Strain-Driven Electronic and Catalytic Modulation of g-C3N4/GeS van der Waals heterostructure for Photocatalytic Water Splitting

Abstract

Photocatalytic water splitting offers a viable pathway for sustainable hydrogen production. In this study, first-principles density functional theory calculations were performed to explore the strain-dependent photocatalytic behaviour of a two-dimensional g-C3N4/GeS heterostructure. The heterostructure shows type-II band alignment with an indirect band gap of 2.17 eV, smaller than those of the individual g-C3N4 (2.81 eV) and GeS (3.31 eV) monolayers. Biaxial tensile strain up to 3% effectively modulates the band gap and band edge positions, allowing suitable alignment with water redox potentials. The calculated Gibbs free energy for the hydrogen evolution reaction ({\Delta}GHER) is 0.2 eV for the pristine heterostructure and approaches near-thermoneutral values (-/+ 0.1 eV) under +1% and +2% strain. Meanwhile, the OER overpotential decreases from 2.17 V to 0.97 V with increasing strain. AIMD simulations and optical absorption in the visible region confirm the thermodynamic stability and promising photocatalytic potential of the heterostructure for hydrogen generation.