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[EN]The CaMnO oxide can reversibly release oxygen over a relatively wide range of temperatures and oxygen partial pressures (pO) and is thus a promising candidate for thermochemical heat storage in Concentrated Solar Power (CSP) plants. Moreover, it is composed of earth-abundant, inexpensive and non-toxic elements and exhibits a high-energy storage density, which are desirable characteristics for decreasing the deployment costs of the system. However, it undergoes decomposition atpO≤ 0.008 atm and temperature ≥ 1100 °C. Here the possibility of overcoming this limitation and extending the operating temperature range by B-site doping with Fe (CaFeMnO) is explored. Two doping levels are investigated,x= 0.1 and 0.3. The enthalpy of reduction was determined from a measurement of continuous equilibrium non-stoichiometry curves (δ,T) at severalpO, enabling an evaluation of the heat storage capacity with high accuracy over widely ranging oxygen non-stoichiometry. Introduction of 0.1 Fe (CaFeMnO) prevented CaMnO decomposition up to 1200 °C atpO= 0.008 atm, thus widening the operating temperature range and the oxygen reduction extent. The increase in the accessible nonstoichiometry translates into an increase in the heat storage capacity (Q(kJ mol)) from ∼272 kJ kgin CaMnOto ∼344 kJ kgin CaFeMnOWhile even larger changes in oxygen content were accessible in CaFeMnO, the oxidation state changes are accompanied by a lower enthalpy of reduction, resulting in a diminished heat storage capacity of ∼221 kJ kg. ; This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 746167. Support of the US Department of Energy, Office of Energy Efficiency and Renewable Energy, Award DE-EE0008089.0000, is also acknowledged. We acknowledge the support with the publication fee by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI).

[EN] CaMnO3 oxide can be considered a promising candidate for high temperature thermochemical heat storage, since it is able to release oxygen in a wide temperature range (800-1000 °C) at different oxygen partial pressures (pO2) suitable for Concentrated Solar Power (CSP) plants. Moreover, it is composed of earth abundant, inexpensive, non-toxic elements. However, it undergoes decomposition at pO2<0.01 atm and at temperature above 1100 °C. In order to overcome this limitation and to extent the operating temperature range, in this study B-site doping with Fe was used as approach for preventing decomposition. The reaction enthalpy was measured through equilibrium non-stoichiometry curves so that the heat storage capacity could be evaluated. It was demonstrated that Fe-doping prevented CaMnO3 decomposition up to 1200 °C at pO2=0.008 thus widening the operating temperature range and the oxygen reduction extent. In addition, the heat storage capacity (ΔH (kJ/molABO3)) of Fe-CaMnO3 (∼324 kJ/kgABO3) is remarkably higher than that of the un-doped CaMnO3 (∼250 kJ/kgABO3 ; This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement N° 74616. Support of the US Department of Energy, Office of Energy Efficiency and Renewable Energy, Award DE-EE0008089.0000, is also acknowledged. ; Peer reviewed