Ternary BaCaZrTi perovskite oxide piezocatalysts dancing for efficient hydrogen peroxide generation

Piezocatalysis is capable of converting mechanical vibrations into chemical energy, portraying a promising alternative technology for hydrogen peroxide (H₂O₂) production. Environmentally benign lead-free barium titanate piezocatalyst has received particular attention due to its ferroelectric property. However, the reported H₂O₂ yield is not ideal and one of the reasons is the undesirable piezoelectricity. Herein, a series of lead-free perovskite oxides consisting of (1-x)Ba(Zr_0.2Ti_0.8)O₃–x(Ba_0.7Ca_0.3)TiO₃ solid solutions are developed for H₂O₂ production by introducing more favorable crystal phases to increase the piezoelectricity. The prepared perovskite oxides were characterized by significantly enhanced piezoeletricities owing to the coexistence of the ternary (orthorhombic, tetragonal and rhombohedral) phases with reduced energy barrier for polarization rotation. Benefiting from the notably improved piezoelectric property and appropriate oxygen vacancy concentration, the optimal composition of 0.5Ba(Zr_0.2Ti_0.8)O₃–0.5(Ba_0.7Ca_0.3)TiO₃ exhibits an outstanding H₂O₂ selective generation and long-lasting stability. Under ultrasonic irradiation, a superior H₂O₂ yield of 692 µmol g^-1 h^-1 with a selectivity of 80% was attained, showing the enhancement by the factors of 3.3, 4.1 and 8.7 compared to Ba_0.7Ca_0.3TiO₃, BaZr_0.2Ti_0.8O₃ and BaTiO₃, respectively. Furthermore, the catalyst is highly stable by delivering a H₂O₂ productivity of 3313 µmol g^-1 in 14 h of piezocatalysis. Mechanism study suggests that H₂O₂ generation stems from an efficient O₂ reduction via a two-electron transfer pathway, during which the piezopotential is of primary importance to provide driving force for the carrier separation and transportation. Moreover, the green and non-toxic piezocatalysis system based on the BaCaZrTi solid solutions can be applied for efficient water disinfection. This study offers guidance towards the rational design of lead-free piezocatalyst and reaction system for H₂O₂ generation and its application.