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 CeO 2 nanoparticles directly deposited on polypyrrole (PPy) nanofibers, and then Bi 2 Fe 4 O 9 (BFO) nanosheets were grown on CeO 2 /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 CeO 2 /PPy/BFO compared to single heterojunction CeO 2 /PPy (∼1.9 μA cm –2 and −0.42 V vs Ag/AgCl). Lowering of charge transfer resistance ( R ct ) 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 CeO 2, CeO 2 /PPy, and CeO 2 /PPy/BFO, respectively, imply facile charge carrier separation with enhanced interfacial band bending after construction of double heterojunctions. Remarkably, CeO 2 /PPy and CeO 2 /PPy/BFO demonstrated 32 and 71 times higher H 2 generation, respectively, than pure CeO 2 . 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.