Use of cellulose nanofibril (CNF)/silver nanoparticles (AgNPs) composite in salt hydrate phase change material for efficient thermal energy storage.

Salt hydrate phase change materials (PCMs) possess the challenge of supercooling, which must be addressed to allow more efficient energy storage and utilisation. In this work, cellulose nanofibril (CNF), a versatile biopolymer was used to support and disperse silver nanoparticles (AgNPs), and the synthesised CNF/AgNPs composite was used to improve the performance of sodium acetate trihydrate (SAT). Results showed that CNF dispersed the AgNPs uniformly and prevented their aggregation. Through the synergistic effect of 1% CNF/AgNPs and 2% sodium phosphate dibasic dodecahydrate, a low supercooling degree of 1.2 °C was achieved. Moreover, AgNPs were uniformly distributed in the prepared PCM composite. Differential scanning calorimetry results indicated that the prepared PCM@CNF/AgNPs composite showed a similar melting point (57.4 °C) and enthalpy (269 kJ/kg), compared to those of pure SAT. Thermogravimetric analysis showed that the PCM composite did not lose all moisture until a heating temperature of 160 °C, showing improved thermal stability. The thermal conductivity of PCM@CNF/AgNPs composite was 31.6% higher than that of SAT. The enthalpy of this composite decreased only around 2% after 100 melting/freezing cycles, showing satisfying thermal reliability. This composite can therefore be used to fabricate high-performance TES systems with negligible supercooling and improved thermal properties.