(DE19721437-A1)      A supported platinum catalyst with good carbon monoxide poisoning resistance, for a polymer electrolyte membrane (PEM) fuel cell, comprises a finely divided conductive support material bearing platinum and ruthenium in highly dispersed unalloyed form, the crystallite size of the platinum being less than 2 nm and that of the ruthenium being less than 1 nm. Also claimed is production of the above catalyst by suspending the support material in water, adding aqueous Pt and/or Ru compound solutions, adjusting the pH to 7-9, depositing the Pt and/or Ru using a reducing agent, filtering off and washing the resulting catalyst, optionally depositing the other precious metal in the same way, and then drying at 200C. Further claimed are a PEM fuel cell gas diffusion electrode, a catalyst-coated proton conductive polymer membrane for PEM fuel cells and a PEM fuel cell membrane-electrode unit with gas diffusion electrodes on both the cathode and anode sides of a proton conductive polymer membrane, in which the catalyst layer on the anode side comprises the above catalyst.    USE -   Especially as anode catalyst for PEM fuel cells useful as traction batteries for vehicles.    ADVANTAGE -   The catalyst allows carbon monoxide contents of more than 100 ppm in the reformed gas supply of the fuel cell without significant fuel cell power losses, thus permitting reduction of the requisite carbon monoxide removal steps, reducing the system costs, improving the system efficiency and reducing the overall system size. The catalyst is suitable for operation with fuel gases containing carbon monoxide, nitrogen and oxygen and exhibits extremely low voltage drop at high current densities.    (JP10334925-A)      A supported platinum catalyst with good carbon monoxide poisoning resistance, for a polymer electrolyte membrane (PEM) fuel cell, comprises a finely divided conductive support material bearing platinum and ruthenium in highly dispersed unalloyed form, the crystallite size of the platinum being less than 2 nm and that of the ruthenium being less than 1 nm. Also claimed is production of the above catalyst by suspending the support material in water, adding aqueous Pt and/or Ru compound solutions, adjusting the pH to 7-9, depositing the Pt and/or Ru using a reducing agent, filtering off and washing the resulting catalyst, optionally depositing the other precious metal in the same way, and then drying at 200C. Further claimed are a PEM fuel cell gas diffusion electrode, a catalyst-coated proton conductive polymer membrane for PEM fuel cells and a PEM fuel cell membrane-electrode unit with gas diffusion electrodes on both the cathode and anode sides of a proton conductive polymer membrane, in which the catalyst layer on the anode side comprises the above catalyst.    USE -   Especially as anode catalyst for PEM fuel cells useful as traction batteries for vehicles.    ADVANTAGE -   The catalyst allows carbon monoxide contents of more than 100 ppm in the reformed gas supply of the fuel cell without significant fuel cell power losses, thus permitting reduction of the requisite carbon monoxide removal steps, reducing the system costs, improving the system efficiency and reducing the overall system size. The catalyst is suitable for operation with fuel gases containing carbon monoxide, nitrogen and oxygen and exhibits extremely low voltage drop at high current densities.    (US6007934-A)      A supported platinum catalyst with good carbon monoxide poisoning resistance, for a polymer electrolyte membrane (PEM) fuel cell, comprises a finely divided conductive support material bearing platinum and ruthenium in highly dispersed unalloyed form, the crystallite size of the platinum being less than 2 nm and that of the ruthenium being less than 1 nm. Also claimed is production of the above catalyst by suspending the support material in water, adding aqueous Pt and/or Ru compound solutions, adjusting the pH to 7-9, depositing the Pt and/or Ru using a reducing agent, filtering off and washing the resulting catalyst, optionally depositing the other precious metal in the same way, and then drying at 200C. Further claimed are a PEM fuel cell gas diffusion electrode, a catalyst-coated proton conductive polymer membrane for PEM fuel cells and a PEM fuel cell membrane-electrode unit with gas diffusion electrodes on both the cathode and anode sides of a proton conductive polymer membrane, in which the catalyst layer on the anode side comprises the above catalyst.    USE -   Especially as anode catalyst for PEM fuel cells useful as traction batteries for vehicles.    ADVANTAGE -   The catalyst allows carbon monoxide contents of more than 100 ppm in the reformed gas supply of the fuel cell without significant fuel cell power losses, thus permitting reduction of the requisite carbon monoxide removal steps, reducing the system costs, improving the system efficiency and reducing the overall system size. The catalyst is suitable for operation with fuel gases containing carbon monoxide, nitrogen and oxygen and exhibits extremely low voltage drop at high current densities.