Interfacial engineering of electrostatic TiN@EG for enhanced photothermal and thermophysical performance of chloride-based composite phase change materials

Chloride-based composite phase change materials (CPCMs) are widely employed in high-temperature solar thermal energy storage due to their high melting temperatures, large heat-storage capacity, and low cost. However, their practical application is limited by molten salt migration, insufficient photothermal conversion efficiency, and agglomeration of functional nanoparticle additives at elevated temperatures. In this work, TiN nanoparticles are electrostatically adsorbed onto the surface of expanded graphite (EG), constructing a uniformly dispersed and strongly coupled TiN@EG interfacial architecture, which is subsequently integrated with a NaCl-KCl eutectic salt and fine MgAl 2 O 4 particles to fabricate a high-stability CPCM. Compared with direct nanoparticle addition, electrostatic adsorption effectively suppresses TiN agglomeration, enhances interfacial bonding, and constructs continuous pathways for light absorption and heat transport. As a result, the electrostatically assembled CPCMs exhibit significantly enhanced broadband solar absorptivity in the 200-2500 nm range and a thermal conductivity exceeding 6 W m −1  K −1 at room temperature. The apparent photothermal conversion efficiency, evaluated from the temperature rise under 1 sun irradiation within 300 s, increases from 48.65% for the pristine sample to 85.93% for the optimized CPCM. Meanwhile, excellent cycling durability is achieved, with a mass loss of 0.61 wt% after 100 thermal cycles, owing to the combined encapsulation effect of EG and fine MgAl 2 O 4 particles that effectively suppress molten salt migration. A comprehensive comparison further demonstrates that the present CPCMs achieve a well-balanced integration of photothermal efficiency, thermal conductivity, and mass stability, highlighting the effectiveness of electrostatic assembly enabled interfacial engineering for developing high-temperature CPCMs for solar thermal energy storage.