A critical experimental evaluation of hexagonal boron nitride, graphene oxide and graphite as thermally conductive fillers in organic PCMs

Composite phase change materials (CPCMs), consisting of nanofillers embedded inside conventional PCMs such as salt hydrates or paraffins, are emerging candidates for large-scale latent heat storage systems or electrochemical applications. High thermal conductivity and thermal diffusivity of CPCMs are crucial prerequisites for practical utilization, in addition to good intrinsic enthalpy of fusion and volumetric heat capacity of the pristine PCMs. This paper presents an exclusive evaluation of graphite, hexagonal boron nitride (HBN), and graphene oxide nanoparticles as thermally conducting nanofillers across different loading ranges inside the paraffin matrix. The thermal performance of these CPCMs is compared by investigating multiple thermal properties, such as the melting temperature, degradation rate, and dispersion efficiency. Despite the similar intrinsic thermal properties of graphite, HBN and graphene oxide, their incorporation enhances the thermal performance of pure paraffin to different extents, by 137.6 %, 192.2 % and 344.1 % in thermal conductivity as well as by 189.0 %, 204.1 % and 202.1 % in thermal diffusivity, respectively, which is attributed to the conductive channels established by these nanofillers and the much-reduced thermal contact resistance across the interphase. Although these three types of particles possess analogously hexagonal structures, it was found that they interacted differently with the paraffin matrix at low (1 wt%) and high (15 wt%) filler loadings. The latent heat capacity of paraffin/GO was 3.8 % higher than that of paraffin/HBN and paraffin/graphite. Overall, this study provides a novel understanding of the transport mechanisms of heat carriers inside CPCMs, so the thermal performance for wider applications can be predicted, which will be invaluable for catering future sustainable energy needs.