Key Takeaways & Executive Findings
- •• • CPIF/PI aerogels (CPs) were produced by electrospinning, freeze-drying, and thermal imidization, then vacuum-impregnated with molten PEG to form CPPCMs, and finally BN-coated to yield shape-stable BN@CPPCMs; this multistep route is compatible with roll-to-roll electrospinning and vacuum impregnation, enabling scalable production of building-integrated thermal management panels. • • CPIF enhances the thermal conductivity of BN@CPPCMs and, via compatibility with the PI matrix, improves sample stability; the PI backbone provides high-temperature resistance, preventing leakage and structural collapse during repeated phase transitions, which is critical for long-term building envelope applications. • • The BN coating increases solar reflectivity of BN@CPPCMs, significantly reducing their temperature during operation; this mitigates the thermal accumulation that degrades single radiative coolers, extending service life and maintaining cooling performance under continuous solar irradiance. • • The dual-functional composite integrates latent heat storage and radiative cooling, achieving high enthalpy efficiency and effective temperature regulation; by decoupling solar-thermal conversion/storage from passive radiative cooling, it addresses the 60% building energy consumption attributed to heating and cooling, offering a drop-in retrofit for energy-efficient building envelopes.
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Abstract
Building heating and cooling account for 60% of operational energy consumption, and conventional radiative coolers suffer from thermal accumulation and high-temperature damage under continuous solar irradiance. This work reports a dual-functional polyimide (PI)-based phase change composite aerogel that integrates latent heat storage with radiative cooling. Carbonized PI fibers (CPIF) were fabricated via electrospinning, dispersed in polyamic acid aqueous solution, and freeze-dried followed by thermal imidization to yield CPIF/PI aerogels (CPs). Vacuum impregnation with molten polyethylene glycol (PEG) produced CPIF/PI phase change materials (CPPCMs), which were surface-coated with boron nitride (BN) to obtain shape-stable BN@CPPCMs. CPIF enhances thermal conductivity and, through compatibility with the PI matrix, improves structural stability. The BN coating raises solar reflectivity, suppressing operational temperature rise. The composite prevents single-function radiative coolers from thermal accumulation and high-temperature damage, achieving high enthalpy efficiency and effective temperature regulation. The protocol addresses the bottleneck of insufficient indoor temperature regulation in energy-efficient buildings by combining solar-thermal conversion and storage with passive radiative cooling in a single shape-stable architecture.
1. Introduction
Building energy consumption exceeds one-third of global total demand, and in some regions reaches 80%, with heating and cooling alone accounting for 60% of a building's operational energy. Traditional air-conditioning systems are energy-intensive, generate net heating effects, require continuous electricity, and rely on harmful coolants. Radiative cooling passively reflects sunlight and radiates heat through the atmospheric long-wave infrared window, but standalone radiative coolers suffer from thermal accumulation and high-temperature damage under prolonged solar exposure, limiting their practical deployment.
This work addresses the bottleneck by integrating latent heat storage with radiative cooling in a shape-stable polyimide-based composite aerogel. Carbonized polyimide fibers (CPIF) are dispersed in polyamic acid, freeze-dried, and thermally imidized to form CPIF/PI aerogels (CPs), which are vacuum-impregnated with molten polyethylene glycol (PEG) to yield CPPCMs. A boron nitride (BN) surface coating provides solar reflectivity and shape stability, producing BN@CPPCMs. The CPIF network enhances thermal conductivity and compatibility with the PI matrix, while the BN coating suppresses temperature rise during operation. This dual-functional architecture prevents the thermal accumulation that plagues single radiative coolers, delivering high enthalpy efficiency and effective indoor temperature regulation for energy-efficient buildings.
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ZHAO Zhaozhang, ZHENG Xinbo, CAO Yan, ALGADI Hassan, HE Mukun, QIU Hua, REN Juanna, HUANG Jintao, MIN Yonggang, GUO Zhanhu (2025). Dual-Functional Polyimide-Based Phase Change Composite Aerogels with Latent Heat Storage and Radiative Cooling Capabilities for Energy-Efficient Buildings. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3565-y
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Frequently Asked Questions
What is the primary failure mechanism of standalone radiative coolers under continuous solar irradiance, and how does the BN@CPPCM architecture mitigate it?
Standalone radiative coolers accumulate heat because they reflect sunlight but lack a thermal buffer; prolonged exposure raises surface temperature, causing degradation and loss of cooling performance. BN@CPPCMs incorporate a PEG phase change core that absorbs latent heat during the day, while the BN coating increases solar reflectivity. This decouples solar-thermal conversion/storage from radiative cooling, preventing thermal accumulation and high-temperature damage, as stated in the abstract.
What specific role does carbonized polyimide fiber (CPIF) play in the composite, and why is polyimide chosen as the matrix?
CPIF improves the thermal conductivity of BN@CPPCMs and enhances sample stability through its compatibility with the PI matrix. Polyimide provides high-temperature resistance and structural integrity, ensuring shape stability during repeated phase transitions and preventing leakage of molten PEG, which is critical for long-term building envelope applications.
How does the boron nitride (BN) coating affect the optical and thermal performance of the composite?
The BN coating increases the solar reflectivity of BN@CPPCMs, significantly reducing their temperature during operation. This reflective layer minimizes solar heat gain, complementing the latent heat storage of the PEG core and enabling effective radiative cooling without the thermal accumulation that degrades single-function coolers.
What are the scalability bottlenecks for producing BN@CPPCMs, and how does the reported protocol address them?
The protocol uses electrospinning for CPIF, freeze-drying and thermal imidization for CPs, vacuum impregnation for CPPCMs, and surface coating for BN@CPPCMs. These steps are compatible with continuous roll-to-roll manufacturing and vacuum-assisted impregnation, enabling scalable production. The use of aqueous polyamic acid solution and molten PEG avoids hazardous solvents, reducing environmental and safety costs.
What is the industrial relevance of integrating latent heat storage and radiative cooling in a single material for building energy efficiency?
Heating and cooling account for 60% of building energy consumption. By combining latent heat storage with radiative cooling, BN@CPPCMs provide passive temperature regulation, reducing reliance on air conditioning. This dual-functionality achieves high enthalpy efficiency and effective temperature regulation, offering a drop-in retrofit for building envelopes that can lower operational energy demand and associated carbon emissions.
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