Enhancing Thermal Conductivity and Photothermal Conversion of Polyethylene Glycol (PEG) With Boron Nitride‐Supported Copper Hybrid Fillers

ABSTRACT Phase change materials (PCMs) typically exhibit low thermal conductivity (TC) and limited light absorption, which restrict their application in solar thermal utilization. In this study, boron nitride microrod‐supported copper (Cu@BNR) was developed as a multifunctional filler and incorporated into polyethene glycol (PEG) to fabricate PEG‐based composite PCMs. The incorporation of Cu promotes the formation of a continuous thermal network and enhances photothermal conversion capability. Due to this unique structure, the PEG/Cu@BNRs composite containing 10 wt% Cu@BNRs achieves a TC of 1.344 W·m −1 K −1 , representing 5.1‐fold and 2.2‐fold increase compared to pure PEG and PEG/BNRs, respectively. Under simulated sunlight (100 mW cm −2 ), the PEG/Cu@BNRs composite reaches a photothermal conversion efficiency of 91.2% and demonstrates excellent shape stability and cycling reliability. As a thermal interface material in LED systems, the PEG/Cu@BNRs composite significantly reduces operating temperatures, confirming its practical thermal management capabilities. Consequently, the prepared composite PCMs integrate solar energy conversion, efficient heat conduction, and thermal storage functions, making them suitable for sustainable energy applications.