by Riko Seibo
Tokyo, Japan (SPX) Feb 02, 2026

As renewable energy deployment accelerates worldwide, managing heat when the sun is not shining or when demand fluctuates remains a core challenge for clean energy systems. Researchers reporting in the journal Biochar have now shown that agricultural waste in the form of discarded neem seeds can be transformed into a high performance and carbon negative thermal energy storage material.

The team developed a biochar based phase change material that can capture, store, and release heat efficiently while simultaneously sequestering carbon. In their work, neem seed waste was converted into biochar by heating the biomass under low oxygen conditions at two different temperatures, 300 and 500 degrees Celsius, to investigate how production temperature affects thermal storage behavior.

The resulting porous carbon materials were then infused with lauric acid, a fatty acid commonly used in thermal energy storage applications, to produce shape stabilized phase change composites. In this configuration, the lauric acid absorbs heat as it melts and releases heat as it solidifies, with the biochar framework preventing the melted phase change material from leaking out of the structure.

According to the researchers, the temperature used to produce the biochar strongly controls its surface area, pore structure, and ultimately its capacity to store thermal energy. Biochar produced at 500 degrees Celsius developed an exceptionally high internal surface area of more than 600 square meters per gram, creating a sponge like architecture that could hold significantly more lauric acid within its pores than material produced at the lower temperature.

Because of this enhanced loading, the high temperature biochar composite stored nearly twice as much latent heat as the composite prepared from biochar made at 300 degrees Celsius. Laboratory measurements showed that the optimized neem seed biochar phase change material could store almost 95 joules of heat per gram while maintaining stable melting and solidification temperatures.

The material also demonstrated strong cycling stability, with thermal behavior remaining consistent over hundreds of heating and cooling cycles. Leakage tests indicated that the lauric acid stayed locked inside the biochar matrix even when the composite was heated above the melting point of the phase change component, an essential requirement for reliable long term operation.

The researchers emphasized that this level of stability is critical for real world uses such as building temperature regulation, solar thermal energy systems, and industrial waste heat recovery. In these settings, thermal storage media must operate for many years without significant degradation, loss of capacity, or leakage of the active material.

Beyond its performance metrics, the approach offers clear sustainability advantages because neem seeds are widely available agricultural residues in many tropical regions and are often discarded after oil extraction. Converting this underused biomass into biochar for energy storage not only adds value to a waste stream but also locks carbon into a stable solid form instead of allowing it to return quickly to the atmosphere.

Unlike many conventional energy storage technologies that depend on mined materials or complex manufacturing processes, biochar based thermal energy storage can be produced using relatively simple equipment and locally sourced feedstocks. This combination of low cost production and use of local resources makes the technology attractive for decentralized energy systems and for communities seeking affordable clean energy solutions.

The study highlights the importance of tuning biochar production conditions, particularly temperature, to tailor pore structure and surface properties for specific energy applications. The authors suggest that with further development and optimization, biochar based phase change materials derived from agricultural residues such as neem seeds could contribute to improved energy efficiency, reduced carbon emissions, and a more sustainable global energy system.

Research Report:Temperature-modulated surface features of neem seed biochar for sustainable thermal energy storage applications

Related Links
Shenyang Agricultural University
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