Bridging mixed potential theory and electrochemical promotion of thermal catalysis during hydroquinone-benzoquinone redox reactions

Electrochemical tools are garnering increasing attention due to their capabilities in both the potential investigation and electrochemical promotion of (thermal) catalysis (EPOC). In this study, we use the thermocatalytic oxidation/hydrogenation of the hydroquinone (HQ)/benzoquinone (BQ) redox couple over Pt catalysts as a model for electrochemical study. We validate the mixed potential theory (MPT) for predicting the thermocatalytic rate by monitoring the working potential of platinum on carbon (Pt/C) electrodes in this system, where two independent electrochemical half-reactions occur over different active sites (Pt for oxygen reduction and C for hydroquinone oxidation). When using platinized Pt foil as the catalyst, the absence of carbon support results in high coverage of adsorbed HQ on Pt, causing a deviation from the mixed potential theory prediction. Furthermore, a promotional effect is observed during thermal HQ oxidation by electrochemically limiting HQ coverage and facilitating oxygen adsorption. This study demonstrates that mixed potential theory can be used to determine whether electrochemical promotion of thermal catalysis is possible, thereby connecting these two similar but distinct phenomena.