The GaSe/g-C6N6 type-II van der Waals heterostructure: A prospective water-splitting photocatalyst under acidic, alkaline and neutral conditions

In this work, we systematically study the structural stabilities, electronic properties, carrier transitions, band edge positions and photocatalytic water-splitting of the GaSe/g-C6N6 heterostructure by first-principles method. The interlayer distances 3.46, 3.58 and 3.51 angstrom respectively for patterns H1, H2 and H3 of the GaSe/g-C6N6 heterostructure show a van der Waals interaction existed at the interface. The negative binding energies show the formations of the GaSe/g-C6N6 heterostructure are energetically favorable, especially the pattern Hl with the lowest value of -18.16 meV angstrom(-2) and thermodynamic stability from ab initio molecular dynamic simulations. The valance band maximum at Gamma point and conduction band minimum at K point donated by GaSe and g-C6N6 respectively show the GaSe/g-C6N6 is a type-II heterostructure with an indirect bandgap of 2.16 eV. The Bader charge analysis indicates about 0.03 e charge spontaneously transfers from g-C6N6 to GaSe and thus resulting in a built-in electric field from g-C6N6 to GaSe. The conduction (valance) band offsets 0.94 (1.18) eV drive the photogenerated electrons (holes) to flow from GaSe to g-C6N6 (from g-C6N6 to GaSe). The photogenerated electron-hole pairs are suppressed by the built-in electric field to recombine and thus the carrier lifetime is extended. The valance band maximum and conduction band minimum straddle the redox potentials of water from pH 0 to 12, indicating the GaSe/g-C6N6 heterostructure could undergo the overall photocatalytic watersplitting under acidic, alkaline and neutral conditions. Our results show the GaSe/g-C6N6 type-II van der Waals heterostructure is a promising candidate for photocatalytic water-splitting.