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 PtxCoy nanoparticles and demonstrate that under certain potentials PtxCoy alloys are more active than Pt. However, the ECH activity does not correlate directly with the hydrogen adsorption energy (ΔGH), unlike what we find for HER. Combined electrochemical measurements, density functional theory (DFT) calculations, and kinetic modeling reveal that ΔGH 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 PtxCoy 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 PtxCoy alloys as a function of applied potential and Co composition.