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Electrochemical and X-ray absorption techniques have been used to determine the influence of heat treatment in electrocatalytic activity for O2 reduction for two cobalt catalysts. The catalysts are cobalt phthalocyanine (catalyst 1) and polyacrylonitrile + cobalt acetate (catalyst 2) adsorbed on carbon black and heat treated at several temperatures. A maximum far the catalytic activity was obtained for PcCo at 850 "C and for the PAN + Co catalyst at 950 "C with subsequent decrease. The results obtained by XANES and EXAFS data clearly show that metallic cobalt aggregates with different size are synthetized in the range of increased activity. In the region of highest activity were observed the smallest cobalt clusters (20 A). For higher temperatures these cobalt aggregates became bigger (100-200 A), which corresponds to the decrease in the catalytic activity.TEM was utilized as a complementary technique and it confirms the influence of the annealing temperature in the size of the cobalt aggregates obtained. XANES measurements at the Co and N K edges confirm that CON, centers and nitrogen atoms are no longer detected after heat treatment in the region of increased activity. 7440-48-4; H,SO,, 7664-93-9; LiCIO,, 7791-03-9; cobalt acetate, 71-48-7; polypyrrole, 30604-8 1-0; pyrrole, 109-97-7; acetonitrile, 75-05-8; carbon, 7440-44-0.

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Many organic conducting polymers such as polyacetylene, PA (1) ; polyparaphenylene, PPP (2) ; polyparaphenylenesulfide, PPS (2); and polypyrrole, PP (3) have been proposed in the literature. These polymers show reversibility of the doping-undoping process, making them of interest in energy storage. One of the key problems, however, is the poor stability of most of these polymers. Polyacetylene, PA, must be prepared and stored under a rigorously O2 free atmosphere and at a low temperature (4). Polypyrrole, PP, although st~able in its conducting state, is also sensitive to 02 in its semiconducting undoped state (5). As a matter of fact, a progressive redoping by 02 occurs due to the value of the polymer oxidation potential (Eox ~ --0.3) which lies in the same range as that for the reduction of O2.PPP and PPS show a higher oxidation stability mainly in the undoped state (Eox ~ ~l.6V), and their sensitivity to O2 is less pronounced, but information on the doped state is scarce. The authors recently reported the electrochemical generation of thin films of new organic conducting polymers, polythiophene, polyfuran, and derivatives (6) which also appear as interesting candidates for organic electrodes for energy storage or display.In this paper, the stability characteristics of these new polymers is presented under various experimental conditions (02, H~O, H +, OH-, temperature).

We show that sum-frequency generation spectroscopy performed in the total internal reflection configuration (TIR–SFG) combined with a dense gold nanoparticles monolayer allows us to study, with an excellent signal to noise ratio and high signal to background ratio, the conformation of adsorbed molecules. Dodecanethiol (DDT) was used as probe molecules in order to assess the potentialities of the approach. An enhancement of more than one order of magnitude of the SFG signals arising from the adsorbed species is observed with the TIR geometry compared to the external reflection one while the SFG non-resonant contribution remains the same for both configurations. Although further work is required to fully understand the origin of the SFG process on nanoparticles, our work opens new possibilities for studying nanostructures.

We report on the first in situ study of the electronic state and the structure of underpotentially deposited submonolayers of Cu on Au(lll) by x-ray-absorption spectroscopy. We found (i) various ordered adlayer structures, dependent on coverage, time, and direction of the potential scan, and (ii) strong interactions of Cu and oxygen and charge transfer from Cu to Au. During the deposition, the initial (VJxVJ) structure at 0.3 monolayer evolved to an equilibrium with the c(5x5). The latter and the (lxl) phases were observed at 0.6 and 1 monolayer, respectively. The three structures are present at 0.6 monolayer during the stripping scan.