Sintering-Resistant Hollow Porous CuO Microspheres with Multi-Shelled Architectures for Durable Renewable Heat-Driven Thermochemical Energy Storage

Multi-shelled hollow (MSH) CuO microspheres were synthesised via a one-pot hydrothermal method to overcome severe sintering that limits the performance of conventional CuO during repeated high-temperature Redox cycling. The MSH microspheres were benchmarked against chemically doped layered double hydroxide (LDH) CuO and physically doped porous granules (PG) with Yttria-stabilised Zirconia (YSZ) CuO, which exhibit good cyclic stability but suffer from significantly reduced energy density due to high dopant contents. All MSH-CuO formulations successfully developed targeted multi-shell architecture, with the best formulation MSH-CuO (F1) achieving the best performance. It delivered the highest measured reaction enthalpy (750.3 J g^-1) and an estimated energy density of 805.18 J g^-1, approximately 71% higher than doped benchmark materials and close to the theoretical limit (810.8 J g^-1). Excellent stability was confirmed through 10 consecutive cyclic redox tests, while SEM/EDS revealed highly porous post-cycled morphologies with no evidence of sintering. These findings demonstrate that the multi-shelled CuO architecture provides high energy density and rapid kinetics, achieving up to 112% higher reduction rates and up to 414% higher oxidation rates relative to the benchmark CuO materials. Most importantly, MSH architecture exhibits intrinsic sintering resistance, offering a promising dopant-free pathway for next-generation thermochemical energy-storage and chemical-looping systems.