Co-modification of Ni-based type Raney electrodeposits for hydrogen evolution reaction in alkaline media

Abstract

[EN] In this work, high performance Ni and Ni-Co porous electrodes are prepared using the Raney strategy by galvanic co-deposition for hydrogen evolution reaction (HER) in alkaline solution (KOH 30 wt.%). The incorporation of Co into the Raney Ni matrix causes a surface morphology modification, from cracked to "cauliflower-like", which dominates the superficial structure of the Co-richest obtained material. The evaluation of these electrodes as H-2-evolving cathodes is done through pseudo-steady-state polarization curves and electrochemical impedance spectroscopy (EIS). Ni Raney electrode (without Co) manifests the highest apparent catalytic activity per unit of geometric surface area, which is attributed to the higher surface roughness factor, determined by EIS. HER on the investigated electrocatalysts proceeds via the Volmer-Heyrovsky mechanism, with Heyrovsky as the rate-determining step (rds). From the kinetic parameters it is derived that Co presence, in a composition range of 5-22 at.%, increases the intrinsic catalytic activity of the developed cathodes per unit of true surface area, as a consequence of the synergism between the properties of Ni and of Co. Nevertheless, this improvement does not compensate the lower surface roughness factor, originated by the surface morphology modification as the Co content increases, reporting lower apparent catalytic activities. (C) 2013 Elsevier B.V. All rights reserved.