Inducing Bulk Polarization in Nonpolar Photocatalysts by Interstitial Li and Charge Compensator Codoping.

Abstract

Establishing a bulk-penetrating built-in electric field is crucial for enhancing charge separation efficiency in nonpolar photocatalysts. Compared with most existing approaches relying on widening surface space charge layers, inducing bulk polarization via doping is more effective. However, this relies on an ordered spatial distribution of dopants throughout nonpolar photocatalysts, requiring a new mechanism enabling spontaneous alignment of spatially separated dopants. Herein, for interstitial Li-doped anatase TiO₂, we reveal that a specific reduction in local symmetry around interstitial Li atoms achieved under an ordered Li spatial distribution leads to a strong s-d hybridization. This promotes the localization of excess electrons donated by interstitial Li atoms, thereby lowering the total energy and rendering the ordered Li spatial distribution the most stable. Combined theoretical and experimental results confirm that the ordered Li spatial distribution, coupled with charge-compensated N-codoping, induces bulk polarization of 2.36 and 3.47 µC/cm² along the [100] and [001] directions, respectively, at 5 at.% doping level. This leads to a 440% improvement in the photocurrent density of Li/N-codoped anatase TiO₂ compared to the pristine one at 1.23 V versus SHE. Moreover, the mechanism has also been generalized to Y₂Ti₂O₅S₂ and SrTaO₂N, demonstrating its universality for inducing bulk polarization in nonpolar photocatalysts.