GIC-formation in neutral aqueous electrolytes: An undesired side-reaction during electrochemical surface oxidation of highly oriented carbon fibres

Abstract

Anodic oxidation of carbon fibres in aqueous electrolytes is a technically important process for the creation of “surface oxides” which are required to improve the adhesion of carbon fibres in synthetic resin composite materials. As a result of carbon surface oxidation - or simply O 2 evolution - the pH of electrolyte goes acidic in the diffusion layer at the carbon anode: C n + A − + H 2 O = “ C nOH ” + H + A − + e − 2H 2O = O 2 + 4 H + + 4 e − Therefore, even in neutral aqueous electrolytes direct current oxidation of high modulus (HM) and hence fairly graphitic carbon fibres may yield higher stage hydrated acid GICs of the type (C n)+A −(HA) x(H 2O) y as a side product of surface oxidation. The intercalation damage can be minimized by agitation of electrolyte and also by alternating current oxidation procedures. Measurements of electronic conductivity parallel to the fibre axis and voltammetric studies of intercalation into preoxidized fibres are powerful and convenient tools to monitor even minor intercalation damage of HM fibres.