A two-dimensional vertical van der Waals heterostructure based on g-GaN and Mg(OH)2 used as a promising photocatalyst for water splitting: A first-principles calculation

In this study, based on first-principles calculation, the structural, electronic, interfacial, and optical properties of two-dimensional (2D) semiconductor vertical heterostructure constructed by g-GaN and Mg(OH)2 are addressed. The g-GaN/Mg(OH)2 heterostructure is discovered to be formed by van der Waals (vdW) forces and possesses a type-II band structure which can promote the separation of photogenerated electron–holes constantly. At the same time, the calculated band edge positions of the heterostructure are decent to induce the oxidation and reduction reactions for water splitting at pH 0. Gibb's free energy change in the redox reaction for the g-GaN/Mg(OH)2 vdW heterostructure is further investigated that the heterostructure can act as a suitable catalyst in hydrogen evolution reaction and oxygen evolution reaction for water splitting. The charge-density difference and the potential drop are calculated across the interface of the g-GaN/Mg(OH)2 vdW heterostructure, and the potential drop can induce a large built-in electric field, which is also a boost to prevent the recombination of the photogenerated charges. Finally, the applied external biaxial strain is studied that it can improve the optical absorption performance of the g-GaN/Mg(OH)2 vdW heterostructure. This study provides a possibility of method to design the 2D vdW heterostructure as a photocatalyst to decompose water.