Electron confinement promoted the electric double layer effect of BiOI/β-Bi2O3 in photocatalytic water splitting

Abstract

In the realm of photocatalysis, understanding the interface issues (solid/solid and solid/liquid) inherent in heterojunction at the atomic level is the ultimate for engineering an efficient photocatalyst. Herein, an electrophoretic deposition technique is adopted to synthesize BiOI/β-Bi₂O₃ heterojunction, exhibiting superior photocatalytic activity and stability in H₂ evolution (91.5 μmol g^-1 h^-1) and H₂O₂ production (11.3 mg L^-1 h^-1). Combined with the experimental and computational results, a lower free energy of hydrogen evolution reaction (252.4 meV) has been observed contrast to BiOI and β-Bi₂O₃ samples. A carrier transfer process of like S-scheme heterojunction is proposed based on density of states (DOS) and carrier distribution calculations. The theoretical calculations illustrate the transition dipole moment, migration and accumulation of carrier in BiOI/β-Bi₂O₃ heterojunction. Subsequent ab initio molecular dynamics (AIMD) results of solid/liquid interface systems (BiOI/β-Bi₂O₃/H₂O and β-Bi₂O₃/H₂O) unravel the interface H₂O (solvent) behaviors. The local aggregation of photo-generated electrons in BiOI/β-Bi₂O₃/H₂O leads to a large potential drop, high proton migration rate and the steady electric double layer (EDL) structure compared to the β-Bi₂O₃/H₂O, which facilitates the occurrence of photocatalytic reactions in solution. In addition to offering new insights into the hydrogen evolution and proton transfer in the EDL model and the association between the heterojunction effect and EDL structure, this work also introduces a novel design strategy for Bi-based heterojunctions.