Hydrogen‐Bonded Perovskite Heterojunction Photocatalytic Membrane with Efficient Proton Supply for Boosting CO2 Methanation

Abstract Efficient proton supply and enhanced *CO intermediate adsorption are crucial strategies for boosting CO 2 methanation. Herein, we construct a hydrogen‐bonded (H‐bonded) photocatalytic membrane by integrating a MAPbBr 3 /cyano‐g‐C 3 N 4 (MPB/CN‐g‐CN) heterojunction with ethyl cellulose (ECE) binder through a simple sol–gel process, achieving significantly enhanced CO 2 methanation efficiency. ECE functions as a novel proton source, with hydroxyl (‐OH) groups that are readily oxidized by photogenerated holes, resulting in efficient proton supply compared to H 2 O. Moreover, ECE facilitates membrane assembly via interfacial H‐bonding between the ‐OH moieties of ECE and the modified nitrogen sites of MPB/CN‐g‐CN, generating proton‐rich interfaces and local H‐bond microenvironments that synergistically enhance proton supply and CO adsorption, thus steering the reaction toward CH 4 production. As a result, the MPB/CN‐g‐CN membrane achieves a remarkable increase in CH 4 yield from 0.01 to 35.85 µmol g −1 h −1 and selectivity from 0.4% to 82% compared to the pristine heterojunction. Furthermore, the MPB/CN‐g‐CN/ECE membrane demonstrates exceptional recyclability through a re‐crosslinking membrane formation process, effectively reactivating proton‐supply sites while maintaining superior CH 4 selectivity across multiple operational cycles.