A novel strategy to direct the oxygen reduction reaction to preferentially produce H(2)O(2) is formulated and evaluated. The approach combines the inertness of Au nanoparticles toward oxidation, with the improved O(2) sticking probability of isolated transition metal "guest" atoms embedded in the Au "host". DFT modeling was employed to screen for the best alloy candidates. Modeling indicates that isolated alloying atoms of Pd, Pt, or Rh placed within the Au surface should enhance the H(2)O(2) production relative to pure Au. Consequently, Au(1-x)Pd(x) nanoalloys with variable Pd content supported on Vulcan XC-72 were prepared to investigate the predicted selectivity toward H(2)O(2) production for Au alloyed with Pd. It is demonstrated that increasing the Pd concentration to 8% leads to an increase of the electrocatalytic H(2)O(2) production selectivity up to nearly 95%, when the nanoparticles are placed in an environment compatible with that of a proton exchange membrane. Further increase of Pd content leads to a drop in H(2)O(2) selectivity, to below 10% for x = 0.5. It is proposed that the enhancement in H(2)O(2) selectivity is caused by the presence of individual surface Pd atoms surrounded by gold, whereas surface ensembles of contiguous Pd atoms support H(2)O formation. The results are discussed in the context of exergonic electrocatalytic H(2)O(2) synthesis in Polymer Electrolyte Fuel Cells for the simultaneous cogeneration of chemicals and electricity, the latter a credit to production costs.

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NO 2 adsorption at a BaO(100) surface is investigated by means of spin polarized GGA density functional theory. A periodic supercell procedure is employed, and two redox reaction channels are mapped out, involving two chemisorbed NO 2 molecules per supercell. The chemisorption is studied in two subsequent steps. The reaction paths are initiated by NO 2 adsorption in the form of a nitrite over a Ba 2+ site. This generates an electron hole among the surrounding surface oxygen atoms. A reaction path branching occurs as the second NO 2 either (a) acts as surface oxidant, forming a surface nitrite-peroxide pair by releasing NO(g), or (b) binds to an Osurf site to form a formal surface nitrate. A redox reaction involving surface nitrite-nitrate interconversion is also addressed. The computed results are employed to interpret experimental observations of surface nitrites, peroxides, NO(g) desorption, and surface Ba(NO 3 ) 2 formation. The understandings are discussed in the context of the NO x storage concept of lean-burn catalysis.

Charged NO x species (x ) 1,2,3) formed upon adsorption of NO 2 on BaO are characterized by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy and theoretical vibrational analysis using the density functional theory (DFT). Experiments at 30 °C reveal nitrite formation. At T > 250 °C, shifts associated with formation of nitrates are observed, indicating an interconversion of oxygen atoms among adsorbates. The theoretical study includes single and pairwise NO 2 adsorption on (BaO) 9 clusters. As has been reported previously [Broqvist, P.; Panas, I.; Fridell, E.; Persson, H. J. Phys. Chem. B 2002, 106, 137], an additional energy gain is calculated for the second adsorbed NO 2 . A vibrational analysis of the investigated adsorption configurations supports the interpretation of nitrite to nitrate interconversion on the BaO surface. Moreover, the calculations demonstrate the sensitivity in the NO 2 vibrational band splitting with respect to adsorption configuration.