Lanthanide Incorporation Orchestrates the Structure–Activity Relationship in Bismuth Oxychloride for Visible-Light-Driven Water Splitting

The rational design of semiconductors combining a visible-light response and efficient charge separation remains a fundamental challenge in photocatalysis. We report a lanthanide incorporation strategy to synthesize a new series of visible-light-responsive bismuth oxychlorides, LnBi₂O₄Cl (Ln = Lu, Yb, Er, Eu, Sm, Nd). The integration of lanthanide ions into the [Bi₂O₂] fluorite layer creates a triple-fluorite [Bi₂LnO₄] structure, inducing structural reorganization through electronic interlayer interactions. This approach enables systematic absorption edge extension from 500 to 620 nm across the series while modulating the electronic structure and halogen layer stacking via van der Waals interactions. The unique lanthanide contraction and 4f electronic configuration enhance the charge carrier dynamics, with ErBi₂O₄Cl exhibiting a 200-fold increased carrier lifetime, 1.21-fold higher carrier mobility, and 10-fold greater carrier density compared to pristine BiOCl. Surface photovoltage and photodeposition experiments confirm spatially separated redox centers and a 20-fold improvement in charge separation efficiency. Photocatalytic hydrogen and oxygen evolution activities follow volcano-type trends with decreasing lanthanide atomic numbers, primarily governed by the charge separation efficiency. RuO_x-loaded LnBi₂O₄Cl (Ln = Lu, Yb, Er) achieves oxygen evolution quantum efficiencies exceeding 8% at 420 nm using Fe²⁺/Fe³⁺ redox shuttle ions, outperforming analogous bismuth oxychlorides. Finally, we demonstrate an efficient Z-scheme system using SrTiO₃:Rh and ErBi₂O₄Cl for overall water splitting. This work establishes lanthanide incorporation as a generalized strategy for designing high-performance, visible-light-responsive layered photocatalysts through the periodic regulation of their structural and electronic properties.