A n-octadecane/hierarchically porous TiO2 form-stable PCM for thermal energy storage

For a phase-change material (PCM) confined in a porous structure, the interfacial interactions between the PCM and the porous skeleton are the decisive factors in latent heat storage performance. In this work, a novel composite PCM based on hierarchically porous TiO2 and n-octadecane was successfully synthesized. The porous TiO2 was prepared by a soft-template method, and the composite PCM was fabricated by introducing n-octadecane under vacuum. Transmission electron microscope and X-ray diffraction (XRD) results revealed that the as-prepared supporting matrix was crystalline TiO2, and N-2 adsorption/desorption isotherms indicated that TiO2 has a hierarchically porous structure. For composite PCMs, Fourier transform infrared spectroscopy and XRD spectra revealed that no chemical bonds were formed between n-octadecane and TiO2. Scanning electron microscopy results showed abundant n-octadecane enclosed within the nanopores and closely bound on the surfaces of the hierarchically porous TiO2, as a result of capillary forces and interfacial tension. Porous TiO2 exhibited high adsorption for n-octadecane (50 wt%), and the relative enthalpy of the composite PCM was as high as 85.8 J/g. Compared with pure n-octadecane, the thermal conductivity of the as-prepared composite PCMs (e.g., 50 wt% n-octadecane sample) was improved by 138% with the addition of porous TiO2. After 800 melting/solidifying cycles, the composite PCMs exhibited excellent thermal reliability and high enthalpy. The influence of the TiO2 pore structure on n-octadecane crystallization behavior is shown in the results. (c) 2019 Elsevier Ltd. All rights reserved.