Calorimetric studies of the chemisorption and desorption of hydrogen on nickel films under ultra high vacuum conditions

Abstract

Heats of chemisorption and desorption of hydrogen on evaporated nickel films have been determined at 273°K with an improved Beeck-type calorimeter. The heats of chemisorption are significantly lower than those previously reported in the literature. They are independent of the coverage up to nearly a complete monolayer. When the adsorption became reversible, differential heats of desorption could also be measured. The change of the electric resistance of the nickel films with increasing hydrogen coverage was simultaneously measured. The resistance passes through a maximum. The differential heat of chemisorption is not altered markedly at this coverage. Repeated adsorption and desorption processes at high coverages indicate a further irreversible sorption of hydrogen by the nickel films.