Two-dimensional Janus perovskite oxynitrides as active photocatalysts for overall water splitting with ferroelectric modulation

Abstract

Two-dimensional (2D) Janus structure is promising for photocatalytic water splitting because its intrinsic built-in electric field can overpass the bandgap requirements of photocatalysts. However, how to achieve overall water splitting spontaneously in one structure is still difficult. Here, we present a novel family of 2D Janus perovskite oxynitrides, BaXNO₂ (X = Ta, Nb, V), with a large intrinsic built-in electric field based on first-principles calculations. Both 2D BaTaNO₂ and BaNbNO₂ exhibit remarkable activity for photocatalytic overall water splitting. For BaNbNO₂, a lowest overpotential of 0.44 V for the oxygen evolution reaction (OER) is realized. The Gibbs free energy of hydrogen adsorption (ΔG_H) is near zero (0.02 eV) for BaTaNO₂ in the hydrogen evolution reaction (HER). Interestingly, 2D BaVNO₂ shows in-plane ferroelectricity due to the displacement of V ions accompanied by a ferroelastic distortion of the lattice, which modulates the band structures, resulting in optimized band alignment. The photocatalytic performance can be further improved by constructing a BaNbNO₂/BaVNO₂ heterostructure, which has an overpotential of 0.47 V for the OER and ΔG_H of 0.16 eV for the HER. Our theoretical investigation provides not only a guidance to design Janus photocatalysts for full water splitting, but also strategies to modulate the photocatalytic performance through ferroelectricity.