Surface phenomena in hydrogen absorption kinetics of metals and intermetallic compounds

Abstract

Oxide layers on metal surfaces impede or prevent hydrogen absorption at temperatures below 400 °C. Passivation can be caused by slow dissociation of hydrogen molecules on the surface, slow transfer of chemisorbed hydrogen atoms into the oxide or slow permeation of hydrogen atoms through the oxide layer. Experiments on the hydrogen absorption kinetics of film samples with known oxygen precoverage yield direct information on reaction models if relevant results of other techniques are taken into account together with inherent thermochemical and atomistic limits. Typical examples are discussed to elucidate this approach for the investigation of complex reaction mechanisms in hydrogen absorption kinetics at room temperature. They indicate that hydrogen dissociation on the surface is a very important partial step in the reaction and plays a substantial role in activation and passivation of hydrogen absorption reactions at room temperature.