In a recent publication in Engineering Science and Technology, an International Journal, researchers B. Kalidasan, A.K. Pandey, Yasir Ali Bhutto, Wenye Lin, Imansyah Ibnu Hakim, Fadia Ramadhania Nurhakim, and Nabil Fadlurahman Raynorasaki presented a breakthrough in green thermal energy storage. Traditional organic phase change materials like octadecane store massive amounts of latent heat but suffer from low intrinsic thermal conductivity, which limits their charging rates. To solve this without using toxic or expensive metallic nanoparticles, the team successfully synthesized an eco-friendly alternative using carbonized agricultural waste. By transforming groundnut shells into highly porous biochar microparticles and dispersing them into octadecane, the study achieved remarkable performance enhancements for building energy regulation and solar harvesting applications.

The findings highlight an extraordinary increase in heat transfer capabilities. Pure octadecane possesses a low thermal conductivity of just 0.139 Watts per meter-Kelvin. When the team integrated 0.7 percent by weight of the groundnut shell biochar, the thermal conductivity soared to 0.268 Watts per meter-Kelvin, representing a massive 113.5 percent improvement. The highly porous carbon architecture forms an interconnected network within the organic matrix, minimizing thermal resistance. When the biochar concentration was increased to 0.9 percent, the conductivity dropped to 0.216 Watts per meter-Kelvin because the particles began to cluster together, showing that optimal balancing is crucial.

Crucially, this doubling of thermal conductivity did not come at the expense of energy storage density. The composite containing 0.7 percent biochar maintained a robust melting latent heat of 244.4 Joules per gram, which is nearly identical to the 244.5 Joules per gram recorded for pure octadecane. Remarkably, at a lower concentration of 0.3 percent biochar, the capacity actually expanded to 245.4 Joules per gram. This occurs because well-dispersed carbon microparticles act as highly effective nucleation sites that facilitate orderly energy absorption and release during phase transitions.

The research also demonstrated exceptional advancements in optical behavior for direct solar harvesting. Pure octadecane is transparent, allowing 60.75 percent of incoming light to pass directly through it. Integrating 0.7 percent groundnut biochar dropped this light transmission down to 27.2 percent, which corresponds to a 161.79 percent spike in light absorbance. The rough surface topography and carbon bonds of the biochar effectively scatter and trap incoming radiation, allowing the composite to directly convert sunlight into stored heat energy at an accelerated pace.

The practical viability hinges on long-term durability, both of which were thoroughly validated. Analysis revealed that the biochar composites remain perfectly stable up to ninety degrees Celsius without experiencing any initial weight loss. Final breakdown occurred safely between 225 and 250 degrees Celsius, as capillary forces between the biochar pores and the octadecane acted as a protective thermal barrier. Furthermore, the material underwent five hundred continuous heating and cooling cycles to simulate real-world operation. Infrared spectroscopy proved that no negative chemical alterations formed over time. The heat storage capacity of the 0.7 percent composite experienced only a minor drop to 226 Joules per gram after five hundred cycles, confirming that this sustainable formulation is exceptionally reliable for long-term commercial integration.

Source: Kalidasan, B., Pandey, A. K., Bhutto, Y. A., Lin, W., Hakim, I. I., Nurhakim, F. R., & Raynorasaki, N. F. (2026). Biochar engineered phase change material: enhancing octadecane for next generation thermal energy storage applications. Engineering Science and Technology, an International Journal, 80, 102432.