Fe-based materials are widely utilized as chemical looping oxygen carriers because of their low price, high mechanical strength and environmentally friendly nature. However, the sintering problem restrains its further improvement on redox reactivity and stability. Here, we developed a yolk–shell structured Fe2O3@Y2O3 oxygen carrier, with a thin, porous Y2O3 shell surrounding a nano-sized Fe2O3 core. The superior thermostability of Y2O3 makes it a promising candidate for yolk–shell structures, as it may protect the active cores from sintering under high temperature, whereas the void can tolerate volume/phase change of metal oxide core during redox cycles. The synthesis procedure consists of three main steps including coating and etching (Figure a), and the morphology of the resulting products was confirmed by TEM (Figure b-e). The performance of the oxygen carrier was preliminarily tested by thermogravimetric analysis (TGA) at 650 °C. In each cycle the sample was reduced in 5% H2 and re-oxidized in air with N2 purge separating the two phases. As shown in Figure f, the Fe2O3@Y2O3 exhibited an unchanged oxygen carrying capacity of 4 wt% during 100 consecutive redox cycles, without any distinguishable structural damage (Figure f top inset). The satisfactory sintering resistance of this proposed structure demonstrates the exploitation of transition metal oxides-based nanoreactors as a powerful tool to improve oxygen carriers’ cycling stability.
