Compressing Two-Dimensional Graphite-Nanosheet-Supported CaO for Optimizing Porous Structures toward High-Volumetric-Performance Heat Storage

The calcium-looping process based on the reversible carbonation/calcination of CaO is an advantageous candidate for thermochemical energy storage (TCES) in concentrated solar power plants. High volumetric energy density combined with high cycling stability is highly desired for CaO-based heat storage material. In this work, we report a simple compression strategy to regulate the meso- and macropores of graphite nanosheet (GNS)-supported CaO, thereby increasing the volumetric energy density of composite materials. Thanks to the separation effect of GNSs on CaO grains, the composite that underwent compression can still maintain high gravimetric energy density and cycle stability. Moreover, as a comparison, the effects of compression on the thermal storage performance of Al-doped CaO and pure CaO were investigated. The results show that compression would reduce the thermal storage stability of Al-doped CaO and pure CaO and worsen the mass transfer of CO2 during the reaction. It further proves the superiority of the combination of compression and GNS-supporting strategies to obtain Ca-based TCES materials with high gravimetric energy density, high volumetric energy density, and excellent cycle stability.