Turning agricultural waste into energy storage: Biochar composites offer durable, high-efficiency thermal solutions

Researchers have developed a new class of sustainable energy storage materials by transforming agricultural waste into high-performance biochar composites that can store and release heat efficiently. The study demonstrates how simple changes in biomass type and production temperature can significantly improve energy storage capacity and durability, offering a promising pathway for low-carbon building technologies and renewable energy systems.

“By carefully tuning the feedstock and pyrolysis conditions, we can design biochar materials that maximize energy storage while remaining low-cost and environmentally friendly,” said the study’s corresponding author. “This approach turns waste into a valuable resource for addressing energy challenges.”

Thermal energy storage is essential for improving the reliability of renewable energy sources such as solar and wind, which naturally fluctuate. Phase-change materials can store heat by melting and release it when solidifying, but they often suffer from leakage, poor stability, and complex manufacturing requirements. To overcome these limitations, the research team developed composite materials by embedding a common phase-change material, hexadecane, into porous biochar derived from plant-based waste.

The biochar was produced from different agricultural residues including rice husk, wheat straw, and Miscanthus straw at temperatures ranging from 550 to 700 degrees Celsius. The resulting materials were then combined with hexadecane using a vacuum infiltration process, allowing the liquid material to fill the microscopic pores of the biochar.

The results show that both the type of biomass and the production temperature strongly influence performance. Biochar made from rice husk at 700 degrees Celsius exhibited the highest surface area and pore volume, enabling greater loading of the phase-change material. This composite achieved an energy storage capacity of approximately 250.9 joules per gram, nearly matching that of the pure material while maintaining structural stability.

Importantly, the composites demonstrated exceptional efficiency. The latent heat efficiency reached up to 100 percent, indicating that the biochar support did not significantly hinder the energy storage capability of the embedded material. In addition, the composites retained up to 91.7 percent of their energy storage capacity after 500 heating and cooling cycles, highlighting their durability for long-term applications.

The materials also showed strong resistance to leakage even at elevated temperatures. Unlike conventional phase-change materials that can melt and flow, the biochar structure effectively confined the liquid within its pores. This stability is critical for practical use in building materials, thermal insulation systems, and energy-saving technologies.

The study further revealed that pore structure plays a key role in performance. Materials with well-developed mesopores allowed better molecular movement and energy storage, while overly small or damaged pore structures reduced efficiency. This insight provides a clear design strategy for optimizing biochar-based composites in future applications.

“These findings demonstrate that sustainable, high-performance energy storage materials can be produced using simple methods and widely available biomass,” the researchers noted. “Such materials could play an important role in improving energy efficiency in buildings and supporting the transition to renewable energy.”

Because the composites operate effectively within a moderate temperature range of 20 to 40 degrees Celsius, they are particularly well suited for indoor thermal regulation, free-cooling ventilation systems, and other low-temperature energy applications.

By combining waste valorization with advanced material design, this research highlights the growing potential of biochar as a versatile platform for energy storage and environmental sustainability.

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Journal Reference: Atinafu, D.G., Choi, J.Y., Nam, J. et al. Insights into the effects of biomass feedstock and pyrolysis conditions on the energy storage capacity and durability of standard biochar-based phase-change composites. Biochar 7, 18 (2025).   

https://doi.org/10.1007/s42773-024-00396-1   

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About Biochar

Biochar (e-ISSN: 2524-7867) is the first journal dedicated exclusively to biochar research, spanning agronomy, environmental science, and materials science. It publishes original studies on biochar production, processing, and applications—such as bioenergy, environmental remediation, soil enhancement, climate mitigation, water treatment, and sustainability analysis. The journal serves as an innovative and professional platform for global researchers to share advances in this rapidly expanding field. 

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