Shape-stable hydrated salt phase change hydrogels for solar energy storage and conversion

Phase change materials (PCMs) with excellent photothermal conversion performance display great potential for increasing the utilization of solar energy. In this study, we synthesized shape-stable phase change hydrogels with integrating hydrated salt particles and hydrogels polymer networks through a simple one-step heat-initiated polymerization procedure. The three-dimensional networks of the hydrogels ensure sufficient supporting space and provides heat transfer pathways. The prepared phase change hydrogels exhibit a high latent heat up to 200.3 J/g, and the thermal conductivity is about 1.45 times that of pure hydrated salt. Meanwhile, the introduction of photothermal additives, the network structure and hydrophilicity of the hydrogels can provide a large number of non-homogeneous nucleation sites for the hydrated salts, which can decrease the supercooling degree of the hydrated salts between 2.2 and 4.6 °C. The phase change hydrogels also possess excellent photothermal conversion performance, with a photothermal conversion efficiency of up to 95.5 %. Furthermore, after 200 cycles, the supercooling degree of the phase change hydrogels is further mitigated, and the phase change hydrogels still maintain a good latent heat value (about 191.5 J/g), which is only 4.39 % lower than that before cycling, showing good thermal cycling performance. This investigation offers a new concept for improving the efficiency of solar energy utilization.