Highly stable n-hexacosane loaded exfoliated graphite nanosheets for enhanced thermal energy storage application

Abstract

In the present work, we demonstrate an in-situ synthesis of phase-change material (n-hexacosane) loaded exfoliated-graphite nanosheets (EGPCM) by modified hydrothermal method, exhibiting high thermal stability over extended thermal cycling. During the hydrothermal method, the exfoliation of graphite enables more surface area to absorb n-hexacosane leading to better interaction between the carbon and phase change material (PCM). The morphological and structural results confirm the PCM loading in porous dendritic structures without any chemical reactions of n-hexacosane. Further, the latent heat, thermal conductivity, and stability of as-prepared EGPCM composites were established by differential scanning calorimetry (DSC), thermo-gravimetric analysis (TGA), and infrared thermography (IR). The charging of EGPCM nanocomposite was observed at 58.07 °C with a latent heat of 167.70 J/g and discharging at 48.51 °C with a latent heat of 149.52 J/g. The EGPCM composites exhibit high thermal conductivity (10.47 W/m K compared to pure n-hexacosane 0.26 W/m K) and a highly stable nature against thermal degradation after 200 charging/discharging cycles. A detailed comparison of the as-prepared EGPCM material with previously reported PCM nanocomposites is also provided, showing the proposed mechanism's enhanced thermal stability and storage capability. The presented work demonstrates a scalable, custom-built latent-heat reservoir using inner-linings of as-prepared nanocomposite material. Infrared thermography and COMSOL simulations pertaining to thermal performance showed significant improvement in the thermal conductivity of the composite compared to n-hexacosane, attributed to the 3D network of exfoliated graphite.