Effect of the structure and morphology of Ni-based porous deposits on their electrocatalytic activity towards hydrogen evolution reaction

Porous nickel and nickel-cobalt alloy deposits were obtained by electrodeposition on a dynamic hydrogen bubble template. Deposition was carried out from chloride electrolytes in a galvanostatic mode at a current density of 0.3 A/cm². The porosity of the obtained deposits is associated with the macro- and micropores. It was found that the nickel and nickel-cobalt alloy deposits feature by different porous layer structures. In case of nickel, a typical foam structure is formed, while the Ni–Co alloy deposit morphology is more like loose (powder) metals. The total porosity of the obtained structures calculated based on experimental data decreased with the deposit thickness: from 0.4 to 0.1 for nickel foams, and from 0.9 to 0.8 for the Ni–Co deposit. It was shown that the dependences of the macropore number and the fraction of the surface occupied by them can be approximated by lognormal distribution. The agreement between the experimental values and values calculated by approximating equations indicates the stochastic nature of the macropore system formation. The catalytic properties of the obtained porous deposits toward the hydrogen evolution reaction in alkali were investigated. It was found that the decrease in the hydrogen evolution potential in comparison with a smooth electrode reaches 370 mV for nickel foams, and 440 mV for porous Ni–Co alloy deposits. However, the high porosity of the Ni–Co alloy caused poor adhesion of the deposit to the substrate; therefore, the porous Ni–Co deposit cannot be used without further strengthening. The dependences of the depolarization value during hydrogen evolution on the average diameter of pores, their number, and the macropore fraction were analyzed. Optimal properties of foams that reduce the potential of hydrogen evolution in alkali are as follows: pore diameters from 30 to 50 μm and their quantity from 50 to 100 pcs/mm².

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