Continuous hydrogen production from sunrise to sunset: Advancing photocatalytic stability via interface-engineered nanocomposite tris-s-triazine g-C3N4/ZnIn2S4 heterostructure

A tris-s-triazine g-C₃N₄/ZnIn₂S₄ heterojunction photocatalyst achieved continuous H₂ generation from sunrise to sunset for the first time, based on batch and day-long experiments at different sunlight intensities. Under a clear sky, H₂ production increased steadily from 6 a.m. to 1 p.m., peaking at 13.6 mmol h⁻¹·g⁻¹_cat at 1 p.m. before declining in the afternoon. Under a cloudy sky the H₂ production was slower, reaching a peak rate of 3.1 mmol h⁻¹·g⁻¹_cat at 1 p.m., highlighting the influence of light intensity and spectral composition on the solar-to-hydrogen conversion efficiency. H₂ production rates in different time slots follow the order of 12–3 p.m. > 9–12 a.m. > 3–6 p.m. > 6–9 a.m. under both sky conditions. This nanohybrid photocatalyst showed enhanced visible light absorption (400–500 nm) and a peak H₂ generation rate of 10.9 mmol h⁻¹·g⁻¹_cat during peak solar hours (10:30 a.m. to 2:30 p.m.). It also maintained consistent H₂ production across multiple photoreactors and over five consecutive days, indicating its potential for industrial scale-up. The formation of heterojunction was confirmed using X-ray diffraction and transmission electron microscopy, whereas photoluminescence, photocurrent density, and electrochemical impedance spectroscopy results demonstrated effective charge carrier separation. Diffuse reflectance ultraviolet–visible spectroscopy, X-ray photoelectron spectroscopy, Mott–Schottky and electron paramagnetic resonance spectroscopy analyses confirmed that the S-scheme junction makes electrons and holes from higher energy potential available for redox reactions and at the same time facilitates recombination of electrons and holes of lower energy potential; combinedly these processes facilitate separation of charge carriers and improve H₂ production. This study provides valuable insights into the electron transfer dynamics, influence of the visible band of solar spectrum, and light intensity on sustainable H₂ production.