On the Nature of Poly(chlorotrifluoroethylene) Composite Electrode Surfaces

A variety of composite materials have been used as electrodes for electrochemical measurement. Such materials include various blends of an electrically insulating polymer (e.g., an epoxy, polyethylene, Teflon, Kel-F, or Nujol) and a powdered conductor (e.g., graphite, carbon black, or precious metal), as well as porous materials such as graphite or reticulated vitreous carbon impregnated with an Insulating polymer such as a wax, polystyrene, or an epoxy. In spite of the widespread use of such materials in electrochemistry, relatively little effort has been devoted to understanding the surface morphology of composite electrode materials and the relationships between surface morphology and electrochemical behavior. In this work we employ four techniques that probe various aspects of the surface microstructure of Kel-F composite electrodes: scanning electron microscopy in conjunction with X-ray element mapping, which provides Information on the spatial distribution of polymer and conductor across the composite surface; X-ray photoelectron spectroscopy, which yields Information on the chemical interactions between polymer and conductor as well as on the distribution of conductor particles between electrically conducting and electrically Insulating surface regions; electrogenerated chemiluminescence Imaging, which provides an optical map of electron-transfer activity across the composite electrode surface; and double-layer capacitance measurements, which probe the degree of micrometer dimension roughness or porosity within the electroactive surface regions. The results of these experiments have enabled us to formulate a conceptual model for Kel-F composite electrode surfaces, certain features of which may be applicable to other composite electrode materials as well.