Preparation of Ni (Cu) / NiMo / NF composite hydrogen evolution electrocatalyst

Abstract

The invention discloses a preparation method and application of a Ni (Cu) / NiMo / NF composite catalyst, a Ni (Cu) nanotube structure is synthesized on foamed nickel by adopting a simple electro-deposition method, and NiMo alloy is deposited by taking the Ni (Cu) nanotube structure as a substrate. The prepared Ni (Cu) / NiMo / NF composite catalyst shows the optimal catalytic activity in an alkaline medium, compared with a NiMo alloy directly deposited on a foamed nickel substrate, the electrocatalytic hydrogen evolution performance of the Ni (Cu) / NiMo / NF composite catalyst is improved, and in a 1M KOH solution, the overpotential corresponding to the 10mAcm <-2 > current density is 64mV. The three-dimensional skeleton structure of the foamed nickel provides excellent growth conditions for the catalyst; the prepared Ni (Cu) nanotube structure provides more loading space for subsequent deposition of NiMo alloy, the agglomeration phenomenon of the NiMo alloy is relieved, exposure of more active sites is facilitated, and therefore the catalytic hydrogen evolution activity of the Ni (Cu) nanotube structure is improved.

Description

Technical Field

[0001] This invention belongs to the field of research on hydrogen evolution performance in water electrolysis, and relates to a method for preparing an electrocatalyst (Ni(Cu) / NiMo / NF) for use in the catalytic water electrolysis hydrogen evolution process. Background Technology

[0002] Hydrogen energy, as a crucial component of clean energy, produces only water and heat upon combustion, causing no environmental pollution. Therefore, developing hydrogen energy can effectively alleviate the energy crisis without harming the ecological environment. To date, the main methods for producing hydrogen are natural gas pyrolysis and coal gasification. However, these processes release the greenhouse gas carbon dioxide, negatively impacting the atmospheric environment. Therefore, an environmentally friendly production method is needed to replace these methods. Water electrolysis demonstrates its inherent superiority due to its low cost and environmental friendliness. In the water electrolysis process, electrocatalysts play a crucial role in the efficiency of the hydrogen evolution reaction (HER). Currently, noble metal-based electrocatalysts are widely developed and applied to the HER in water electrolysis. However, the high cost and scarcity of these materials significantly hinder their practical development and widespread application. Therefore, developing efficient, stable, and inexpensive catalysts is essential for the development of HER in water electrolysis.

[0003] The water electrolysis reaction consists of the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). The HER is a crucial process for hydrogen energy storage and conversion, and its performance directly determines the efficiency of the hydrogen energy system. At 25°C and 1 atm, the theoretical decomposition voltage of water is 1.23V, while the actual voltage of water electrolysis in industrial electrolyzers is 1.8-2.6V, much higher than the theoretical decomposition voltage. This is due to the overpotential generated by the HER and OER reactions, as well as the ohmic voltage drop caused by solution resistance and contact resistance, which increases the decomposition voltage and reduces the energy efficiency of hydrogen production from water electrolysis. Therefore, it is necessary to reduce the overpotential and ohmic voltage drop to improve the hydrogen production efficiency of water electrolysis. Optimizing the electrolyzer can reduce the ohmic voltage drop, but the selection and preparation of the catalyst are crucial for reducing the overpotential. Platinum group metals have excellent HER catalytic performance; however, their scarcity and high price limit their widespread application. Therefore, developing efficient and low-cost catalysts is key to achieving large-scale water electrolysis for hydrogen production.

[0004] Transition metal-based (TMCs, such as nickel, cobalt, molybdenum, and iron) catalysts are widely used in hydrogen production due to their low hydrogen evolution overpotential and low cost. Whether in the early preparation of noble metal catalysts or the research of transition metal-based catalysts, the supporting structure has always been a common goal, namely, preparing catalysts with nanoporous structures through 3D substrates or templates. Researchers have constructed nickel-copper nanotube structures through dealloying, which is beneficial for increasing the active surface area and improving hydrogen evolution catalytic activity. According to the Engel-Brewer valence bond theory, when transition metals with empty or poorly filled d orbitals, such as Mo, are alloyed with transition metals with more filled d orbitals, such as Ni, a synergistic effect can occur between the metals, improving hydrogen evolution catalytic performance. Furthermore, nickel and molybdenum are cheaper than platinum; therefore, nickel-molybdenum-based catalysts can be prepared and studied as hydrogen evolution catalysts, making their application in hydrogen production economically feasible. Summary of the Invention

[0005] This invention provides a method for synthesizing a Ni(Cu) / NiMo / NF electrocatalyst and applying it to the hydrogen evolution reaction (HER). First, selective copper etching is performed to prepare a Ni(Cu) / NF nanotube structure. Then, a NiMo alloy is deposited on this structure as a substrate. The Ni(Cu) / NF nanotube structure enhances the interfacial surface area, providing abundant nucleation sites for the growth of the NiMo alloy, while effectively mitigating its agglomeration, thereby improving the HER performance of the NiMo alloy.

[0006] The technical solution provided by this invention includes the following steps:

[0007] 1. Synthesis of catalysts

[0008] 0.15 M Na₂MoO₄·2H₂O, 0.2 M NiSO₄·6H₂O, and 0.3 M C₆O₇H₅Na₃·2H₂O were dissolved in 60 mL of deionized water and stirred with a magnetic rotor for 2 hours to form a homogeneous mixed solution. Similarly, 0.5 M NiSO₄·6H₂O, 0.075 M CuSO₄, and 0.5 M H₃BO₃ were dissolved in 60 mL of deionized water and stirred with a magnetic rotor for 2 hours to form a homogeneous electrolyte solution. Following the preparation method and deposition parameters described in the literature, a constant-pressure deposition method was used to deposit NiCu on a nickel foam substrate using an electrochemical workstation. Copper was then dissolved from the alloy using a dealloying method to form a Ni(Cu) / NF template. This Ni(Cu) / NF was used as the substrate for depositing the NiMo coating to prepare the Ni(Cu) / NiMo / NF catalyst. After the reaction was complete, the resulting product (Ni(Cu) / NiMo / NF) was washed several times with deionized water and ethanol, and then vacuum-dried at 60 °C for 12 hours.

[0009] 2. Electrochemical Measurement

[0010] All electrochemical tests in this experiment were performed at the Princeton Electrochemical Station using a standard three-electrode system. The prepared composite material could be directly used as the working electrode. A platinum sheet electrode (Pt) and mercuric oxide (Hg / HgO) served as the counter and reference electrodes, respectively. The electrolyte was a 1M KOH solution. The electrocatalytic performance of the material was evaluated using linear sweep voltammetry (LSV). The potential was converted to the reversible hydrogen electrode potential (RHE) according to the following formula.

[0011] Reversible hydrogen electrode (RHE): E(RHE) = E(Hg / HgO) + 0.0591pH + 0.098V

[0012] 3. Characterization

[0013] The morphology of the samples was characterized by scanning electron microscopy (FESEM, Gemini SEM500), and the crystal structure of the materials was characterized by field emission high-resolution transmission electron microscopy (HR-TEM, JEM-F200). The diffraction patterns of the samples were obtained by X-ray diffraction (XRD, D8ADVANCE) in the scanning angle range of 5°–80°. Attached Figure Description

[0014] Figure 1 SEM images of Ni(Cu) / NiMo / NF

[0015] Figure 2 HRTEM image of Ni(Cu) / NiMo / NF

[0016] Figure 3 XRD patterns of Ni(Cu) / NiMo / NF

[0017] Figure 4 This is an image showing the electrochemical performance of Ni(Cu) / NiMo / NF. Detailed Implementation

[0018] To better understand the present invention, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings. However, the scope of protection of the present invention is not limited to the scope shown in the embodiments.

[0019] 1) This embodiment observes the SEM images of Ni(Cu) / NiMo / NF.

[0020] The SEM images reveal that the Ni(Cu) / NiMo / NF alloy exhibits a nanotubular structure. The images show successful growth of the Ni(Cu) nanotubular structure, with a pore size ranging from 100 nm to 200 nm. While covering the Ni(Cu) nanotubular structure, the NiMo nanospheres retain the original nanotubular structure, but with a reduced pore size ranging from 80 nm to 160 nm. This nanotubular structure effectively increases the interfacial surface area, providing abundant nucleation sites for the growth of the nickel-molybdenum alloy and increasing the number of hydrogen evolution active sites.

[0021] 2) In this embodiment, HRTEM images of Ni(Cu) / NiMo / NF were observed.

[0022] Upon close observation, lattice fringes are clearly visible, with interplanar spacings of 0.204 nm and 0.176 nm, corresponding precisely to the (111) and (200) crystal planes of nickel. This is entirely consistent with the XRD results. Furthermore, no copper lattice fringes were found, indicating that most of the copper has been removed, completing the dealloying process of the nickel-copper alloy, which is also consistent with the SEM results. In addition, some amorphous regions without obvious lattice fringes were also discovered (these are marked with red circles). Since no other lattice fringes were found besides those of Ni, this paper concludes that the NiMo alloy exists in an amorphous state.

[0023] 3) In this embodiment, XRD images of Ni(Cu) / NiMo / NF were observed.

[0024] The crystal structures of Ni(Cu) / NiMo / NF and NiCu / NiMo / NF were characterized by XRD. All three samples showed three main diffraction peaks at 44°, 52°, and 76°, representing the (111), (200), and (220) crystal planes of metallic nickel (JCPDS No. 04-085), respectively. No obvious Cu phase signal was detected in Ni(Cu) / NiMo / NF, indicating that Cu was effectively removed. Apart from the nickel diffraction peak, no other diffraction peaks were observed in Ni(Cu) / NiMo / NF, indicating that the electrodeposited NiMo alloy coating is amorphous, which is consistent with the HRTEM results.

[0025] 4) This embodiment observes the electrochemical performance graph of Ni(Cu) / NiMo / NF.

[0026] As shown in the figure, at 10mA cm -2At the given current density, the overpotential of Ni(Cu) / NiMo / NF is 64 mV, while NiMo / NF has an overpotential of 126 mV at the same current density, which is higher than that of Ni(Cu) / NiMo / NF. This result clearly shows that the Ni(Cu) / NiMo / NF composite material has superior HER activity compared to NiMo / NF.

[0027] In summary, this invention prepared a Ni(Cu) / NiMo / NF composite catalyst via a simple electrodeposition method and conducted electrochemical tests on the composite catalyst in an alkaline environment. Material characterization results confirmed the successful preparation of the Ni(Cu) / NiMo / NF composite material. Electrochemical tests showed that the Ni(Cu) / NiMo / NF composite material exhibited a smaller hydrogen evolution reaction overpotential, indicating that the catalyst possesses good hydrogen evolution catalytic activity. This good hydrogen evolution activity is attributed to the increased specific surface area due to the nanotube structure, which mitigates the agglomeration of the NiMo alloy and facilitates the exposure of more active sites.

Claims

1. Preparation process of a Ni(Cu) / NiMo / NF composite hydrogen evolution electrocatalyst: Ni(Cu) / NiMo / NF catalyst was successfully synthesized by electrodeposition using nickel foam (NF) as substrate. First, Ni(Cu) / NF nanotube structure was prepared, and then NiMo alloy was deposited on this substrate in a three-electrode system.

2. The preparation process according to claim 1, characterized in that: Weigh out 0.15M Na2MoO4 2H2O, 0.2M NiSO4 6H2O and 0.3M C6O7H5Na3 2H2O, and dissolve them in deionized water.

3. The preparation process according to claim 1, characterized in that: The deposition time of the NiMo alloy was 600 s.

4. The preparation process according to claim 1, characterized in that: The deposition current density of the NiMo alloy is 0.13A.

5. The three-electrode system according to claim 1, comprising nickel foam as the working electrode, platinum sheet as the counter electrode, and Ag / AgCl electrode as the reference electrode.

6. The electrochemical performance testing of the hydrogen evolution electrocatalyst according to claim 1 includes testing the voltammetric curve (LSV) using an electrochemical workstation.

7. Characterization tests performed on the structure according to claim 1, including SEM testing, HRTEM testing, and XRD testing.

8. The characterization test result according to claim 7, characterized in that: Nanotube structures can increase the contact area between the catalyst and the solution.

9. The test method according to claim 6, in 1M KOH, tests the electrocatalytic hydrogen evolution activity of the catalyst.

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