Enhanced photo-thermal conversion in phase change materials by Cu-Zn Bi-metallic metal-organic framework and expanded graphite

Photothermal phase change materials (PCM) are employed for the efficient conversion and storage of solar energy. In this work, a Cu-Zn bi-metallic metal-organic framework (MOF) was synthesized and combined with expanded graphite (EG), followed by high-temperature carbonization to prepare the supporting material for polyethylene glycol (PEG). Through the high-temperature carbonization process, nano-metallic copper is uniformly dispersed on the surface of the EG, accompanied by the formation of a new porous structure resulting from the evaporation of Zn vapour. The nano metallic copper particles enhance the thermal conductivity and photo-thermal conversion efficiency of the composite PCM, while the porous structure generated by Zn vapour improves the adsorption capacity of PEG. The composite PCM demonstrated a high phase change enthalpy of 174.6 J/g and excellent thermal reliability, with only a 2.29 % reduction in enthalpy after 200 melting-freezing cycles. Additionally, the thermal conductivity of the composite PCM reached 6.096 W/(m·K) which is 26.1 times higher than that of pure PEG, while the photo-thermal conversion efficiency achieved was 88.69 %. These properties indicate that the PEG/EG/Cu-Zn-MOF derived carbon composite PCM has great potential for applications in solar energy storage and conversion.