Rational design of ZnO/SrTiO3 S-scheme heterojunction for photo-enhanced piezocatalytic hydrogen production

Photopiezocatalysis have been frequently investigated for hydrogen evolution reactions in recent years. Herein, ZnO, SrTiO3 and ZnO/SrTiO3 S-scheme heterojunction were investigated for photo/piezocatalytic hydrogen production. Piezocatalytic hydrogen production under ultrasonic vibration by using ZnO, SrTiO3 and ZnO/SrTiO3 was obtained as 270 mu mol g(-1)h(-1), 200 mu mol g(-1)h(-1) and 1265 mu mol g(-1)h(-1), respectively. In addition, ZnO/SrTiO3 S-scheme heterojunction showed 2200 mu mol g(-1)h(-1) photopiezocatalytic hydrogen production under simultaneous exposure to white LED light and ultrasonic sound. ZnO/SrTiO3 heterojunction displayed significantly higher hydrogen production rate due to the decreased charge recombination, increased charge transfer with strong piezoelectric polarization and internal electrical field. The piezoelectric effect of ZnO/SrTiO3 heterojunction is also confirmed by piezoresponse force microscope technique with butterfly and phase hysteresis loops. Also, piezoelectric coefficient of ZnO/SrTiO3 found about 2-folds higher than those of their pristine forms. Electron transfer and reaction mechanism of ZnO/SrTiO3 and activity differences are confirmed by advanced optical and electrochemical techniques such as diffuse reflectance spectroscopy, electronic impedance spectroscopy, Mott-Schottky calculation and chronoamperometry. The whole electrochemical measurements have been performed with or without mechanical stress and light irradiation, which signify their band bending properties, electron transfer mechanism and catalytic activities.