Lignosulfonate-Decorated Boron Nitride/Cellulose Nanofibril Porous Foam: Multifunctional Phase Change Composites for Leakage-Free Thermal Energy Storage and Photothermal Conversion

To address the challenges of low thermal conductivity and leakage in phase change materials (PCMs), a composite PCM (CPCM) was developed by integrating lignosulfonate-functionalized boron nitride nanosheets (BNNS@LS) into a cellulose nanofiber (CNF)-based porous foam scaffold via directional freezing. Polyethylene glycol (PEG) was vacuum-impregnated into the scaffold to form a shape-stable CPCM. The 3D porous foam structure effectively prevented PCM leakage during phase transitions, achieving 177.2 J/g latent heat (93.56% of pristine PEG) and excellent cycling stability. The synergistic BNNS@LS-CNF network effectively enhanced the thermal conductivity of CPCM, achieving a value of 1.00 W/m·K (a 2.1-fold improvement) at a filler content as low as 1.8 wt %. Notably, the CPCM demonstrated unique photothermal conversion capability, enabling efficient solar energy storage. This work presents a rational design strategy for multifunctional PCMs with integrated thermal management, leakage resistance, and light-to-thermal energy conversion properties.