The Type-II g-C6N6/As Heterojunction for Photocatalytic Overall Water Splitting in the Visible-Light Region: A Theoretical Investigation

Strategically engineering heterojunctions through the integration of two or more monolayer materials presents a promising avenue for augmenting the efficiency of solar-driven overall water splitting, which holds the potential for mitigating the escalating environmental challenges. Herein, based on first-principles calculations, the functional type-II g-C6N6/As heterojunction is first constructed by g-C6N6 and As, then, systematically investigated its structural stability, optoelectronic properties and photocatalytic mechanism and potential for catalyzing water splitting, respectively. Owing to the band-bending effect and the built-in electric field induced across the heterojunction interface, the photogenerated electrons and holes on the surface could effectively separate and extend their carrier lifetimes. The heterojunction as a type-II system photocatalyst with the hydrogen and oxygen evolution reactions occurring, respectively, happen at g-C6N6 and As surfaces. The heterojunction requires only an additional voltage of 0.29 V to ensure the photoinduced holes provide sufficient energy to drive the OER process. The introduction of single-layer As could effectively adjust the reaction energy barrier of the HER activity for single-layer g-C6N6, thus ultimately significantly enhancing HER performance of heterojunction. More significantly, the heterojunction breaks the optical-capturing obstacle of the g-C6N6 and exhibits strong optical capture capability in the regions from the infrared to visible light. Meanwhile, the value of the STH efficiency for heterojunction is up to 28.18%, which exceeds the value of the economically feasible requirement (10%). The above results are beneficial for the quantified design and application of photocatalytic heterojunction for overall water splitting and offer valuable insights for potential commercial implementations.