A COULOMETRIC NORMALIZATION PROCEDURE FOR COMPARING HIGH-SURFACE-AREAMETHANOL ANODE CATALYSTS BY ROTATING-DISK ELECTRODE VOLTAMMETRY

A new method that allows one to normalize the current observed at elec trocatalytic rotating disk electrodes (RDEs), based on coulometric ana lysis of hydrogen desorption waves, is presented. Current-voltage curv es for methanol oxidation, using various platinum alloy compositions a nd application methods, were analyzed by this method. Mass-normalized I-V curves showed considerable scatter among similar alloys (Pt, Pt-Ru , and Pt-Ru-Os) applied by different methods and in different degrees of dispersion. The same curves normalized coulometrically are grouped more closely with respect to composition. Since the coulometric normal ization procedure takes into account the electrochemically active surf ace area rather than the total mass of electrocatalyst, it provides a more precise correlation of catalytic activity with composition than d oes mass normalization. Combined with mass normalization, the procedur e gives a useful estimate of catalyst utilization for different compos itions and electrode preparations, under electrochemical conditions th at are mimetic of direct methanol fuel cell operation. Comparison of n ormalized RDE currents at 25 and 50 degrees C clearly shows that a ter nary Pt-Ru-Os (65:25:10) composition is a more active anode catalyst t han Pt-Ru (50:50) when both are prepared by borohydride reduction.