Structural changes of a pyrolytic graphite surface oxidized by electrochemical and plasma treatment

Abstract

Pyrolytic graphite (PG) surfaces have been oxidized by electrochemical and oxygen plasma treatment. The oxidized PG surfaces have been studied by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared attenuated total reflection spectroscopy (FT-IR-ATR). Oxidation caused by the plasma treatment results in a small increment of the oxygen: carbon (O/C) ratio, compared to electrochemical treatment. Moreover, the increment of the O/C ratio for the plasma treated edge surface is smaller than that for the plasma treated basal surface. A steep gradient in oxygen concentration exists within the edge subsurface of PG for samples subjected to severe electrochemical treatment, as compared to those samples subjected to plasma treatment. For the electrochemical treatment, carbonyl, carboxyl, ester and lactone groups are introduced to the edge surface following relatively severe treatment. The ratio of ester and lactone groups to carboxyl groups increases with the extent of electrochemical treatment. For plasma treated samples, other types of oxygen-containing groups, which are probably keto-enol groups, are added to the edge surface, unlike during electrochemical treatment.