Evaluation of terminal composition of palladium-silver hydrides in plateau region by electronic structure calculations

The electronic structures of palladium, palladium-silver alloys (Pd-Ag) and their hydrides were calculated to evaluate the terminal composition in the plateau region in the pressure-composition isotherm. The electronic structures were calculated by the Korringa-Kohn-Rostoker coherent potential approximation (KKR-CPA), MACHIKANEYAMA 2002 developed by Akai. The Fermi level of palladium at various hydrogen contents moved to the edge of the d-band with increasing the hydrogen content and the Fermi level of PdH_0.6 reached the edge of the d-band. This hydrogen composition, [H]/[Pd] = 0.6, agreed well with the terminal composition in the plateau region. The Fermi level of Pd-Ag was similarly lifted up to the edge of the d-band with increasing the hydrogen content. The terminal compositions in isotherms of Pd-Ag alloys were estimated from the Fermi level position and the density of states at the Fermi level. The estimated compositions agreed with those experimentally obtained. Therefore, the terminal composition in the plateau region in the pressure-composition isotherms of Pd-Ag alloys could be evaluated by using with the KKR-CPA method.