A model of hydrogen absorption by metals

Abstract

The influence of the electron spectrum of transition metals on the hydrogen absorption process is considered. An absorption model is proposed where electrons, followed by protons, from adsorbed molecules or atoms of hydrogen transit into the metal. In terms of this model, the driving force of the absorption process ΔX is equal to the difference of the total electron energies in a hydrogen atom and in a metal at the Fermi level: ΔX = E _H − (E _F + A _work). The equilibrium state in the absorption process corresponds to the equation 13.53 = E _F + A _work, which makes it possible to find the Fermi energy of transition metals and the valence of hydrogen absorbing metals, to define the molecular formula of hydrides, and to calculate the maximum hydrogen content in hydride phases. The hydrogen content in the composition of hydrides is shown to decrease in approaching the middle of the transition-metal rows. In groups, on the contrary, the hydrogen content grows as the atomic weight of metals increases. A good agreement of calculated and experimental compositions of hydride phases is found for the transition metals whose d band is less than half-filled with electrons.