Reassessment of thermochemical energy storage in perovskite-like manganites at comparative studies of RP SrCa3Mn3O10-δ vs. orthorhombic Sr0.25Ca0.75MnO3-δ

摘要

? 2022The structural stability, thermal expansion, oxygen exchange thermodynamics, and thermochemical storage (TCS) capacity of perovskite-like Sr0.25Ca0.75MnO3-δ and Ruddlesden-Popper SrCa3Mn3O10-δ manganites are studied by the combined use of experimental techniques, thermodynamic modeling of the defect formation reactions, and energy calculations utilizing density functional theory (DFT). It is argued that conservative estimates of the storage capacity can be made by the use of the Dulong-Petit limit for high-temperature heat capacity and oxygen partial enthalpy independent of both temperature and oxygen content. The respectively recalculated literature data and the obtained results show that the thermodynamic limit for the TCS capacity (~800 kJ/kg) of Sr0.25Ca0.75MnO3-δ is one of the highest at thermal cycling within the oxygen partial pressure range of 10 ?4–0.21 atm. At the same time, the storage capacity of SrCa3Mn3O10-δ achieves only about 600 kJ/kg. The TCS cycling tests demonstrate the stability of SrCa3Mn3O10-δ while a decline in the energy storage capacity is observed for Sr0.25Ca0.75MnO3-δ. According to the EDX analysis, this effect may reflect surface degradation of Sr0.25Ca0.75MnO3-δ. The energy storage capacities of SrCa3Mn3O10-δ and Sr0.25Ca0.75MnO3-δ decrease to 510 and 560 kJ/kg, respectively, because of the rather sluggish reduction kinetics. It is concluded that further improvement of manganites as energy storage materials can be achieved using new doping strategies.