Polarization and external-field enhanced photocatalysis

Photocatalysis, which can directly convert solar light into chemical energy, is considered one of the most promising green techniques for sustainable energy and environmental remediation. However, owing to the fast recombination of photogenerated carriers, photocatalytic efficiency is still far from satisfactory. To solve this issue, construction of a built-in electric field has been demonstrated as one of the most efficient strategies for improving charge separation and transfer. An emerging strategy is to integrate polarization, photoexcitation, and semiconductor properties to induce a built-in electric field by internal spontaneous polarization and/or external fields. This technique can be applied to facilitate carrier separation both in the bulk phase and at the surfaces of semiconductors. In this review, the different types of polarization and external fields, which are believed to critically influence the photocatalytic performance, are classified. The fundamental mechanisms, including band bending and carrier separation, are also discussed. The state-of-the-art progress in polarization and external-field enhanced photocatalysis in water splitting, pollutant degradation, CO2 reduction, and energy harvesting is summarized. Finally, an outlook for future developments in this promising research field is presented.