Insights into the Electrochemical Oxygen Evolution Reaction with ab Initio Calculations and Microkinetic Modeling: Beyond the Limiting Potential Volcano

Density
functional theory calculations are potentially useful for
both understanding the activity of experimentally tested catalysts
and screening for new catalyst materials. For electrochemical oxygen
evolution reaction (OER) catalysts, these analyses are usually performed
considering only the thermodynamics of the reaction path, which typically
consists of adsorbed OH*, O*, and OOH*. Scaling relationships between
the stability of these intermediates lead to a limiting potential
volcano whose optimum is constrained by the roughly constant offset
between the binding energies of OH* and OOH*. In this work, we evaluate
OER kinetics at rutile IrO2, RuO2, RhO2, and PtO2 surfaces by computing reaction barriers with
an explicit model of the electrochemical interface. We conclude that
the kinetics of proton transfer between oxygen atoms at the surface
and in the electrolyte is facile and that O–O bond formation
is most likely rate-determining in all cases. Combining these results
with a microkinetic model and a scaling relationship for the OOH*
formation barrier, we construct a new activity volcano whose optimum
is similar to that of the limiting potential volcano for typical current
densities. This kinetic volcano is also shown to agree reasonably
well with experimental observations. Based on this analysis, we propose
a more precise requirement for improving OER catalysts beyond the
state of the art: the transition state for OOH* formation must be
stabilized as opposed to the fully formed OOH* final state as has
been previously presumed.