Enhanced thermal conductivity and phase change performance of paraffin-based materials using nanostructured additives for thermal energy storage applications

Phase-change materials (PCMs) provide high-density Solar Thermal Energy Storage (STES) for solar applications but suffer from low thermal conductivity, excessive subcooling, and cycling degradation. This study systematically compares five nanostructure classes—graphene nanoplatelets (GNP), multi-walled carbon nanotubes (MWCNT), metallic nanoparticles (Cu, Ag), and metal oxides (Al₂O₃, TiO₂)—incorporated into paraffin and sodium nitrate PCMs to address these limitations. Nanostructures were characterized using XRD, FTIR, BET, SEM, and TEM to establish morphology-performance relationships. BET surface area (320.5 m2/g for GNPs, 265.4 m2/g for MWCNTs) correlated strongly with thermal conductivity enhancement (R2 = 0.87, p < 0.001), confirming that high-aspect-ratio structures enable percolation network formation. At 3 wt% loading—identified as the optimal concentration through percolation analysis—carbon-based composites achieved 150% (GNPs) and 131% (MWCNTs) conductivity gains at 25 ℃. DSC analysis revealed 60% subcooling suppression with GNPs, reducing crystallization lag from 5.5 ℃ to 2.2 ℃ through heterogeneous nucleation. Charging-discharging experiments verified 30–34% reductions in thermal response time, with temperature uniformity improving by 67%. Statistical analysis using one-way ANOVA with Tukey's HSD test (p < 0.05) confirmed significant performance hierarchies: carbon-based > metallic > metal oxides across all metrics. Extended cycling tests (1000 melt-freeze cycles) validated superior durability, with carbon-enhanced paraffin and oxide-enhanced sodium nitrate retaining >93% of their latent heat capacity, compared with <83% for pristine PCMs. Post-cycling analysis confirmed the maintenance of nanoparticle dispersion and chemical stability. Comparison with recent literature validates that this work advances the field by systematic multi-additive evaluation, extended durability validation (2–3 times longer than typical studies), and dual-PCM coverage spanning 50–350 ℃. The quantified conductivity-loading relationships, percolation thresholds, and 1000-cycle performance data provide engineering guidelines for STES across residential to industrial temperature ranges.

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