Oxygen reduction characteristics of several valve metal oxide electrodes in HClO4 solution

In the search for active cathode catalysts for polymer electrolyte fuel cells (PEFCs) using inexpensive materials, several valve metal oxide electrodes, TiO_x, ZrO_x, and TaO_x, with corresponding binary oxide electrodes were selected for the evaluation of catalytic activity for oxygen reduction reaction (ORR) by means of cyclic voltammetry in 0.1 M HClO₄ at 60 °C. These oxide electrodes were prepared mainly by the dip-coating method on a titanium plate substrate at a temperature between 400 °C and 500 °C and were characterized by scanning electron microscopy (SEM), X-ray diffractometry (XRD), and X-ray photoelectron spectroscopy (XPS). Among the oxide-coated electrodes investigated, Ti_0.7Zr_0.3O_x/Ti provided the highest ORR specific activity, with an onset potential, E_ORR, of 0.86 V vs. RHE during the cathodic potential sweep. Fine TaO_x particles prepared as an extension of the dip-coating method, showed very high catalytic activity determined by means of hydrodynamic voltammetry in 0.1 M HClO₄ at 30 °C with an E_ORR of 0.90 V vs. RHE.