Fabrication and characterization of polyurethane-grafted reduced graphene oxide as solid-solid phase change materials for solar energy conversion and storage

A novel solid–solid phase change material (SSPCM), namely, polyurethane-grafted reduced graphene oxide (rGO-PU), composed by polyethylene glycol (PEG), 4,4-diphenylmethane diisocyanate (MDI) and rGO was fabricated by in-situ polymerization, esterification and reduction reaction. The successful synthesis and chemical structure of rGO-PU SSPCMs were confirmed by various spectroscopy and microscopy techniques. A series of characterizations were used to study the thermal properties of rGO-PU SSPCMs. The thermal conductivity of rGO-PU SSPCM was dramatic improved by rGO, the highest thermal conductivity of rGO-PU SSPCM could reach 0.696 W/m·K, which was131.2 % higher than PU. The undercooling of rGO-PU SSPCMs were lower than PEG and PU, the highest latent heats of melting and crystallization of rGO-PU SSPCM are 138.7 J/g and 130.9 J/g, respectively. The degradation temperature of rGO-PU SSPCM is approximately 4 °C and 24 °C higher than that of PEG and PU, respectively, indicating that it has good thermal stability. rGO-PU SSPCM exhibits good shape-stability, excellent thermal reliability and structural stability. Furthermore, the light-to-heat conversion efficiency of the rGO-PU SSPCM can reach 81.8%. Therefore, the synthesized rGO-PU SSPCMs have considerable potential for light-to-thermal energy storage applications such solar energy collector system.