The Nature of Hydrogen Adsorption on Platinum in the Aqueous Phase.

The thermodynamic state of H adsorbed on Pt in the aqueous phase was determined by kinetic analysis of H reacting with D O to HDO, HD, and D , and by DFT-based ab initio molecular dynamics simulations of H adsorption on Pt(111), Pt(110), and Pt nanoparticles. Dissociative adsorption of H on Pt is significantly weakened in the aqueous phase compared to adsorption at gas-solid interfaces. Water destabilizes the adsorbed H atoms, decreasing the heat of adsorption by 19-22 kJ  while inducing an additional entropy loss of 50-70 J   K . Upon dissociative adsorption of H , the average distance of water from the Pt surface increases and the liquid adopts a structure that is more ordered than before close to the Pt surface, which limits the translation mobility of the adsorbed H atoms. The presence of hydrated hydronium ions next to the Pt surface further lowers the H-Pt bond strength.