Supercooled sugar alcohols stabilized by alkali hydroxides for long-term room-temperature phase change solar-thermal energy storage

Seasonal thermal energy storage within organic phase change materials (PCMs) offers a promising way to solve intermittency of renewable energy, but the charged PCMs tend to undergo spontaneous crystallization and lose the stored latent heat to cold environment during storage. Herein, we report introduction of alkali hydroxides into sugar alcohols to increase the activation energy barrier for liquid-to-solid phase transition and stabilize the supercooling state, thereby realizing long-term phase change thermal energy storage. Owing to increased intermolecular hydrogen bonding interaction, the charged composites can maintain the supercooled state and conserve latent heat (∼200 J/g) during storage at room temperature or extremely cold temperatures for months. Further compounding with polydopamine organic pigments, the composites demonstrate high solar absorptance (∼91.6 %) and thus enable seasonable storage of solar-thermal energy as latent heat at room temperature. The stored heat can be readily released through adding seed crystals or applying mechanical deformation, which triggers cold crystallization of the supercooled composites and releases latent heat within a suitable temperature range of 40–60 °C. Such phase change composites not only eliminate complicated thermal insulation engineering required in conventional long-term thermal storage processes, but also unlock diverse application opportunities for thermal energy systems.