Rationalizing the Overall H₂O₂ Selectivity of Metal Dichalcogenide Electrocatalysts for the Two-Electron Oxygen Reduction Reaction Using Microkinetic Modeling

Electrocatalytic production of hydrogen peroxide (H2O2) via the two-electron oxygen reduction reaction (2e– ORR) in acidic solution enables numerous potential applications, including water treatment and degradation of pollutants via the electro-Fenton process. However, prior studies of H2O2 electrosynthesis have not accounted for the detailed and quantitative competition between the 2e– and 4e– pathways or the reactivity of the generated H2O2, nor the surprising selectivity differences of related electrocatalysts under high overpotentials. Here, we combine first-principles calculations and microkinetic modeling, including both thermal and electrochemical steps, to elucidate the factors governing the selectivity and maximum H2O2 accumulation of Ni- and Co-based transition metal dichalcogenide electrocatalysts. The predicted catalytic current densities, selectivity, and maximum H2O2 accumulation from our kinetic model are in good agreement with the corresponding experimental results. Further analysis of the kinetic model establishes the key role of the reductive elimination barrier of surface adsorbed H2O2* in modulating the H2O2 selectivity and accumulation on different catalysts, yielding mechanistic insights to design improved 2e– ORR electrocatalysts and potential avenues for future electrocatalyst optimization.