Dual Polarization Strategy for Boosting Electron–Hole Separation toward Overall Water Splitting within Ferroelectric β-AIBIIIO2 (BIII = P3+, As3+, Sb3+, and Bi3+ for Lone Pairs)

Ferroelectric materials, leveraging an inherent built-in electric field, are excellent in suppressing electron-hole recombination. However, the reliance solely on bulk polarization remains insufficient in enhancing carriers' separation and migration, limiting their practical application in photocatalytic overall water splitting (POWS). To address this, we incorporated cations with ns² lone pairs (P³⁺, As³⁺, Sb³⁺, and Bi³⁺) into ferroelectric semiconductors, successfully constructing 44 β-A^IB^IIIO₂ photocatalysts with dual polarization. Through rigorous first-principles calculations and screenings for stability, band characteristics, and polarization, we identified four promising candidates: β-LiSbO₂, β-NaSbO₂, β-LiBiO₂, and β-TlBiO₂. Within these materials, lone pairs induce local polarization in the xy-plane. Additionally, out of the plane, there is robust bulk polarization along the z-direction. This synergistic effect of the combined local and bulk polarization significantly improves the separation efficiency of electron-hole pairs. Explicitly, the electron mobility of the four candidates ranges from 10⁵ to 10⁶ cm² s^-1 V^-1, while the hole mobility also increases significantly compared to single-phase polarized materials, up to 10⁶ cm² s^-1 V^-1. Notably, β-TlBiO₂ is predicted to achieve a solar-to-hydrogen (STH) efficiency of 17.2%. This study not only offers insights for water-splitting catalyst screening but also pioneers a path for electron-hole separation through the dual polarization strategy.