Maria Luisa Foresti

Ethanol Oxidation on Electrocatalysts Obtained by Spontaneous Deposition of Palladium onto Nickel-Zinc Materials

Ni-Zn and Ni-Zn-P alloys supported on Vulcan XC-72 are effective materials for the spontaneous deposition of palladium through redox transmetalation with Pd(IV) salts. The materials obtained, Pd-(Ni-Zn)/C and Pd-(Ni-Zn-P)/C, have been characterized by a variety of techniques. The analytical and spectroscopic data show that the surface of Pd-(Ni-Zn)/C and Pd-(Ni-Zn-P)/C contain very small, highly dispersed, and highly crystalline palladium clusters as well as single palladium sites, likely stabilized by interaction with oxygen atoms from Ni--O moieties. As a reference material, a nanostructured Pd/C material was prepared by reduction of an aqueous solution of PdCl(2)/HCl with ethylene glycol in the presence of Vulcan XC-72. In Pd/C, the Pd particles are larger, less dispersed, and much less crystalline. Glassy carbon electrodes coated with the Pd-(Ni-Zn)/C and Pd-(Ni-Zn-P)/C materials, containing very low Pd loadings (22-25 microg cm(-2)), were studied for the oxidation of ethanol in alkaline media in half cells and provided excellent results in terms of both specific current (as high as 3600 A g(Pd)(-1) at room temperature) and onset potential (as low as -0.6 V vs Ag/AgCl/KCl(sat)).

Formation of ZnSe on Ag(111) by electrochemical atomic layer epitaxy

ZnSe is an ideal candidate for optoelectronic devices. However, modern technology is quite demanding as to the quality of materials employed. The electrochemical atomic layer epitaxy (ECALE) method ensures good atomic-level control of thin film formation, as it is based on the alternated deposition of atomic layers of the elements making up the compound. The electrochemical conditions necessary to form ZnSe deposits of up to 35 Zn layers and 35 Se layers on Ag(111) by ECALE are described here. The 1:1 stoichiometric ratio of Zn to Se suggests that ZnSe is formed. A miniaturized electrochemical cell is also described.

CdS and ZnS Deposition on Ag(111) by Electrochemical Atomic Layer Epitaxy

We applied the electrochemical atomic layer epitaxy (ECALE) methodology to obtain deposits of CdS and ZnS on Ag (111) by alternate underpotential deposition of the elements forming the compounds. The amounts of the elements deposited, determined by stripping coulometry, always yielded a stoichiometric 1:1 ratio. The deposits were formed using an automated electrochemical deposition system, described here, making use of a simple distribution valve.

Trends in the adsorption behaviour of n-aliphatic alcohols on mercury from aqueous 0.5 M Na2SO4

Abstract The electrosorption behaviour of n-aliphatic alcohols from n-butanol to n-octanol at the mercury/water interface was determined from capacitive charge measurements by using a computerized chronocoulometric technique. The surface area A occupied by one adsorbed alcohol molecule at maximum coverage was found to increase by about 0.06 nm2 per each CH2 group, thus suggesting strongly that the alcohols are adsorbed on mercury from aqueous solutions of 0.5 M Na2SO4 in a flat orientation up to maximum coverage. This interpretation is further supported by the approximate constancy of the differential capacity at maximum coverage for all alcohols investigated, and by the gradual increase in the coefficient with an increase in chain length, where ΔGoads is the standard Gibbs energy of adsorption and σm is the charge density of maximum adsorption. This adsorption behaviour differs from that from aqueous 0.1 M NaF as reported by B.B. Damaskin, A.A. Survila and L.E. Rybalka (Elektrokhimiya, 3 (1967)146); in fact, the latter behaviour suggests a vertical orientation of the hydrocarbon chains at maximum coverage.

Electrostatic effect of specifically adsorbed electroinactive ions upon electrode processes

Abstract The electrostatic effect exerted by specifically adsorbed electroinactive ions upon electrode processes is accounted for by introducing into the Frumkin equation the average potential at the position occupied by the reacting particle in the transition state. The value of this potential is obtained from a simple model of the double layer in the presence of specific ionic adsorption. It is thus shown that the logarithm of the rate constant k f at constant applied potential is expected to vary linearly with the charge density q i at the inner Helmholtz plane. Some examples in support to the above theoretical prediction are reported.

Electrochemical aspects of CdTe growth on the face (111) of silver by ECALE

CdTe deposition on Ag(111) was obtained by Electrochemical Atomic Layer Epitaxy (ECALE) method, that is by the alternated underpotential deposition of tellurium and cadmium. The voltammetric analysis of the first TeUPD and CdUPD peaks indicates a mechanism of two-dimensional growth, which is consistent with an epitaxial growth. The ratio Cd:Te determined on the basis of electrochemical measurements is very close to the 1:1 stoichiometric ratio, which is indicative of a compound formation.

Trace Copper(II) or Zinc(II) Ions Drastically Modify the Aggregation Behavior of Amyloid-beta(1-42): An AFM Study

Formation of amyloid-beta (Abeta){1-42} amyloid fibrils, a characteristic feature of Alzheimers disease (AD), was monitored in situ through atomic force microscopy (AFM). Well-structured amyloid fibrils slowly formed in solution within 24 hours for which high quality AFM pictures could be obtained. Remarkably, addition of either copper(II) or zinc(II) ions to the incubation medium, even at extremely low molar ratios, dramatically changed the Abeta {1-42} aggregation profile and prevented fibril formation. Aggregates of different morphology appeared in accordance with previous observations: small globular aggregates upon addition of zinc; ill-structured micro-aggregates in the case of copper. The implications of these AFM results are discussed in the context of current concepts for AD metallobiology.

Statistical-mechanical treatment of an adsorbed monolayer with local order: Part III. Its use in the interpretation of the adsorption behaviour of aliphatic compounds☆

Abstract The statistical-mechanical treatment of Part II of thi series is applied to a monolayer of water molecules and open-chain polymeric solute molecules consisting of structurally indistinguishable segments. Water molecules are assumed to interact between themselves both via dipole-dipole forces and via H-bonds, whereas water-solute and solute-solute interactions are considered to be of the dipole-dipole type. The resulting adsorption isotherm explains several features of the adsorption behaviour of aliphatic compounds, such as the Frumkin isotherm behaviour with an attractive interaction factor, the parabolic dependence of the standard Gibbs energy of adsorption Δ G ° ads on charge σ m , the correct order of magnitude for b  ∂ Δ G ° ads /∂(σ m  σ max ) 2 , and the experimental dependence of b on the charge of maximum adsorption σ max . The model also accounts satisfactorily for the shape of the experimental curves of the potential drop Δφ across the inner layer against surface coverage at constant charge. An explanation of two-dimensional condensation based on inhibition of H-bond formation between adsorbed and non-adsorbed water molecules is proposed.

A Monte Carlo simulation of water molecules near a charged wall

A Monte Carlo simulation of liquid water near a charged wall has been carried out for different values of the surface charge density. The surface excess of electric potential as a function of charge density has been determined from the polarization profiles. The differential capacity of the simulated system is compared with the differential capacity of the mercury/water interface.

Crystal face effects on adsorption of ionic and non-ionic species on Ag electrodes: an electrochemical and STM study

Abstract The behaviour of the low-index faces of silver towards specific adsorption from aqueous solutions was investigated by measuring the adsorption of n-hexanol and tert-pentanol, which exemplifies the behaviour of physisorbed neutral compounds, the adsorption of bromide ions, which exemplifies the behaviour of chemisorbed ions, and the adsorption of uracil. STM images of specifically adsorbed bromide and iodide ions on Ag(111) were determined. The increase in the adsorptivity of the two aliphatic alcohols in the order Ag(110)