Importance of the Walden Inversion for the Activity Volcano Plot of Oxygen Evolution

Abstract

Since the birth of the computational hydrogen electrode approach, it is considered that activity trends of electrocatalysts in a homologous series can be quantified by the construction of volcano plots. This method aims to steer materials discovery by the identification of catalysts with an improved reaction kinetics, though evaluated by means of thermodynamic descriptors. The conventional approach for the volcano plot of the oxygen evolution reaction (OER) relies on the assumption of the mononuclear mechanism, comprising the *OH, *O, and *OOH intermediates. In the present manuscript, two new mechanistic pathways, comprising the idea of the Walden inversion in that bond‐breaking and bond‐making occurs simultaneously, are factored into a potential‐dependent OER activity volcano plot. Surprisingly, it turns out that the Walden inversion plays an important role since the activity volcano is governed by mechanistic pathways comprising Walden steps rather than by the traditionally assumed reaction mechanisms under typical OER conditions.

Four Generations of Volcano Plots for the Oxygen Evolution Reaction: Beyond Proton-Coupled Electron Transfer Steps?

“…Figure 4 d). 4 This view is further substantiated by a recent computational study on the oxygen reduction of a Fe–N–C catalyst where a Walden step was identified as the RDS under reaction conditions. 45 In summary, the fourth generation of volcano plots has improved their mechanistic description by moving beyond a single pathway and including the possibility of concurrent adsorption–desorption processes in the realm of Walden-type steps in the analysis.…”

“…Figure c), and volcano plots by the descriptor G max ( U ) underpin their relevance to the description of the oxygen electrocatalysis: particularly highly active OER catalysts may follow a Walden pathway rather than the conventional description of sequential desorption and adsorption steps (cf. Figure d) . This view is further substantiated by a recent computational study on the oxygen reduction of a Fe–N–C catalyst where a Walden step was identified as the RDS under reaction conditions .…”

“…Particularly highly active OER catalysts at the volcano apex follow a Walden-type pathway rather than a traditional mechanism consisting of sequential desorption and adsorption steps. Reproduced with permission from ref ( 4 ). Copyright 2023, Wiley VCH.…”

“… 2023 10 2305505 . 4 Expansion of the mechanistic volcano plot for oxygen evolution toward the inclusion of reaction mechanisms with simultaneous bond-breaking and bond-making, reminiscent of the Walden inversion from organic chemistry. Pathways comprising Walden steps govern the volcano plot of oxygen evolution to a large extent .…”