부산대학교 도서관

Metal oxides with multiple accessible oxidation states are considered as promising candidates for high-temperature thermochemical energy storage materials. To shed light on the chemical processes involved in redox thermochemical energy storage materials, in-situ powder diffraction was used in combination with atmospheric control to investigate the redox-reactions of Co 3 O 4 , MnO 2 and PbO 2 under various conditions. Thermogravimetry and differential scanning calorimetry under the same conditions provided information on heat-flows and mass-changes. In contrast to theoretical thermodynamic considerations, only Co 3 O 4 and Mn 2 O 3 /Mn 3 O 4 (originating from MnO 2 ) were found fully reversible. In the case of PbO 2 for none of the numerous intermediate phases any kind of reversibility was observed. The effect of the O 2 -concentration in the reactive atmosphere was most distinct for the Mn 2 O 3 system, notably affecting the reduction/oxidation temperatures, whereas for the Co 3 O 4 system only a moderate influence of the O 2 concentration was found. Based on the stability of the intermediate phases under various atmospheres, an isothermal TCES-cycle for Co 3 O 4 and Mn 2 O 3 was investigated, triggering the redox-process by an abrupt change of reactive-gas atmosphere. The fast reaction rate combined with a significant down-shift of the reaction temperatures compared to an isokinetic redox reaction suggests application as a chemical heat pump, as well towards a broadened operational profile not only in combination with concentrating solar power plants, but also with e.g. recycling of industrial flue gas heat. [ABSTRACT FROM AUTHOR]