Carbonized cork/polyethylene glycol composite phase change materials with high encapsulation for efficient photothermal utilization

Phase change materials (PCMs) exhibit considerable promise in energy accumulation applications owing to their high energy density and stable phase change temperatures, yet they are plagued by leakage issues, low thermal conductivity, and inadequate photothermal conversion efficiency. Cork, a renewable biomass with a natural honeycomb structure, has low permeability due to suberin in its cell walls, limiting efficient PCM loading. Herein, carbonized cork (CC) was prepared by high-temperature carbonization to remove these organic components, addressing the permeability issue. Composite PCMs (CC/PEG) were fabricated via vacuum impregnation of polyethylene glycol (PEG) into CC. Carbonization eliminated suberin, lignin, and cellulose, increased specific surface area to 224.02 m 2 /g while retaining the honeycomb structure, and enabling the PEG encapsulation rate to exceed 85 %. CC's graphitized structure enhanced thermal conductivity: CC/PEG prepared at 700 °C (CC-700/PEG) reached 0.398 W/m·K (56.7 % higher than pure PEG) with a high phase change enthalpy of 155.4 J/g. Furthermore, the synergistic effect of CC's conjugated π-bond system and honeycomb structure enhances broad-spectrum absorption, boosting CC-700/PEG's photothermal conversion efficiency to 87.71 %. This not only performs well in photothermal conversion, but also supports its use in building walls to cut annual heating energy consumption (0–30 MJ/m 2 savings) across climates for urban civil residential buildings. This work realizes a synergistic enhancement in leakage resistance, thermal conductive performance, and photothermal conversion capability in composite PCMs via a carbonization-regulated cork structure, providing a viable strategy for low-cost, high-performance photothermal energy storage materials. • Carbonized cork enables >85 % PCM encapsulation, solving leakage. • Composite PCMs show thermal conductivity 78.74 % higher than pure PEG. • CC's π-bonds and honeycomb structure achieve 87.71 % photothermal efficiency. • Low-cost, high-performance material aids photothermal energy storage.