(450c) Redox Thermodynamics of Fe-Doped Magnesium Manganate for Thermochemical Energy Storage

Thermochemical energy storage (TCES) is an alternative technology to sensible and latent heat storage that can provide higher energy storage density. TCES can be paired with existing technologies such as concentrates solar thermal plants or grid electricity to provide long duration energy storage. High-temperature TCES is of particular interest as it can be coupled with high efficiency power cycles providing a unique opportunity for large scale energy storage. Existing research has investigated TCES systems utilizing various storage materials including metallic hydrides, carbonates, hydroxides, and metal oxides. Of these materials, the Mn₃O₄/MnO system has been studied for its relatively high reaction enthalpy in addition to a low cost, however, it faces limitations as it is susceptible to sintering reducing its reversibility and energy storage density upon cycling. Combining magnesium with manganese oxide in MgMn₂O₄ actively reduces the sintering of manganese, providing full reversibility over hundreds of cycles as well as a large energy storage density when combining sensible and thermochemical heat. Further improvements are envisioned by the addition of a small concentration of dopants to increase energy storage density by changing the underlying thermodynamics of the material. In this work, we will present how doping MgMn₂O₄ with Fe allows for increased energy density while maintaining reactive stability. The fundamental thermodynamic description of the materials reduction and oxidation behavior derived from van’t Hoff analysis using thermogravimetric data will be presented. The material characterization confirms the phase purity and phase transitions of the doped material.