Characterization of electro-oxidation catalysts prepared by ion-exchange of platinum salts with surface oxide groups on carbon

Abstract

It has been demonstrated, by the combined use of chemical titrations, cyclic voltammetry and X-ray photoelectron spectroscopy, that the surface oxide groups formed on carbon-fibre paper electrodes are predominantly weakly acidic in nature and similar to phenolic-OH in character. The oxides formed by electrochemical oxidation and treatment in concentrated, acidic solutions are similar. The uptake of platinum salts by these oxidized surfaces following impregnation or ion exchange follows the sequence, Pt(NH₃)₂(NO₂)₂ > Pt(NH₃)₄(OH)₂ > Pt(NH₃)₄Cl₂ > H₂PtCl₆, as would be expected on the basis of their relative acidities and the ion-exchange nature of the interaction between the platinum salt and the weakly acidic surface oxides. The most active catalysts for methanol oxidation are prepared by activation in air at ≈ 573 K following electrochemical pretreatment of the carbon surface in 1 % v/v HNO₃ for 90 min and ion-exchange with Pt(NH₃)₄(OH)₂.