MgCr₂O₄-Modified CuO/Cu₂O for High-Temperature Thermochemical Energy Storage with High Redox Activity and Sintering Resistance

Metal oxides as high-temperature thermochemical energy storage systems with high energy density based on the gas–solid reaction are a critical demand for the future development of concentrated solar power plants. A copper-based system has high enthalpy change and low cost, but its serious sintering leads to poor reactivity. In this study, MgCr2O4 is decorated on the CuO/Cu2O surface to effectively increase the sintering temperature and alleviate the sintering problem. The re-oxidation degree is increased from 46 to 99.9%, and the reaction time is shortened by 3.7 times. The thermochemical energy density of storage and release reach −818.23 and 812.90 kJ/kg, respectively. After 600 cycles, the oxidation activity remains 98.77%. Material characterization elucidates that nanosized MgCr2O4 is uniformly loaded on the surface of CuO/Cu2O during the reversible reaction, and there is a strong interaction between metal oxides and prompter. Density functional theory (DFT) calculation further confirms that CuO/Cu2O–MgCr2O4 has large binding energy and the formation energy of copper vacancy increases, which can effectively inhibit sintering. The modification mechanism of CuO/Cu2O by MgCr2O4 is revealed, which can provide guidance for the reasonable design of thermochemical energy storage materials with sintering resistance and redox activity.