Activated carbons effectively purified by post-heat treatment under vacuum conditions

Abstract

The effect of heat treatment and vacuum conditions on the textural properties and electrochemical performance of commercially available activated carbons (ACs) was investigated. The AC after post-heat treatment was characterized by nitrogen adsorption–desorption, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and Fourier-transform infrared spectroscopy measurements. The ACs treated under vacuum conditions exhibit a higher specific surface area and micropore surface area than those treated under nitrogen atmospheric pressure without significantly affecting the graphite structure of the AC. Under 800 °C temperature and vacuum conditions (AC-V800), the AC with the highest Brunauer–Emmett–Teller surface area of 1951.9 m2 g−1 (16.4% improvement relative to that of the original AC (1677.2 m2 g−1)) was obtained. This is attributed to the removal of oxygen-containing functional groups and volatile matters in the carbon by thermal treatment under vacuum conditions. Consequently, the electric double-layer capacitor using ACs treated under vacuum conditions (1 kPa) at 800 °C (AC-V800) shows considerably improved electrochemical performance in terms of higher specific capacitance and better cycling stability at a high working voltage (3.1 V), compared to the nitrogen-treated and commercial ACs.