Surface modification of carbons for enhanced electrochemical activity

Graphitic materials have at least two distinct types of surface sites, namely the basal plane and edge plane sites. It is generally regarded that the active sites for electrochemical reactions are associated with the edge plane sites, while the basal plane is relatively inactive. In this study, controlled gas-phase reactions for oxidation/reduction were used to modify the surface of highly oriented pyrolytic graphite and carbon fibers by introducing edge plane sites. In some experiments, catalysts were used to enhance the formation of edge sites. The effects of the gas-phase treatments were monitored by electrochemical measurements of the double layer capacitance and the kinetics of oxygen reduction in alkaline electrolyte. The correlation between the electrochemical results and changes to the surface microstructure is discussed. The measurements clearly show that the electrochemical behavior is improved by introducing more edge sites or defects on the carbon surface. These results are consistent with other studies. (C) 1997 Elsevier Science S.A.