Si/Carbon-dots with Surface N-C Sites Promoting Proton and Electron Transfers in Oxygen Reduction Reaction

The oxygen reduction reaction (ORR) can proceed through either a two- or four-electron pathway, both of which are important for a wide range of applications. The intermediate conversion of *O₂⁻ + H⁺ → *OOH recognized as the rate-determining step in ORR, with its efficiency strongly dependent on the nature of active sites at the surface of a catalyst. Herein, Si-supported carbon dots (Si-CDs) are introduced as cocatalysts in a photocatalytic system, where their nitrogen-carbon sites play a pivotal role in lowering the energy barrier for *OOH formation by promoting proton and electron transfers, thus enhancing the H₂O₂ production rate in ORR. This strategy is broadly applicable across a wide range of photocatalysts, both with and without use of sacrificial agents. The H₂O₂ production rate for Zn_0.5Cd_0.5S (30 mg) increased from 13.0 to 40.9 µmol h^-1 when 0.6 mg of Si-CDs were added. In-situ characterizations and theoretical simulations are conducted to reveal the reaction pathway and the reduced energy requirements for the *O₂⁻ + H⁺ → *OOH conversion. This study provides a unique example of overcoming a key barrier in ORR using a metal-free catalyst and promotes potential applications in various fields.