Efficient photocatalytic H2O2 production over K+-intercalated crystalline g-C3N4 with regulated oxygen reduction pathway

Photocatalytic H2O2 production via the oxygen reduction pathway is an ideal sustainable technique, while it faces challenges such as sluggish exciton dissociation and charge transfer, as well as limited oxygen adsorption. Here, we successfully synthesized K+-intercalated porous crystalline carbon nitride nanosheets with cyano group modification (KCN) using a one-step potassium salt-assisted thermal copolymerization strategy. The incorporation of K+, high crystallinity and cyano group result in an enhancement of light absorption, as well as the promotion of carrier separation and bulk charge migration. The facilitated adsorption and transfer of O2 and H+ accelerate surface reaction kinetics. The optimal H2O2 production rate of KCN-1 (11.2 mmol‧g−1‧h−1) is approximately 17 times higher than that of pristine CN (0.616 mmol‧g−1‧h−1). Additionally, KCN-1 demonstrates exceptional stability and high two-electron reduction selectivity. DFT calculations were employed to elucidate the role of K+ in both structural composition and activity improvement. KCN-1 not only can generate more O2− for H2O2 synthesis, but also facilitates the one-step two-electron direct reduction pathway from O2 and a novel formation reaction from 1O2 intermediate to H2O2. This study confirms that effective regulation of molecular structure and optimization of reaction pathways are advantageous for constructing efficient H2O2 synthesis systems.