First-principles study on two-dimensional direct Z-scheme g-GeC/MoSe2 heterostructure for overall photocatalytic water splitting

Recently, the direct Z-scheme heterostructures are getting tremendous attention in the photocatalytic research filed due to their strong redox capabilities, excellent sunlight harvesting and the effective separation of photogenerated charge carriers. Herein, by using density functional theory (DFT) calculations, the structural, electronic and optical properties of g-GeC/MoSe2 van der Waals heterostructure (vdWH) are investigated. The gGeC/MoSe2 vdWH with AA1 stacking configuration is found to be energetically and thermodynamically stable. By revealing the staggered band alignment and the intrinsic interfacial charge transfer, we find the photocatalytic process of the g-GeC/MoSe2 vdWH follows the Z-scheme mechanism, which is favorable for prolonging the exciton lifetime and improving the photocatalytic performance. The band edges of the reduction photocatalyst (g-GeC) and the oxidation photocatalyst (MoSe2) are found to straddle the redox and oxidation levels for water-splitting at any pH value. Further analysis based on the Gibbs free energy variation presents an exothermal characteristic for the hydrogen evolution reaction (HER) on g-GeC surface under light illumination, suggesting the spontaneity of the HER process. While an energy barrier of 0.97 eV for the rate-determining step in the oxygen evolution reaction (OER) process is calculated, which is relatively lower than the barrier height of OER on the pristine MoSe2 monolayer. Moreover, compared with g-GeC and MoSe2 monolayers, the vdWH exhibits improved light-harvesting capability both in the visible and the ultraviolet wavelength ranges. Overall, our work demonstrates that g-GeC/MoSe2 vdWH has a promising application prospect for photocatalytic overall water splitting.