Metal-Oxides for Thermochemical Energy Storage – from Gas-Triggered Isothermal Cycling to Low-Temperature Applications with Increased O2 Pressure
Abstract
Abstract Metal oxides providing various, reversibly accessible oxidation states are in the focus as auspicious materials for high-temperature thermochemical energy storage (TCES) materials. Among all principally suitable metal oxides due to equilibrium temperature and, in particular, reaction rate and reversibility, only the couple Co3O4 / CoO and to a smaller extend Mn2O3 / Mn3O4 are considered as suitable candidates. Based on recent studies on isothermal TCES-cycles, the impact of temperature and increased O2-pressure on the reaction rate was investigated by varying the O2-partial pressure in the low-temperature oxidation of the reduced oxide. Whereas Mn3O4 was found to react too slow for a process at lower temperatures, CoO was found suitable. For an increase of the O2 pressure to 6 bar between 500 – 550 °C an attractive oxidation behavior was observed. At 900 °C Co3O4 / CoO could be cycled within 4.5 minutes between both oxidation states by changing the atmosphere from N2 to O2 and vice versa.