Ag ₂ O Merged in Potassium‐Incorporated Polymeric Carbon Nitride Photoanodes with Efficient Charge Transfer for Photoelectrochemical Water Splitting

Escalating energy demands and environmental imperatives necessitate sustainable hydrogen production, with photoelectrochemical (PEC) water splitting emerging as a vital approach. Though polymeric carbon nitride (PCN)‐based photoanodes offer enormous promise, their efficacy is hampered by the inadequate charge transfer efficiency. Herein, Ag 2 O was in situ integrated into potassium‐incorporated PCN (KCN) photoanodes (AgKCN), primarily forming the intimate heterojunctions at the KCN/FTO interface. Importantly, AgKCN maintains a 2.56 eV bandgap while preserving the crystalline architecture of KCN. Within this structure, Ag 2 O establishes a thermodynamically favorable band alignment that enables the directional hole transfer from the valence band of KCN to that of Ag 2 O, thereby mitigating charge carrier recombination and lowering charge transfer resistance. Consequently, the optimized AgKCN achieves a benchmark photocurrent density of 378 μA cm −2 at 1.23 V versus reversible hydrogen electrode (RHE) in a 1.0 M NaOH electrolyte under AM1.5G illumination, which is ca. 4 times that of the pristine KCN, accompanied by a 90.5% surface charge injection efficiency. This work highlights the transformative role of Ag 2 O in enhancing PEC performance via heterojunction‐mediated carrier regulation, providing the design principles for advanced PCN‐based photoanodes.