Reactivation of nickel cathodes by dissolved vanadium species during hydrogen evolution in alkaline media

Abstract

Abstract Nickel undergoes significant deactivation as a cathode during alkaline water electrolysis in 8 mol/l KOH at 70 °C. Addition of dissolved V 2 O 5 was found to result in reactivation of the nickel cathode and formation of a vanadium-bearing deposit. Tafel measurements at different electrode states indicated no change in the Tafel parameters for the fresh (or initial) and vanadium-modified states. Furthermore, vanadium addition did not appear to enhance the electrocatalytic activity beyond that for fresh nickel. A rotating ring-disk electrode was used for detection of solution intermediates of the hydrogen evolution reaction in KOH with and without dissolved V 2 O 5 . Based on cyclic voltammograms for the ring (with a hydrogen-evolving Ni disk), no solution intermediates were detected before or after vanadium addition. The action of vanadium was through a solid surface species as opposed to a homogeneous species in solution. A mercury electrode was then used to shift hydrogen evolution cathodically, revealing the potential region masked by large hydrogen currents on a nickel electrode. Cyclic voltammetry on mercury in KOH with dissolved V 2 O 5 showed a cathodic peak that was absent in voltammograms for blank KOH. Therefore, formation of the deposit occurred at a potential coincident with that of hydrogen evolution on nickel.