Enhancing electrochemical properties of bacterial cellulose-derived carbon nanofibers through physical CO2 activation

Abstract

Carbon nanofiber (CNF) derived from carbonization of bacterial cellulose (BC), with a unique three-dimensional porous nanostructure, has received significant interest in electrochemical applications. In this study, CNF samples were physically activated in CO₂ at different temperatures and durations. Raman spectroscopy and FTIR analysis showed that CO₂ activation caused hexagonal lattice defects, disorder, and oxygen-related functional groups in an amorphous carbon structure. CNF surface morphology changed after physical activation, reducing fiber diameter to 55 nm and introducing mesopores. Through activation temperature and time adjustments, surface area (870.1 m²/g) and micropore surface area (535.6 m²/g) and pore volume (0.2148 cm³/g) increased. EDX elemental analysis showed that activated CNF had a carbon concentration of > 90 %, while XPS analysis showed surface functional groups like C-C (sp²) and C-C (sp³) hybridization, which could improve electrolyte ion adsorption and accessibility. Electrochemical properties improved owing to CO₂ activation. The optimal activation condition of 800 ℃ for 60 min resulted in the highest specific area capacitance of 552 mF cm⁻² at 1 mA cm⁻². This activated CNF electrode retained capacitance nearly unchanged up to 3,000 cycles. It also achieved the highest energy density of 76.7 mWh cm⁻² at 500 mW cm⁻². This study demonstrates the efficacy of CO₂ physical activation for enhancing the electrochemical properties of CNF electrodes. The findings also highlight the importance of tailoring activation conditions, providing valuable insights for the design of advanced energy storage materials.