Polarisation tuneable piezo-catalytic activity of Nb-doped PZT with low Curie temperature for efficient CO2 reduction and H2 generation

Abstract

The reduction of CO₂ into useful hydrocarbon chemicals has attracted significant attention in light of the depletion in fossil resources and the global demand for sustainable sources of energy. In this paper, we demonstrate piezo-catalytic electrochemical reduction of CO₂ by exploiting low Curie temperature, T _c ∼ 38 °C, Nb-doped lead zirconate titanate (PZTN) piezoelectric particulates. The large change in spontaneous polarisation of PZTN due to the acoustic pressures from to the application of ultrasound in the vicinity of the T _c creates free charges for CO₂ reduction. The effect of applied acoustic power, particulate agglomeration and the impact of T _c on piezo-catalytic performance are explored. By optimization of the piezo-catalytic effect a promising piezo-catalytic CO₂ reduction rate of 789 μmol g^-1 h^-1 is achieved, which is much larger than the those obtained from pyro-catalytic effects. This efficient and polarisation tunable piezo-catalytic route has potential to promote the development of CO₂ reduction via the utilization of vibrational energy for environmental improvement.

Fig. 1. Schematic of the complete experimental setup for piezo-catalysis based on a double-bath-type sonoreactor.

Fig. 2. (A) Effect of catalyst particle dosage on the delivered acoustic intensity into the reactor; (B) relationship between acoustic intensity and sono-chemical production of hydrogen and carbon monoxide (T_bath = 25 °C, t_react = 30 min). In this case the sample contains zero dosage of particles.

Fig. 3. (A) XRD pattern of Nb-doped PZT powders (PZTN) powders. (B) Relative permittivity as a function of the temperature. SEM images of (C) PZTN and (D) Al₂O₃ (control) powders. PFM spectrum on the local evidence of the existence of ferroelectricity in the Nb-doped PZT powders (E) out-of-plane PFM amplitude and (F) local hysteresis loop behaviour for the amplitude and phase.

Fig. 4. (A) XPS survey spectrum obtained from the PZTN powders, and high-resolution spectrum of (B) O 1s, (C) Pb 4f, (D) Nb 3d, (E) Ti 2p, (F) Zr 3d.

Fig. 5. (A) Effect of catalyst dosage on the sono-piezo catalytic hydrogen and (B) CO production rate (T_bath = 25 °C, t_react = 30 min); (C) effect of PZTN catalyst dosage on the piezo-catalytic production of hydrogen and carbon monoxide expressed in units of μmol h⁻¹, and (D) mmol h⁻¹ g⁻¹.

Fig. 6. (A) Effect of working temperature on the hydrogen and (B) CO production rate (catalyst dosage 0.1 g L⁻¹, t_react = 30 min).

Fig. 7. Schematic of mechanism for CO₂ reduction and H₂ generation based on the application of ultrasound vibrations to ferroelectric PZTN. (A) electrochemical reactions during ultrasonic excitation, (B) enhanced CO production and H₂ generation achieved due to piezo-catalytic and sono-chemical effects when T < T_c.