The Catalyst Operating Potential as an Emergent Interfacial Descriptor in Heterogeneous Catalysis

Abstract

The electrical potential of a heterogeneous catalyst, measured as the open-circuit potential (OCP) or the catalyst operating potential (Ecat), provides an integrated experimental readout of its dynamically established interfacial state. However, relating this macroscopic observable to individual molecular processes remains challenging because multiple contributions, including adsorption, charge transfer, interfacial dipole formation, and simultaneous oxidation and reduction reactions, can influence the measured potential. In this contribution, a physicochemical framework for interpreting Ecat is demonstrated as an emergent property arising from coupled non-Faradaic and Faradaic processes at interfaces between catalyst and reaction medium. We first distinguish changes in the operating potential originating from competitive adsorption and adsorbate-induced dipoles from those generated by net interfacial electron transfer. We then discuss how concurrent redox reactions establish mixed potentials and how the resulting Ecat reflects reaction rates, surface coverages, and charge-transfer kinetics under catalytic conditions. Particular attention is given to the mechanistic information that can, and cannot, be extracted from steady-state potentials, potential transients, and controlled electrochemical perturbations. Viewing Ecat as a measurable but system-level interfacial descriptor provides a unified basis for investigating complex heterogeneous catalytic reactions and for connecting thermal, electrochemical, and hybrid catalytic systems.