A study published in the journal Biochar by authors Dimberu G. Atinafu, Harn Wei Kua, Yujin Kang, and Sumin Kim presents a biochar-based phase-change composite integrated into a paper membrane system. Rapid urbanization and energy consumption in built environments require scalable, sustainable technologies to regulate indoor temperatures and humidity levels without incurring high energy penalties. Phase-change materials store and release thermal energy during temperature fluctuations, but traditional organic phase-change materials suffer from liquid leakage, poor thermal conductivity, and limited structural stability. To overcome these physical constraints, researchers engineered a porous carbon scaffold using food waste converted into biochar through slow carbonization and chemical activation, followed by graphene integration to improve conductivity and surface chemistry.

The structural evaluation revealed that biochar carbonized at four hundred degrees Celsius and activated with potassium hydroxide at seven hundred degrees Celsius formed an interconnected, hierarchical porous network. This material exhibited a specific surface area of three hundred twenty-three square meters per gram with a high mesopore proportion of eighty-two percent, creating an optimal framework for holding the phase-change material docosane. Incorporating low concentrations of graphene onto the biochar surface enhanced matrix crystallinity and reduced structural defect sites without clogging essential pore channels. The resulting hybrid matrix effectively held liquid phase-change molecules inside its micro- and mesoporous network through capillary forces and surface tension, preventing leakage even when heated above the melting point of the organic phase-change material.

Thermal testing demonstrated that the engineered biochar-graphene composite achieved significant performance improvements over pristine organic phase-change materials and unmodified biochar supports. The graphitized hybrid composite reached a high latent heat energy storage capacity while dramatically accelerating heat diffusion kinetics. When subjected to accelerated thermal cycling to evaluate long-term durability, the composite maintained structural integrity and retained over ninety percent of its original phase-change enthalpy after one thousand continuous heating and cooling cycles, simulating approximately three years of operational use in ventilation systems. The balanced pore architecture provided swift thermal transport while preserving high energy storage density, resolving the typical performance trade-off between heat storage and thermal conductivity.

To demonstrate real-world application, the phase-change composite was bonded directly to commercial paper membranes used in energy recovery ventilators. The hybrid membrane achieved a thermal conductivity ninety-six percent higher than pristine reference membranes, allowing rapid heat exchange across ventilation channels. Concurrently, hygrothermal experiments confirmed that the composite-coated paper maintained high water-vapor permeability, recording an equivalent air-layer thickness value of zero point seven one meters, comfortably below the standard threshold required for breathable, moisture-regulating membranes. By simultaneously optimizing sensible heat conduction, latent heat storage, and water-vapor transport, this engineered biohybrid paper membrane presents a sustainable pathway for low-carbon building thermal management and energy recovery.

Source: Atinafu, D. G., Kua, H. W., Kang, Y., & Kim, S. (2026). Engineered biochar-graphene hybrid paper membranes for long-term thermal energy storage and ventilation energy recovery. Biochar, 8, 132.