Efficient CO2 reduction to reveal the piezocatalytic mechanism: From displacement current to active sites

Piezocatalysis has attracted the increasing interest of researchers as a novel catalytic method. To date, there are two popular mechanisms regarding the piezocatalysis, i.e., the piezoelectric effect and the energy band theory. However, both mechanisms cannot fully explain the piezocatalytic process: the electrons generated by the piezoelectric effect will not spontaneously participate in the piezocatalysis, while not all piezoelectric materials have an appropriate energy band structure. In this work, displacement current and the principle of piezoelectric nanogenerator are introduced to fully comprehend the piezocatalytic mechanism for the first time. As a proof-of-concept catalytic system, we synthesize Co-N-C@BaTiO3 piezocatalyst for the CO2 reduction reaction (CO2RR) under ultrasonic vibration. A promising piezocatalytic CO2 reduction rate of 261.8 mol g(-1)h(-1) is achieved with a high CO selectivity up to 93.8% under 50 kHz ultrasonic vibration. The CO yields of this catalytic system outperform most of the reported photocatalytic CO2RR and piezocatalytic CO2RR. Moreover, a comprehensive piezocatalytic mechanism from displacement current to active sites is proposed and supported by combining CoN-C@BaTiO3 piezoelectric nanogenerator, COMSOL simulation and energy band structure analysis. Under the ultrasonic vibration, the electrons generated by the piezoelectric effect are driven by the time-varying electrostatic potential formed by the displacement current. The suitable band structure of piezoelectric provider that satisfies the potential of reaction promotes electrons to participate in CO2RR on active sites. Overall, our work provides an insightful understanding of piezocatalysis and paves a new path for its development.