Introduction of sustainable food waste-derived biochar for phase change material assembly to enhance energy storage capacity and enable circular economy

Production and utilization of renewable materials receive considerable attention to achieve the goals of carbon neutrality and carbon peaking and create a sustainable society. Phase-change materials (PCMs) have emerged as a novel energy storage technology but usually suffer inherent insufficient thermal stability and liquid leakage, thereby requiring solid supporting materials. However, there are complications in the synthesis of PCM-supporting materials, including environmental issues. In this regard, upcycling biowaste into higher value carbon materials, inspired by the low cost and availability of feedstocks, is a promising strategy for dealing with challenges caused by waste and global climate change. Thus, we designed food waste-derived biochar-supported PCMs using a facile vacuum impregnation method to overcome these limitations. Porous biochar materials with a certain degree of graphitization, high specific surface area (SSA), (up to 1195 m² g⁻¹), and micro-/mesopore distribution were prepared from sustainable and commercially available food waste through carbonization and activation. They displayed greater carbon lattice expansion after undergoing KOH activation and being washed than that shown by carbon materials synthesized without activation. Thereby, the graphitic carbon materials presented high loading ratios and corresponding enthalpy values that were 243.9, 302, 346.9, and 251.4 % higher than those of the composites prepared without activation, encapsulated only 15 wt% of octadecane. Additionally, the composite PCMs exhibited high thermal stability without leakage above the melting temperature of pristine PCM. Textural properties, including the SSA, interconnected pores, activation, graphite-like characteristics, and intermolecular interactions between the composite constituents, were integral to the enhanced thermal performance of the as-synthesized composite PCMs. Furthermore, the composite demonstrated high durability, showing potential for thermal management, sustainable management of food waste, and mitigation of climate change.