The nature of reduced CO, adsorbates, as well as the mechanisms for their electro-oxidation on platinum, have been reviewed through the light of new experimental data obtained by cyclic voltammetry and by Fourier transform infrared reflectance spectroscopy. Three different "reduced" CO, adsorbates are described as "'ensembles". It is suggested that they involve different extents of adsorbed entities, among which weakly bound and strongly bound hydrogen atoms play the most important role.

Gold nanoparticles with a diameter of approximately 20 nm have been observed at the polarized water/2-octanone interface by the nonlinear optical technique of second harmonic generation. Electric field induced adsorption of the gold particles at this liquid/liquid interface is clearly observed and confirms that these are negatively charged. The process is quasi-reversible at high potential sweep rates, but aggregation at the interface is observed at slower sweep rates through the loss of the nonlinear optical signal. The time evolution of the second harmonic signal is also reported during potential step experiments. After a rapid increase due to adsorption, a continuous decrease in the nonlinear optical signal intensity is observed due to aggregation of the particles into large islands at the interface. Diffusion of these large islands at the interface was observed for a longer timescale through large signal fluctuations.

The geometries and binding energies of CO2 adsorbates on Pt(100) and Pt(111) cluster surfaces were calculated by means of an improved version of the extended Hü ckel molecular orbital method. The polarization of the surface by an applied electric potential and coadsorption of H atoms were included in the model. For simulated applied potentials in the range -1.0 to 1.0 V, CO2 coordination geometries (side-on, formate) involving two adsorbate atoms bonded to the surface are favored, regardless the surface topology and the presence of coadsorbed H atoms. In agreement with experiment, larger binding energies are always calculated for the Pt(100) cluster surface.a VSIP ≡ valence state ionization potential. b oe1,2 ≡ orbital exponents of the base generating functions. c c1,2 ≡ linear coefficients of the double zeta Pt d-orbitals.

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The interaction of propargyl alcohol and ally1 alcohol with a platinum (Pt) electrode modified by the presence of reduced CO, adsorbates (r-CO,) is studied through voltammetry and potentiostatic current transients by using a flow cell technique. The interaction between each alcohol and r-CO2 is promoted at three constant potentials corresponding to different degrees of R surface coverage by Hatoms. For both alcohols the anodic stripping peaks and the charge balance are interpreted in terms of the formation of composed adsorbates. Based upon the probabler-COr structure and H-bonding interactions between r-CO* and the alcohol molecules or their adsorbed residues, average alcohol residues/r-CO, molecular ratios are estimated.