Smooth Raney nickel coatings for cathodic hydrogen evolution by chemical gas phase reaction of nickel electrode surfaces

Two different processes to prepare smooth* Raney nickel coatings are investigated. Both are based on preparing a precursor coating by gas-phase reaction of nickel at temperatures of around 400°C. Sherardizing of nickel electrodes, that is, reaction with zinc vapour, leads to formation of the γ-phase of Ni–Zn alloy with the approximate composition of 75 to 85wt% Zn (balance: Ni), and gas-phase sulfidizing of nickel electrodes with hydrogen sulfide produces nickel sulfide coatings composed of the phases Ni3S2, αNi7S6 and αNiS. Both types of coating are transformed in situ, the first by caustic leaching and the second during cathodic hydrogen evolution by relatively slow cathodic reduction into smooth, almost closed nanoporous Raney nickel coatings. The comparison of the catalysts from the two different methods reveals the superiority of the second. The hydrogen evolution overpotential is lowest and, during more than 3000h of continuous operation, the catalyst does not deteriorate. Electrodeposited nickel sulfide gives a poorer and less stable RN catalyst than gas phase sulfidized nickel sulfide.