Core-Shell Encapsulation of Salt Hydrates into Mesoporous Silica Shells for Thermochemical Energy Storage

The 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, and SrBr2·6H2O are being actively studied for TcES in buildings due to both high energy storage density (1-2.5 GJ/m3) and high storage duration. In this work, we report the core-shell composites "salt in hollow SiO2 spheres with mesopores"(salt = LiCl·H2O, CaCl2·6H2O, SrBr2·6H2O) for domestic TcES. The salt hydrates were encapsulated into submicrometer-sized hollow SiO2 (HS) capsules as confirmed by transmission electron microscopy (TEM) and N2 sorption analyses. High sorption/desorption rates due to mesopores of the shells were shown by thermogravimetric analysis (TGA). The sorption equilibrium for salt@HS was reported, and the applicability of the materials for domestic heat batteries was analyzed. As a result of almost the densest packing of salt@HS, the composites were shown to provide a state-of-the-art energy storage density up to 0.86 GJ/m3 on the bed level for the high-temperature lift of 32-47 °C, showing high energy storage capacity. The stability in at least 50 charging/discharging cycles was confirmed by TGA and TEM

Stabilization of K2CO3 in vermiculite for thermochemical energy storage

Thermochemical energy storage (TCES) is an emerging technology promising for domestic applications. Recently, K2CO3 was identified and studied as a TCES material. In this work, the composite “K2CO3 in expanded vermiculite” (69 wt. % of the salt) was prepared and studied for thermochemical energy storage bearing in mind its application for space heating. The hydration rate was found to be higher for the confined K2CO3 in comparison with K2CO3 granules of the same size. While morphology and texture of the composite alter after 74 hydration/dehydration cycles, its chemical composition and average grain size do not change. The energy storage density of the composite bed can reach 0.9 GJ/m3 (250 kWh/m3) for cycles with deliquescence which makes the composite an inexpensive thermochemical material for space heating. Stable conversion for deliquescence conditions was shown for at least 47 cycles

Caesium doping accelerates the hydration rate of potassium carbonate in thermal energy storage

Potassium carbonate has recently been identified as a promising candidate for thermochemical energy storage. However, as for many salt hydrates, its reaction kinetics is relatively slow. K2CO3 has a metastable zone, where the reaction is kinetically hindered, which limits the temperature operating window. This work aims to improve the material performance, focusing on two aspects; improving the kinetics outside the metastable zone and reducing the metastable zone width. This work shows that doping with Cs2CO3, can improve both. Moreover, it is shown that the dopant enhances the hydration rate by introducing mobility due to local deliquescence. This lays the foundation for further material research using dopants to enhance the performance of salt hydrates

Adapting the MgO-CO\u3csub\u3e2\u3c/sub\u3e working pair for thermochemical energy storage by doping with salts:effect of the (LIK)NO\u3csub\u3e3\u3c/sub\u3e content \u3csup\u3e†\u3c/sup\u3e

\u3cp\u3eThe MgO-CO\u3csub\u3e2\u3c/sub\u3e working pair has been regarded as prospective for thermochemical energy storage (TCES) due to its relatively high heat storage capacity, low cost, and wide availability. This study is aimed at the optimization of the molar salt content, α, for the MgO modified with the eutectic mixture of LiNO\u3csub\u3e3\u3c/sub\u3e and KNO\u3csub\u3e3\u3c/sub\u3e (Li\u3csub\u3e0.42\u3c/sub\u3eK\u3csub\u3e0.58\u3c/sub\u3eNO\u3csub\u3e3\u3c/sub\u3e) which was earlier shown to provide high conversion, ∆x, in heat-storage/release processes at 300–400 \u3csup\u3e◦\u3c/sup\u3eC. The composites that have different salt content were prepared and carbonation kinetics was investigated under various conditions (carbonation temperature, T\u3csub\u3ecarb.\u3c/sub\u3e, is 290–360 \u3csup\u3e◦\u3c/sup\u3eC and CO\u3csub\u3e2\u3c/sub\u3e pressure, P(CO\u3csub\u3e2\u3c/sub\u3e), is 50–101 kPa). Significant accelerating effect was revealed at α ≥ 0.05, and the ∆x value was maximized at α = 0.10–0.20. The largest conversion of 0.70 was detected at α = 0.10 and T\u3csub\u3ecarb.\u3c/sub\u3e = 350 \u3csup\u3e◦\u3c/sup\u3eC that corresponds to the specific useful heat (Q\u3csub\u3ecomp.\u3c/sub\u3e) is 1.63 MJ/kg-composite. However, the salt content of 0.20 ensures the high conversion, ∆x = 0.63–0.67 and Q\u3csub\u3ecomp.\u3c/sub\u3e = 1.18–1.25 MJ/kg-composite in the whole temperature range between 290 and 350 \u3csup\u3e◦\u3c/sup\u3eC. The (LiK)NO\u3csub\u3e3\u3c/sub\u3e/MgO composite with an optimal salt content of 0.20 exhibits reasonable durability through cyclic experiment at 330 \u3csup\u3e◦\u3c/sup\u3eC, namely, the stabilized reacted conversion ∆x = 0.34 (Q\u3csub\u3ecomp.\u3c/sub\u3e = 0.64 MJ/kg-composite). The studied (Li\u3csub\u3e0.42\u3c/sub\u3eK\u3csub\u3e0.58\u3c/sub\u3e)NO\u3csub\u3e3\u3c/sub\u3e promoted MgO-CO\u3csub\u3e2\u3c/sub\u3e working pair has good potential as thermochemical storage material of middle temperature heat (300–400 \u3csup\u3e◦\u3c/sup\u3eC).\u3c/p\u3

Adapting the MgO-CO2 working pair for thermochemical energy storage by doping with salts: effect of the (LIK)NO3 content †

The MgO-CO2 working pair has been regarded as prospective for thermochemical energy storage (TCES) due to its relatively high heat storage capacity, low cost, and wide availability. This study is aimed at the optimization of the molar salt content, α, for the MgO modified with the eutectic mixture of LiNO3 and KNO3 (Li0.42K0.58NO3) which was earlier shown to provide high conversion, ∆x, in heat-storage/release processes at 300–400 ◦C. The composites that have different salt content were prepared and carbonation kinetics was investigated under various conditions (carbonation temperature, Tcarb., is 290–360 ◦C and CO2 pressure, P(CO2), is 50–101 kPa). Significant accelerating effect was revealed at α ≥ 0.05, and the ∆x value was maximized at α = 0.10–0.20. The largest conversion of 0.70 was detected at α = 0.10 and Tcarb. = 350 ◦C that corresponds to the specific useful heat (Qcomp.) is 1.63 MJ/kg-composite. However, the salt content of 0.20 ensures the high conversion, ∆x = 0.63–0.67 and Qcomp. = 1.18–1.25 MJ/kg-composite in the whole temperature range between 290 and 350 ◦C. The (LiK)NO3/MgO composite with an optimal salt content of 0.20 exhibits reasonable durability through cyclic experiment at 330 ◦C, namely, the stabilized reacted conversion ∆x = 0.34 (Qcomp. = 0.64 MJ/kg-composite). The studied (Li0.42K0.58)NO3 promoted MgO-CO2 working pair has good potential as thermochemical storage material of middle temperature heat (300–400 ◦C)

Novel adsorption method for moisture and heat recuperation in ventilation: Composites “LiCl/matrix” tailored for cold climate

Nowadays, advanced technologies for rational use of energy in dwellings have aroused a considerable interest. In cold countries huge amounts of heat and moisture are wasted through the air infiltration due to the large difference between indoor and outdoor temperatures. In this work, an advanced adsorption approach to heat and moisture recuperation in ventilation, called VentireC, is suggested. In this approach, the moisture and sensible heat from outgoing air are absorbed on the adsorbent and heat storing beds and then withdrawn into the inflowing outdoor air, thus, maintaining the indoor temperature and humidity balance. Thermal coupling between two adsorbent beds, which work out of phase, allows latent and sensible loads to be managed separately to enhance the humidity recuperation. For harmonizing the adsorbent properties with the operating conditions of the VentireC process, the requirements for optimal sorbents are formulated based on the thermodynamic analysis of the process. New sorbents based on LiCl incorporated in four matrices with the various mesoporous structure are synthesized and investigated. The water sorption/desorption equilibrium for the most promising sorbent is reported. This composite exchanges over 0.5 g-H2O/g under a typical VentireC cycle, which is promising for effective heat and moisture regeneration