Electrochemical impedance spectroscopy analysis of plasma-treated, spray-coated single-walled carbon-nanotube film electrodes for chemical and electrochemical devices

Abstract

In this study, carbon-nanotube (CNT) surfaces were treated with oxygen plasma, and the improvement in surface inertness was analyzed using electrochemical impedance spectroscopy (EIS). Among nanomaterials, CNTs are the most attractive owing to their outstanding properties. However, the chemical inertness of CNT surfaces hinders the widespread implementation of CNTs in bioanalytical applications. Therefore, we present in detail the electrochemical properties of CNTs treated in various plasma conditions. The single-walled carbon nanotube (SWCNT) films were spray-coated onto working electrodes with a three-electrode configuration fabricated on a glass substrate and activated at various plasma conditions. The EIS spectra of the SWCNT film revealed typical porous structure characteristics. As the thickness of the SWCNT film increased by spray coating, the charge-transfer resistance sharply increased owing to the reduction of the effective electrode area caused by the decreased roughness and porosity of the SWCNT film. The Nyquist plots of the plasma-treated SWCNT electrodes featured two semicircular regions at high and intermediate frequencies, as well as one straight line at low frequencies. The plasma-treated SWCNT electrode had a less distinct separation of the second arc and straight line than the untreated SWCNT electrode because the time constant was lowered owing to the diffusion process generated where the charge-transfer reaction occurred. We analyzed the change in the electrodes through EIS, which can identify individual contributions to the total impedance of an electrochemical system.