Bio-based phase change materials integrated with expanded graphite and Prussian blue for high thermal and photothermal performance in solar energy storage

Cheng, W. and Mo, S. and Fu, K. and Du, Y. and Yang, Z. and Jia, L. and Chen, Y. (2026) Bio-based phase change materials integrated with expanded graphite and Prussian blue for high thermal and photothermal performance in solar energy storage. Journal of Energy Storage, 167: 122540. ISSN 2352-152X

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Abstract

The global shift toward renewable energy has significantly heightened the demand for efficient and sustainable materials for thermal energy storage. Conventional paraffin-based phase change materials (PCMs) are hampered by intrinsic limitations, including poor renewability, susceptibility to leakage, low thermal conductivity and photothermal conversion efficiency. To address these challenges, this study introduces the design and synthesis of novel bio-based eutectic phase change materials (EPCMs) derived from hexadecanol (HD) and various diols. Among them, the hexadecanol–1,12-dodecanediol (HD–DDD) EPCM exhibits the highest latent heat. This EPCM was then integrated with expanded graphite (EG) and Prussian blue (PB) to fabricate a composite PCM for solar thermal energy storage. Through optimization of the EG-to-PB mass ratio, the composite labeled EG14PB10 emerged as the optimal formulation, delivering a latent heat of 180.6 kJ/kg. Its thermal conductivity reached 9.62 W/(m·K), approximately 24.7 times higher than that of pure HD–DDD. Accelerated thermal cycling tests confirmed excellent long-term stability of the composite. Remarkably, the synergistic effect of PB and EG substantially extends solar absorption across the solar spectrum, enabling a photothermal conversion efficiency as high as 93.7%. Owing to its superior thermal performance, high cycling durability, and bio-based composition, the developed EPCM composite stands out as a highly promising candidate for eco-friendly solar thermal energy storage applications.