Preparation and characterization of a solar-driven sodium acetate trihydrate composite phase change material with Ti4O7 particles

Thermal energy storage using phase change materials has received much attention as it can effectively relieve the contradiction of renewable energy between supply and demand. The novel bifunctional sodium acetate trihydrate (SAT) composite phase change materials with photo-thermal conversion and heat storage properties were developed to promote the thermal utilization of solar energy. The Ti4O7 particles were selected as photo-thermal conversion media with full spectral absorption of sunlight and efficient photo-thermal conversion performance. 5 wt% disodium hydrogen phosphate dodecahydrate (DSP) and 3 wt% carboxymethyl cellulose were used to decrease supercooling and restrain phase separation of SAT, respectively. The as-prepared SAT composites with different content of Ti4O7 possess a low supercooling degree of 0.9–1.5 °C and high latent heat of 228.6–257.7 kJ kg-1. Ti4O7 has a stable absorption capacity covering the full solar spectrum (200–2500 nm) and the absorption capacity of SAT and DSP in the infrared light even more than Ti4O7 at 1900 nm–2500 nm. The SAT composite sample with 10 wt% Ti4O7 has the best total solar absorption capacity of 93.33% more than Ti4O7 of 92.76% because SAT and DSP have outstanding absorption capacity in the long-wave infrared wavelength. The photo-thermal storage efficiency of all SAT composite photo-thermal conversion phase change materials exceeds 50%, of which the composite with 10 wt% Ti4O7 has the optimal photo-thermal conversion storage efficiency of 76.63%. The composite photo-thermal storage phase change materials have potential applications in solar energy systems.