Electrocatalysis of hydrogen evolution by transition metal complexes

Voltammetric reduction of monothiocyanate complexes of the iron group metal s is accompanied by catalytic evolution of hydrogen in two potential region s. Around -1.3 V vs SCE, hydrogen is evolved at the surface of the electrod eposited metal, around -1.6 V at the surface of mercury. The catalyst is th e protonated reduced, zero-valent form of the complex which has limited sta bility. Minor differences in behaviour of the complexes of the three metals are due to different values of their complexation constant.