Tunable Redox Temperature of a Co3-xMnxO4 (0 ≤ x ≤ 3) Continuous Solid Solution for Thermochemical Energy Storage.

Heat-storage technologies are well suited to improve the energy efficiency of power plants and the recovery of process heat. A good option for high storage capacities, especially at high temperatures, is storing thermal energy by reversible thermochemical reactions. In particular, the Co3O4/CoO and Mn2O3/Mn3O4 redox-active couples are known to be very promising systems. However, cost and toxicity issues for Co oxides and the sluggish oxidation rate (leading to poor reversibility) for Mn oxide hinder the applicability of these single oxides. Considering, instead, binary Co-Mn oxide mixtures could mitigate the above-mentioned shortcomings. To examine this in detail, here, we combine first-principles atomistic calculations and experiments to provide a structural characterization and observe the thermal behavior of novel mixed-metal oxides based on cobalt/manganese metals with the spinel structure Co3-xMnxO4. We show that novel Co3-xMnxO4 phases indeed enhance the enthalpy of the redox reactions, facilitate reversibility, and mitigate energy losses when compared to pure metal oxide systems. Our results expand therefore the limited list of currently available thermochemical heat-storage materials and pave the way toward the implementation of tunable redox temperature materials for practical applications.