Exploring Cu-Based Spinel/Delafossite Couples for Thermochemical Energy Storage at Medium-High Temperature

Cu-based spinel/delafossite couples with Mn and Fe as second cations were synthesized using the Pechini method for medium-high temperature thermochemical energy storage. Physicochemical properties of each sample were investigated. Only CuMn2O4/CuMnO2 exhibited favorable redox behavior in the range of 500–1000 °C. Cu-based delafossite can reoxidize at a lower temperature (∼600 °C), which may be related to the existence of a MO6 octahedra structure. Through the isothermal oxidation method, CuMn2O4/CuMnO2 couple showed a larger oxidation enthalpy of 258.32 ± 15.31 kJ/kg (1402.68 ± 83.13 kJ/L) than 190.35 ± 4.81 kJ/kg (1048.83 ± 26.50 kJ/L) of CuFe2O4/CuFeO2 couple. CuMn2O4 was chosen for further cyclability test with 20 cycles; the depth of reduction increased gradually and stabilized at 4% change in mass after 13 cycles.