Experimental investigation of supercooled thermal energy storage and triggered exothermic crystallization in phase change materials

Inorganic phase change materials (PCMs) address the mismatch between intermittent solar energy availability and building energy demand by enabling seasonal heat storage and on-demand flexible energy supply. However, traditional PCMs often exhibit a critical trade-off between long-term thermal storage stability and rapid heat delivery, severely restricting their practical applications across multiple timescales. To overcome these limitations, this study developed a novel composite PCM (SEG-4) by synergistically incorporating sodium edetate (EDTA-4/Na) and gelatin (GEL) into sodium acetate trihydrate (SAT). This dual-modification strategy is designed to concurrently suppress supercooling instability, suppress phase separation, and enable rapid, controllable crystallization. A comprehensive experimental investigation was conducted to evaluate the thermophysical properties, long-term cycling stability, electrically triggered crystallization behavior, and heat storage/release performance of the SEG composites. Furthermore, the mechanisms by which the composite system influences the internal energy storage and release behaviors of the SEG PCMs were investigated. The results demonstrate that the optimized SEG-4 composite exhibits a high latent heat of 249 kJ/kg and a deep, stable supercooling limit down to −28 °C, while retaining over 95% of its latent heat after 100 thermal cycles. Under a 1.5 V electrical trigger, it achieves a crystallization front velocity of 5.8 mm/s, enabling rapid and controllable heat release. Compared to pure SAT, SEG-4 enhances the heat-storage and release powers by 44.7% and 13.6%, respectively. Thus, this study overcomes the trade-off between long-term stable heat storage and short-term rapid energy delivery, providing a feasible design strategy and theoretical foundation for advanced PCMs in seasonal solar utilization and flexible thermal management.