Water oxidation of visible-light-responsive bismuth-yttrium oxychloride promoted by a dual-ion doping strategy for assembly of Z-scheme overall water splitting

Abstract

Bismuth yttrium oxychloride (Bi₂YO₄Cl) is one of the most popular visible-light-responsive photocatalysts; however, it is still challenging to use it in the construction of overall water splitting (OWS) systems. Herein, we introduce a novel dual-ion doping strategy to modulate its structure and water oxidation activity, based on which a feasible Z-scheme OWS system can be assembled. In particular, the doping effect of dual ions (Y³⁺ and Br⁻) on the structure and water splitting performance was examined and discussed by combining various characterization studies such as photoelectrochemical current, electrochemical impedance spectroscopy, (time-resolved) photoluminescence spectra, and density functional theory calculations. It was observed that a clear synergistic promotion effect occurs on the dual ion-doped sample (Bi_3−xY_xO₄Cl_1−yBr_y), making it exhibit a significantly higher O₂ evolution rate compared to a single ion-doped sample. The activity was also observed to strongly depend on the content of dual ions, and the optimized Bi_1.2Y_1.8O₄Cl_0.88Br_0.12 sample exhibited a remarkable visible-light-responsive O₂ production rate of 116 μmol h⁻¹ (the apparent quantum efficiency (AQE) = 5.4% at 420 nm), which was 10 and 20 times higher than those of the Br-/Y-doped sample and pristine Bi₂YO₄Cl, respectively. The substantially promoted charge separation and reduced activation energy were demonstrated to be responsible for the excellent O₂-evolution rate. Finally, we successfully fabricated a feasible Z-scheme OWS system based on the colorless IO₃⁻/I⁻ shuttle redox pair by employing modified Bi_1.2Y_1.8O₄Cl_0.88Br_0.12 as the O₂-evolving photocatalyst along with ZrO₂/TaON as the H₂-evolving photocatalyst. The dual-ion doping strategy may be extended to several other photocatalysts for enhanced photocatalytic activities.