surface:

[0063] Add 0.697 g of Ni(NO3)2·6H2O, 0.225 g of NH4F, and 0.714 g of (NH2)2CO to 35 mL of H2O, and continuously stir for 30 min to obtain a clear light green solution. Transfer the obtained clear light green solution to a reaction kettle, then immerse the clean carbon cloth substrate obtained in step (1) into it, and heat it to 120 °C and keep the reaction for 6 h. After the reaction is completed, cool it to room temperature, take out the carbon cloth substrate and wash it with H2O and C2H5OH multiple times to obtain a carbon cloth substrate with Ni(OH)2 grown on the surface.

[0064] (3) Preparation of carbon cloth substrate with Rh 3+ -Ni(OH)2 grown on the surface:

[0065] Weigh 0.02 g of RhCl3·xH2O and dissolve it in 10 mL of C2H5OH by ultrasonic treatment to obtain a solution containing Rh 3+ ; Immerse the carbon cloth substrate with Ni(OH)2 grown on the surface into the solution containing Rh 3+Let it stand in the solution for 2 h. Subsequently, take out the carbon cloth substrate with Ni(OH)2 grown on the surface adsorbed with Rh 3+ and wash it with C2H5OH multiple times. After drying at room temperature, a carbon cloth substrate with Rh 3+ -Ni(OH)2 grown on the surface is obtained.

[0066] (4) Preparation of 3D-RhNi electrocatalyst:

[0067] Under the condition that the reducing atmosphere is 5% volume H2 and 95% volume Ar, place the carbon cloth substrate with Rh 3+ -Ni(OH)2 grown on the surface (2.0×3.0 cm 2 ) at the center of the tubular furnace for annealing treatment. After the tubular furnace is heated to 400 °C at a rate of 2 °C / min and kept for 2 h, then cooled to room temperature at a rate of 2 °C / min, a black product is obtained, and its areal loading is 2.5 mg / cm 2 , named 3D-RhNi composite electrocatalyst.

[0068] (5) Hydrogen evolution performance test:

[0069] All electrochemical tests are completed by a CHI 760e electrochemical workstation configured with a standard three-electrode system. Take the CC (2.0×3.0 cm 2 ) grown with the active material 3D-RuNi as the working electrode and a graphite rod as the counter electrode. In an alkaline solution (1.0 M KOH), choose Hg / HgO as the reference electrode; in an acidic solution (0.5 M H2SO4), choose Ag / AgCl saturated with KCl as the reference electrode. At room temperature, collect the polarization curve using the LSV program with a scan rate of 2.0 mV / s.

[0070] In 1.0 M KOH, the potential can be calibrated to the reversible hydrogen electrode according to the following formula:

[0071] E RHE = E Hg / Hgo + 0.059×pH + 0.098 (3)

[0072] In 0.5 M H2SO4, the potential can be calibrated to the reversible hydrogen electrode according to the following formula:

[0073] E RHE = E Ag / AgCl + 0.059×pH + 0.198 (4)

[0074] Unless otherwise stated, all HER curves obtained in this experiment were IR-calibrated in this work. The solution resistance was evaluated by electrochemical impedance spectroscopy (EIS) in the frequency range of 100 - 0.01 kHz. To calculate the electrochemically active surface area (ECSA), cyclic voltammetry (CV) measurements were carried out in the non-Faradaic region (0.07 - 0.17 V vs. RHE in 1.0 M KOH, 0.34 - 0.44 V vs. RHE in H2SO4) to obtain the electrochemical double-layer capacitance (C dl ) As shown in Equation (5), C dl is linearly related to the ECSA, where Cs represents the smooth plane capacitance:

[0075] ECSA = C dl / C s (5)

[0076] (6) Stability test of 3D-RhNi:

[0077] An electrochemical stability test was carried out using a CHI 760e electrochemical workstation configured with a standard three-electrode system. The 3D-RhNi composite electrocatalyst (0.5×1.0 cm 2 ) was used as the working electrode, and a graphite rod was used as the counter electrode. In an alkaline solution (1.0 M KOH), Hg / HgO was selected as the reference electrode; in an acidic solution (0.5 M H2SO4), Ag / AgCl saturated with KCl was selected as the reference electrode. The chronoamperometry technique was used to collect the stability data of the samples.

[0078] As shown in Table 1, the Rh / Ni atomic ratio of the synthesized 3D-RhNi composite electrocatalyst is close to about 0.001, indicating a low Rh content. As Figure 1 shown in b, only the diffraction peaks of metallic Ni were observed after hydrogen reduction, and no peaks of Rh or RhNi alloy were observed. It may be that the Rh content is too low to be detected by XRD. At the same time, the diffraction peaks of Ni shifted significantly negatively, from which it is inferred that Rh 3+ may enter the lattice of Ni. Figure 3 c is a high-magnification transmission image of 3D-RhNi. It can be seen that the interplanar spacing has increased, further indicating that the doping of Rh with a larger atomic radius causes the lattice of Ni to expand. As Figure 5 shown in b, Rh in 3D-RhNi exists in the zero-valent state. In the subsequent LSV electrochemical test, 3D-RhNi exhibited the most excellent electrocatalytic hydrogen evolution performance. In 1.0 M KOH, 3D-RhNi only requires an overpotential of 37 mV to reach a current density of 10 mA / cm 2 . Figure 6b shows that the Tafel slope value of 3D-RhNi is the smallest, which is 44 mV / dec. Figure 7 b shows that in a 0.5 M H2SO4 solution, 3D-RhNi requires an overpotential of 18 mV to reach a current density of 10 mA / cm 2 ². The Tafel slope value of 3D-RhNi is 19 mV / dec. In addition, the 3D-RhNi composite electrocatalyst also exhibits good hydrogen evolution stability: it can achieve a stability test of more than 100 hours in 1.0 M KOH, and at the same time, it can reach a stability test of more than 60 hours in a 0.5 M H2SO4 solution without obvious current decay. In summary, it is advisable to select the preparation of 3D-RhNi composite electrocatalyst as a low-cost, highly efficient, and stable hydrogen evolution electrocatalyst.

Claims

1. Preparation method of RhNi composite electrocatalyst for electrocatalytic hydrogen evolution, the steps are as follows: (1) Preparation of carbon cloth substrate with Ni(OH)2 grown on the surface Add 0.5 - 0.7 g of Ni(NO3)2·6H2O, 0.2 - 0.3 g of NH4F and 0.6 - 0.8 g of (NH2)2CO to 30 - 40 mL of H2O, and continuously stir for 20 - 40 min to obtain a clear light green solution; then immerse the clean carbon cloth substrate into the light green solution, and react at 110 - 130 °C for 4 - 8 h; after cooling to room temperature, take out the carbon cloth substrate and wash it with H2O and C2H5OH for multiple times to obtain the carbon cloth substrate with Ni(OH)2 grown on the surface; (2) Surface growth of Rh 3+ Preparation of carbon cloth substrate for -Ni(OH)2 Dissolve 0.02 g of RhCl3·xH2O in 8 - 15 mL of C2H5OH by ultrasonic treatment to obtain a solution containing Rh 3+ Immerse the carbon cloth substrate with Ni(OH)2 grown on its surface in step (1) into the solution containing Rh 3+ and let it stand for 1.5 - 3.0 h to obtain a carbon cloth substrate with Rh 3+ -Ni(OH)2 precursor grown on its surface; Take out the carbon cloth substrate, wash it with C2H5OH multiple times, and dry it at room temperature to obtain a carbon cloth substrate with Rh 3+ -Ni(OH)2 grown on its surface; (3) Preparation of 3D-RhNi electrocatalyst Under the condition that the reducing atmosphere is 5% volume H2 and 95% volume Ar, heat the carbon cloth substrate with surface-grown Rh 3+ -Ni(OH)2 obtained in step (2) to 380-420 °C and keep it for 1.5-3.0 h for annealing treatment; then cool it to room temperature to obtain the 3D-RhNi electrocatalyst.

2. The preparation method of the RhNi composite electrocatalyst for electrocatalytic hydrogen evolution according to claim 1, wherein: Place the carbon cloth in a mixed solution with a volume ratio of 35% concentrated nitric acid to 98% concentrated sulfuric acid of 1:3, and treat it at 85 - 95 °C for 4 - 8 h to remove impurities and pollutants on the surface of the carbon cloth; after cooling to room temperature, wash the carbon cloth with H2O and C2H5OH for multiple times, and dry it at room temperature to obtain a clean carbon cloth substrate.

3. The preparation method of a RhNi composite electrocatalyst for electrocatalytic hydrogen evolution according to claim 1, characterized in that: In step (3), the heating rate of heating is 1.5 - 3.0 °C / min.

4. A RhNi composite electrocatalyst for electrocatalytic hydrogen evolution, characterized in that: It is prepared by the method described in any one of claims 1, 2 or 3.

5. The RhNi composite electrocatalyst for electrocatalytic hydrogen evolution according to claim 4, wherein: The loading amount of the RhNi composite electrocatalyst on the surface of the carbon cloth substrate is 2 - 3 mg / cm 2 .

Images