Thermophysical properties enhancement of ternary carbonates with carbon materials for high-temperature thermal energy storage

Ternary carbonates in the form of Li₂CO₃-Na₂CO₃-K₂CO₃ enforced by expanded graphite, graphene nanosheets and multi-walled carbon nanotubes are originally prepared though the solution-evaporation with the purpose of enhancing heat transfer for employment in concentrating solar power. FT-IR, XRD and SEM results indicate that three carbon materials are physically dispersed into composite carbonates with the effect of supporting structural support as well as improved thermal properties. The presence of carbon materials presents a slight effect on the melting and freezing temperature of ternary carbonates. It is apparent that enhancement of carbon materials on the heat transfer of the composite carbonates is mainly manifested in the aspect of thermal conductivity improvement. Expanded graphite, graphene nanosheets and multi-walled carbon nanotubes show respectively the enhancement of approximately 59.1%, 32.9% and 24.8% on average to thermal conductivity. Carbon materials also illustrate obvious improvement on the specific heat and the strengthening effect of liquid composite carbonates is generally better than that of solid carbonates. Average specific heat of composite carbonates modified by expanded graphene, graphene nanosheets and multi-walled carbon nanotubes is 1.278, 1.322 and 1.299 J/(g·°C) for solid and 1.502, 1.638, and 1.533 J/(g·°C) for liquid, respectively. Additionally, prepared composite carbonates exhibit superior cyclic stability and it is concluded that composite carbonates with carbon materials as effective latent heat storage materials will have great potential for application in thermal energy storage in terms of satisfactory thermal properties.