Computational Design of a Strain-Induced 2D/2D g-C3N4/ZnO S-Scheme Heterostructured Photocatalyst for Water Splitting

Electron–hole recombination is one of the major issues inhibiting practical use of photocatalysts for water splitting to generate clean hydrogen energy. Engineering a heterostructure with an S-scheme heterojunction has been reported to promote e–h separation and maximize potential of photogenerated charge carriers, which, in turn, dramatically improve photocatalytic activity. Herein, based on density functional calculations, we proposed a design of a 2D/2D g-C3N4/ZnO heterostructure to achieve an S-scheme heterojunction with high catalytic activity toward the overall water splitting reaction. We find that the heterostructure constructed from high tensile strain of the ZnO monolayer and the equilibrium g-C3N4 monolayer exhibits an S-scheme heterojunction. The built-in electric field generated at the interface effectively separates electrons to locate at the g-C3N4 side and holes at the ZnO side leading to lower e–h recombination. The heterostructure improves sunlight utilization where its absorption edge is red-shifted into the visible-light region with a higher absorption coefficient when compared to that of individual monolayers. In addition, the mechanistic study reveals that potential of holes at the valence band of the ZnO side can overcome the potential limiting step of the oxygen evolution reaction, while the hydrogen evolution reaction prefers to occur at the g-C3N4 side, which is also where the electrons are accumulated. Our study demonstrates how we can rationally design high-performance 2D/2D heterostructure photocatalysts for overall water splitting based on first-principles modeling.