Self-assembly of MXene-decorated stearic acid/ionic liquid phase change material emulsion for effective photo-thermal conversion and storage

As a typical latent functionally thermal fluid with large energy storage capacity and good liquidity, phase change material emulsion (PCME) plays a broad and important role in solar energy utilization. However, the high-temperature instability and supercooling problems of PCME limit its practical application. The ionic liquid (IL)-based PCME allows for the possibility of being used as a heat transfer fluid (HTF) under more extreme temperature conditions. In this work, stearic acid (SA)/IL PCME, prepared by one-step self-assembly of MXene nanosheets at the SA/IL interface, can effectively absorb and convert solar energy into thermal energy. Furthermore, MXene-decorated SA/IL PCMEs have good high-temperature stability, little supercooling degree (0.9–3.1 °C), and large energy storage capacity. The maximum apparent specific heat capacity and average absorbance of the MXene-decorated SA/IL PCME are 4.5 and 303.1 times higher than those of IL, respectively. Under 2 sun irradiation, the 0.05–20 wt% MXene-decorated SA/IL PCME achieves high photo-thermal conversion efficiencies (91.3% at 68.9 °C, 39.4% at 115.1 °C) due to its large energy storage capacity and excellent optical absorption property. The simple interfacial self-assembly provides a promising strategy to prepare high-performance SA/IL PCME used as a novel HTF for medium-temperature solar energy utilization systems.