Eco-friendly porous carbon from Capparis waste: A green biomass-derived material for high performance thermal energy...

Thermal energy storage (TES) is an emerging and important pillar of a sustainable energy future; it is a key technology for effectively managing heat supply and demand in solar thermal systems. In this context, fatty acids stand out as promising phase change materials (PCMs) for low-temperature TES due to their favorable thermophysical properties, including high latent heat capacity, reliable phase transition behavior, and chemical compatibility. However, their practical application is often hindered by leakage and low thermal conductivity. To address these limitations, a novel shape-stabilized PCM (ss-PCM) was developed using porous carbon derived from Capparis waste as an innovative supporting matrix. Carbon material derived from biomass waste can exhibit a uniform pore distribution, which can successfully stabilize the eutectic mixture of capric acid-palmitic acid (CA-PA) within its pores. The SEM images of porous carbon reveal a well-developed, and highly porous structure from micropores to macropores, which facilitates the impregnation of CA-PA binary eutectic PCM. The pores appear partially or completely filled, confirming the success of the encapsulation process. These results are in line with BET analysis, which further confirms the relatively high surface area of the porous nature of the carbon matrix that allows PCM to be captured. FTIR analysis demonstrated the chemical compatibility of ss-PCM by showing characteristic absorption peaks of both the carbon matrix and PCM. The developed ss-PCM exhibited excellent shape stability and improved thermal conductivity. The thermal conductivity increased from 0.17 W/(m·K) for raw CA-PA to 0.74 W/(m·K) for the CA-PA@CC composite, achieving an improvement of 335.29 % compared to binary PCM. Furthermore, the latent heat of melting and freezing of the ss-PCM was 71.4 kJ/kg and 72.8 kJ/kg, corresponding to melting and freezing temperatures of 20.16 and 18.12 °C, respectively. This improvement ensures better heat transfer efficiency, making the composite a promising candidate for thermal regulation applications, particularly in building energy management.