Scientists have transformed seafood waste into a type of carbon aerogel, which can efficiently store heat during the melting process and does not leak. 
A team of materials scientists has developed a bio-based carbon material that holds promise for addressing one of the most challenging issues in thermal energy storage: the problem of material leakage during melting. This new material can efficiently store heat and maintain its shape intact even when the heat storage compound transitions from a solid state to a liquid state. The research focuses on phase change materials, which absorb and release heat during melting and solidification. 
These materials have been extensively studied and applied in various fields such as building temperature control, solar energy storage, and electronic thermal management. However, many organic phase-change materials tend to leak during melting, which limits their durability and practical application. 
To address this issue, researchers turned their attention to chitin - a natural polymer found in the shells of crustaceans and fungi. Chitin is abundant, renewable, and is often discarded as waste, making it an attractive candidate in the field of sustainable materials engineering. In this new study, scientists converted chitin into ultra-light aerogels, and then carbonized them to form porous carbon frameworks. This structure was designed to serve as a carrier for stearic acid. Stearic acid is a common organic phase-change material, known for its high heat storage capacity, but also suffers from persistent leakage problems. 
Turning waste into carbon 
This carbon aerogel derived from chitin has a highly interconnected pore network and a large pore volume. These pores physically capture the molten stearic acid, and capillary forces and hydrogen bonds can prevent it from flowing out during the melting process. The corresponding author Li Hui (transliteration) said: "Our goal is to design a low-cost, environmentally friendly carrier that can accommodate a large amount of phase change materials without leakage. Chitin is abundant, renewable, and naturally rich in nitrogen." 
The resulting composite material can accommodate up to 60% of stearic acid by weight without any visible leakage. Even if stearic acid melts, the overall structure remains solid, which solves the main challenges faced by many organic phase change systems. Thermal tests show that the melting enthalpy of this composite material reaches approximately 118 joules per gram, which is higher than that of many previously reported biomass-derived phase change materials. The carbon framework also improves the thermal conductivity, enabling heat to flow more efficiently into and out of the material. 
Designed for recycling use 
Durability is another key point of this research. After 100 heating and cooling cycles, the composite material retained over 97% of its original heat storage capacity, and the phase transition temperature changed very little. Li Hui said: "Long-term reliability is crucial for real-world energy storage systems. Our research results show that this carbon aerogel based on chitin can repeatedly store and release heat." 
The researchers also discovered that the nanoscale confinement effect within the carbon pores increased the activation energy required for the phase transition of stearic acid. This indicates that the thermal stability of the material has been improved by the interaction between the nitrogen-doped carbon surface and organic molecules. Since chitin can be obtained from seafood waste and fungal biomass, this method provides a way to convert biological by-products into high-value energy materials. The team believes that this strategy can be applied to other phase change materials and temperature ranges, opening the door to greener thermal energy storage systems. 
This research was published in the journal "Sustainable Carbon Materials".