Half cell tests were carried out in an air-scaled glass that had three separate compartments for the working, counter, and reference electrode. Teflon-bonded carbon supported electrodes with lOw/o Pt, 20w/o Pt, and 20w/o Pt-lOw/o Ru catalysts coated on carbon paper (Toray T-90)was used for working electrodes having geometric area of 0.9cm2 in this study. A platinum gauze(99.999%) was used as the counter electrode. A saturated calomel electrode(SCE) was used for the reference electrode. Potentiodynamic polarization and cyclic voltammetiy experiments were performed in IMH2SO4 at constant temperature of 60°C using an EG&G potcntiostat/galvanostat.

For single cell performance tests, carbon supported Pt-Ru and unsupported Pt-RuOx binary metal powders were used for the anode catalyst Carbon supported anode electrode was prepared with 20w/o Pt-lOw/o Ru(Johnson-Matthey) mixed homogeneously with 20w/o of FEP (Fluoethylcne propylene) solution and solvent(Micsol). The mixed paste was coated on carbon paper, then, was dried in the oven under nitrogen atmosphere at 100°C for lhour. The cathode catalyst layer was prepared with 20w/o Pt/C(Johnson-Matthey) employing the same preparation method as anode catalyst layer.

Pt-RuOx metal powder(atomic ratio Pt:Ru=l:l, E-TEK) was used for the unsupported anode catalyst and Pt-black(20 m2/g, Johnson-Metthey) was used for the cathode catalyst. The catalyst inks were prepared by adding 5% Nafion solution(Aldrich Inc.) to water-wetted metal catalysts. Compositions of dry ink were 85w/o Pt-RuOx with 15w/o Nafion for anode ink, and 93 w/o Pt-black with 7w/o Nafion for cathode ink.3' To prepare the catalyst layer, appropriate amounts of anode and cathode ink were uniformly applied to carbon paper of 8.4 cm2 area to give metal catalyst loading of approximately 4mg/ cm2, then, dried as mentioned above. Nafion membrane(117) was cleaned and converted into the acid form by boiling the membrane in 3% H202, DI water,5% H2SO4, and then DI water again for over 1 hour each step. Membrane and electrode assembly(M&EA) was made by hot pressing at 120 °C with 100 kg/ cm2 for 120 scconds after applying about 0.6 mg/ cm2 of Nafion solution on the surface of anode and cathode elcctrodcs. M&EA was inserted into fuel cell hardware consisted of graphite block with machined serial flow channcl, copper current collectors, and

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