Towards the elucidation of the high oxygen electroreduction activity of PtxY: surface science and electrochemical studies of Y/Pt(111).

We have prepared an yttrium modified Pt(111) single crystal under ultra-high vacuum conditions, simulating a bulk alloy. A Pt overlayer is formed upon annealing the crystal above 800 K. The annealed structure binds CO weaker than Pt(111), with a pronounced peak at 295 K in the temperature programmed desorption of CO. When depositing a large amount of yttrium at 1173 K, a (1.88 × 1.88)R30° structure relative to Pt(111) was observed by low energy electron diffraction. Such an electron diffraction pattern could correspond to a (2 × 2)R30° structure under 6% compressive strain. This structure is in agreement with the structure of the vacancies in a Pt Kagomé layer in Pt5Y rotated 30° with respect to the bulk of the Pt(111). The Pt overlayer is relatively stable in air; however, after performing oxygen reduction activity measurements in an electrochemical cell, a thick Pt overlayer was measured by the angle resolved X-ray photoelectron spectroscopy depth profile. The activity of the annealed Y/Pt(111) for the oxygen reduction reaction was similar to that of polycrystalline Pt3Y.

Alloys of platinum and early transition metals as oxygen reduction electrocatalysts.

The widespread use of low-temperature polymer electrolyte membrane fuel cells for mobile applications will require significant reductions in the amount of expensive Pt contained within their cathodes, which drive the oxygen reduction reaction (ORR). Although progress has been made in this respect, further reductions through the development of more active and stable electrocatalysts are still necessary. Here we describe a new set of ORR electrocatalysts consisting of Pd or Pt alloyed with early transition metals such as Sc or Y. They were identified using density functional theory calculations as being the most stable Pt- and Pd-based binary alloys with ORR activity likely to be better than Pt. Electrochemical measurements show that the activity of polycrystalline Pt(3)Sc and Pt(3)Y electrodes is enhanced relative to pure Pt by a factor of 1.5-1.8 and 6-10, respectively, in the range 0.9-0.87 V.

Sum frequency generation study of Langmuir Blodgett film architecture.

We present sum frequency generation vibrational spectroscopy data on monolayer films of pure stearonitrile and mixed films of stearonitrile and ferric stearate deposited by the Langmuir Blodgett technique. Films ranging in composition from pure stearonitrile to 65% stearonitrile/35% ferric stearate deposit in a head-to-tail, Z-type architecture while films of composition <65% stearonitrile deposit in a head-to-head, tail-to-tail, Y-type structure. The vibrational spectra of the monolayer films corresponding to these two different architectures show distinct and characteristic features in their CH stretching regions. Spectral analysis indicates little difference in the modes associated with the terminal methyl groups but large differences in the methylene CH(2) vibrational modes. These spectral differences are consistent with alkyl chains that possess uncompensated methylene oscillator strength arising from portions of the chain that are bent. This behavior is consistent with the energetics expected from a close-packed monolayer of stearonitrile molecules whose CN headgroups possess sizable dipole moments and are expected to adopt a large center-to-center angle to minimize electrostatic, dipole-dipole repulsive interactions.