Investigating the voltammetric reduction of methylviologen at gold and carbon based electrode materials. Evidence for a surface bound adsorption mechanism leading to electrode 'protection' using multi-walled carbon nanotubes

Cyclic voltammetry was recorded in an aqueous solution of 1,1'-dimethyl-4,4' bipyridinium dichloride (methylviologen or paraquat) at a variety of electrode materials namely gold, boron doped diamond (BDD), edge (eppg) and basal plane (bppg) pyrolytic graphite electrode. Previous mechanisms reported in the literature to describe the observed voltammetry are critically assessed and an alternative mechanistic interpretation is presented involving evidence for surface adsorption of intermediate species in the redox behaviour of methylviologen (MV) rather than any disproportionation or comproportionation as was previously claimed for the specific case of gold electrodes. Various electrodes were then modified with multi-walled carbon nanotubes (MWCNTs) where the formation of solid MV0 on the electrode surface was prevented due to preferential adsorption of MV0 on the MWCNTs. Thus coating an electrode with MWCNTs can protect the electrode surface from fouling, providing scope for diffusion dominated voltammetry at electrodes where surface inhibition has hitherto dominated.