Abstract
Hydrogen permeation and diffusivity were studied electrochemically at 25°C for iron, nickel and palladium. Permeability, diffusivity and solubility were calculated from these data. The mechanism of hydrogen evolution and entry into iron and nickel involves coupled discharge-chemical desorption. The absorption efficiency of hydrogen in palladium is close to 100% at charging current densities within the Tafel region. The mechanism of hydrogen evolution and entry into palladium involves a rate-determining step of proton discharge, followed by immediate absorption of the adsorbed hydrogen atom intermediate into the palladium lattice. Gas phase and electrochemical permeation measurements are not directly comparable because gas phase permeation is proportional to (fugacity) 1/2, whereas cathodic charge permeation is proportional to (current) 1/2 for iron and nickel, and proportional to current for palladium.
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