Molecular hydrogen diffusion or hydride component of overpotential at “black” noble metal electrodes

Abstract

Comparison of overpotential parameters at “black” cathodes of platinum, palladium and nickel indicates that the slowest intermediate step in the cathodic discharge of hydrogen at highly catalytically active surfaces at low current densities can be the diffusion of molecular hydrogen away from the electrode out through the Brunner-Nernst diffusion layer. Under these conditions a complementary major component of the total apparent overpotential reflects the hydrogen content of the electrode in steady-state equilibrium with the concentration of hydrogen molecules at the inner (interfacial) boundary of the Brunner-Nernst layer. It is proposed that this component of overpotential should be designated ηH₂.