Abstract
We present a method for quantifying the kinetic current of the hydrogen oxidation reaction (HOR) on Pt in acidic media using the adsorption and activation free energies as the intrinsic kinetic parameters. Our approach involves deriving the HOR intermediate's adsorption isotherm based on the same dual-pathway reaction model as for the kinetic equation. Coupled with density functional theory calculations of the coverage- and site-dependent hydrogen dissociation free energies, we analyzed the adsorption isotherms for H on atop (HAtop) sites and in hollow/bridge (HH/B) sites obtained respectively from infrared spectroscopic and electrochemical measurements. Although the hydrogen dissociative adsorption energy is not site-sensitive on Pt, HAtop has an order of magnitude lower coverage and higher activity than HH/B. We attributed this distinction to their different entropies; HH/B is less accessible to water than HAtop, and the formation of a hydrogen bond is essential in the oxidative generation of H3O+. Usin...
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