Anomalous kinetic characteristics of hydrogen transport through Pd–Cu membranes modified by pentatwinned flower-shaped palladium nanocrystallites with high-index facets

A method has been developed that has allowed a fivefold symmetry to be achieved for the first time in palladium nanocrystallites grown on the Pd–Cu film surface. Modification of the Pd–40% Cu membrane by pentatwinned (branched) palladium nanocrystallites with high-index facets ensured ultrahigh permeability for hydrogen reaching up to 10.1 mmol s$^{-1}$ m$^{-2}$ at 100$^\circ$C. This level (comparable with the permeability of high-temperature analogs) is anomalous, since the expected values must be more than two times lower than obtained. This result is explained by the acceleration of dissociative adsorption and recombinative desorption due to the ultrahigh activity of pentatwinned particles in reactions involving hydrogen, which is confirmed by data on the selectivity of the modified membranes.