Synergy of Charged Domain Walls in 2D In-Plane Polarized Ferroelectric GeS for Photocatalytic Water Splitting

Two-dimensional (2D) ferroelectric (FE) materials have exhibited significant prospects for applications in photocatalysis due to their unique properties. However, studies of 2D FE catalysts have been mostly focused on the electric potential difference between different surfaces of out-of-plane-polarized FE materials. Herein, based on ab initio density functional calculations, we investigate the effects of in-plane (IP) polarizations on the photocatalytic water splitting process by considering the existence of charged domain walls (DWs) in the 2D FEs. Our results show that the metallic states at the DWs significantly expand the optical absorption range and improve the absorbance in the visible-light region. The built-in electric field spreading over the FE domains promotes the separation of photogenerated charges by driving the electrons/holes to the positively/negatively charged DWs. The charged DWs can also affect the active sites on the surface and effectively lower the energy barrier during pathways of both hydrogen reduction and water oxidation half reactions. With all of these effects, the charged DWs are shown to play the synergistic role of cocatalysts and effectively enhance the performance of GeS in the photocatalytic water splitting reaction. Our study provides not only a new insight into the applications of 2D FEs but also an effective way for regulating the photocatalytic performance of 2D IP FE materials.