Exploration of Highly Porous Biochar Derived from Dead Leaves to Immobilize LiOH·H2O Nanoparticles for Efficient Thermochemical Heat Storage Applications

Abstract

The inadequate utilization of low‐grade energy from industrial waste heat and solar energy calls for an efficient thermochemical heat storage material. The fabrication of a low‐cost but highly efficient composite comprising highly porous biochar and LiOH·H2O nanoparticles for heat storage applications is reported. The biochar is prepared by the KOH‐assisted pyrolysis of dead banyan leaves, and its microstructure and surface properties can be finely tuned by varying the KOH‐to‐biomass ratio. Such biochar can be mediated to possess a large specific surface area and total pore volume reaching as high as 1255.03 m2 g−1 and 3.65 cm3 g−1, respectively, superior to most previously reported biochar/biocarbon derived from different kinds of waste biomass. Besides, adequate functional groups and a hierarchical porous structure consisting of micropores and mesopores are demonstrated in the prepared biochar. The subsequent hydrothermal reaction with a short duration yields a biochar‐LiOH·H2O composite, where LiOH·H2O can be homogeneously immobilized with a nanoscale size within the porous biochar matrix. Thus, an enormous biochar/LiOH·H2O nanoparticles interface can be obtained, resulting in fast hydration reactions with water molecules. Consequently, a significant heat storage density of as high as 3089.6 kJ kg−1 is achieved within only 10 min, outstripping some recently reported thermochemical heat storage systems.