Fabrication and surface characterization of single crystal PtBi and PtPb (100) and (001) surfaces.

High quality single crystal PtM (M = Bi or Pb) (100) and (001) surfaces have been generated from solid state bulk materials. The specific orientation was determined via X-ray Laue back-reflection and the miscut angles of the single crystal surfaces were ∼0.3° which was limited by instrumental resolution. The PtM (001) electrode had a Pt termination based on cyclic voltammetric (CV) profiles. The surface structure and composition of single crystal PtM surfaces have been studied by synchrotron-based in situ X-ray grazing incidence diffraction (GID) under active electrochemical control. Cycling of the potential to increasingly high values resulted in dramatic changes to the surface crystalline structure and composition of these single crystal electrodes. Well-defined Pt nano-domains in a hexagonal pattern with a 23° offset angle to the substrate were formed on the PtM (001) surface after electrochemical pretreatment in supporting electrolyte (0.1M H(2)SO(4)), especially for E(ulp) (E(ulp) = upper limit potential) of +0.80 V or beyond. From an analysis of the diffraction peaks, the size of the Pt domains was estimated to be ∼15 nm. The Pt domain formation on the single crystal surfaces, similar to results on polycrystalline intermetallic phases, was due to leaching of the less-noble elements (Bi or Pb) from the intermetallic matrix and sintering of the Pt atoms on the surfaces. On the other hand, Pt domains with a preferential direction but no offset angle to the substrate were formed on PtM (100) surface after similar electrochemical pretreatment. PtBi and PtPb single crystal surfaces exhibited different anisotropic electrocatalytic activities towards the electrooxidation of formic acid and other potential fuels for fuel cell applications. The reactivities of these single crystal electrodes towards the oxidation of small organic molecules were a function of E(ulp) values and maximal activities were around +0.60 V for PtBi(001) surface which might be due to formation of partially oxidized surfaces but around +1.20 V for PtPb(100) and (001) surfaces which might be due to the increasing boundary lines of Pt and PtPb grains.

Catalyst supports for polymer electrolyte fuel cells.

A major challenge in obtaining long-term durability in fuel cells is to discover catalyst supports that do not corrode, or corrode much more slowly than the current carbon blacks used in today's polymer electrolyte membrane fuel cells. Such materials must be sufficiently stable at low pH (acidic conditions) and high potential, in contact with the polymer membrane and under exposure to hydrogen gas and oxygen at temperatures up to perhaps 120 degrees C. Here, we report the initial discovery of a promising class of doped oxide materials for this purpose: Ti(1-x)M(x)O(2), where M=a variety of transition metals. Specifically, we show that Ti(0.7)W(0.3)O(2) is electrochemically inert over the appropriate potential range. Although the process is not yet optimized, when Pt nanoparticles are deposited on this oxide, electrochemical experiments show that hydrogen is oxidized and oxygen reduced at rates comparable to those seen using a commercial Pt on carbon black support.