Enhancing the solar absorption capacity of expanded graphite-paraffin wax composite phase change materials by introducing carbon nanotubes additives

The potential solar thermal utilization of solar energy based on phase change materials (PCMs) is limited by their low thermal conductivity and weak solar absorption capacity. Among various additives used to enhance the thermal conductivity of PCMs, expanded graphite (EG) has been proved to be a low-cost but effective choice. This work aims to further enhance the solar absorption capacity of EG-paraffin wax composite PCMs by adding small amounts of carbon nanotubes (CNTs) as the light absorbent. The prepared composite PCMs with 5 wt.% EG and 2 wt.% CNTs show superior thermal conductivity (2.05 W/m⋅K), high solar absorption capacity (94.2%) while maintaining the high latent heat (159 kJ/kg). Moreover, these superior thermal and optical properties can be maintained after 1000 melting-freezing cycles. Our results provide a high-performance composite PCM that may be used in solar-thermal conversion applications.