Harvesting the Vibration Energy of BiFeO₃ Nanosheets for Hydrogen Evolution

In this study, mechanical vibration is used for hydrogen generation and decomposition of dye molecules, with the help of BiFeO₃ (BFO) square nanosheets. A high hydrogen production rate of ≈124.1 μmol g^-1 is achieved under mechanical vibration (100 W) for 1 h at the resonant frequency of the BFO nanosheets. The decomposition ratio of Rhodamine B dye reaches up to ≈94.1 % after mechanical vibration of the BFO catalyst for 50 min. The vibration-induced catalysis of the BFO square nanosheets may be attributed to the piezocatalytic properties of BFO and the high specific surface area of the nanosheets. The uncompensated piezoelectric charges on the surfaces of BFO nanosheets induced by mechanical vibration result in a built-in electric field across the nanosheets. Unlike a photocatalyst for water splitting, which requires a proper band edge position for hydrogen evolution, such a requirement is not needed in piezocatalytic water splitting, where the band tilting under the induced piezoelectric field will make the conduction band of BFO more negative than the H₂ /H₂ O redox potential (0 V) for hydrogen generation.