Sr-doped SmMnO₃ perovskites for high-performance near-isothermal solar thermochemical CO₂-to-fuel conversion

Solar thermochemical CO₂-to-fuel conversion via two-step redox cycles is a promising strategy to solve climate change and energy storage challenges simultaneously. However, ideal thermochemical materials possessing moderate operation temperature, high yield, good stability, and rapid kinetics operating under isothermal and near-isothermal conditions are still missing. Here, we propose Sr-doped SmMnO₃ for moderate-temperature near-isothermal CO₂-to-fuel conversions. A record-high isothermal cycle CO yield (376.1 μmol g^-1) at no more than 1300 °C is reported based on Sm_0.6Sr_0.4MnO₃. No obvious decay is observed during 14 cycles although grain sizes have increased to some extent. The weakened Mn-O bond induced by Sr doping helps to create more oxygen vacancies, and thus contributes to enhanced yield of both O₂ and CO. The oxidation reaction is fast with a CO yield of 58.6 μmol g^-1 in 15 minutes, which is 5.6 times as high as that of CeO₂ under the same cycling conditions between 1300 °C and 1000 °C. Detailed kinetics for the oxidation step is unveiled based on the Šesták-Berggren model. In addition, Sm_xSr_1-xMnO₃ can capture full-spectrum solar energy with a solar absorptance of more than 86.6% in stark contrast to 13.5% for CeO₂, making the required concentration ratio to drive reactions decrease by 33.4%. This work provides new materials for high yield and stable thermochemical CO₂-to-fuel conversion under moderate-temperature near-isothermal conditions, and paves the way for the development of CO₂ splitting techniques directly driven by low-concentration solar energy with high efficiencies.