PNNL

Abstract

H2 adsorption properties on Pt in aqueous phase was determined by a reaction kinetic measurement of gas H2 reacting with liquid D2O into liquid HDO, gas HD and D2, and a DFT based ab inito molecular dynamic simulation of H2 adsorption on Pt (111) in the presence and absence of water. Both approaches show that the H2 adsorption on Pt in water is much weaker than that in the gas phase. The presence of interfacial water destabilizes the adsorbed H on Pt via decreasing the adsorption heat (hydrogen binding energy) by 19 - 22 kJ·molH2-1 and inducing an extra entropy loss of 50 - 70 J·mol H2-1·K-1. Upon H adsorption on Pt, the closest water layer near Pt surface shifts to a larger distance from the surface and re-orientates to a more ordered structure; in turn, the water layer limits the translation mobility of adsorbed H on Pt. The influence of interfacial water property on H2 adsorption is also reflected by the decrease of adsorption heat with the decrease of local pH provided by the support. Research was funded by the Laboratory Directed Research and Development program at Pacific Northwest National Laboratory.