Catalytic activity of noble metals promoting hydrogen uptake

The engineering of pure and metal alloy catalysts for hydrogen absorption is needed to improve the kinetics of hydrogen-related devices. We introduce a new route to search for alloys that can yield superior catalytic behavior for hydrogen absorption, using an optical technique to measure the catalytic activity for hydrogen sorption of thin films. The catalytic activity of the noble metals Pd, Ni, Cu, Ag, Pt, and Au is studied as a function of hydrogen pressure and temperature. The rate-limiting step is identified by the pressure dependence and the normal isotope effect for hydrogen absorption. The measured rates and activation energies are correlated to such physical properties as activation barrier for dissociation and heat of solution. The observed compensation effect is explained in the framework of interplay between surface and bulk processes. From the experimentally derived model, a guiding principle for the search for catalysts promoting hydrogen absorption is drawn.