Cations Determine the Mechanism and Selectivity of Alkaline Oxygen Reduction Reaction on Pt(111)

• Published in: Angewandte Chemie International Edition 2023-12, Vol.62 (51), p.e202312841-n/a
• Main Authors: Kumeda, Tomoaki, Laverdure, Laura, Honkala, Karoliina, Melander, Marko M., Sakaushi, Ken
• Format: Article
• Language: English
• Subjects: Active control; Catalysts; Cations; Chemical reduction; Constrained DFT; Electrocatalysis; Electrochemistry; Electrodes; Electrolytes; Electron transfer; Energy Conversion; Kinetic Isotope Effects; Marcus Theory; Oxidoreductions; Oxygen; Oxygen reduction reactions
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.202312841

The proton‐coupled electron transfer (PCET) mechanism of the oxygen reduction reaction (ORR) is a long‐standing enigma in electrocatalysis. Despite decades of research, the factors determining the microscopic mechanism of ORR‐PCET as a function of pH, electrolyte, and electrode potential remain unresolved, even on the prototypical Pt(111) surface. Herein, we integrate advanced experiments, simulations, and theory to uncover the mechanism of the cation effects on alkaline ORR on well‐defined Pt(111). We unveil a dual‐cation effect where cations simultaneously determine i) the active electrode surface by controlling the formation of Pt−O and Pt−OH overlayers and ii) the competition between inner‐ and outer‐sphere PCET steps. The cation‐dependent transition from Pt−O to Pt−OH determines the ORR mechanism, activity, and selectivity. These findings provide direct evidence that the electrolyte affects the ORR mechanism and performance, with important consequences for the practical design of electrochemical systems and computational catalyst screening studies. Our work highlights the importance of complementary insight from experiments and simulations to understand how different components of the electrochemical interface contribute to electrocatalytic processes. The electron/proton transfer (ET/PT) mechanism of the alkaline oxygen reduction reaction (ORR) on the Pt(111) electrode is dependent on electrolyte cations. In KOH, the 4e− inner‐sphere (IS) ET/PT pathway proceeds on the surface, and adsorbed oxide species block the IS pathway. In LiOH, adsorbed OH and interfacial water stabilized by hydrated Li+ promote the 2e− outer‐sphere (OS) ET/PT pathway in parallel with the IS pathway.