Effectiveness of Zr and Hf incorporation into LaCoO3 towards fast and thermodynamically favorable solar thermochemical CO production studied with density functional theory

Abstract

As prominent oxygen carriers for the solar thermochemical (STC) cycle, the current Co-based perovskites suffer from a low CO production rate and CO₂-to-CO conversion ratio. To enhance the above performance metrics, the adsorption and dissociation processes of CO₂ on the LaCoO₃(010) defect surface are studied. A transition state with a high activation energy (E_a) of 66.8 kJ mol⁻¹ is determined at the CO₂-splitting step, leading to the slow CO production by the LaCoO₃-based system. However, we find that E_a could be reduced to 51.3 and 52.9 kJ mol⁻¹ with 12.5% Zr and Hf doped at the B position of LaCoO₃, as a result of which the CO₂-splitting rate could increase up to 8 and 6.4 times at T = 900 K. Meanwhile, the results of the Gibbs free energy change indicate that LaCo_0.875Zr_0.125O₃ and LaCo_0.875Hf_0.125O₃ feature a larger thermodynamic driving force of CO₂-splitting. In addition, the Hf dopant is also favorable for oxygen vacancy formation of LaCoO₃. Our results demonstrate the feasibility of LaCo_0.875Hf_0.125O₃ for fast STC CO production with high solar-to-fuel efficiency.