W.E. O'Grady

Electroreduction of oxygen on reduced platinum in 85% phosphoric acid☆

Abstract Oxygen reduction in highly purified 85% H 3 PO 4 has been studied on reduced platinum by rotating ring-disc techniques. The interpretation of these data suggests that the oxygen reduction proceeds by the parallel mechanisms of direct four-electron transfer to H 2 O and through the multistep mechanism involving peroxide-intermediate. However, in this study the rate constants ( k 1 and k 2 ) for the direct reaction to H 2 O and the first step to H 2 O 2 were found to have different dependences on the potential. Also, a value of 7.6×10 −7 cm 2 s −1 has been determined for the diffusion coefficient in 85% H 3 PO 4 at 25°C.

Mechanism of chlorine evolution on oxide anodes. Study of pH effects

Abstract Chlorine evolution on oxides such as polycrystalline RuO2, IrO2, Co3O4, NiCo2O4, RuO2 + IrO2 and the (110) face of RuO2 single crystals proceeds with the same Tafel slope of 40 mV and the same reaction order of 1 with respect to Cl−. On all oxides but RuO2 (110) the reaction rate is depressed by the acidity, which results in a reaction order with respect to H+ of −1 for IrO2, Co3O4 and NiCO2O4, of 0 for RuO2 (110) and variable for RuO2. Possible reasons for pH effects are discussed, and several plausible reaction mechanisms are examined.

Single crystal RuO2/Ti and RuO2/TiO2 interface: LEED, Auger and XPS study

The interactions at the evolving RuO2/titanium interface have been studied by LEED, AES and XPS. Titanium films of up to 5 monolayers were evaporated onto well ordered and ion sputtered ruthenium dioxide crystal surfaces of (110) and (100) orientation. Stabilization of the surface oxygen content under thermal treatment in UHV (up to 600°C) with increasing titanium coverage was established. After extended (up to 4 h) annealing in O2 at 600°C an epitaxial ordering of TiO2 on RuO2(110) was observed. The (1 × 1) LEED patterns from the epitaxial layer exhibit a reduced background level when compared to the RuO2 substrate itself. These findings are correlated with the XPS data and are interpreted in connection with the disappearance of the defect RuO2 phase in the surface layer of the RuO2. The appearance of the (1 × 2) surface reconstruction at the RuO2(100)/Ti interface is discussed in the context of maximum cation coordination by oxygen atoms.

EXAFS: A new tool for the study of battery and fuel cell materials

Abstract Extended X-ray absorption fine structure (EXAFS) is a powerful technique for probing the atomic structure of battery and fuel cell materials. The major

Single crystal RuO2 (110): Surface structure*

Abstract The surface structure of RuO2 (110) has been studied with LEED, AES and XPS. The “as-grown” surface shows no LEED patterns and both AES and XPS indicate that the surface is depleted in oxygen in high vacuum. After extensive annealing in an O2 atmosphere reproducible LEED patterns characteristic of the (110) surface were obtained. For the well-ordered surface the oxygen XPS results revealed oxygen associated with the bulk RuO2, the presence of RuO3 and oxygen bound to surface atoms.

Electrochemistry of sub-monolayer silver deposits on single crystal RuO2 (110), (001) and (111) electrodes

Abstract Asymmetric stripping peaks for sub-monolayer Ag films deposited on RuO2 single crystal electrodes have been observed for (110) and (001) surfaces where both Ru and O sites are available on the ideal surface. Interpretation of this observation in terms of irreversible and quasi-reversible adsorption of silver leads to an interaction coefficient g close to −4 which may result in the formation of Ag islands (new phase) due to the strong attractive lateral forces. On the other hand, a symmetric Ag stripping peak is characteristic for the RuO2 (111) surface where only Ru sites are available on the ideal surface. This indicates a reversible adsorption process for which the value of g was determined to be −1. The weaker lateral attraction forces seem to be associated with the different geometrical arrangement of Ag adatoms on different crystallographic faces of the RuO2 single crystals rather than with increased substrate-adatom interactions since no major shifts in the peak potential were observed.

Electrochemical methods for the in situ regeneration of active surface area of aged fuel cell type electrodes

One of the main reasons for the decay in performance of phosphoric acid fuel cells (150° C) is the decrease in surface area of the platinum catalyst with time. It was found that fast potentiostatic cycling (50 mVs−1) could regenerate the surface area of the Pt and recover the performance. The mechanism of regeneration is likely to be charge injection, resulting in electrostatic repulsion of the platinum particles in the loosely held agglomerates.