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

Abstract

The CO-tolerance mechanism of a carbon-supported Pt-Fe alloy catalyst with two atomic layers of stabilized Pt-skin (Pt2AL-PtFe/C) was investigated, in comparison with commercial Pt2Ru3/C (c-Pt2Ru3/C), by in situ attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy in 0.1 M HClO4 solution at 60°C. When 1% CO (H2-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 COad, reaching the coverage θCO ≈ 0.99. The bands in the IR spectra observed on both catalysts were successfully assigned to linearly adsorbed CO (COL) and bridged CO (COB), both of which consisted of multiple components (COL or COB at terraces and step/edge sites). The Pt2AL-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-Pt2Ru3/C after 2 h, which can be ascribed to a suppression of linearly adsorbed CO at terrace sites (COL, terrace). In contrast, the HOR activities of both catalysts with pre-adsorbed CO recovered appreciably after bubbling with CO-free pure H2. 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 COL, terrace to COL, step/edge, without removal of COad from the surface. The Pt2AL-PtFe/C catalyst showed a larger decrease in the band intensity of COL, terrace. A possible mechanism for the CO-tolerant HOR is also discussed.