Sulfur-doped carbon nanotubes as a conducting agent in supercapacitor electrodes

Abstract

The electrochemical performance of sulfur-doped carbon nanotubes (S-CNTs) was investigated to confirm the S-doping effects and the possibility of their application as conducting agents in supercapacitor electrodes. S-CNTs were successfully synthesized via chemical vapor deposition using dimethyl disulfide as the carbon source. They were purified to obtain purified S-CNTs (P–S-CNTs) with diameters 30–50 nm and S content of 0.65 at%. The doped S atoms were removed partially from the P–S-CNTs by heat treatment in H2 atmosphere (De-P-S-CNTs). To compare the electrochemical performances of various conducting materials for supercapacitor electrodes, commercial activated carbon (MSP20) was used as the active material and commercial conducting agent (Super-P), commercial multi-walled CNTs (MWCNTs), De-P-S-CNTs, and P–S-CNTs were used as the conducting agents. The electrode with P–S-CNTs exhibited the highest specific capacitance at a high discharge current density of 100 mA cm−2 (120.2 F g−1) and the lowest charge-transfer resistance (6.19 Ω) that are significantly superior to those of Super-P (83.9 F g−1 and 15.16 Ω), MWCNTs (87.8 F g−1 and 17.02 Ω), and De-P-S-CNTs (90.1 F g−1 and 22.33 Ω). The superior electrochemical performance of P–S-CNTs can be attributed to the excellent electrical conductivity and pseudocapacitive contribution of the S-doping effect.