Enhancement of oxygen reduction by incorporation of heteropolytungstate into the electrocatalytic ink of carbon supported platinum nanoparticles

Nafion stabilized inks of Vulcan XC-72 supported platinum (20 wt.%) nanoparticles (Pt/XC-72) were utilized to produce electrocatalytic films on glassy carbon. The catalysts were modified (activated) with phosphododecatungstic acid H3PW12O40 (PW12). Comparison was made to bare (PW12-free) electrocatalytic films. Electroreduction of dioxygen was studied at 25 °C in 0.5 mol dm−3 H2SO4 electrolyte using rotating disk voltammetry. For the same loading of platinum (≈95 μg cm−2) and for the approximately identical distribution of the catalyst, the reduction of oxygen at a glassy carbon electrode modified with the ink containing PW12 proceeded at ca. 30–60 mV more positive potential (depending on the PW12 content), and the system was characterized by a higher kinetic parameter (rate of heterogeneous electron transfer), when compared to the PW12-free electrocatalyst. Gas diffusion electrodes with Pt/XC-72 supported on carbon paper (Pt loading 1 mg cm−2) were also tested. Under the same experimental conditions, while the exchange current density and the total resistance contribution to polarization components, computed from the galvanostatic polarization curves were found to be clearly higher and lower, respectively, for the ink modified with PW12 relative to the unmodified system. The results demonstrate that addition of heteropolytungstatic acid (together with Nafion) enhances the electrocatalytic activity of platinum towards reduction of oxygen.