A biochar-based thermal sponge stores heat during the day and releases it at night, cutting cooling energy by over 50%.
As global temperatures rise, buildings face increasing cooling demands, putting pressure on energy systems and driving up electricity consumption. Conventional materials offer limited thermal storage, forcing reliance on energy-intensive air conditioning to maintain comfortable indoor conditions. Efficient, scalable thermal storage materials are needed to reduce energy use and smooth temperature fluctuations.
Researchers at Yonsei University have developed EMBC16, a “thermal sponge” composite that functions as a compact thermal battery for buildings. The material stores excess heat during the day and releases it as temperatures drop, buffering indoor environments against extreme heat and reducing annual cooling energy use by 54% while cutting overall cooling demand by 24.3%.
The material achieves a 223% increase in energy storage compared with simple clay composites, storing 121.3 joules per gram. Its thermal conductivity is 78% higher, and it demonstrates long-term stability with over 95.9% capacity retention after 1,000 heating and cooling cycles and less than 2.2% leakage of its paraffin component. The composite is made by infusing hexadecane into a 3D porous framework of biochar and montmorillonite clay, engineered for high surface area and efficient heat transfer.
Key features of the research include:
- High energy storage of 121.3 J/g, 223% above clay composites
- 78% improved thermal conductivity for faster heat transfer
- Long-term durability: 95.9% capacity retention after 1,000 cycles
- Low leakage of paraffin phase change material (<2.2%)
- Biomineral framework using biochar and montmorillonite clay
Dimberu G. Atinafu, who led this research work, says, “By engineering a greener support framework for paraffin, we can capture more heat, move it more efficiently, and do it with materials sourced from biomass and earth minerals.”
