Implications of the M-OO∙∙OO-M recombination mechanism on materials screening and the oxygen evolution reaction

Abstract

Identification of active electrocatalysts for the oxygen evolution reaction (OER), corresponding to the bottleneck in electrolyzers to produce gaseous hydrogen as energy vector, by electronic structure calculations relies on the assumption of the mononuclear mechanism, comprising the *OH, *O, and *OOH intermediates. This mechanistic description is thermodynamically hampered by a scaling relation between the *OH and *OOH adsorbates, which may serve as an explanation why OER catalysts commonly require large overpotentials to reach sufficient current densities. Recently, an alternate OER pathway was proposed that, in contrast to the mononuclear description, consists of the formation of two adjacent *OO adsorbates, and gaseous oxygen is produced by chemical recombination of the neighboring *OO intermediates. In the present manuscript, a data-driven model based on a dedicated assessment of the elementary reaction steps is deduced, which enables evaluating the mononuclear and *OO pathways by the same set of parameters. Potential-dependent volcano plots are constructed to comprehend the energetics of the competing mechanisms. It is demonstrated that the alternate OER pathway consisting of the *OO∙∙*OO recombination step may excel the mononuclear description at overpotentials corresponding to typical OER conditions. Consequently, it is suggested that future studies, aiming at the identification of OER materials, may not omit the *OO∙∙*OO recombination mechanism when using concepts of materials screening in a heuristic fashion or multiscale modeling.