Proton-Coupled Electron Transfer in the Catalytic Hydrogenation of Hydroxyacetone: A pH-Induced Switch from Potential Pinning to Kinetic Coupling

equilibrium─to a "kinetic coupled" mixed-potential regime at high pH, in which competing reactions jointly influence the catalyst potential. Both regimes are governed by the same mixed-potential framework, and the transition reflects the relative proportion of the HA reduction current to the HOR/HER exchange current. These results reflect the intrinsic complexity at the metal-aqueous interfaces and call for a more complete understanding of kinetic coupling when mixed-potential concepts are used to describe thermocatalytic reactions.