Al-Modified CuO/CuO for High-Temperature Thermochemical Energy Storage: from Reaction Performance to Modification Mechanism.

Next-generation concentrated solar power plants with high-temperature energy storage requirements stimulate the pursuit of advanced thermochemical energy storage materials. Copper oxide emerges as an attractive option with advantages of high energy density and low cost. But its easy sinterability limits its reversibility and cyclic stability performance. In this work, aluminum-doped copper oxides are synthesized and evaluated via thermogravimetric analysis. The reversibility of Cu-Al oxides reaches 99.5% in the first redox cycle and maintains 81.1% of the initial capacity after 120 cycles. The Al element can modify the CuO particle surface in the form of CuAlO, which separates the copper oxide particles from each other during redox cycles to avoid agglomeration and participates in the redox reaction. Through DFT analysis, the introduction of Al is found to increase the formation energy of copper vacancies in copper oxides, which helps avoid the sintering problem and thus improves the oxidation rate. This study provides a generalizable operational mechanism of element doping and can serve as a guideline for the optimization of high-performance materials in thermochemical energy storage.