Ferroelectric Polarization Modulated Facet‐selective Charge Separation in Bi₄NbO₈Cl Single Crystal for Boosting Visible‐light Driven Bifunctional Water Splitting

Abstract

Developing bifunctional water-splitting photocatalysts is meaningful, but challenged by the harsh requirements of specific-facet single crystals with spatially separated reactive sites and anisotropic charge transfer paths contributed by well-built charge driving force. Herein, tunable ferroelectric polarization is introduced in Bi₄ NbO₈ Cl single crystal nanosheets to strengthen the orthogonal charge transfer channels. By manipulating the in-plane polarization from octahedral off-centering of Nb⁵⁺ and out-of-plane polarization from lone pair electron effect of anisotropic Bi³⁺ , both the fast charge recombination in bulk catalyst and the process of charge trapping into surface states can be effectively modulated. Collaborating with modest polarization electric field and facet junction induced built-in electric field, cooperative charge tractive force is constructed, which reinforces the spatial separation and migration of photogenerated electrons and holes to {110} reductive site facet and {001} oxidation site facet, respectively. While excessive polarization charges impair the facet-selective charge separation characteristics and conversely promote charge recombination on the surface. As a result, polarity-optimized Bi₄ NbO₈ Cl shows an excellent H₂ and O₂ evolution rate of 54.21 and 36.08 μmol ⋅ h^-1 in the presence of sacrificial reagents under visible light irradiation. This work unveils the function of ferroelectric polarization in tuning the intrinsic facet-selective charge transfer process of photocatalysts.