Coupling Piezocatalysis and Photocatalysis in Bi4NbO8X (X = Cl, Br) Polar Single Crystals

Reactive oxygen species (ROS) as green oxidants are of great importance for environmental and biological applications. Photocatalysis is one of the major routes for ROS evolution, which is seriously restricted by rapid charge recombination. Herein, piezocatalysis and photocatalysis (i.e., piezo-photocatalysis) are coupled to efficiently produce superoxide radicals (center dot O-2(-)), hydrogen peroxide (H2O2), and hydroxyl radicals (center dot OH) via oxygen reduction reaction (ORR), by using Bi4NbO8X (X = Cl, Br) single crystalline nanoplates. Significantly, the piezo-photocatalytic process leads to the highest ORR performance of the Bi4NbO8Br nanoplates, exhibiting center dot O-2(-), H2O2, and center dot OH evolution rates of 98.7, 792, and 33.2 mu mol g(-1) h(-1), respectively. The formation of a polarized electric field and band bending allows directional separation of charge carriers, promoting the catalytic activity. Furthermore, the reductive active sites are found enriched on all the facets in the piezo-photocatalytic process, also contributing to the ORR. By piezo-photodeposition of Pt to artificially plant reductive reactive sites, the Bi4NbO8Br plates demonstrate largely enhanced photocatalytic H-2 production activity with a rate of 203.7 mu mol g(-1) h(-1). The present work advances piezo-photocatalysis as a new route for ROS generation, but also discloses the potential of piezo-photocatalytic active sites enriching for H-2 evolution.