Thermal Performance and Cyclic Stability of Coconut Shell Biochar‐Enhanced Phase Change Materials for Thermal Energy Storage

Efficient thermal energy storage materials are needed to improve the use of renewable and low‐grade thermal energy. Organic phase change materials (PCMs) are attractive because of their suitable phase transition temperature and chemical stability, but their application is limited by low thermal conductivity, melting leakage, and reliability loss during cycling. This study investigates coconut shell biochar (CSB) as a sustainable low‐loading additive to enhance the heat‐transfer performance and stability of A58 organic PCM. CSB was synthesized via high‐temperature pyrolysis at 1000°C under nitrogen and incorporated PCM at 0.25, 0.5, 0.75, and 1 wt% using a two‐step melting and ultrasonic dispersion method. CSB showed a carbon‐rich porous structure, with a surface area of 268.0006 ± 9.6940 m 2 /g and a total pore volume of 0.145195 cm 3 /g. Fourier transforms infrared spectrometer analysis confirmed physical compatibility between CSB and PCM without new chemical bond formation. The highest thermal conductivity was obtained at 0.5 wt% CSB, increasing from 0.185 ± 0.021 to 0.407 ± 0.046 W/mK, corresponding to a 120.18% enhancement. Infrared thermography showed faster and more uniform heating, while cooling tests indicated improved thermal retention. Leakage decreased from 2.51% for pure PCM to 1.13%–1.20% for the best‐performing composites. After 200 cycles, CSB‐PCM2 and CSB‐PCM3 showed low mass losses of 1.04% and 1.40%, respectively, with thermal conductivity reductions below 6%. These results demonstrate that low‐loading CSB is an effective, low‐cost, and sustainable additive for improving organic PCM performance for medium‐temperature thermal energy storage applications.