Activation-dependent molecular confinement and interfacial interactions of myristic acid in pistachio endocarp biochar for thermal energy storage

초록

The present investigation reports a methodical exploration into biochar-derived phase change material (PCM) composites as an innovative strategy toward sustainable thermal energy storage via solid waste valorization. By employing ZnCl2-activated (PEZ) and KOH-activated (PEK) pistachio endocarp (PE) biochars as structural matrices, this study examines the physicochemical congruity between carbonaceous scaffolds and myristic acid (MA). Advanced spectroscopic (FTIR, XPS), microscopic (SEM-EDS), porosimetric (BET/BJH), and thermal (TGA, DSC, IR thermography) characterizations reveal the pivotal role of nitrogen-rich functional moieties and amide-like interactions in modulating interfacial adhesion and latent heat retention. PEZ exhibits an extensive Langmuir surface area (851.53 m2/g), enhancing molecular confinement, while PEK demonstrates superior pore diameters (34.12 Å), improving encapsulation capacity. For the optimized composites MPEZ-2 and MPEK-2, thermal reliability persists over 500 heating-cooling cycles with negligible enthalpy loss (ΔHm retention '98.5%, ΔHs retention '99.4%). Shape stabilization and relative enthalpy efficiency (Rs ∼ 60.5%; η '98%) substantiate the composites' resistance to leakage under elevated thermal gradients. Infrared thermography revealed homogeneous heat absorption, retention, and dissipation dynamics, reinforcing thermal congruency. These findings suggest that engineered biochar-PCM systems are promising candidates for architectural insulation, electronics thermal regulation, and low-carbon energy infrastructure, supporting their further development as scalable, environmentally sustainable thermal energy storage materials. © 2026 Elsevier B.V.

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