Ionic Mixture of Binary Sugar Alcohols and a Polymer: Composition Optimization for Long-Term Thermal Energy Storage

Abstract

A new cold crystallizing material (NaPP) is analyzed for longterm thermal energy storage (TES). NaPP comprises a mixture of erythritol and mannitol as the binary phase change material (PCM) in the scaffold of polyvinyl alcohol (PVA) cross-linked with sodium citrate (SC). The material demonstrates a unique behavior of stable supercooling and vitrification during cooling and cold crystallization during subsequent heating, which enables a reliable long-term storage of the melting enthalpy and a controllable heat release. The use of several components in the material composition, however, impedes optimization of the thermal properties for the storage. As such, differential scanning calorimetry (DSC) was applied to expose the effect of the material components on the thermal properties, and the mixture experimental methodology (MEM) was used to model and optimize these properties. Successful modeling yielded a linear response for the thermal performance, which was significantly affected by the content of SC. Increasing the amount of SC (from 0 to 18 wt %) elevated the ionic strength of the system, which caused reduction in the amount of active PCM (confirmed by X-ray diffraction and DSC) and coarsening of the surface morphology (revealed by optical and scanning electron microscopies). This was also manifested as gradual disappearance of cold crystallization which limits the use of the material to compositions with the glass-transition temperature below −15 °C. MEM identified the optimal composition as 88.9 wt % PCM and 11.1 wt % SC, which showed a melting enthalpy of 194 J/g at 105 °C. Yet, the composition comprising 80 wt % PCM, 10 wt % PVA, and 10 wt % SC showed both high melting enthalpy (176 J/g) and shape stability facilitating larger scale applications. These compositions demonstrated a temperature increase of 10−20 °C during cold crystallization of a 10 g sample, confirming the suitability of the optimization model and the operation of the new material for long-term TES.

Supercooled erythritol for high-performance seasonal thermal energy storage

“…With increasing CG loading, the supercooling behavior becomes more stable. Especially, the two most concentrated samples (10 wt.% and 15 wt.%) could maintain an ultrastable supercooled state in a severely cold environment, even when the temperature drops down to around −50°C until the supercooled sample becomes vitrificated 69 , as indicated by the inflection on the discharging curve of the 15 wt.% case in Fig. 3a-iv .…”

“…As mentioned, some climate regions, especially the monsoon climate regions, feature scorching summers and severe winters, requiring the PCM to perform under extremely cold conditions, e.g., being able to remain in a supercooled liquid state down to −30°C or even lower. This situation poses a great challenge for all existing natural PCMs, making it imperative to develop better PCMs that exhibit ultrastable supercooling behavior 69 , 70 . Therefore, erythritol is deemed to be the most promising starting point for developing such an ideal seasonal PCM.…”

Spatiotemporal Utilization of Latent Heat in Erythritol‐based Phase Change Materials as Solar Thermal Fuels

“…All of these impressive features make it an ideal candidate for the technique of long-term thermal energy storage. [28][29][30] Although a crystallization enthalpy as high as 181 J/g for an ERY-based STPCM was achieved in our previous study, [14] it still needs further improvement to attain higher energy storage density. In addition, ERY cannot directly absorb sunlight and convert it into thermal energy, which seriously limits its application in solar thermal storage.…”

“…Moreover, its low specific heat capacity can minimize heat loss during the supercooling process. All of these impressive features make it an ideal candidate for the technique of long‐term thermal energy storage [28–30] . Although a crystallization enthalpy as high as 181 J/g for an ERY‐based STPCM was achieved in our previous study, [14] it still needs further improvement to attain higher energy storage density.…”

Flexible and Conductive Nanofiber Textiles for Leakage-Free Electro-Thermal Energy Conversion and Storage

“…Form stabilization is one of the solutions to addressing these drawbacks effectively. As such, considerable efforts have been made to design and fabricate form-stable PCM composites [9,10]. Electrospinning, as a simple and convenient method, offers a straightforward continuous fabrication process for stabilizing PCMs in the network of different polymers without leakage [11,12].…”