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Porous high internal phase emulsion templated polymers (PHPs) with/without carbon nanofiber (CNF) frameworks were synthesized for shape-stabilization of hexadecanol (HD) selected as phase change material (PCM) for thermal energy storage (TES) applications. This impregnation process was resulted in creation of seepage-free composite PCMs with high latent heat storage (LHS) capacity and enhanced thermal conductivity. Morphology, chemical structure, LHS properties and thermal stability of prepared composites were characterized by SEM, FT-IR, DSC and TGA techniques. DSC analysis indicated that the PHP/HD and PHP@CNF/HD(80wt%) composites have a LHS capacity of over 200 J/g at about 46–47 °C. The cycled-composite PCMs showed outstanding thermal reliability and chemical stability. Thermal decomposition temperature of HD was considerably extended after impregnation with PHP and PHP/CNF scaffolds. Thermal conductivity of PHP/HD and PHP@CNF/HD was enhanced compared to that of pure HD. The reduction in heat storing/releasing times of PHP@CNF/HD composites relative to PHP/HD composite was proved by considering the measured temperature-time change. Accordingly, especially PHP@CNF/HD composites PCMs have promising prospective for medium temperature-TES practices.

Two kinds of bio-carbons were developed by carbonization/and chemical activation of walnut shell (WS) as lightweight, porous, low-cost and environmental friendly supporting matrix. The produced walnut shell carbon (WSC) and activated WSC (AWSC) were evaluated as novel shape stabilizer and thermal conductivity enhancer for methyl palmitate (MP) preferred as phase change materials (PCM) for thermal controlling applications in buildings. The surface area and pore volume of WS was increased by 1.47 and 1.44 times, respectively after its chemical activation process. WSC and activated AWSC significantly prevented the leakage of liquid MP through phase change due to their suitable adsorption capacities reaching 43 and 55%, respectively. The SEM investigation demonstrated that the MP was well confined into pores of CHW and ACHW carriers. The FTIR and XRD examinations proved the presence of well physicochemical compatibility between the components of the leak-free composites. The DSC measurements indicated that the melting temperatures of WSC/MP and AWSC/MP were 26.27 and 26.65°C, and corresponding fusion enthalpies were 108.3 and 138.1 J/g, respectively. The leak-free composite PCMs were showed remarkable chemical structural stability and thermal reliability after 1000 heating/cooling cycles. Both composites had considerably high thermal degradation stability. The thermal conductivity of leak-free WSC/MP and AWSC/MP was measured as about 1.9 and 1.58 times higher than that of MP. All findings revealed that the leak-free composite PCMs can be used as admixture in the manufacture of lightweight, cost-effective, eco-friendly and energy-saving construction elements utilized for solar thermal controlling of buildings.

Organic phase change materials (PCMs) are the most common heat storage components in latent heat based thermal energy storage (TES) systems. Among the different organic PCMs, fatty acids (FAs) have shown a real potential in important areas, such as, food and medical transportation, passive solar heating and cooling of buildings, etc., because of the suitable thermodynamic and kinetic properties. However, like all other organic PCMs, FAs also suffer from low thermal conductivity (TC) and sometimes seepage issues. Various conducting alien components (metal nanoparticles, metal oxides, etc.) and different carbon-based materials (expanded graphite, graphene, graphene oxide, carbon nanotubes, activated carbon, carbon nanofibers, and carbon black) have been evaluated extensively to enhance the TC. However, carbon-based materials were observed to be superior due to their excellent thermal conductivity, stability, lightweight, and lower cost. While analyzing the literature for this review article, it was found that the bulk of work focuses on FAs, and FAs based composite PCMs with carbon-based fillers and resulting PCMs demonstrated a good performance under the experimental conditions. No obvious discussion exists on the choice of carbon-based filler from a commercial point of view. So, this review attempts to critically evaluate the research work reported to date on the FAs and FA based composite PCMs, where carbon-based fillers have been used. This discussion is followed by comparative analysis to narrow the selection window for specific carbon filler in terms of the best performance.