Effects of Fe2O3 addition and mechanical activation on thermochemical heat storage properties of the Co3O4/CoO system

Effects of Fe2O3 addition (2-20 wt%) with 1 h mechanical activation on redox reactions of Co3O4 were studied by TG/DSC, SEM, and XRD analyses. The results showed that a Fe2O3 addition from 2 to 15 wt% increases the oxygen release from 1.4 to 3.4 wt% and decreases the reduction onset temperature from 1030 to 960 ℃, while it increases the oxygen uptake value and re-oxidation onset temperature respectively from 1.5 to 3.3 wt% and from 930 to 1010 °C. The increase in iron oxide to 20 wt% resulted in loss of heat storage properties due to significant reduction in oxygen release and uptake. Moreover, TG/DSC analyses revealed that reduction enthalpy of as-received Co3O4, 1 h ball milled Co3O4, and 1 h ball milled Co3O4-15% Fe2O3 are 622, 496, and 895 kJ/kg, respectively. Phase identification and TG experiments under argon atmosphere demonstrated that Fe2O3 participates in the reduction process. Furthermore, adding 15 wt% of iron oxide to cobalt oxide and 1 h mechanical activation improved the redox cyclability of cobalt oxide.