Electrochemical characterisation of ultrathin carbon nanofiber-chitosan multi-layer films

Carbon nanofibers can be oxidized and solubilised in alkaline or neutral aqueous media. Deposition of the solution by solvent evaporation allows well-defined amounts,of carbon nanofiber material to be deposited onto tin-doped indium oxide (ITO) electrodes and studied electrochemically. Next, a layer-by-layer deposition process is employed to produce homogeneous and ultrathin films of carbon nanofibers with a chitosan binder with controlled thickness. Films with a thickness similar to the nanofiber diameter, 50-200 nm, are produced and characterized via electron microscopy, conductivity measurements, and quartz crystal microbalance gravimetry. Electrochemically, even very thin films of hydrophilised carbon nanofibers are readily detected due to their (pseudo-)capacitive current response (ca. 150 F g(-1) over a limited potential range). Electrochemical reactions, such as the oxidation of hydroquinone in aqueous phosphate buffer, are shown to be catalysed by the presence of hydrophilised carbon nanofiber fragments (with respect to the same process at a bare ITO electrode). Based on voltammetric responses. the electron transfer across a barrier between carbon nanofibers and the ITO substrate is identified as rate limiting in the presence of chitosan. Possible applications of ultrathin carbon/chitosan deposits, for example as transparent carbon electrodes. are discussed.