NON-FARADAIC ELECTROCHEMICAL MODIFICATION OF THE CATALYTIC ACTIVITY OF PT FOR H-2 OXIDATION IN AQUEOUS ALKALINE MEDIA

The heterogeneous catalytic oxidation of H-2 on Pt was investigated on Pt black and Pt-graphite electrodes, also serving as heterogeneous ca talysts, in aqueous alkaline solutions as a function of electrode pote ntial and current. Hydrogen-oxygen mixtures were bubbled over the surf ace of the Pt electrode through a porous Teflon frit, and the rates of H-2 and O-2 consumption were measured via on-line mass spectrometry a nd gas chromatography. It was found that positive current application enhances the catalytic rate of H-2 oxidation by up to 500% and that th e increase in the catalytic rate is up to 100 times larger than the in crease 1/2F of the electrocatalytic rate corresponding to Faraday's la w. The results show that the heterogeneously catalyzed H-2 oxidation p roceeds in parallel with the electrocatalytic anodic Hz oxidation and that its rate is markedly affected by the catalyst potential and work function. This electrochemically induced and controlled reversible pro motion of the catalytic properties of Pt bears many similarities to th e effect of electrochemical promotion when using solid electrolytes an d can be rationalized by considering the effect of varying potential a nd work function on the coverages and binding strengths of dissociativ ely chemisorbed hydrogen and oxygen.