Design of sustainable V-based hydrogen separation membranes based on grain boundary segregation

• Inter-diffusion between V and Pd layers in V-based membranes is examined.
• Dominant mechanism of the inter-diffusion is the grain boundary diffusion.
• Grain boundary segregation is an efficient way to inhibit the inter-diffusion.
• Effect of Y is discussed from the view point of the grain boundary segregation.
• Pre-annealing process can maximize the diffusion barrier effect.

Inter-diffusion between vanadium and palladium coating layers in vanadium-based hydrogen separation membranes is investigated by using a computational approach based on first-principles calculations and semi-empirical atomistic simulations, paying attention to the surface stability and the prevention of the degradation of hydrogen permeability. It is found that the governing mechanism of the inter-diffusion is the grain boundary diffusion, and therefore a diffusion barrier based on the grain boundary segregation of impurities can be an efficient way to inhibit the inter-diffusion that causes the degradation. An interesting aspect in previous experimental works that showed a good resistance to the inter-diffusion by an addition of a trace amount of yttrium is discussed from the view point of the grain boundary segregation. An experiment that proves the validity of the present alloy design scheme (inhibition of inter-diffusion using grain boundary segregation) is carried out, and a process to maximize the sustainability of the membrane is also proposed.