Unlocking the Synergistic Dual-Active Site Mechanism by Loading Pd Single Atom onto α-MnO 2 for Efficient Electrocatalytic Epoxidation

The electrocatalytic epoxidation of olefins using water as the oxygen source represents a promising strategy for the production of sustainable epoxides under ambient conditions. However, its practical application remains hindered by low efficiency, primarily due to the competitive oxygen evolution reaction in the current pathways. In this study, we report a single-atom Pd catalyst supported on α-MnO 2 (Pd 1 /MnO 2 ) that facilitates the electrocatalytic epoxidation of cyclooctene via a dual-site mechanism. This so-called oxide path mechanism (OPM) enables *O and *cyclooctene to accumulate on Pd and Mn sites, respectively, allowing their direct coupling to generate cyclooctene oxide. The Pd 1 /MnO 2 catalyst achieved high faradaic efficiency (>70%) up to a current density of 16.1 mA cm –2 (1.4 V vs Fc/Fc + ), which is much higher than those of MnO 2 (28.9%) and PdO (30.2%), respectively. A series of experiments were conducted to identify the adsorption sites for each reactant and detect reaction intermediates, thereby validating the proposed OPM pathway. Density functional theory calculations further confirmed the mechanism by demonstrating a reduced energy barrier for the reaction. This work underscores the distinct reaction pathways enabled under electrochemical conditions and provides new insights into the design of advanced electrocatalysts for olefin epoxidation using water as an oxygen source.