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 catalysts, in aqueous alkaline solutions as a function of electrode potential and current. Hydrogen-oxygen mixtures were bubbled over the surface 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 and gas chromatography. It was found that positive current application enhances the catalytic rate of H-2 oxidation by up to 500% and that the increase in the catalytic rate is up to 100 times larger than the increase 1/2F of the electrocatalytic rate corresponding to Faraday's law. The results show that the heterogeneously catalyzed H-2 oxidation proceeds 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 promotion of the catalytic properties of Pt bears many similarities to the effect of electrochemical promotion when using solid electrolytes and can be rationalized by considering the effect of varying potential and work function on the coverages and binding strengths of dissociatively chemisorbed hydrogen and oxygen.