In this paper, the foam substrate-Ni-graphene composite electrode was prepared by depositing graphene as the second phase particle on the foam substrate. The concentration gradient of graphene was 0 mg·L–1, 50 mg·L–1, 10 mg·L–1, 150 mg·L–1, 200 mg·L–1, and 250 mg·L–1. It was expected to change the surface state of the composite material with the three-dimensional porous structure of the foam substrate and the ultra-high specific surface area of the graphene, so as to obtain the electrocatalytic hydrogen evolution performance of the high coating. After graphene was embedded as the second phase coating, the surface morphology of the composite coating was obviously changed, and its existence form was granular. At a magnification of 2 000, the coating surface had a particle diameter of about 1 μm. With the increase of the concentration of graphene, the particle distribution density gradually increased first and then decreased, and the particle size became larger. The particle accumulation was the highest at the graphene concentration of 150 mg·L–1. Combined with the summary table of EDS composition analysis, it was found that with the increase of graphene concentration, the carbon content in the coating solution increased, and the C content in the composite coating gradually increased, with the highest concentration of 200 mg·L–1, and then 250 mg/L was slightly reduced. At the same time, with the increase of graphene concentration, the Ni content gradually decreased, and the Fe content was negligible. It showed that the composite coating could cover the substrate surface well and be thicker. The polarization curve and Tafel slope curve indicated that the reaction pathway of hydrogen evolution reaction (HER) with composite coating was Volmer-Heyrovsky, and the electrocatalytic adsorption step was the reaction control step. The coating prepared at 150 mg·L–1 had the lowest Tafel slope, which was 105.3 mV·dec–1. And the hydrogen evolution potential of composite coating with graphene was lower than that of coatings without graphene. At a current density of 10 mA·cm–2, the coatings prepared at 150 mg·L–1 had the lowest hydrogen evolution overpotential. AC impedance map showed that the arc resistance diameter of the Ni base graphene composite coating was less than that of the graphene-free Ni coating. Combined with the fitting data and relevant theories, the electrochemical surface area (ESCA) of the coatings joined with graphene was higher than that without graphene, and graphene increased the ESCA on the coating surface, thus improving the electrocatalytic hydrogen evolution activity of the coated electrode. In addition, the effects of coating thickness and substrate morphology on electrode electrocatalytic hydrogen evolution performance were explored. And it was found that the electrocatalytic hydrogen precipitation activity of different thickness composite coatings were basically the same. The electrocatalytic hydrogen evolution activity of foam substrate coating was significantly better than that of plate substrate coating. The timing potential test of the foam substrate-Ni-Graphene composite coating electrode at 100 mA·cm–2 constant current density showed that the initial potential of the coating electrode was about –1.48 V (vs. SCE), and the potential dropped to about –1.50 V in the first 1 000 s, the fluctuation was slightly obvious, not stable in the early stage. The fluctuation of the potential in the rest of the time was not large. The change value was only 0.01 V, and the curve was flat. It showed that the electrode electrolysis had good water stability. In conclusion, the introduction of graphene and three-dimensional porous structure of the foam substrate increase the specific surface area of the composite coating, which is the key to the good electrocatalytic hydrogen evolution activity of the electrode. © 2024 Chongqing Wujiu Periodicals Press. All rights reserved.
