Functionalized Polyethylene Glycol Composite Phase Change Materials: A Review

As the impacts of climate change become increasingly severe, the transformation and optimization of energy structures are critical. Phase change energy storage, as an innovative thermal energy storage (TES) technology, receives growing attention. Polyethylene glycol (PEG), a widely used organic phase change material (PCM), offers excellent thermal storage capacity. However, its practical application is limited by low thermal conductivity and leakage issues. This article reviews the fundamental properties of pure PEG, PEG‐based eutectic mixtures, and PEG‐based composite PCMs. The synergistic effects of PEG combined with high thermal conductivity matrices (carbon nanotubes (CNTs), graphene oxide (GO), expanded graphite (EG)) and shape‐stabilizing materials (polymers and porous media) are analyzed to enhance thermal conductivity and address shape‐stabilization issues. The article also explores functional modifications of PEG‐based PCMs, including thermochromic behavior, photothermal conversion, and mechanical flexibility. Applications in battery thermal management, solar TES, and building envelope heat storage demonstrate the broad application prospects of PEG in various fields due to its high thermal storage density and other advantages. Finally, the article outlines current challenges and proposes future research directions to further advance PEG‐based composite PCMs for efficient and stable energy storage solutions.