Lignin-Enabled Cell Wall Engineering of Wood for Integrated Photothermal Conversion and Phase Change Energy Storage

Wood-based phase-change composites are promising for solar-thermal energy storage and thermal regulation. However, native wood limits phase-change material (PCM) uptake, whereas extensive delignification removes lignin’s intrinsic light-harvesting capacity. We developed a cell−wall nano-engineering approach using aqueous p-toluenesulfonic acid to partially remove hemicellulose and redistribute retained lignin. This treatment increased cell-wall accessibility while preserving the wood's photothermal function. After impregnation with poly(ethylene glycol) impregnation, the resulting composite achieved a melting enthalpy of 154.9 J g−1 and an encapsulation efficiency of 78.5%. It showed no visible leakage at 80 °C and maintained stable thermal-storage performance over 100 heating−cooling cycles (differential scanning calorimetry). Lignin redistribution and reassembly within the cell wall also improved water repellency and moisture resistance. Compared with native- and delignified-wood controls, the composite showed stronger broadband absorption and an apparent photothermal conversion efficiency of 83.2% under two-sun irradiation. This lignin-retaining strategy integrates physical PCM confinement, thermal storage, and intrinsic photothermal conversion without requiring additional light absorbers.