Recent advances in biochar-based composite phase change materials

Phase change materials (PCMs) are promising for thermal energy storage but face limitations, including low thermal conductivity, leakage, and poor structural stability. Biochar, a carbon-rich, porous material derived from biomass pyrolysis, has emerged as an effective matrix to overcome these challenges. While there is a growing body of literature, variations in feedstocks, activation methods, and performance metrics highlight the value of a comprehensive review. This work consolidates recent advances and highlights how feedstock selection, pyrolysis, and activation methods influence the performance of biochar-based composite PCM. These composites show thermal conductivity enhancements of ∼25–150 %, latent heat values from 60 to 223 J/g, leakage-free operation up to 60–80 °C, and good latent heat retention after 200–1000 cycles. The review also explores key applications of biochar-based composite PCMs in building energy management, renewable energy storage, and passive thermal regulation. It addresses challenges related to sustainability and scalability, while highlighting biochar's carbon-negative potential and cost-effectiveness. By providing a unified perspective, this work identifies existing research gaps and outlines future opportunities to advance the commercialization of biochar-based composite PCMs, ultimately contributing to the development of sustainable thermal energy storage technologies. • Biochar enhances PCM thermal conductivity by ∼25–150 %. • Pyrolysis and activation methods influence biochar's PCM performance. • Leakage-free operation up to 60–80 °C with durable 200–1000 cycle stability. • Applications span from buildings to solar and renewable energy systems. • Performance ranges (60–223 J/g, 0.25–2.42 W/m·K) guide scalable development.