(101a) Earth Abundant Perovskite Oxides for Low Temperature CO2 Conversion

Depletion of fossil fuel reserves along with the associated negative environmental impacts of their use have led to a focus on alternative energy. Solar energy has garnered a lot of attention and coupling this abundant form of energy for efficient reutilization of waste CO₂ presents a novel approach. However, even with significant research efforts over the last decade, CO₂ conversion is still plagued by issues that limit its implementation at large scale. Solar thermochemical (STC)^1,2 processes were perceived as the solution to poor conversion rates. However STC operates at above 1000 °C, making to unfit for industrial purpose. Reverse water gas shift chemical looping (RWGS-CL)³ works on similar principle as STC, the only difference being hydrogen is used as a reducing agent. This allows for reducing the temperatures of operation to ~600 °C. The success of this methods relies on the oxygen vacancy formation characteristics of the perovskite oxides (ABO₃) used as the platforms of CO₂ conversion cycles. Perovskite oxides also present a vast opportunity for material property tuning by simply varying the compositions of ‘A’ and ‘B’ sites. Thus, using DFT-calculated oxygen vacancy formation energy as the descriptor for this process, we predicted several earth abundant materials (ABO_3, A1_0.5A2_0.5BO₃, AB1_0.5B2_0.5O₃, and A1_0.5A2_0.5B1_0.5B2_0.5O₃) with CO₂ conversion capabilities.⁴ These materials were synthesized via Pechini method and demonstrated unprecedented CO₂ conversion rates. The lanthanum and calcium based materials revealed highest CO₂ conversion rates at lowest temperatures (450-500 °C) via RWGS-CL.⁴ These materials also showed long term stability presenting themselves as possible candidates for industrial operation. Efficient conversion of CO₂ to CO via this process enables thermal integration with Fischer Tropsch (FTS) for sustainable generation of hydrocarbons. An empirical model has also been proposed for oxygen vacancy formation energy allowing for future prediction of materials. A detailed composition space investigation has been done on La_(1-x)Ca_xMn_(1-y)Fe_yO₃ to further the CO­₂ conversion capabilities of these perovskite oxides.

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