Nano-sized mesoporous biochar derived from biomass pyrolysis as electrochemical energy storage supercapacitor

Energy storage is essential to conserve and deliver energy to end-user with continuity and durability. A sustainable energy supply with minimal process losses requires cost-effective and environmentally friendly energy storage material. In this study, self-co-dopes N (3.65 %) and O (6.44 %) porous biochar were produced from pyrolysis of biomass pellets (made from garden wastes) and examined for energy storage application. The presence of co-doped-heteroatoms within the carbon matrix of biochar resulted in enhanced surface wettability, fast charge transfers, increased electrical conductivity, and low internal resistance. Biochar produced at 800 ℃ (i.e. biochar-800) showed desirable pseudocapacitive nature induced by self-co-doped heteroatoms. Two-electrode measurements in aqueous 1 M H<inf>2</inf>SO<inf>4</inf> revealed that biochar-800 possessed 228F g⁻¹ of specific capacitance at a current density of 1 Ag⁻¹. Additionally, biochar-800 exhibited a high energy density of 7.91 Wh kg⁻¹ in aqueous electrolyte and promising cycling stability with 88% capacitance retention after 5000 cycles at 10 A g⁻¹. Enhanced capacitive performance of biochar-800 was assigned to the presence of self-co-doped heteroatom, the high specific surface area of 312 m²g⁻¹, and self-formed mesopores (pore size around 15.2 nm). This study demonstrates the great promise of porous biochar derived from biomass pellets as a low-cost electrode material for high-performance energy storage devices.