Surface hydrogen processes studied by isotope exchange reactions on a Pd membrane cathode

Abstract

The exchange reaction of hydrogen on the surface was studied using a Pd membrane cathode where deuterium was supplied from the subsurface. The current density of H formation j H, current density of D formation j D and the extent of equilibration x( HD) x( HD) eq were determined from the isotope distributions of gaseous hydrogen. These represent the ease of H formation from the solution by charge transfer, that of D formation from the subsurface and that of diffusion/shuffle at the surface respectively. In sulphuric acid, relatively high values of j H and j D were observed and x( HD) x( HD) eq was unity. By assuming that these values represent those for an inhibition-free electrode surface, the parameters for alkaline solutions were measured. All three parameters were smallest in LiOH. The decrease in j D was particularly notable. The suppression of these parameters suggests the adsorption of alkali metal cations on the surface. Their poisoning effects are discussed in relation to the hydrogen processes in the hydrogen evolution reaction.