Optimization of the Preparation Procedure of SWCNT Films and Fibers for Electrochemical Applications

The work is aimed at the optimization of the preparation procedure of films and fibers from single-walled carbon nanotubes (SWCNTs) for their application as the electrode material. The multistage preparation procedure is proposed that includes thermal and chemical treatment (HClconc, 9% HNO3 + H2SO4, 15% H2O2). The SWCNT films are synthesized by chemical vapor deposition from ethanol and ferrocene. The fibers are obtained by the wet pulling technique from SWCNT films. The effect of each stage on the structural and electrical characteristics of nanotubes is evaluated by TEM, Raman, and FTIR spectroscopy and the four-probe measurement of the surface resistance. By the TEM analysis a decrease is found in the fraction of catalytic particles after thermal treatment in the air at 330 °C in combination with HCl treatment. By the FTIR analysis it is found that thermal treatment of SWCNT films removes organic contaminations. The ID/IG ratio is estimated at each stage of the treatment using the Raman spectral data. The availability of the prepared fiber electrodes is evaluated electrochemically by chronopotentiometry and cyclic voltammetry. The obtained electrical capacitance values from 10 mF/cm2 to 14 mF/cm2 involve the substantial pseudocapacitive component due to the occurrence of surface functional groups, which allows the use of fibers in energy storage devices. The 15% H2O2 treatment of fibers provides the most acceptable results from the standpoint of minimization of background currents, which is necessary to take into account when using these fibers in analytical applications, e.g., for the voltammetric determination of electroactive compounds.