In situ transformation of CuBi2O4 to heterogeneous Bi2O3/Cu2O mixed phase using thermal method for exceptional H2 production.

Photoelectrochemical water splitting using semiconductor materials is a viable approach to produce green hydrogen (H₂). CuBi₂O₄ is a promising option because of its high redox potential and advantageous band gap; however, its use is hindered by significant charge carrier recombination and inadequate interfacial contact. We synthesized CuBi₂O₄ using a simple thermal method and examined the impact of polyvinyl alcohol on its structural and morphological characteristics. We observed a phase transformation from a mixed-phase CuBi₂O₄ to a highly efficient α-Bi₂O₃/β-Bi₂O₃/Cu₂O heterostructure. The optimized heterostructure (α-Bi₂O₃/β-Bi₂O₃/Cu₂O) showed a remarkable photocatalytic H₂ evolution rate of 776 µmol g^-1 compared with the pristine (CuBi₂O₄) structure, which achieved a rate of 166 µmol g^-1. The exceptional photocatalytic H₂ production of the heterogeneous sample arises from the efficient charge transfer mechanism and separation of photogenerated electron-hole pairs facilitated by the interfaces produced between the distinct phases. The enhanced transient photoresponse of α-Bi₂O₃/β-Bi₂O₃/Cu₂O (9.76 µA) compared with that of the pure sample (5.13 µA) validates the effective generation and separation of photogenerated charge carriers resulting from the appropriate band alignment and in situ p-n junctions formed during the synthesis process. Furthermore, the electrochemical impedance spectra showed a reduced charge transfer resistance for the optimized heterostructure compared with that of the pure structure, thereby validating the superior photocatalytic H₂ evolution of the heterostructure. Consequently, using the thermal approach establishes a simple synthesis route for heterogeneous catalysts with exceptional H₂ evolution performance. Moreover, this study advances the development of H₂ technology by providing a cost-effective strategy for designing efficient catalysts.