Absorption of electrolytic hydrogen and deuterium by Pd: the effect of cyanide adsorption

Abstract

The absorption of hydrogen and deuterium in Pd, at potentials positive to hydrogen evolution, was studied by cyclic voltammetry. Results in 0.1 M NaOH, LiOH and LiOD were compared. In LiOH hydrogen ingress into Pd is faster than in NaOH. However, hydrogen egress is inhibited. In LiOD all processes are slower than those in LiOH. Addition of 10 −3 M CN − to these electrolytes resulted in several major effects. The formation of the oxide and the ingress of hydrogen and deuterium were inhibited. Egress of hydrogen and deuterium from Pd was essentially completely inhibited until the adsorbed cyanide was displaced by oxide at positive potentials. Hydrogen permeation measurements through Pd membranes were made in 0.1 M NaOH and in 0.1 M NaOH + 10 −3 M NaCN. Cyanide adsorption decreased the permeation rate and had large effects on the permeation decay transients. The permeation transients show evidence of either trapping of hydrogen or a concentration dependence of the diffusivity.