Smooth Polycrystalline Platinum Electrodes Research Articles

Order-disorder effects in competitive irreversible adsorption of aromatic compounds at platinum electrodes: 1,4-naphthohydroquinone and 2,2′,5,5′-tetrahydroxybiphenyl

The competitive irreversible adsorption of 1,4-naphthohydroquinone (NHQ) and 2,2′,5,5′-tetrahydroxybiphenyl (THBP) from aqueous solutions onto smooth (annealed) polycrystalline platinum electrodes has been studied at room temperature. Coadsorption coverage measurements were based on thin-layer coulometry. Preferential adsorption of NHQ over THBP was exhibited at all bulk concentrations studied. The mixed adsorption profiles showed minima in total packing density which were accompanied by minima in the fraction of edge-pendant oriented THBP, indicating that packing in oriented mixed-polyphenol layers involves ordered structures which are favored by intermolecular hydrogen-bonding. In the edge-orientation, traces of one compound in a layer composed primarily of another compound introduced disorder into the layer.

Effect of nonaqueous solvents on the chemisorption and orientation of aromatic compounds at smooth polycrystalline platinum electrodes: naphthohydroquinone in water-benzene solutions

Effect of nonaqueous solvents on the chemisorption and orientation of aromatic compounds at smooth polycrystalline platinum electrodes: naphthohydroquinone in water-benzene solutions

The adsorption and orientation of aromatic compounds at smooth polycrystalline platinum electrodes: The effect of surface-active organic impurities

Changes in the adsorption profiles of 1,4-naphthohydroquinone (NHQ) on smooth polycrystalline platinum electrodes in aqueous 1 M HClO 4 brought about by varying levels of surface-active organic impurities [typified by hydroquinone (HQ) and benzene] have been studied by thin-layer electrochemical techniques, 10 −5 M HQ is sufficient to alter the adsorption profile of NHQ; above 10 −4 M HQ, the packing density transitions prominent from pure NHQ solutions were completely suppressed. Similar results were obtained when benzene was used as the contaminant. Packing density measurements indicated that the subject surface-active impurities inhibited formation of flat-, but not edge-, adsorbed NHQ; this is in agreement with data from a previous study [M.P. Soriaga, J.H. White, D. Song and A.T. Hubbard, J. Electroanal. Chem., 171 (1984) 359] which showed that low-levels of iodide, a surface-active anion, enforced formation of edge-adsorbed NHQ even at (low) concentrations where flat-adsrobed species would have formed from pure NHQ solutions. The presence of surface-active impurities may help account for the profound differences in adsorption measurements reported in the literature for various aromatic compounds.

Adsorption and orientation of aromatic compounds at smooth polycrystalline platinum electrodes: The effect of halide electrolytes

Etude de l'influence des halogenures, des electrolytes de base, sur l'adsorption et l'orientation de l'hydroquinone et de la naphtohydroquinone-1,4 sur des electrodes polycristallines de Pt

Ligand (adsorbate) substitutions at metal surfaces: aromatic compounds and halides at smooth polycrystalline platinum electrodes

Etudes des reactions de substitution de coordinats (adsorbats) entre des composes aromatiques et des halogenures, sur une surface lisse de Pt, polycristallin, en solution. Les mesures d'adsorption et de desorption sont fondees sur des methodes electrochimiques en couche mince. L'hydroquinone (HQ) est etudiee en presence de F − , Cl − et Br − et la naphto-1,4-hydroquinone (NHQ) en presence de Br − et de I −

The effect of orientation of adsorbed intermediates on the electrochemical oxidation of aromatic compounds

The electrochemical oxidation of aromatic compounds spontaneously and irreversibly adsorbed from solution onto smooth polycrystalline platinum electrodes has been studied as a function of adsorbate orientation. Experiments were done in aqueous 1 M HClO4 at ambient temperatures using thin-layer electrochemical techniques. Eight homocyclic aromatic compounds, shown previously to re-orient from flat to edgewise orientations as the solution concentration is increased, were studied: simple diphenols, alkyl diphenols, tetrahydroxybiphenyl and dihydroxynaphthalene. The measured values of nox (the number of electrons for electrocatalytic oxidation of chemisorbed aromatic) indicate that the subject compounds attached in the flat orientation are oxidized essentially completely to CO2, whereas oxidation of intermediates adsorbed in the edge orientation may lead to products in lower oxidation states. In any orientation, the adsorbed intermediate undergoes irreversible oxidation more readily than the unadsorbed starting material. Some comparisons with homogeneous metal-catalyzed oxidations are considered.