Agricultural Waste Turned Into Biochar Composites for Smarter Heat Storage

Published date:15/04/2026 | Last updated date:15/04/2026

Researchers have developed a new class of sustainable thermal energy storage materials by converting agricultural waste into high-performance biochar composites that can efficiently store and release heat. The work points to a practical route for improving low-carbon buildings and strengthening renewable energy systems, while also creating higher-value uses for plant-based waste.

The study shows that relatively simple changes in biomass feedstock and pyrolysis temperature can significantly influence storage capacity, structural stability, and long-term durability.

Waste biomass becomes a functional energy material

Thermal energy storage is becoming increasingly important as renewable power systems expand. Solar and wind energy are inherently variable, which means systems that can absorb, store, and release heat at the right time are gaining attention across both building technology and broader energy infrastructure.

Phase-change materials are widely studied for this purpose because they store thermal energy during melting and release it during solidification. However, their practical use has often been limited by persistent problems such as:

• material leakage during phase transition
• weak long-term cycling stability
• difficult or costly manufacturing routes

To address these barriers, the research team developed composite materials by loading hexadecane, a common phase-change material, into porous biochar made from agricultural residues.

Feedstock choice and temperature make a major difference

The biochar was produced from several forms of biomass waste, including:

• rice husk
• wheat straw
• Miscanthus straw

The materials were processed at pyrolysis temperatures ranging from 550°C to 700°C, then combined with hexadecane through vacuum infiltration, allowing the liquid phase-change material to fill the microscopic pore network of the biochar.

The results make one point clear: not all biochar performs the same.

Biochar made from rice husk at 700°C delivered the best overall structure, with the highest surface area and pore volume. That enabled greater loading of the phase-change material and produced a composite with an energy storage capacity of about 250.9 joules per gram, close to the performance of the pure phase-change material itself.

High efficiency without sacrificing stability

One of the most important findings is that the supporting biochar did not significantly reduce the thermal storage function of the embedded material.

The composites achieved latent heat efficiency of up to 100%, a strong sign that the porous support structure was effectively holding the phase-change material without blocking its thermal behavior.

Durability was also notable. After 500 heating and cooling cycles, the materials retained as much as 91.7% of their energy storage capacity, suggesting they could remain viable in long-term service rather than only in laboratory demonstrations.

That level of retention matters for real deployment, especially in applications where repeated cycling is unavoidable.

Leakage resistance improves practical usability

A major challenge with conventional phase-change systems is that once the material melts, it can leak or migrate, reducing performance and making installation difficult.

In this study, the porous biochar network acted as a confinement structure, keeping the liquid phase-change material trapped inside the pore system even at elevated temperatures.

This gives the material a much stronger practical profile for use in:

• building envelopes
• thermal insulation systems
• indoor climate regulation
• low-temperature energy-saving technologies

For engineers and product developers, this is where the research becomes commercially relevant. Good thermal capacity alone is not enough. The material must also stay physically stable during operation.

Pore structure emerges as the real design lever

The study also highlights a deeper materials insight: pore architecture plays a decisive role in performance.

Biochars with well-developed mesopores supported better molecular movement and stronger energy storage behavior. By contrast, materials with pore structures that were too small, damaged, or poorly connected showed weaker efficiency.

This gives future developers a clearer design direction. The route to better biochar-based heat storage materials is not simply to add more phase-change material, but to engineer the support structure more precisely.

That changes the conversation from waste reuse alone to targeted material design.

Strong potential for buildings and renewable systems

Because the composites perform well within a moderate temperature window of roughly 20°C to 40°C, they are especially suitable for low-temperature thermal management applications.

Potential uses include:

• indoor temperature regulation
• passive cooling and free-cooling ventilation
• low-energy building systems
• distributed renewable energy storage

This temperature range is important because it aligns closely with real operational conditions in buildings, where thermal comfort and efficiency improvements can deliver immediate value.

A broader shift in sustainable materials development

What makes this research especially relevant is that it combines two priorities that are often treated separately: waste valorization and energy efficiency.

Instead of treating agricultural residues as disposal problems, the study shows they can serve as feedstocks for functional materials with meaningful thermal performance. That gives biochar a broader role than its more familiar uses in soil science or carbon management.

It also reinforces a growing trend in advanced materials research: sustainability claims are becoming more credible when they are tied to real performance metrics, process simplicity, and scalable feedstocks.

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Editor’s Note

This is not just another lab-scale story about a green material with theoretical promise. The study offers a practical materials strategy: use abundant agricultural waste, tune the pyrolysis conditions carefully, control the pore structure, and build a composite that performs close to the benchmark phase-change material while solving leakage and durability problems.

That combination is what gives the work real weight.

If these biochar-based composites can be scaled economically, they may find a meaningful place in next-generation thermal management systems, particularly in buildings where moderate-temperature storage can improve both energy efficiency and renewable integration.

In that sense, the research does more than improve a material. It suggests a more useful future for agricultural waste itself.