Polar Layered Bismuth‐Rich Oxyhalide Piezoelectrics Bi4O5X2 (XBr, I): Efficient Piezocatalytic Pure Water Splitting and Interlayer Anion‐Dependent Activity

Abstract Piezocatalytic pure water splitting for H 2 evolution carries the virtues of efficacious utilization of mechanical energy, easy operation, and high value‐added products, while lacking desirable piezoelectrics for high chemical energy production. Here, two polar layered bismuth‐rich oxyhalides Bi 4 O 5 X 2 (XBr, I) thin nanosheets (≈4 nm) are first exploited as efficient piezocatalysts to be capable of dissociating pure water. The unique asymmetrical layered structures of Bi 4 O 5 X 2 (XBr, I) composed of the interleaved Bi 4 O 5 2+ layer and double X − ions slabs along the 1 0 1_ orientation cause large intrinsic dipole moment, excellent piezoelectricity and easy deformation. Without any cocatalyst and sacrificial agent, Bi 4 O 5 Br 2 and Bi 4 O 5 I 2 thin nanosheets display remarkable piezocatalytic H 2 production rate of 1149. 0 and 764. 5 µmol g −1 h −1, respectively, standing among the best piezocatalysts, accompanied by H 2 O 2 and hydroxyl radicals (·OH) as oxidative products. The smaller radius and higher electronegativity of interleaved Br than I cause a more strongly polar crystal structure in Bi 4 O 5 Br 2, contributing to the higher piezocatalytic activity compared to Bi 4 O 5 I 2. This study broadens the scope of piezoelectric materials applied to sustainable energy catalysis by efficiently converting mechanical energy and illustrates the importance of crystal configuration and composition in fabricating efficient piezocatalytic systems.