Strong, Scalable and Anisotropic Wood Composites for High-Performance Thermal Energy Storage in Buildings

Thermoregulation in America’s buildings by heating, ventilation, and air conditioning (HVAC) consumes 11% of the nation’s total energy use and emits 309 million metric tons of CO₂ in a single year. A promising solution for energy-efficient thermoregulation is to implement thermal energy storage (TES) in buildings through phase change materials (PCMs) integrated into wood, which is the most used building construction material. Recent efforts have explored the encapsulation of solid-to-liquid PCMs in delignified wood. However, the resulting wood composite is weak due to the removal of lignin, which is the natural binding agent in wood. Additionally, the scalability of delignification methods is limited due to the slow and inhomogeneous permeation kinetics of the chemical treatment. To resolve these issues, we herein report an approach to transform the wood into a microporous, anisotropic, strong, and scalable matrix for PCM encapsulation by selectively removing hemicellulose in wood using a chemical-free, pressurized hot water treatment process that preserves lignin. The exterior of the wood was selectively densified by controlled hot-pressing, enhancing its mechanical strength while allowing high PCM loading within the microporous core of the matrix. Following the PCM infiltration, the composite exhibits a mechanical strength of 51 MPa, comparable to that of natural wood, and achieves a latent heat of 62 J/g for TES. The low-carbon fabrication of the composite in addition to the reduced HVAC-associated carbon emissions enabled by TES holds promise to promote the sustainability of the built environment.