Polydopamine based silver coated cenosphere microcapsule for thermal energy storage

Abstract

In the present work, low-cost and eco-friendly metallic multi-shell wall microcapsules having paraffin wax were synthesized by encapsulating them with industrial waste cenosphere. Acid etching of the cenosphere shell wall was carried out to create multiple pores through which liquefied paraffin was vacuum infiltrated. Later, metallic coating of Ag was done through surface functionalizing the microcapsule with bio-polymer polydopamine (PD). The metallic coating is adapted to provide a dual function in terms of sealing the pores as well as increasing the thermal conductivity of the microcapsules. Further, the coating also provides additional mechanical strength of the microcapsule. Scanning electron microscopy (SEM) images showed that the mean diameter of the cenospheres was ∼67 µm and the pore diameter was ∼2 µm. The thickness of the Ag coating was ∼773 nm. The Fourier transform infrared (FTIR) Spectroscopy and X-ray photoelectron spectroscopy (XPS) results of the functionalized microcapsules showed additional peaks attributing to functional groups introduced after PD polymerization. Differential scanning calorimetry (DSC) and thermogravimetric analyzer (TGA) results inferred that the thermal storage capacity of the microcapsule was 99.92% with high thermal reliability. Furthermore, silver coated microcapsules showed ∼33% enhanced heat transfer performance than uncoated microcapsules as evidenced by TT-curve. The metallic coating at the outer shell and PCM at the inner core of the cenosphere enable it to be a potential thermal energy storage (TES) material for versatile engineering applications.