Figure 2: Identification of oxygenated species on Pt cathode.
From: Direct observation of the oxygenated species during oxygen reduction on a platinum fuel cell cathode
(a) O 1s XPS spectra of a fuel cell cathode. The incident photon energy was 670 eV. Dots and solid lines correspond to experimental results and smoothened curves (first-order binomial), respectively. Spectra between 0.5 and 0.9 V were collected while exposing the anode to 600 Torr of humidified forming gas and the cathode to 0.4 Torr O2. The spectrum at 0.1 V was taken in the absence of oxygen. (b) O 1s XPS spectra of oxygen gas in the vicinity of the cathode. The electrochemical potential of the cathode quoted against standard hydrogen electrode (SHE), USHE, was measured simultaneously against the anode. The observed multiplet splitting is due to the coupling between the unpaired spins in the valence and core levels in a paramagnetic oxygen molecule33. (c) Plot of the measured cathode potential versus the change in work function. The bottom and top of bar correspond to the cathode electrochemical potential measured at the beginning and end of XPS data accumulation, respectively. (d) O 1s XPS spectra of oxygenated surface species on Pt(111). Bottom to top: multilayer H2O24; H2O(ad)24; adsorbed H2O-OH25; adsorbed OH-O measured in 0.05 Torr O2 and 0.05 Torr H2 at 450 K. (e) Schematic models and BE for oxygenated species: H2O(ad) (orange, 532.2 eV), H2O-OH (red, 531.6 eV), H2O-OH (blue, 530.1 eV), O-OH (cyan, 531 eV) and O-OH (green, 529.9 eV).
