Designing C6N6/C2N van der Waals heterostructures for Photogenerated Charge Carrier Separation

Photocatalytic water splitting mechanism boosted by two-dimensional catalyst materials has become the vibrant field of research toward clean energy initiative. Here, we propose a new two-dimensional (2D) van der Waals type-II heterostructure based on C6N6/C2N composites as an efficient photocatalyst. The structural, electronic and optical properties of the free-standing monolayer as well as their heterostructure have been investigated by first principles based density functional theory (DFT). The band edge positions of C6N6/C2N heterostructures satisfy the photocatalytic water splitting requirements. The potential drop at the interface of the heterostructure induces a large built-in electric field directed from the C6N6 layer to the C2N layer, thereby facilitating the charge transfer from C2N to C6N6 layer. The higher hole mobility as compared to that of electrons aids in separation of charge carriers and thus prohibiting the recombination of the photogenerated charge carriers by separating them in different layers. This is also reflected in the planar averaged charge density difference and partial charge density calculation. The wide band gap semiconductor (C6N6) in combination with a moderate band gap semiconductor (C2N) allows one to harness solar energy efficiently in the visible region for water splitting as also confirmed in the optical absorption spectra. The favorable band edge position with respect to the water redox potential makes it an ideal substrate for the visible light induced oxygen evolution reaction and the hydrogen evolution reaction.