The role played by edge-plane like defects at the open ends of multi-walled carbon nanotubes and at hole defects in the tube walls was explored using cyclic voltammetry with two charged redox probes and one neutral redox probe. The effect of oxygen-containing functional groups (phenol, quinonyl, carboxyl), which decorated the edge-plane defect sites, upon the voltammetric response of the multi-walled carbon nanotubes was also explored. To this end, three different pre-treatments were used on pristine multi-walled carbon nanotubes using the arc-discharge method. These arc-treated nanotubes were subjected to acid oxidation so as to form acid multi-walled nanotubes. Open-ended multi-walled carbon nanotubes, also containing numerous hole defects, exhibited a large number of edge-plane like sites that were heavily decorated with surface functional groups. Acid-treated nanotubes were subsequently vacuum-annealed at 900C to remove the functional groups but leave the many undecorated edge-plane like sites exposed. The annealed nanotubes were subjected to a further vacuum super-annealing stage at 1750C which caused the hole defects to close, and also closed the tube ends thereby restoring the original pristine almost edge-plane defect-free multi-walled carbon nanotube structure. The results of the voltammetric characterization of the variously treated nanotubes provided further evidence that edge-plane like sites were the electroactive sites on multi-walled carbon nanotubes. The presence of oxygen-containing surface groups was found to inhibit the rate of electron transfer at these sites under the present conditions. The two charged standard redox probes were found to undergo strong interactions with oxygen-containing surface groups. Caution was advised when using redox probes to characterize multi-walled carbon nanotubes voltammetrically.The Influence of Edge-Plane Defects and Oxygen-Containing Surface Groups on the Voltammetry of Acid-Treated, Annealed and "Super-Annealed" Multiwalled Carbon Nanotubes. A.F.Holloway, G.G.Wildgoose, R.G.Compton, L.Shao, M.L.H.Green: Journal of Solid State Electrochemistry, 2008, 12[10], 1337-48