Direct Z-scheme CdTe/g-C₃N₄ van der Waals heterojunction for enhanced solar-to-hydrogen efficiency and spontaneous photocatalytic water splitting

The development of an efficient photocatalyst for water splitting to produce hydrogen represents a promising solution to the energy crisis and environmental pollution. Using first-principles calculations, a CdTe/g-C₃N₄ van der Waals heterojunction, which exhibits outstanding stability with a direct band gap of 1.67 eV, is proposed and investigated in this work. The CdTe/g-C₃N₄ heterojunction functions as a direct Z-scheme heterojunction with band edges favorable for water splitting at pH = 0–14. Gibbs free energy (Δ_G) calculations demonstrate the potential provided by photogenerated carriers can effectively drive spontaneous overall water splitting. Compared with CdTe and g-C₃N₄ monolayers, the CdTe/g-C₃N₄ heterojunction demonstrates superior light absorption efficiency in the visible light region, and its high electron mobility (7648.10 cm²/Vs) significantly improves photocatalytic performance. Furthermore, the solar-to-hydrogen (STH) efficiency is as high as 28.42 %. Biaxial strain ranging from -10 % to 10 % was applied to further modulate its electronic and optical properties. Notably, when the tensile strain is applied, the band gap decreases and the heterojunction exhibits a redshifted absorption peak, which enhances the absorption of visible light. Therefore, the CdTe/g-C₃N₄ vdW heterojunction is expected to be developed as an efficient photocatalyst for water splitting hydrogen evolution.