Reactive Phase‐Change Materials for Enhanced Thermal Energy Storage

Abstract

Effective storage and release of low‐to‐moderate temperature thermal energy (e.g., solar thermal or geothermal) could be transformational for applications such as space heating/cooling, domestic hot water, or off‐grid cooking. Good candidates for thermal energy storage in this temperature range include latent heat storage (LHS) systems and thermochemical energy storage (TCES) systems using reversible salt‐hydrate dehydration reactions. Here, we propose that an energy‐storage system by use of magnesium nitrate hexahydrate can potentially improve upon independent TCES or LHS systems by utilizing both the thermochemical hydration reaction and the latent heat available through the solid–liquid phase change of one magnesium nitrate hydrate eutectic. This chemistry is investigated through thermogravimetric analysis (TGA)/differential scanning calorimetry (DSC) analysis and shows a total energy density of approximately 1170±94 kJ kg−1 when dehydrating the material up to 145 °C. Reversible latent heat cycling at a eutectic melting temperature of 130 °C is shown by the DSC signal and estimated to be on the order of 115±9.2 kJ kg−1—a 10 % increase over the thermochemical energy storage alone. Although the latent energy release was found to decrease slightly over several cycles, the mass was found to stabilize near an asymptotic value corresponding to the published eutectic composition. These results suggest the concept of reactive phase‐change materials could be a promising solution to increasing the stored volumetric energy density.

Water sorption-based thermochemical storage materials: A review from material candidates to manufacturing routes

“…The dehydration occurs in three steps; from the hexahydrate to the dihydrate showing that the slow dehydration is stable at lower hydrate states before decomposing at 400 °C. Two decomposition steps were observed by Paulik et al (1988) and Drake et al (2018), one from 300 to 400 °C with 56% mass loss of the initial hexahydrate and 450-500 °C with 17%. Drake et al (2018) combined two energy storage methods aiming to harness the advantages of both (latent heat and thermochemical) by studying the eutectic composition of magnesium nitrate and water.…”

“…Two decomposition steps were observed by Paulik et al (1988) and Drake et al (2018), one from 300 to 400 °C with 56% mass loss of the initial hexahydrate and 450-500 °C with 17%. Drake et al (2018) combined two energy storage methods aiming to harness the advantages of both (latent heat and thermochemical) by studying the eutectic composition of magnesium nitrate and water. For that purpose, they studied the melting and dehydration of magnesium nitrate.…”

Hydrothermal Carbon Doped Form‐Stable Inorganic Hydrate Salts Phase Change Materials with Excellent Reutilization

“…In recent decades, latent heat energy storage technology has become a very active research direction in the field of energy conservation, which has been applied in various areas, such as solar energy systems, waste heat recovery, building energy conservation, temperature‐regulating textiles, and thermal storage tanks . PCMs are one of the most popular classes of materials in heat storage technology, which can be categorized into three types, namely, inorganic PCMs, organic PCMs, and eutectic mixtures .…”

“…Thermal energy storage is one of the most importantr esearch interests,i ncluding sensible heat storage,l atent heat storage,a nd chemical reactionh eat storage.T he correspondingh eat storage materials are sensible heat materials,l atent heat materials (phase-change materials,P CMs), chemical reaction heat storage materials,a nd composite heat storage materials. [1,2] In recent decades,l atent heat energy storage technology has becomeavery active research direction in the field of energy conservation, [3][4][5][6][7][8] which has been applied in various areas,s uch as solar energy systems, [9] waste heat recovery, [10] buildinge nergy conservation, [11] temperature-regulating textiles, [12] and thermal storage tanks. [13,14] PCMsa re one of the most popular classes of materials in heat storage technology, which can be categorized into three types,n amely,i norganic PCMs,o rganic PCMs, and eutectic mixtures.…”

Influence of Impurity SO42− on the Thermal Performance of Molten Nitrates Used for Thermal Energy Storage

“…Besides, some researchers have been actively developing molten salts with low melting point and high decomposition temperature in recent years. Drake et al . proposed that an energy storage system by use of Ca(NO 3 ) 2 ⋅ 6H 2 O can potentially improve upon independent latent heat storage or thermochemical energy storage systems by utilizing both the thermochemical hydration reaction and the latent heat available through the solid‐liquid phase change of the nitrate.…”