Screening of optimal dopants on cobalt-based ceramics for high-temperature thermochemical energy storage

To date, numerous dopants have been investigated to promote the initial heat storage performance or sintering resistance of Co3O4 for thermochemical energy storage. Owing to the different synthesis methods and heat storage test conditions, the performances of these materials are not comparable. In this work, nine dopants, including four unreported dopants, were systematically compared and screened under the same conditions. Results demonstrated that for five redox cycles, the Si-and Mg-doped sample had adverse effects on the con-version rate, and the others maintained the conversion rate above 0.95. Cu and Zr doping exhibited the highest re-oxidation rate values, and those of the others were lower than that of pure cobalt oxide. Moreover, except for Cu and Zr, all dopants adversely affected energy density. According to aforementioned heat storage properties, Cu-, Zr-doped samples, and pure cobalt oxide were subjected to 100 cycles for further comparison. The Cu-doped sample exhibited a higher re-oxidation rate and energy density, and the Zr-doped sample exhibited more stable cyclability. Finally, by doping Cu and Zr, the micromorphology evolution was more stable than that of pure oxide for multiple cycles, and X-ray photoelectron spectroscopy results revealed that the higher surface oxygen was the primary reason for the superior performance facilitated by Cu and Zr. The Cu-and Zr-modified cobalt oxides were the potential candidates for thermochemical energy storage.