In Situ FTIR Analysis of CO-Tolerance of a Pt-Fe Alloy with Stabilized Pt Skin Layers as a Hydrogen Anode Catalyst for Polymer Electrolyte Fuel Cells

摘要

The CO-tolerance mechanism of a carbon-supported Pt-Fe alloy catalyst with two atomic layers of stabilized Pt-skin (Pt 2AL –PtFe/C) was investigated, in comparison with commercial Pt 2 Ru 3 /C (c-Pt 2 Ru 3 /C), by in situ attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy in 0.1 M HClO 4 solution at 60 °C. When 1% CO (H 2 -balance) was bubbled continuously in the solution, the hydrogen oxidation reaction (HOR) activities of both catalysts decreased severely because the active sites were blocked by CO ad , reaching the coverage θ CO ≈ 0.99. The bands in the IR spectra observed on both catalysts were successfully assigned to linearly adsorbed CO (CO L ) and bridged CO (CO B ), both of which consisted of multiple components (CO L or CO B at terraces and step/edge sites). The Pt 2AL –PtFe/C catalyst lost 99% of its initial mass activity ( MA ) for the HOR after 30 min, whereas about 10% of the initial MA was maintained on c-Pt 2 Ru 3 /C after 2 h, which can be ascribed to a suppression of linearly adsorbed CO at terrace sites (CO L, terrace ). In contrast, the HOR activities of both catalysts with pre-adsorbed CO recovered appreciably after bubbling with CO-free pure H 2 . We clarify, for the first time, that such a recovery of activity can be ascribed to an increased number of active sites by a transfer of CO L, terrace to CO L, step/edge , without removal of CO ad from the surface. The Pt 2AL –PtFe/C catalyst showed a larger decrease in the band intensity of CO L, terrace . A possible mechanism for the CO-tolerant HOR is also discussed.