Results And Discussion

Fig. 1 shows cyclic voltamogram for carbon supported anode electrodes with 20w/o Pt and 20w/o Pt - lOw/o Ru obtained at a scan rate of 20mVs"' in 1M H2S04 + 1M CH3OH solution at 60°C. As applied potential increases, anodic reaction current peaks are observed in the range 0.95 V vs. SCE and 0.7 V vs SCE. As the potential scan reverses, the current peaks are also observed at about of 0.5 V vs SCE and 0.4 V vs SCE. It is known that the anodic reaction peaks on the positive potential scan are related to the oxidation of CH3OH and other peaks on the negative-going sweep are the reduction of oxygen-containing species on the platinum catalyst."0 As shown in the figure, when the carbon supported Pt - Ru catalyst is used for an anode electrode, the reaction current peaks of methanol are appeared at lower potential than that of the carbon supported Pt electrode. These seem to be related with that Ru plays an important role in accelerating the reaction rate of CH3OH electro-oxidation. Several mechanisms have been postulated including modification of the electronic nature of the surface, blocking of the poison formation reaction, and co-adsorption of oxygen containing species which can then take part in the main oxidation reaction. The adsorption and dchydrogenation of methanol on Pt surface atom ensembles are followed by the oxidative removal of methanol dchydrogenation fragments via oxygen-containing species on adjacent Ru atoms.

Fig. 2 shows the performance of the single cell using carbon supported Pt-Ru catalyst as an anode electrode and carbon supported Pt catalyst as a cathode electrode for various methanol concentrations at a constant temperature of 130°C. Each datum represent typical steady state voltage which was taken after continuous operation for 5 minutes at the indicated current density. The results show that at high operating current densities, the highest cell voltage is obtained with 2.5M methanol, while relatively lower voltages are obtained with 4M and 0.5M methanol concentration. The poor performance of the cell at highest methanol concentration is seems to be attributed to the methanol cross-over from anode side to cathode side.

Fig. 3 shows the performance of the single cell using unsupported Pt-Ru binary metal catalyst as an anode electrode and a platinum black as a cathode catalyst at the temperature ranges of 60 - 130°C with 2.5M methanol as an anode fuel. As shown in the figure, at potential of 0.4V at the temperature ranges of 100, 110, 120 °C, and 130°C, the current densities are 160, 210, 230 mA/cm2- and over than 250 mA/ cm2 , respectively. From the experimental, it shown that anode electrode made of unsupported Pt-Ru catalyst was superior to the electrode made of supported Pt-Ru catalyst. At high temperature, the high performance is attributed to the combined effects of a reduction of ohmic resistance and polarization.

Fig. 4 shows the performance of single cell at various operating prcssures.The pressure of anode side is constant at 0 kg/cm2(gauge) whereas the cathode side vary from 0 to 3 kg/ cm2. As shown in the figure,The higher cell voltage and open circuit voltage were measured when the cell was operated at the pressure difference of 2 and 3 kg/cm2 than at the pressure difference of 0 kg/ cm2. It seems that if the pressure of cathode side was higher than the anode side, it could prohibit effectively the cross-over of methanol from anode side to cathode side, and easy to some extent to eliminate water formed at cathode by electroclicmical reaction and increase the reaction activity of catalyst in the electrode.

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