Electrocatalytic behavior of non-equilibrium b.c.c. nickel

Abstract

We report on the electrocatalytic activity for the hydrogen evolution reaction (HER) on non-equilibrium b.c.c. nickel electrodes in a concentrated alkaline solution (30 wt.% NaOH). These electrodes were prepared by mechanical alloying a mixture of nickel and aluminum powders, followed by a leaching treatment. Transmission electron microscopy observations and X-ray diffraction patterns show the transformation of the pure elemental powders to a nanocrystalline phase with a B2-type structure. After being treated with 20 wt.% KOH at 70 °C, nearly all the aluminum atoms were removed and a porous b.c.c. Raney nickel was obtained. It was found that the thermodynamic potential of Ni/Ni 2+ was 23 mV lower on the metastable b.c.c. nickel than that on the f.c.c. nickel electrode. The analysis of the HER kinetic parameters indicates a lower activity of the b.c.c. nickel, when compared with that of the f.c.c. Raney nickel catalyst. Both b.c.c. and f.c.c. nickel catalysts show a Tafel slope of about 120 mV decade −1, but a lower roughness factor of the b.c.c. nickel surface was deduced from the coulometric measurements.