The Nature of Hydrogen Adsorption on Platinum in the Aqueous Phase

The thermodynamic state of H 2 adsorbed on Pt in the aqueous phase was determined by kinetic analysis of H 2 reacting with D 2 O to HDO, HD, and D 2 , and by DFT‐based ab initio molecular dynamics simulations of H 2 adsorption on Pt(111), Pt(110), and Pt nanoparticles. Dissociative adsorption of H 2 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  m o l H 2- 1while inducing an additional entropy loss of 50–70 J  m o l H 2- 1 K −1 . Upon dissociative adsorption of H 2 , 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.