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Quantum-to-Classical Transition of Proton-Transfer in Electrocatalytic Oxygen Reduction

The four-electron oxygen reduction reaction on Pt catalyst in alkaline solution undergoes proton transfer via tunneling mechanism. The hydrogen/deuterium kinetic isotopic rate constant ratio (kH/kD ) = 33 in a low overpotential region, indicating the importance of the quantum-proton-tunneling at the rate-determining step (RDS). However, kH/kD goes down to 4.1 in a high overpotential region, suggesting the classical proton-transfer (PT) scheme. Therefore, there is a quantum-to-classical transition of PT process as a function of potential, which is confirmed by theoretical study.