Influence of Surface Treatment on the Kinetics of the Hydrogen Evolution Reaction on Bulk and Porous Nickel Materials

Abstract

The hydrogen evolution reaction (HER) occurring at porous Ni foam (Incofoam) and bulk polycrystalline Ni electrodes in 0.50 M aqueous KOH solution is studied at low overpotentials (down to − 0.35 V vs. RHE) in the 277 ≤ T ≤ 308 K range. The experiments are conducted using “as received” and chemically etched Ni foams as well as polished and chemically etched polycrystalline Ni rods for comparative analysis. The chemical etching removes the oxide/hydroxide layer from the material’s surface and modifies its morphology. Scanning electron microscopy and X-ray photoelectron spectroscopy are employed to examine the surface morphology and the surface chemical composition of the Ni foam prior to and after the chemical etching. Cyclic voltammetry and steady-state Tafel polarization measurements are conducted to analyze the electrochemical behavior of the Ni materials. It is found that the electrocatalytic activity of Ni materials towards the HER depends on the material’s pre-treatment. The electrodes subjected to the chemical etching exhibit higher values of the Tafel slope and the exchange current density as compared to non-etched surfaces. The most pronounced effect is observed for the etched Ni foam for which the pre-treatment also affects the activation energy. This behavior is attributed to the removal of surface oxides/hydroxides and to surface roughening brought about by the “chemical etching.” Together, these results reveal that the mechanism of the HER depends on the morphology and chemical state of the Ni material. In addition, it shows that suitable surface treatment can decrease the overpotential required to achieve a desired reaction rate (current density).