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 ₂

ABSTRACT Nitrogen‐rich carbon nitride (g‐C 3 N 5 ) is an environmentally friendly and metal‐free organic semiconductor photocatalyst. In this study, a multistage‐enhanced photocatalyst was developed using g‐C 3 N 5 and Ti 3 C 2 MXene. Potassium salt and strong alkali regulation of g‐C 3 N 5 yielded a modified nitrogen‐rich carbon nitride (KCN). Subsequently, MKCN was formed via electrostatic self‐assembly with Ti 3 C 2 MXene, creating a “photogenerated electron capacitor” structure where KCN generates photogenerated electrons as the “positive electrode”, and Ti 3 C 2 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 Ti 3 C 2 MXene offers stronger O 2 adsorption sites, increasing electron‐O 2 reaction probability and boosting two‐electron oxygen reduction reaction (2e–ORR) activity for H 2 O 2 production. In the composite system, rapid removal of photogenerated electrons from KCN increases hole concentration, inducing upward surface band bending and driving H 2 O oxidation to generate •OH. In situ spectra confirm this additional pathway for H 2 O 2 generation. Thus, MKCN exhibits excellent H 2 O 2 yield (32.61 mmol g −1 h −1 ), with good cycling stability. This work provide a new strategy and structure system for efficient photocatalytic H 2 O 2 synthesis.