Hydrogel-Encapsulated Sodium Acetate Trihydrate/Paraffin Wax Hybrid Phase Change Materials with Suppressed Supercooling and Enhanced Thermal Reliability

Organic–inorganic hybrid phase change materials (PCMs) offer a promising approach to combine the high latent-heat storage capacity of hydrated salts with the phase stability of organic PCMs; however, interfacial incompatibility, phase separation, leakage, dehydration, and severe supercooling continue to limit their practical application. Herein, a shape-stable sodium acetate trihydrate/paraffin wax (SAT:PW) hybrid PCM was developed via an A200 silica-stabilized Pickering emulsion and subsequently encapsulated within an acrylamide-based hydrogel network. The Pickering emulsion enabled stable integration of the hydrophilic SAT phase and hydrophobic PW phase, while the hydrogel framework physically confined the hybrid PCM, suppressing leakage, reducing cumulative thermal mass loss, and improving thermal reliability during repeated phase transitions. Among the investigated formulations, SAT:PW90 provided the most favorable overall balance of latent-heat storage, crystallization performance, supercooling suppression, and leakage resistance in hydrogel encapsulation, exhibiting a melting peak temperature of 64.70 °C, a crystallization peak temperature of 47.74 °C, a melting enthalpy of 228.8 ± 1.0 kJ kg–1, a thermal conductivity of 0.556 ± 0.03 W m–1 K–1, and a low supercooling degree of 2.1 ± 0.85 °C. Under the investigated TGA conditions, hydrogel confinement reduced the cumulative mass loss to ∼1.25% at 75 °C and ∼2.2% at 155 °C, compared with ∼7.2 and ∼22%, respectively, for SAT:PW90, while retaining a melting enthalpy of 146.7 ± 1.5 kJ kg–1, a melting peak temperature of 63.96 °C, and a low supercooling degree of 4.0 °C. Following 100 heating–cooling cycles, the composite retained 95.8% of its initial melting enthalpy, with a supercooling degree of only 4.7 °C, demonstrating promising thermal reliability. These findings establish Pickering-emulsion stabilization combined with hydrogel confinement as an effective strategy for developing shape-stable hybrid PCMs for low-temperature solar thermal energy storage and building thermal-management applications.