Dual Active Site Mediated Photocatalytic H₂ Evolution through Water Splitting Using CeO₂/PPy/BFO Double Heterojunction Catalyst

Photocatalytic water splitting generates hydrogen from water and sunlight, but one bottleneck for widespread usage is the poor performance of semiconductor photocatalysts. Manipulating the surface of a catalytic material by introducing different components can tune phase composition and extend the catalytic activity by delayed charge recombination, superior charge transfer, and enhanced light harvesting. A double heterojunction has been fabricated using CeO2 nanoparticles directly deposited on polypyrrole (PPy) nanofibers, and then Bi2Fe4O9 (BFO) nanosheets were grown on CeO2/PPy with a significant improvement in visible light absorption. A high photocurrent density of 5.5 μA cm–2 with more negative Flat band potential (−0.47 V vs Ag/AgCl) has been obtained for CeO2/PPy/BFO compared to single heterojunction CeO2/PPy (∼1.9 μA cm–2 and −0.42 V vs Ag/AgCl). Lowering of charge transfer resistance (Rct) values from 612 kΩ to 488 kΩ and 415 kΩ and longer charge carrier lifetimes of 4.8, 5.8, and 7.3 μs for CeO2, CeO2/PPy, and CeO2/PPy/BFO, respectively, imply facile charge carrier separation with enhanced interfacial band bending after construction of double heterojunctions. Remarkably, CeO2/PPy and CeO2/PPy/BFO demonstrated 32 and 71 times higher H2 generation, respectively, than pure CeO2. Based on the possible band edge positions of semiconductors, a double heterojunction n-n-Z-scheme charge transfer pathway has been proposed. Our demonstration provides a paradigm to improve catalytic performance for water splitting through surface engineering of semiconductor photocatalysts.