Hydrogel-stabilized supercooled salt hydrates for seasonal storage and controlled release of solar-thermal energy

Seasonal storage of solar-thermal energy within salt hydrate phase change materials (PCMs), which are known for their large latent heat capacity, suitable phase change temperature range and cost-effectiveness, has garnered tremendous attention. Salt hydrates, however, suffer from poor phase change and physical stability, low solar absorptance, and leakage issues after melting. In this work, we report impregnating sodium acetate trihydrate (SAT) within polyacrylamide hydrogel networks decorated with solar-absorbing polydopamine particles, and explore their applications for direct harvesting, long-term storage and controllable release of solar-thermal energy. Owing to the formation of intermolecular hydrogen bonding, the hydrogel-impregnated SAT composites retain their stable supercooling during both long-term heat storage at room temperature for 2 years and repeated heating/cooling cycles. Through applying electrical pulses, the crystallization of supercooled PCM composites and the release of latent heat can be triggered in a programmable manner. The hydrogel networks also prevent phase separation and leakage of melted SATs while retaining a latent heat enthalpy higher than 180 J g−1. We demonstrate that such flexible, self-adhesive, leakage-proof, supercooled PCM composites could not only enable seasonal harvesting of renewable solar-thermal energy and provide intelligent thermal regulation for both buildings and the human body, but also have the potential to facilitate widespread terminal usage of thermal storage technology.