Electrocatalytic hydrogenation of phenol on platinum-cobalt alloys

Here we investigate platinum-cobalt alloys to determine catalyst properties that control electrocatalytic hydrogenation (ECH) of phenol and the competing hydrogen evolution reaction (HER). We perform ECH of phenol on Pt x Co y nanoparticles and demonstrate that under certain potentials Pt x Co y alloys are more active than Pt. However, the ECH activity does not correlate directly with the hydrogen adsorption energy (Δ G H ), unlike what we find for HER. Combined electrochemical measurements, density functional theory (DFT) calculations, and kinetic modeling reveal that Δ G H is an insufficient descriptor for phenol ECH because the activation enthalpies for hydrogenation elementary steps scale more closely with their reaction enthalpies, which are more endothermic on Pt x Co y compared to Pt. Through DFT modeling we show the relationship between hydrogenation activation enthalpies and Co content depends strongly on whether the catalyst surface is a Pt skin or contains both Pt and Co atoms. By incorporating the computed activation enthalpies into a kinetic model, we describe the qualitative trends in experimental ECH kinetics of phenol on Pt x Co y alloys as a function of applied potential and Co composition.