Thermochemical energy storage at high temperature via redox cycles of Mn and Co oxides: Pure oxides versus mixed ones

• Thermochemical energy storage based redox cycles can enhance CSP dispatchability.
• Mn2O3 and Co3O4 redox cycles fit the temperature conditions of future CSP plants.
• Pure Mn and Co oxides show better performance than mixed phases.
• Un-doped Mn2O3 is promising due to lower cost and perfect cyclability.
• Pure Co3O4 is also interesting due to higher energy density and remarkable stability.

Development of thermal energy storage (TES) systems for concentrated solar power (CSP) is essential in order to match a variable electricity demand with an intermittent energy source supply, enhancing energy generation dispatchability. The high energy storage densities and the possibility of working at higher temperature ranges make thermochemical heat storage (TCS) via reduction–oxidation (redox) cycles of metal oxides a promising concept for energy storage. For this purpose, manganese and cobalt oxides have been selected as feasible candidates due to their favourable thermodynamic properties. In order to explore the potential of these materials, the capacity of both pure (Mn2O3 and Co3O4) and mixed oxides (Mn3−xCoxO4) to withstand several charge–discharge cycles was evaluated by thermogravimetrical analysis. Results showed better cyclability for the mixed oxides with low Mn content (x≥2.94) and, specially, for the corresponding pure oxides, confirming that these materials may be a viable option for TCS.