19F Ex Situ Solid-State NMR Study on Structural Differences in Pores of Activated Carbon Series Derived from Chemical and Physical Activation Processes for EDLCs

Abstract

This study demonstrates the differences in the capacitive behaviors between the pore structures generated by physical and chemical activation and infiltrated electrolyte ions in the pores. Three paired samples were successfully synthesized with similar specific surface areas and average pore widths through steam activation (physical) and KOH activation (chemical) processes. Their capacitive behaviors were investigated with their effective charge (β) values through 19F ex situ solid-state NMR and electrochemical methods. Despite their similar pore characteristics, their capacitive behaviors were totally different because of the differences in their surface structures such as the edge-rich for KOH activation and basal-rich for steam activation. The KOH-activated series displayed higher capacitances and β values than those of the steam-activated series due to the existence of an edge-rich surface structure, which induced more effective charging under electrochemical polarization. Additionally, the pore development model (domain theory) through the KOH and steam activation approaches was discussed by using the β values and chemical shifts by using this 19F ex situ solid-state NMR technique.