Polyurethane (PU) based phase change materials (PCMs) undergo the solid-solid phase transition and offer state-of-the-art thermal energy storage (TES). Nevertheless, the exploration of these PCMs in real-life applicable smart devices...

Figure 1. a) An illustration of the phase-change process. b) The working phenomena of S-S phase-change transition. c) The comparative characteristics of S-S PCMs and S-L PCMs. d) Representative highlights along with the major developments of S-S PCMs including polyalcohols, polymeric, inorganic, and hybrid-based materials for advanced TES. Image for "PU-PCMs": Reproduced with permission.

Phase change materials (PCMs) provide a state-of-the-art thermal energy storage capability and offer enormous potential for solar energy storage systems. However, the widespread adaptation of PCMs in advanced energy systems is often limited by low energy harvesting efficiency and poor shape stability. Thus, developing shape-stable PCMs for high-efficiency solar-thermal energy storage has remained an impediment to further advancement. Herein, we devised novel shapestable composite PCMs based on monodispersed CuS disk-like nanoparticles and solid−solid PCM polyurethane (PU). In our devised composite system, the incorporated CuS nanoparticles act as a photonic nanoheater and the PU matrix acts as the heat reservoir which can store thermal energy via the latent heat while the phase transition occurs. The fabricated CuS@PU composite with 4 wt % doping of CuS nanodisks exhibits a phase change enthalpy of around 120 J/g, which is only 14% lower than that of the neat PU PCM. Owing to the solid-state phase transition of the PU PCM, only 0.6% of energy storage loss occurred over 100 repeated heating and cooling cycles. Besides, the solar-thermal energy storage efficiency of the CuS@PU composite exceeds 92% at 1 sun illumination under the full solar spectrum. Based on these outstanding thermophysical properties such as excellent shape stability, thermal stability, and thermal reliability, the developed CuS@PU composite PCMs are imperative candidates for real-world applications.