Voltammetry at carbon nanofiber electrodes

Carbon nanofibers with diameters in the range 10-500 nm have been evaluated as novel electrode materials for electrochemical applications. Compared with other forms of nanostructured carbons, such as aerogels or activated charcoal, carbon nanofibers exhibit low BET surface areas, 50 vs. 500 m² g^-1, because their surfaces are not readily penetrated by gaseous nitrogen. But somewhat surprisingly, they exhibit higher electrochemical capacitances (ca. 60 vs. 20 F g^-1) because the spaces between the fibers are readily penetrated by electrolyte solution. As a result, capacitive currents tend to mask voltammetric currents during cyclic voltammetry. The situation is quite different when the spaces between carbon nanofibers are impregnated by an inert dielectric material, such as high-melting paraffin wax. Then the carbon nanofibers form a high-density composite electrode with good conductivity and low capacitance. Indeed, well-defined voltammetric responses are readily observed for the reduction of Ru(NH₃)₆³⁺ in aqueous solution, even in the absence of supporting electrolyte. Metal deposition and anodic stripping processes can also be observed for the reduction of Pb²⁺ in aqueous nitric acid. This suggests that carbon nanofibers represent a new class of material suitable for electroanalytical applications.