Mechanism of CO production around oxygen vacancy of LaMnO3: an efficient and rapid evaluation of the doping effect on the kinetics and thermodynamic driving force of CO2-splitting

Abstract

Lanthanum–manganese perovskites have been shown to be promising oxygen carriers for the solar-driven thermochemical production of CO due to their low reduction temperature and considerable CO production. However, to increase their energy conversion efficiency, it is also important to overcome the CO₂-splitting thermodynamic constraints and reduce the time for the complete re-oxidation of perovskites. Thus, herein, the mechanism of CO production around the oxygen vacancy of LaMnO₃ has been elucidated for the first time. One transition state with an activation energy (E_a) of 19 kJ mol⁻¹ was explored and confirmed by the quantity and direction of the imaginary frequency. Based on the analysis of E_a, the evaluated ratio of the CO₂-splitting time for La_1−xSr_xMnO₃ (x = 0.1, 0.2 and 0.3) is 1 : 5.2 : 32.8, which is similar to the experimental ratio of 1 : 4.5 : 29.3. Furthermore, the kinetic characteristics of La_0.625Sr_0.375Mn_0.5B_0.5O₃ and La_0.625Ca_0.375Mn_0.5B_0.5O₃ (B = Al, Ga, Cr and Fe) were predicted, which showed good consistency with experiments. In addition, we found a strong negative correlation between the thermodynamic driving force and the energy difference (ΔE) between the CO₂ and CO adsorption configurations. Thus, all the results indicate the reliability of E_a and ΔE in the prediction and evaluation of the CO₂-splitting activity. Finally, La_0.625Sr_0.375Mn_0.5Cr_0.5O₃ and La_0.625Ca_0.375Mn_0.5Cr_0.5O₃ are suggested as potential STC materials with a fast CO₂-splitting rate and high solar-to-fuel efficiency.