Carbon Nitrides with Grafted Dual-Functional Ligands as Electron Acceptors and Active Sites for Ultra-stable Photocatalytic H₂O₂ Production

Photocatalyticproduction of H2O2 from earth-abundantwater and oxygen using low-cost metal-free carbon nitrides (CNs) throughoxygen reduction is a prospective route toward a greener future. However,the H2O2 productivity is restricted by rapidelectron-hole separation and the low oxygen reduction activityof CNs. Herein, we rationally designed a series of CNs with covalentlybonded dual-functional ligands acting as electron acceptors and activesites to achieve high photocatalytic H2O2 productionand superior stability. The best-performing carbon nitride displaysa H2O2 production rate of 7.3 mmol/g h withan apparent quantum efficiency of 20.2% at 420 nm using formic acidas the electron donor. Moreover, the modified CNs show excellent stableH(2)O(2) generation over 110 h without significantdecline. Mechanistic studies reveal that H2O2 was produced through a 2e(-) oxygen reduction reactionroute. Photoluminescence, photo-electrochemical, and Kelvin probeforce microscopy results together with theoretical calculations haverevealed that the excellent photocatalytic performance originatesfrom the dual-functional ligand. It not only acts as an electron acceptorto promote photogenerated charge carrier separation by withdrawingelectrons but also works as an active site to accelerate oxygen reductionby lowering the oxygen adsorption and activation energy. Moreover,this facial strategy of grafting ligands provides a universal approachto synthesize photocatalysts with enhanced reactivity under mild conditionsby choosing the proper ligands for a specific reaction.