Te-vacancy defect triggering photocatalytic overall water splitting for MoTe2/GeN Z-scheme heterostructure

Abstract

Developing proper semiconductor photocatalysts is urgently needed to solve energy and environmental crises. Especially, photocatalysts for water splitting with a Z-scheme mechanism are desirable materials. Herein, a two-dimensional VTe-MoTe2/GeN heterostructure (VTe-HS), including single Te vacancy, is theoretically proved to function as a direct Z-scheme photocatalyst with the wide light-harvesting range, the effective spatial separation for carriers, and the high catalytic activity for water splitting. An enhanced optical absorption coefficient of 105 cm−1 is observed and the absorption edge (∼1.0 eV) is red-shifted into the infrared light region. Separating photogenerated electron–hole pairs enhances the photocatalytic efficiency due to the staggered band alignment. Interlayer charge migration of about 0.154 electrons induces an intrinsic built-in electric field in the heterostructure, allowing forming the Z-scheme mechanism with a reduction potential of –4.01 eV and an oxidation potential of –7.13 eV. Gibbs free energies confirm that water redox reactions can proceed spontaneously under sunshine. Moreover, the Heyrovsky reaction is kinetically more favorable than the Tafel reaction because of a little energy barrier (0.071 eV). These features show that the VTe-HS is a desirable water-splitting photocatalyst, providing a valuable clue to constructing high-efficiency photocatalysts.