Figure 3: XPS spectra of cathode under operating conditions.
From: Direct observation of the oxygenated species during oxygen reduction on a platinum fuel cell cathode
(a) O 1s XPS spectra obtained for an operating (closed circuit) fuel cell cathode. The incident photon energy was 670 eV. Spectra were collected under 600 Torr of humidified forming gas at the anode and varying O2 pressures at the cathode, as shown. The resulting current outputs, Icell, and the elucidated cathode potential, USHE, measured using XPS (see Methods: Comparison of XPS spectra and Supplementary Fig. S2) are indicated. Dots correspond to experimental results and solid lines correspond to smoothened curves (first-order binomial). The spectral changes were reversible with respect to p(O2). The blue dotted lines correspond to the model structures on Pt(111) discussed in Fig. 2b. (b) Peak-fitted O 1s XPS spectrum in 0.8 Torr oxygen. The spectra were deconvoluted using Gaussian-broadened Doniach–Šunjić functions. Because of the large number of species and parameters, this peak fitting is more qualitative than quantitative in its nature, guiding the reader’s eye to the different surface species: multilayer H2O (purple), H2O(ad) (orange), H2O-OH (red), OH-O (cyan), H2O-OH (blue) and OH-O (green).
