Alkali Metal Cations as Charge-Transfer Bridge for Polarization Promoted Solar-to-H2 Conversion

Abstract

Utilization of spontaneous polarization electric field of ferroelectric materials to realize the spatial separation and fast transfer of photogenerated charges has been regarded as a promising strategy to fabricate highly efficient photocatalysts. Herein, a novel heterostructure is constructed by coupling potassium poly(heptazine imide) (K-PHI) with ferroelectric BaxSr1-xTiO3 (BxST) through a facile electrostatic self-assembly strategy. The ionic species of K-PHI can neutralize the polarized charges in BxST to form intimate interfacial contact, substantially boosting the internal electric field. Notably, K+ cations intercalated into K-PHI act as charge-transfer bridge to promote migration and separation of photogenerated charge carriers. As a result, a significantly improved H2-evolution rate of 1087.4 µmol h−1 g−1 with an apparent quantum yield (AQY) of 8.05% at 420 nm is achieved over 5% K-PHI/B0.8ST, standing among the best polymeric carbon nitride-based photocatalysts reported up to date. Moreover, the extreme stability of the catalysts is evidenced by remaining outstanding catalytic performance even after storage for half a year. This strategy can be extended to other alkali metal (Na+ and Cs+) modified polymeric materials, highlighting the key role of the bridging ions in constructing polarized heterostructure, which sheds light on the design of ferroelectric-assisted photocatalysts.