Utilization of biomass-derived activated carbon from Miscanthus for dual energy storage: Enhanced performance in phase change material and supercapacitor applications

In this study, bio-derived activated carbons (ACs) obtained from Miscanthus under two distinct synthesis conditions denoted as optimum condition 1 (OC1) and optimum condition 2 (OC2) were systematically investigated for their applicability in dual-mode energy storage. Their performance was assessed in two roles: as supporting materials to enhance the thermal properties of phase change materials, and as electrode materials for electrochemical energy storage systems, such as supercapacitors. This dual evaluation aims to demonstrate the versatility and multifunctionality of Miscanthus-based ACs in both thermal and electrochemical storage platforms. For thermal energy storage, an eutectic blend of stearic acid and palmitic acid (SP) was utilized as the phase change material (PCM), and activated carbon was employed to create shape-stabilized PCM via vacuum impregnation methods, resulting in composite PCMs named SP-OC1 and SP-OC2. SP-OC2 demonstrated a significantly higher encapsulation ratio of 88.95% and an enhanced thermal conductivity of 0.597 Wm⁻¹K⁻¹. It melted at 54.79°C and solidified at 51.89°C, with latent heat values of 133.26 Jg⁻¹ and 135.84 Jg⁻¹, respectively, exhibiting a significant enhancement in thermal conductivity, increasing by up to 117% compared to the eutectic SP. In supercapacitor applications, OC1 cell exhibited superior performance with a capacitance of 131 Fg⁻¹, a power density of 488 Wkg⁻¹, and an energy density of 35.30 Whkg⁻¹, whereas OC2 cell showed a capacitance of 67 Fg⁻¹, a power density of 480 Wkg⁻¹, and an energy density of 15.25 Whkg⁻¹. This difference is ascribed to the matching of ionic liquid ion diameters with the pore sizes of OC1. These results highlight the viability of Miscanthus-derived activated carbons as a cost-effective and sustainable precursor for developing high-performance electrode materials in energy storage systems.