enhancing h 2 evolution by optimizing h adatom combination and desorption over pd nanocatalyst
catalytic hydrogen evolution plays a significant role in hydrogen production and utilization. the combinative desorption of hydrogen (tafel step, i.e., 2h * →h 2 ) from metal catalysts has been extensively reported as the rate-determining step. however, a full atomic-level understanding on how the h-metal binding strength affects on the elementary tafel steps is still lacking. in the current study, h 2 evolution over pd catalysts was investigated by combining theoretical and experimental techniques. density functional theory calculations revealed that h 2 evolution was governed by either the combination barriers of 2h * or the desorption barriers of molecular h 2 from the surface of the palladium catalyst, which was strongly dependent on the size of pd particles: the rate-limiting step of h 2 evolution for large nanoparticles (nps) is diffusive combination of h * across the metal surface, while both 2h * combination and h2 desorption are difficult for subnanometer-sized pd clusters. by tuning the combined effect of h adatom combination and h 2 desorption, a highly performance pd catalyst for hydrogen evolution both for temperature-programmed palladium hydride decomposition and catalytic dehydrogenation of formate was designed and synthesized. tio 2 -supported pd nps that were 202nm in size exhibited excellent activity for formate dehydrogenation with an tof value that was as high as 218402h 611 at 29802k.