Electrochemistry at pristine single-walled carbon nanotubes

Abstract

This thesis aims to develop an understanding of the fundamentals and applications of electrochermistry at pristine single-walled carbon nanotubes (SWNTs), synthesised by the chemical vapour deposition (CVD) method. The SWNTs grown by CVD on the insulating SiO2 substrates were chosen for the reason being clean, free of amorphous carbon and readiness of nanotube morphology control. 2D random SWNT networks and individual ultra-long flow-aligned SWNTs were employed in the electrochemical studies throughout. SWNT networks were studied either by the microcapillary electrochemical method (MCEM) or in the format of disk-shaped ultramicroelectrodes (UMEs). By challenging the SWNT UMEs with enhanced mass-transport rates in a thin-layer cell (TLC) reversible quasi-steady state cyclic voltammogramms (CVs) were acquired, which allowed the numerical simulations of the voltammetric response and derivation limits for the standard electron transfer (ET) rate constants. Individual SWNTs also generate very high intrinsic mass-transport rates and were studied by the MCEM method, coupled with finite element modelling, highlighting that SWNT sidewalls are active towards outer-sphere redox reactions. By using a sparse surface coverage (typically less than 1%) of pristine SWNTs on an insulating substrate, it has also been demonstrated that electrodeposition of nanoparticles (NPs) is highly directional. By varying electrodeposition driving force (potential) and time one can control the NP density and size. The findings suggest that nucleation of Au on SWNTs is essentially 'instantaneous', and that the nucleation density increases with increase of the deposition potential. This knowledge has enabled the synthesis of a range of different nanostructures, from isolated Au NPs to Au nanowires (NWs), which were used as expedient platforms for analytical and electrocatalytical purposes. While some common inner-sphere redox processes do not readily undergo electrochemical reactions on the carbon nanotubes, which was established in experiments employed SWNT UMEs and individual ultra-long SWNTs, the outer-sphere redox processes were shown to be reversible on the same nanotube electrodes. Novel scanning electrochemical cell microscopy (SECCM) studies allowed individual Pt NPs, electrically connected by the sub-centimeter long SWNT, to be electrochemically assessed. Significantly, this work highlights that individual NPs have their intrinsic electrochemical characteristics