An electrode-kinetic investigation of CO and CO/H2 oxidation in phosphotungstic acid (H3PW12O40) electrolyte

Art electrode-kinetic investigation of the oxidation of CO and CO/H-2 mixtures on a Pt-Ru/C catalyst was carried out in phosphotungstic acid (PWA) electrolyte. The chemical, structure and surface properties of the Pt-Ru/C catalyst were investigated by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The influence of temperature, CO partial pressure and proton concentration on the electrochemical oxidation rate was studied by steady-state galvanostatic polarization measurements. An apparent activation energy of about 50 kJ.mol(-1) at 0.6 V vs. NHE was observed for CO oxidation. Fractional reaction orders close to 0.5 and -0.4 with respect to carbon monoxide and proton concentration, respectively, were determined The PWA electrolyte appeared to promote the water discharging process. Tafel slopes of about 138 mV.dec(-1) and 127 mV.dec(-1) were observed for CO and CO/H-2 oxidation, respectively, indicating that a single electron transfer was involved in the r.d.s. These results appear to be consistent with the bifunctional theory. Both the surface migration of adsorbed species and the oxidative removal of CO seem to contribute to the slow step of the electro-oxidation process.