Thermochemical energy storage performances of Co3O4-based honeycombs with multi-scale composite pores

Metal oxide redox system characterized open -loop operation, high energy density, and high reversibility, which is one of the most promising thermochemical energy storage technologies for the next-generation concentrated solar power plants. Most of the previous studies focused on the material properties, while the energy storage performance of oxide monolithic bodies, such as energy storage density and heat storage/release rate, has rarely been reported. In this paper, a novel and effective method for the improvement of the energy storage performance of oxide honeycombs with multi-scale composite pores is proposed and presented. Methyl cellulose and four common biomass materials, including bagasse, loofah, juniper leaf, and pine needle, were used as poreforming agents for oxide honeycombs. The pyrolysis of methyl cellulose forms small-scale pores in the honeycomb bodies and contributes the major pore volume. The biomass templates further optimize the pore characteristics, all biomass-templated Co3O4-based honeycomb bodies have higher total pore volume and permeability than that of biomass-free honeycomb body. The honeycomb with 2.5 wt% pine needle achieves the highest energy storage density, with an average of 694.62 kJ/kg during the second to fifteenth cycles. In addition, the honeycomb containing 7.5 wt% pine needle has the highest energy store/release rate. Biomass-templated Co3O4- based honeycomb shows a high crushing strength, and there are no obvious cracks and structural deformations on its surface after 15 thermal cycles. The findings demonstrate that the methyl cellulose and biomass template method can effectively optimize the pore structure and energy storage properties of the oxide honeycombs, thereby expanding the application prospects of Co3O4-based honeycombs in thermochemical energy storage.