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 Sm0.6Sr0.4MnO3. 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, SmxSr1−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.
Hongming Liu,Jingxin Wang,Hai Xiong,Yue Chen,Jianzhong Xiao,Chao Wang
Restricted by an insufficient understanding of the compositional and structural characteristics of the sensing materials that affect the sensing performances, the YSZ-based CO gas sensor remains in a dilemma in terms of further promoting sensitivity, selectivity and long-term stability. In this work, two bimetallic oxides with different crystal structures, perovskite SmMnO 3 and mullite SmMn 2 O 5 , were prepared and adopted to elucidate the roles of the Mn 3+ , Mn 4+ and surface oxygen vacancies . Compared with SmMnO 3 , the coexisting coordination modes of Mn 3+ and Mn 4+ in SmMn 2 O 5 is conducive to generating oxygen vacancies. Furthermore, a SmMn 2 O 5 -based sensor with more oxygen vacancies demonstrates a relatively faster response/recovery speed and enhanced sensitivity of 2.05 times that of SmMnO 3 under the same operation conditions. Such work may broaden insight into the development of efficient sensing materials that introduce oxygen vacancies through the construction of phase structures without complicated operations. Overall, the sensor attached to SmMn 2 O 5 exhibits a low detection limit (5 ppm), a feasible response/recovery speed (24 s/28 s toward 40 ppm CO operating at 450 °C), satisfactory CO selectivity and long-term stability, highlighting its potential for CO monitoring in harsh environments.
Jia Yuan Min,Long Long Yu,Pei Song Tang,Hai Feng Chen
Using samarium (III) nitrate hexahydrate, manganese nitrate and citric acid as main raw materials, the SmMnO3 gel was prepared by sol-gel process. The gel was kept at 100 °C for 24 h to get the xerogel. Then, the xerogel was respectively calcined in muffle furnace at 600 °C, 700 °C, 800 °C and 900 °C. The structure and morphology of samples were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier Transform Infrared (FT-IR) spectroscopy. The UV photocatalytic activities of SmMnO3 were investigated by methyl orange which was used as simulated sewage. The results show that the pure SmMnO3 can be obtained through calcination between 700 °C and 800 °C, and the SmMnO3 have an average particle size of 80 nm. The SmMnO3 samples calcined at 700 °C and 800 °C show high photocatalytic activity for decomposition of methyl orange under UV-light irradiation. The SmMnO3 samples are consistent with first-order kinetics for the degradation of methyl orange. And the apparent rate constants are respectively k700 =0.01206 min-1and k800=0.01088 min-1.
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