To understand the polarization loss due to poisoning by CO of a porous Pt anode under various conditions, poisoning losses have been measured in a half‐cell in the temperature range 110°–190°C in 100 weight percent H3PO4 for various mixtures of H2 , CO , and CO2 gases. At a fixed current density, the poisoning loss, normalΔVnormalpois , was observed to vary linearly with ln false[COfalse]/false[H2false] . Deviation from linearity was observed at lower temperatures and higher current densities for high false[COfalse]/false[H2false] ratios. Considering only the linear portions, it has been possible to derive a general relationship for normalΔVnormalpois with temperature, CO concentration, and current density. The surface coverage by CO was calculated at various temperatures and was found to bear a linear relationship with ln false[COfalse]/false[H2false] . From the experimental Temkin isotherms, a general adsorption relationship has been obtained. The standard free energies for CO adsorption were calculated and were found to vary from −14.5 to −12.1 kcal/mol in the temperature range 130°–190°C. The standard entropy for CO adsorption was calculated to be −39 cal/mol K. Interpretations of the data indicate that CO adsorption occurs through 1:1 replacement of H by CO through the process of selective site poisoning. Under conditions where a nonlinearity in the poisoning relationship occurs, CO molecules undergo some orientation, favored by the increasing positive charges on the Pt surface.

A study was undertaken to measure polarization losses due to the presence of CO2 and CO in the H2 fuel for a practical fuel cell Pt/C anode. A porous Pt anode (0.3 mg/cm2 Pt) was tested as a floating electrode in a half‐cell assembly to measure performance in 100 weight percent H3PO4 at 190°C in presence of H2 , and H2 , CO2 , and CO gas mixtures. The additional polarization loss over that of H2 due to CO2 dilution followed closely the expected loss from the Nernst equation in the range of current density 0–300 mA/cm2. The combined loss due to poisoning by CO and the dilution by CO and CO2 was analyzed and found to be additive of the poisoning and dilution losses. The poisoning loss by CO was calculated by subtracting the dilution loss from the combined dilution and poisoning loss. Such data were found to be linearly dependent on the logarithm of false[COfalse]/false[H2false] ratio. This is consistent with CO poisoning by replacement of H2 sites on the porous Pt electrode. The calculated values of surface coverage by CO ranged from 0.089 to 0.31 as the ratio false[COfalse]/false[H2false] varied from 0.01 to 0.025. The values of surface coverage were consistent with the dual site elimination model for the replacement of H2 by CO molecules. The exchange current densities for H2 oxidation varied from 309 to 142 mA/cm2 as the ratio false[COfalse]/false[H2false] changed from 0 to 0.025. By comparing the experimental isotherm for CO adsorption with the Temkin isotherm, the interaction parameter was calculated to be 3.83 kcal/mol, and the standard free energy of adsorption, −10.96 kcal/mol. The latter value indicated an adsorption of CO which is comparable to H2 .

The polarization of a fuel cell Pt/ Canode has been mearsured under conditions similar to that of an operating fuel cell at atmospheric pressure (100 Wt.‐% H3PO4, 190°C) in the presence of H2 and mixtures of H2, CO2, and CO.

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