Boosting Photocatalytic H ₂ O ₂ Generation via Interfacial Engineering in a 2D S‐Scheme Hydroxyethyl Cellulose‐Modified Graphitic Carbon Nitride/Bismuth Oxybromide Heterojunction

Although scalable artificial photosynthesis for H 2 O 2 production is a promising technique, it is not yet widely adopted as an industrially viable process. Herein, a 2D n–n heterojunction photocatalyst has been fabricated by integrating hydroxyethyl cellulose (HEC)‐modified g‐C 3 N 4 with BiOBr. The heterojunction is denoted as CN‐ x /BOB‐ y , where x and y represent the mass ratios of HEC/g‐C 3 N 4 and g‐C 3 N 4 /BiOBr, respectively. Under simulated visible light irradiation, CN‐0.4/BOB‐0.5 achieves a remarkable H 2 O 2 production rate of 5897 μM g −1 h −1 , outperforming BiOBr and HEC/g‐C 3 N 4 by factors of 2.04 and 2.38, respectively. It also records an apparent quantum yield (AQY) and mass‐normalized AQY of 0.167% and 8.34E‐02 molecules·photon −1 ·g −1 , respectively. The synergy between HEC modification and heterojunction construction underpins the superior performance, driving efficient charge carrier separation alongside a marked increase in specific surface area. Energy band alignment analysis and scavenger trapping experiments collectively reveal that charge carriers in CN‐0.4/BOB‐0.5 follow an S‐scheme charge transfer pathway, enabling enhanced redox capability and efficient charge separation across the built‐in electric field within a well‐engineered heterojunction. This work presents a novel strategy for constructing a highly efficient photocatalytic system for H 2 O 2 generation under visible light irradiation.