Enabling unidirectional thermal conduction of wood-supported phase change material for photo-to-thermal energy conversion and heat regulation

Abstract

Phase change materials (PCMs) enable passive thermal management by minimizing energy waste. However, a limitation of organic PCMs is their low thermal conductivity, which leads to uneven phase transitions. Herein, we introduce a composite following a green and simple synthesis strategy that uses wood's fiber anisotropy and microporosity to support an organic PCM (polyethylene glycol, PEG). We first incorporate exfoliated boron nitride (BN) and polyethylenimine (PEI) in a layer-by-layer (LbL) assembly followed by capping with conductive polypyrrole. This modification of the wood framework endows non-leaking filling with PCM and simultaneous light absorption and thermal conduction. The loaded BN provides enhanced thermal conductivity, 4.4 and 26 times higher compared to neat PEG and delignified wood. As a result, the multicomponent system is effective for solar-to-thermal energy conversion with a latent heat of melting of up to ∼160J/g (∼78% PEG encapsulation). Moreover, the modified wood composite shows thermal durability and stability for at least 50 heating and cooling cycles. Overall, we take advantage of unidirectional heat transport for light conversion and storage and demonstrate the operation principle using a proof-of-concept prototype system.