Electrocatalysis beyond the reversible hydrogen electrode

The reversible and computational hydrogen electrodes have proven invaluable as reference electrodes in aqueous electrocatalysis, allowing an evaluation of the combined chemical potential of the proton–electron pair in experiments and computations. By construction, they cancel the pH dependence in most capacitive processes. However, for electrocatalysis, which is dominated by faradaic processes, this characteristic is rarely observed.

In this short review, we discuss the origins of deviations from the Nernstian behavior in capacitive and faradaic processes, their manifestation in experimental observables, and attempts to incorporate them in simulations. On this basis, we discuss how deviations from Nernstian behavior can be exploited in mechanistic analysis and highlight the use of electrostatic descriptors in computational screening to account for non-Nernstian effects explicitly.