Reveal Brønsted–Evans–Polanyi relation and attack mechanisms of reactive oxygen species for photocatalytic H2O2 production

The generation of H+ by active species attacking proton donor (PD) is a key step in photocatalytic H2O2 production (PHP). Deeply analyzing the involved mechanism may be a crucial factor to break through the bottleneck of H2O2 yield. Here, nitrogen-deficient and boron-doped g-C3N4 are synthesized for PHP and the interaction mechanisms between active species and PD are revealed. The prepared photocatalyst exhibits a high H2O2 production rate (455 μM h−1 g−1). The 1O2, •O2- and hole promoted by modification site dominate twelve different reaction mechanisms, respectively. For the oxidation pathways dominated by hole, H2O2 generation is limited by the dissociation of PD or desorption of H+ on catalyst surface. Interestingly, •O2- and 1O2 could directly attack PD, or diffuse into solution to react with PD to produce H2O2 with lower barriers. Moreover, there is a synergistic effect between doped-boron, 1O2 and water bridge, which further reduces the reaction barrier.