Development and thermo-functional performance insights of bio-based organic-inorganic eutectic phase change material composites

The growing need for efficient and sustainable thermal energy storage solutions has intensified research on phase change materials (PCMs), especially for thermal energy storage (TES) systems. Disodium Hydrogen Phosphate Dodecahydrate (DHPD, Na₂HPO₄.12H₂O), an inorganic PCM with high energy density and a distinct melting point, faces significant challenges such as super cooling and phase segregation, which compromise its thermal reliability and long-term stability. To address these limitations, this study develops sustainable eutectic PCM composites (CPCMs) by formulating beeswax (BW) and DHPD as base PCMs, reinforced with 0.25–1 wt% graphene nanoplatelets (GE) as nucleating agents and 2.5 wt% xanthan gum (XG) as a bio-polymer stabilizer, aiming to enhance thermal performance while ensuring environmentally sustainable formulation and processing. Eutectic PCM compositions are predicted using the Schroeder-Van Laar equation and subsequently synthesized. The samples are thermal cycled (500 nos.) to assess durability and reliability. Performance characteristics of the eutectic PCMs are comprehensively evaluated through analyses of morphology, crystallinity, degree of graphitization, chemical and thermal stability, thermal conductivity and thermal energy storage capacity. The phase- and thermally-stabilized CPCM containing 0.5 wt% GE and 2.5 wt% XG exhibits superior thermal conductivity (0.735 W/mK), better energy density (174.2/91.4 J/g), reduced super cooling (1.4 °C), and thermal storage capability (88.3%). The phase change rate assessment confirms CPCM's suitability for TES in solar energy systems, highlighting its sustainable and high-performance potential in line with SDGs 7, 9, and 12.