WEB Core-shell composites salt@SiO2 for thermochemical energy storage with high storage densityWednesday (01.01.2020) 00:00 - 00:15 Part of:
Advent of thermochemical energy storage (TCES), that is, storage of thermal energy by means of reversible chemical reactions, incites finding pathways of stabilization of thermochemical materials for thermal batteries of the future. Currently, salt hydrates such as LiCl·H2O, CaCl2·6H2O, SrBr2·6H2O are being actively studied for TCES in buildings due to both high energy storage densities (1-2.5 GJ/m3) and high storage duration . These materials can be charged by an external heat source (e.g. the Sun) to yield anhydrous materials which can be later treated with water vapor to release the stored heat (discharging of a thermal battery).
In this work, we report core-shell composites salt@SiO2 (salt = LiCl·H2O, CaCl2·6H2O, SrBr2·6H2O) with mesoporous shell to facilitate water vapor transport. The hollow capsules of mesoporous SiO2 were prepared by soft templating while the composites were prepared by impregnation of the corresponding salt solutions into the capsules followed by vacuum drying.
The Hollow porous SiO2 Spheres (referred to as HS) possess water capacity of 1.4 cm3/g, superior to most of SiO2 matrices typically used for preparation of salt composites . The packing of the spheres (average diameter 365 nm, average shell thickness = 50 nm) in a bed is close to the densest packing (packing factor 0.67 ~ 0.74). The study of phase composition (XRD), imaging (SEM, HRTEM) and analysis of N2 sorption isotherms showed that salt particles are encapsulated into the porous shells.
Water sorption isotherms and hydration kinetics were reported for LiCl@HS, CaCl2@HS and SrBr2@HS at T = 45-60oC and RH = 1-80%. Cycling stability was proven for LiCl@HS for at least 50 cycles involving the salt deliquescence. SrBr2@HS and CaCl2@HS exhibited stable conversion for at least 20 cycles. HRTEM imaging of the cycled composites showed that capsules are not disintegrated and remain mechanically stable. The volumetric heat storage density of the materials is estimated to reach 0.8-1.2 GJ/m3 in bed for conditions of a domestic heat storage cycle. Thus, the novel core-shell composites with high energy density of the bed and good cyclic stability may be promising for thermochemical energy storage applications in buildings.
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