Alkali-assisted synthesis of polymeric carbon nitride photoanodes with defect and crystallinity-mediated charge transfer for efficient photoelectrochemical water splitting†

Defect and crystallinity engineering play vital roles in boosting the bulk charge transfer kinetics of polymeric carbon nitride (PCN)-based photoanodes, thereby enhancing their photoelectrochemical (PEC) performance. Herein, a PCN-based photoanode with an N-defect structure and improved crystallinity (KPCN) has been developed by an alkali-assisted synthesis method for PEC water splitting. The PEC performance of the KPCN photoanode is notably improved, delivering a photocurrent density of ca. 162 μA cm⁻² at 1.23 V vs. RHE under AM 1.5G illumination, marking a 13.5-fold boost over that of the pristine PCN photoanodes. Detailed analysis indicates that the observed enhancement is chiefly related to the defect and crystallinity-mediated charge transfer of KPCN. Moreover, the enhanced crystallinity and increased π-electron delocalization also contribute to the improved visible light absorption of KPCN. This work draws attention to the combined impact of defects and crystallinity on optimizing charge transfer in PCN photoanodes, offering new methods for designing high-performance PEC water splitting systems.