A Study on the Anode Effect in KF-2HF System. II. Difference in Anodic Behavior between Edge Plane and Layer-plane of Pyrolytic Graphite

Abstract

Abstract The anodic behavior of pyrolytic graphite has been studied by voltammetry and ESCA analysis in the molten KF-2HF system at 100°C, attention being given to the difference in anodic behavior between the edge plane and layer-plane of the pyrolytic graphite. The polarization current obtained by a linear potential sweep experiment decreased rapidly with increasing potential after the onset of the anode effect. When the edge plane was used as a working electrode surface the current density was recovered on the subsequent sweep toward negative potentials, whereas the current density was hardly recovered on the layer-plane surface of the electrode. The difference in polarization behavior was interpreted on the basis of the difference in the rate of decomposition reaction of graphite fluoride, (CF)n, formed on the electrode surface. ESCA spectra of the electrodes polarized at various potentials indicate that (CF)n was formed even at 2.0 V vs. Pt, below the fluorine evolution potential, on the edge plane of the pyrolytic graphite and that its amount did not increase appreciably with increasing potential. On the layer-plane, however, no formation of (CF)n was observed at 2 V vs. Pt, its amount increasing appreciably with potential at the potentials above 3 V vs. Pt.