Dynamic high potential treatment with dilute acids for lifting the capacitive performance of carbon nanotube/conducting polymer electrodes

• MWCNTs/PEDOT–PSS electrodes were treated with dynamic high potentials.
• Capacitive performance of the treated electrodes is lifted.
• Excessive treatment deteriorates the capacitive performance of the electrodes.
• The chemical structure of MWCNTs after treatment remains unchanged.
• The polar functional groups on PEDOT are generated by the treatment.

The capacitive behavior of the electrodes, fabricated from multiwalled carbon nanotubes (MWCNTs) and poly-3,4-ethlyenedioxythiophene–polystyrene sulfonate (PEDOT–PSS), before and after dynamic high potential treatment with dilute HNO3 solutions, is investigated. The specific capacitance (Csp) of the treated MWCNTs/PEDOT–PSS electrodes can be ~ 2.5 times higher than that of the untreated electrodes. The drop of Csp in cycliability study for the treated electrodes is 0.8%, and much less than that for the untreated electrodes (16%). However, excessive treatment can deteriorate the capacitive performance of the electrodes. The morphology of MWCNTs/PEDOT–PSS composites revealed by transmission electron microscopy has no change after the treatment. The data of Raman spectroscopy show that the chemical structure of MWCNTs in the treated MWCNTs/PEDOT–PSS composites remains unchanged. The newly formed functional groups (COOH, CO and SO) are deemed to be generated by electrochemical oxidation of PEDOT, according to the X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy data. It is suggested that the Csp of the treated MWCNTs/PEDOT–PSS electrodes is due to the interplay between two effects: 1) the degradation of PEDOT leads to the loss of capacitive characteristics; and 2) the newly formed functional groups in PEDOT in the treated electrodes result in the increase in the Csp.

Newly formed polar functional groups (COOH, CO, and SO) in PEDOT after the high dynamic potential treatment with dilute acids contribute to the faradic processes during charge and discharge, compared with the untreated composites. In addition, these functional groups can provide more active sites to adsorb more ions from electrolytes on the electrodes, hence increase the electrostatic double-layer capacitance of the treated MWCNTs/PEDOT–PSS electrodes relative to the untreated ones.Figure optionsDownload as PowerPoint slide