Ti ₃ C ₂ MXene Nanosheets and K ⁺ /Strong Base Synergistically Regulated g‐C ₃ N ₅ Jointly Construct a Novel Photogenerated Electron Capacitor for Efficient Photosynthesis of H ₂ O <su

Nitrogen-rich carbon nitride (g-C₃N₅) is an environmentally friendly and metal-free organic semiconductor photocatalyst. In this study, a multistage-enhanced photocatalyst was developed using g-C₃N₅ and Ti₃C₂ MXene. Potassium salt and strong alkali regulation of g-C₃N₅ yielded a modified nitrogen-rich carbon nitride (KCN). Subsequently, MKCN was formed via electrostatic self-assembly with Ti₃C₂ MXene, creating a "photogenerated electron capacitor" structure where KCN generates photogenerated electrons as the "positive electrode", and Ti₃C₂ MXene receives electrons as the "negative electrode". Time-resolved photoluminescence (TRPL), femtosecond transient absorption (fs-TA), and Kelvin probe force microscopy (KPFM) results indicate that the "capacitor" structure enables effective spatial charge separation and uniform surface potential, prolonging carrier lifetimes and enhancing catalytic participation. First-principles calculations reveal that Ti₃C₂ MXene offers stronger O₂ adsorption sites, increasing electron-O₂ reaction probability and boosting two-electron oxygen reduction reaction (2e-ORR) activity for H₂O₂ production. In the composite system, rapid removal of photogenerated electrons from KCN increases hole concentration, inducing upward surface band bending and driving H₂O oxidation to generate •OH. In situ spectra confirm this additional pathway for H₂O₂ generation. Thus, MKCN exhibits excellent H₂O₂ yield (32.61 mmol g^-1h^-1), with good cycling stability. This work provide a new strategy and structure system for efficient photocatalytic H₂O₂ synthesis.