GaN/MgI₂ van der Waals heterostructure: a two-factor tunable photocatalyst for hydrogen evolution

With the increasing environmental pollution and energy crisis, it is significant to develop environmentally friendly and adjustable photocatalysts for water splitting. Here we explored the optoelectronic properties of several H-GaN/MgI₂ vdW heterostructures by regulating different polarization surfaces and numbers of GaN layers. Our results demonstrate that all structures, except 2L-Ga-GaN/MgI₂, exhibit excellent physical stability. Moreover, the band structures and band edge positions demonstrate that only the heterostructure of 3L-Ga-GaN/MgI₂ with both suitable band alignment (type-II) and an acceptable band gap (∼1.92 eV) is most satisfactory for water splitting. Additionally, the absorption coefficient of the 3L-Ga-GaN/MgI₂ heterostructure can reach over ∼10⁵ cm^-1, which has further confirmed its excellent advantage in photocatalysis. Finally, in the case of 6% external strain for the 3L-Ga-GaN/MgI₂ heterostructure, a rollover in band alignment (from type-II to type-I) is exhibited. These promising features of the GaN/MgI₂ vdW heterostructure give a new paradigm for developing novel efficient and adjustable photocatalytic water-splitting materials.