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

Abstract

Heat storage technologies are well suited to improve energy efficiency of power plants and recovery of process heat. A good option for high storage capacities, especially at high temperatures, is storing thermal energy by reversible thermo-chemical 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 sluggish oxidation rate (leading to poor reversibility) for Mn oxide, hinder the applicability of these singles 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 thermal behavior of novel mixed metal oxides based on cobalt/manganese metals with spinel structure Co3-xMnxO4. We show that novel Co3-xMnxO4 phases enhance indeed the enthalpy of the redox reactions, facilitate reversibility, and mitigate energy losses when compared to pure metal oxide systems. Our results enlarge therefore the limited list of today's available thermochemical heat storage materials and pave the way towards the implementation of tunable redox temperature materials for practical applications.