Redox cycles of manganese oxides (Mn2 O3 /Mn3 O4 ) are a promising alternative for thermochemical heat storage systems coupled to concentrated solar power plants as manganese oxides are abundant and inexpensive materials. Although their cyclability for such a purpose has been proved, sintering processes, related to the high-temperature conditions at which charge-discharge cycles are performed, generally cause a cycle-to-cycle decrease in the oxidation rate of Mn3 O4 . To guarantee proper operation, both reactions should present stable reaction rates. In this study, it has been demonstrated that the incorporation of Fe, which is also an abundant material, into the manganese oxides improves the redox performance of this system by increasing the heat storage density, narrowing the redox thermal hysteresis, and, above all, stabilizing and enhancing the oxidation rate over long-term operation, which counteracts the negative effects caused by sintering, although its presence is not avoided.
Keywords: iron; manganese; redox chemistry; renewable resources; thermochemistry.
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