Bismuth oxyiodide‐based Bifunctional Z‐scheme Heterostructures for Photoelectrochemical Water Splitting

Abstract BACKGROUND The increasing global energy crisis and environmental pollution necessitate the development of clean and sustainable energy sources. Photoelectrochemical (PEC) water splitting is a promising approach for hydrogen production, utilizing semiconductor materials to convert solar energy into chemical energy. However, single semiconductors suffer from high electron–hole recombination, limiting their efficiency. To address this, a bifunctional Z‐scheme heterojunction was constructed using bismuth oxyiodide (BiOI) and carbon‐doped graphitic carbon nitride (C‐gC₃N₄), with carbon nanotubes (CNTs) as mediators, to enhance charge separation and PEC performance. RESULTS The fabricated C‐gC₃N₄/CNT/BiOI heterojunction exhibited the lowest bandgap energy (1.25 eV), improving light absorption and charge carrier separation. The enhanced conductivity and heterostructure formation resulted in a significantly increased photocurrent density, with reduced overpotential (70 mV) and lower Tafel slopes (89 mV dec −1 ) for the hydrogen evolution reaction and oxygen evolution reaction. UV–visible spectroscopy confirmed a broadened absorption range, and electrochemical impedance spectroscopy demonstrated improved charge transfer efficiency. Transmission electron microscopy, X‐ray diffraction and Mott–Schottky analysis confirmed the structural integrity and surface morphology and successful fabrication of the heterojunction. CONCLUSION The sequential layering of BiOI and C‐gC₃N₄ in a bifunctional Z‐scheme heterojunction significantly improved PEC water‐splitting efficiency. The incorporation of CNTs further enhanced charge transfer, stability and conductivity. These findings highlight the potential of BiOI/C‐gC₃N₄ heterostructures as efficient photoelectrocatalysts for sustainable hydrogen production. © 2025 Society of Chemical Industry (SCI).