The phase change material (PCM) sodium sulfate decahydrate (Na2SO4.10H2O, SSD) is a promising candidate for thermal energy storage. SSD has the potential to revolutionize the energy storage industry, but significant phase separation hampers its thermal stability performance and prevents its widespread use at the moment. To deal with these stability issues, we employ stabilizing agents such sodium polyacrylate (SPA), potassium polyacrylate (PPA), carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), cellulose nanofiber (CNF), dextran sulfate sodium (DSS), and poly (sodium 4-styrenesulfonate) (PSS). The influence of the seven additives on phase stability, energy storage capacity, and rheology of SSD is investigated in order to identify the best performing stabilizing agent for SSD. Polymeric thickened composites with SPA, PPA, and CNF declined by at least 40% in energy storage capacity after 10 cycles. This thermal cycling test indicates that physical thickening alone is not effective for increasing long-term thermal performance of SSD. DSS-modified composites, nevertheless, were more stable. The composites preserved 94% of their initial energy storage capacity after 50 melt-freeze cycles. Phase separation is impeded by the electrostatic interaction between DSS and SSD, which encases salt particles in a stable homogenous solution and keeps them suspended. Given the superior performance of polyelectrolyte based DSS over pure physical thickened PCM composites, it is clear that electrostatic interaction plays a crucial role in SSD phase and thermal stabilization. Therefore, the use of a polyelectrolyte-salt hydrate composite for energy storage is proposed as a unique approach to increasing the thermal stability of salt hydrate PCMs.

Thermal and rheological properties of composite salt hydrate phase change materials with various stabilization mechanisms

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