Placing a layer of Ru atop a Pt anode increases the carbon monoxide tolerance of proton-exchange membrane fuel cells when oxygen is added to the fuel stream. Sputter-deposited Ru filter anodes composed of a single Ru layer and three Ru layers separated by Nafion-carbon ink, respectively, were compared to Pt, Pt: Ru alloy, and an ink-based Ru filter anodes. The amount of Pt in each anode was 0.15 mg/cm(2) and the amount of Ru in each Ru-containing anode was 0.080 mg/cm(2). For an anode feed consisting of hydrogen, 200 ppm CO, and 2% O-2 (in the form of an air bleed!, all Ru filter anodes outperformed the Pt: Ru alloy. The performance of the Pt + single-layer sputtered Ru filter was double that of the Pt: Ru alloy (0.205 vs. 0.103 A/cm(2) at 0.6 V). The performance was also significantly greater than that of the ink-based Ru filter (0.149 A/cm(2) at 0.6 V). Within the filter region of the anode, it is likely that the decreased hydrogen kinetics of the Ru (compared to Pt) allow for more of the OHads formed from oxygen in the fuel stream to oxidize adsorbed CO to CO2.