Influence of anodic oxidation of glassy carbon surface on voltammetric behavior of Nafion®-coated glassy carbon electrodes

Abstract

To improve the performance of proton-exchange membrane fuel cells (PEMFCs), it is necessary to optimize the structure of the interface between polymer electrolyte and catalyst particles in the electrodes of PEMFCs. However, the interaction at the interface between electrodes and the perfluorosulfonate ionomer used in PEMFCs has not yet been sufficiently clarified. In the present study, the Nafion®/glassy carbon (GC) interface was investigated using cyclic voltammetry at a GC disk electrode with its surface electrochemically oxidized to impart hydrophilicity. The surface oxidation generated oxygen-containing surface functional groups, especially quinone-like ones. The contact angle of water drops on the surface-oxidized GC decreased with increase in surface-oxidation time. Using as an index the charge consumed in the positive and negative scans of cyclic voltammetry, evaluation was performed of the ratio on the GC surface of the hydrophilic ionic cluster region, where electrode reactions occur on Nafion®-coated GC electrodes. The ionic cluster region at the interface expanded with increase in surface-oxidation time. This behavior was attributed to weakening of the interaction between the hydrophobic perfluorocarbon region and the GC surface. This dependency suggests the possibility of controlling the structure of the interface between Nafion® and carbon.