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

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.