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The structural features and catalytic activities of PtIr electrocatalysts derived from vertical IrO2 nanotubes (IrO2NT) of 1100 nm in height and 80−100 nm in diameter have been studied using scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction, and cyclic voltammetry toward COad and methanol oxidation. Lattice oxygen of IrO2NT is removed under high-vacuum thermal annealing to facilitate nucleation of 3−5 nm Ir grains and subsequent synthesis of PtIr catalyst on the tube walls. Interestingly, the apparent dimensions and orientation of IrO2NT can be preserved via pore generation in the oxygen removal process. The tubular wall was transformed from a thin dense plate of IrO2(110) single crystal into a porous plate consisting of connected Ir grains that exhibit lattice fringes of the Ir{110} spacing with preferential orientation of Ir[11̄0] parallel to the IrO2NT growth direction. The amount of Ir being reduced, the Ir grain size, and the deposited Pt size strongly influence the surface area and the catalytic activity. The Pt−Ir−IrO2NT catalyst reduced at 500 °C exhibits a significantly higher activity than Pt−IrO2NT and Pt−IrNT in methanol oxidation and also a higher current density than that of a Johnson−Matthey PtRu catalyst in the high potential region.

Dissociative adsorption of Si2H6 and Ge2H6 on various buckled dimers of SiGe(100)-2 × 1 surface has been studied using density functional theory at the B3LYP level. Two paths, individually leading to (I) two chemisorbed SiH3 or GeH3 and (II) surface hydrides plus a gas-phase SiH4 or GeH4, are considered in the energetics calculation. Contrary to the intuitive mechanism involving a four-center transition state (TS) that yields two SiH3(a) or GeH3(a) in one step, the intermolecular bond scission on a dimer is accomplished in two consecutive steps of three-center TS, in which the first step is rate-limiting. The calculated energy barrier of the first step in Si−Si bond scission is higher than that of the H−Si bond scission on Si*−Si dimer by 9 kcal/mol. Therefore, in contrast to the conventional wisdom of favoring Si−Si bond cleavage over H−Si as the first step in chemisorption on Si(100)-2 × 1, the calculation result supports Niwano and co-workers' experiments that concluded that Si2H6 adsorption without breaking the Si−Si bond was preferred. On the other hand, the Ge alloying on the surface reduces the barrier height difference between these two paths. Hence, the energy blockade between dehydrogenation and intermolecular bond scission decreases when Ge2H6 is added in Si2H6 chemical vapor deposition. Rate constants are also calculated and the results are qualitatively in line with the Ge2H6 reactivity on Si(100) measured by Lam et al.

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Ab initio calculations have been carried out to investigate the pathways of H-atom migration and H2 desorption on a mixed SiGe(100)-2×1 surface using the cluster model. The H2 recombinative desorption is the rate-determining step in hydrogen migration and desorption on SiGe(100) surfaces, since the energy barrier to H-atom migration is generally lower than that of H2 desorption. The energy barriers for H2 desorption from the interdimer, the Si–Ge pair, (52.8 kcal/mol), and the Ge–Ge pair, (45.1 kcal/mol), are lower than that for the Si–Si pair by 7.5 and 15.2 kcal/mol, respectively. Thus, the SiGe(100)-2×1 surface in chemical vapor deposition provides more dangling bonds than the Si(100)-2×1 surface because of Ge inclusion. In contrast, the chemisorbed H tends to stay on the Si-site, since the barrier for H-migration from the Ge-site to the Si-site is lower that in the opposite direction by 5.6 kcal/mol. Hence, a considerably higher percentage of Ge sites are dangling bonds, compared with Si sites on the SiGe(100) surface. Related transition state structures in the migration and desorption steps are also discussed.