A consistent description of the hydrogen permeation through metal membrane based on hydrogen chemical potential proposed has been explained in detail. The hydrogen flux is proportional to the PCT factor, f PCT, consistently, which reflects the shape of the pressure-composition-isotherm (PCT curve) of the material. In addition, in view of the PCT factor, f PCT, and the ductile-to-brittle transition hydrogen concentration, DBTC, a concept for alloy design with high hydrogen permeability and strong resistance to hydrogen embrittlement has been proposed. In this concept, it is important to design alloy composition with appropriate PCT curve under the given pressure and temperature condition. As an example, V–9 mol% Al alloy has been designed, which exhibits high hydrogen flux without brittle fracture under given condition. Thus, the new consistent description is useful not only for the understanding of the hydrogen permeation property but also for the alloy design.
