Effect of thin films coated steel membrane on electrochemical hydrogen permeation measurement: Palladium vs. nickel

The effects of thin films plated on steel membranes on the electrochemical hydrogen permeation behaviors were examined using the hydrogen permeation transients of two coating materials, Pd and Ni, with varying thicknesses. The complete Ni film plated on a steel membrane can be preferable over a complete Pd film in that there is no dependence on the film thickness for measuring the hydrogen oxidation rates in anodic side of the permeation experiment. By contrast, the increase in thickness of the Pd film resulted in much slower oxidation kinetics, which may have resulted from the slower diffusion of atomic hydrogen through the film by the hydrogen trapping at any lattice defects in the film, delaying hydrogen transport. Nevertheless, the use of Ni film has a drawback in that the time required to reach a background current density was longer due presumably to its lower electrochemical stability under a high anodic potential.