Single atom hot-spots at Au-Pd nanoalloys for electrocatalytic H2O2 production.

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.

Kinetics of electrocatalytic reduction of oxygen and hydrogen peroxide on dispersed gold nanoparticles.

The electrocatalytic properties of Au nanoparticles of mean size between 4.2 to 9.5 nm have been investigated for the oxygen reduction reaction (ORR). The particles were prepared on dispersed Vulcan XC-72R carbon black by reduction of a gold salt and by deposition of polymer stabilised gold sols. These were then attached to a glassy carbon disc electrode from their dispersion in a Nafion solution. The dependence on particle size of activity and selectivity for H(2)O(2) formation and the rate constants for oxygen and hydrogen peroxide reduction have been investigated using Rotating (Ring) Disc Electrode measurements. The electrocatalytic activity showed a maximum for a mean particle size of 5.7 nm and decreased significantly with particle size. The number of electrons exchanged per O(2) molecule increased from a value close to 2 to 3.4 as the potential was made more negative. The oxygen reduction selectivity for H(2)O(2) production was higher for mean particle sizes below 6 nm.

Polypeptide semicarbazide glass slide microarrays: characterization and comparison with amine slides in serodetection studies.

We have described in the accompanying article the preparation of peptide-protein semicarbazide microarrays and their use for the simultaneous serodetection of antibodies directed against different pathogens. Here, we present a comparative study between semicarbazide and amine glass slides in an immunofluorescent serodetection assay using HIV (Gp120, Gp41), HCV (mix-HCV, core, NS3, and NS4), and HBV (HBs) recombinant antigens. Amine and semicarbazide surfaces displayed the same sensitivity for antibodies detection just after printing. However, the reactivity of protein antigens changed rapidly upon aging on amine slides but not on semicarbazide slides. Peptide or protein semicarbazide microarrays were found to be remarkably stable for months. Additional data concerning the characterization of the semicarbazide surface (homogeneity of the slides, chemical stability, contact angle measurements, atomic force microscopy studies, reproducibility of serodetection results) are also presented and discussed.