Observation of an Inverse Kinetic Isotope Effect in Oxygen Evolution Electrochemistry

Earth-abundant and inexpensive catalysts with low overpotential and high durability are central to the development of efficient water-splitting electrolyzers. However, improvements in catalyst design and preparation are currently hampered by the lack of a detailed understanding of the reaction mechanisms of the oxygen evolution reaction (OER) facilitated by nonprecious-metal (NPM) catalysts. In this paper, we conducted a kinetic isotope effect (KIE) study in an effort to identify the rate-determining step (RDS) of these intricate electrocatalytic reactions involving multiple proton-coupled electron transfer (PCET) processes. We observed an inverse KIE for OER catalyzed by Ni and Co electrodes. These results contribute to a more complete understanding of the OER mechanism and allow for the future development of improved NPM catalysts.