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
2020
Fu, Mingkai | Wang, Lei | Ma, Tianzeng | Ma, Haitao | Xu, Huajun | Li, Xin
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 (Eₐ) of 19 kJ mol⁻¹ was explored and confirmed by the quantity and direction of the imaginary frequency. Based on the analysis of Eₐ, the evaluated ratio of the CO₂-splitting time for La₁₋ₓSrₓMnO₃ (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 La₀.₆₂₅Sr₀.₃₇₅Mn₀.₅B₀.₅O₃ and La₀.₆₂₅Ca₀.₃₇₅Mn₀.₅B₀.₅O₃ (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 Eₐ and ΔE in the prediction and evaluation of the CO₂-splitting activity. Finally, La₀.₆₂₅Sr₀.₃₇₅Mn₀.₅Cr₀.₅O₃ and La₀.₆₂₅Ca₀.₃₇₅Mn₀.₅Cr₀.₅O₃ are suggested as potential STC materials with a fast CO₂-splitting rate and high solar-to-fuel efficiency.
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