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⁻¹h⁻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 Co-N-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.