Thermochemical Heat Storage Properties of Co3O4-X wt % Al2O3 and Co3O4-X wt % Y2O3 Composites (X=1, 2, 5, 8, 10)

Abstract

The effect of Al₂O₃ (1-10 wt %) and Y₂O₃ (1-10 wt %) additions on thermochemical heat storage properties of Co₃O₄/CoO system was investigated by thermogravimetry, XRD, and SEM analyses. Results showed that the addition of Al₂O₃ to Co₃O₄at constant 8 h mechanical activation improved the redox cycle stability and increased oxygen sorption value and rate. It was found that oxygen sorption and their rate decreased with increasing the alumina content to more than 8 wt %. The formation of the spinel phase and an increase in its amount by increasing the alumina content led to a decrease in the oxygen sorption capacity. SEM studies showed that Al₂O₃ prevented the sintering and particle growth of cobalt oxide particles during reduction and re-oxidation processes. In addition, results showed that the addition of Y₂O₃ in all ranges to Co₃O₄improved the redox cycle stability of cobalt oxide; however, it significantly decreased the oxygen sorption in the Co₃O₄/CoO system. XRD patterns of a sample containing 10 wt % yttria before the redox process indicated the presence of only Co₃O₄phase; however, after three redox cycles, other phases including CoO and Y₂O₃ appeared.