Polar Layered Bismuth-Rich Oxyhalide Piezoelectrics Bi4O5X2 (X=Br, I): Efficient Piezocatalytic Pure Water Splitting and Interlayer Anion-Dependent Activity

Piezocatalytic pure water splitting for H2 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 Bi4O5X2 ((Formula presented.), I) thin nanosheets (≈4 nm) are first exploited as efficient piezocatalysts to be capable of dissociating pure water. The unique asymmetrical layered structures of Bi4O5X2 ((Formula presented.), I) composed of the interleaved [Bi4O5]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, Bi4O5Br2 and Bi4O5I2 thin nanosheets display remarkable piezocatalytic H2 production rate of 1149.0 and 764.5 µmol g−1 h−1, respectively, standing among the best piezocatalysts, accompanied by H2O2 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 Bi4O5Br2, contributing to the higher piezocatalytic activity compared to Bi4O5I2. 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.