The kinetics of the hydrogen evolution reaction on LnNi2Ge2 (Ln = lanthanide) electrodes in alkaline solution

Abstract

The kinetics of hydrogen evolution reaction on the intermetallic compounds LnNi2Ge2 (Ln = Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Lu) in 1 M KOH solution were studied using polarization measurements and electrochemical impedance spectroscopy. The Tafel constants vary in the intervals: а = 0.475–0.52 V; b = 0.070–0.078 V. The cathodic process was shown to be the combination of the hydrogen evolution reaction and hydrogen absorption reaction; the reaction of H2 evolution proceeds through the Volmer – Heyrovsky mechanism with the rate-determining Heyrovsky reaction. The values of the rate constants of the elementary steps were estimated. The dependences of the rate constants on the atomic number of Ln pass through extremums, these are assumed to correspond to a maximal metal-hydrogen bond strength.