Mixed metal catalysts containing Pt, Ir, Ru, Os, and Rh were synthesized on three different conductive oxide supports, Ebonex, which is a mixture of Ti 4 O 7 and other phases, phase-pure microcrystalline Ti 4 O 7 , and Ti 0.9 Nb 0.1 O 2 , a doped rutile compound. Ebonex-supported catalysts were prepared as arrays and screened combinatorially for activity and stability as bifunctional oxygen reduction/water oxidation catalysts. The highest activity and stability was found in the Pt-Ru-Ir ternary

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... region at compositions near Pt 4 Ru 4 Ir 1 . X-ray near edge absorption spectra indicated a significant electronic interaction between the catalyst and the support, and a substantial increase in catalyst utilization was observed, even though the support surface areas were relatively low. Both Ebonex and Ti 4 O 7 have short-lived electrochemical stability under conditions of oxygen evolution at ϩ1.6 V vs. RHE in 0.5 M H 2 SO 4 . Current at these supported catalysts gradually decreases, and the decrease is attributed to loss of electronic conductivity. Ebonex and Ti 4 O 7 are also thermally oxidized in air at temperatures above 400°C. In contrast, Ti 0.9 Nb 0.1 O 2 , which has a nondefective oxygen lattice, is quite resistant to electrochemical and thermal oxidation. Conditioning of Ti 0.9 Nb 0.1 O 2 -supported Pt 4 Ru 4 Ir 1 at positive potentials had little effect on the activity of the catalyst.