The energetic convenience of electrolytic water splitting is limited by thermodynamics. Consequently, significant levels of hydrogen production can only be obtained with an electrical energy consumption exceeding 45 kWh kg À 1 H 2 . Electrochemical reforming allows the overcoming of such thermodynamic limitations by replacing oxygen evolution with the oxidation of biomass-derived alcohols. Here we show that the use of an original anode material consisting of palladium nanoparticles deposited on to a three-dimensional architecture of titania nanotubes allows electrical energy savings up to 26.5 kWh kg À 1 H 2 as compared with proton electrolyte membrane water electrolysis. A net energy analysis shows that for bio-ethanol with energy return of the invested energy larger than 5.1 (for example, cellulose), the electrochemical reforming energy balance is advantageous over proton electrolyte membrane water electrolysis.

The oxidative underpotential deposition of sulfur on Ag(111) from alkaline solutions of Na 2 S was investigated by in situ scanning tunneling microscopy (STM), cyclic voltammetry, and chronocoulometry. Proceeding toward more positive potentials, the cyclic voltammetric curve shows three partially overlapping peaks A-C and an isolated and more acute peak D. The STM images of the overlayer of adsorbed sulfur over the potential region between peaks C and D reveal a ( 3 × 3)R30°structure; those at potentials positive to peak D a ( 7 × 7)R19°structure: each lattice site of the latter structure is occupied by a triplet of sulfur atoms. The fractional coverage, 1 / 3 , for the ( 3 × 3)R30°structure is in perfect agreement with the maximum surface concentration, Γ max ) 7.7 × 10 -10 mol cm -2 , obtained from a thermodynamic analysis of the chronocoulometric charge vs potential curves; 2FΓ max is about 10% larger than the charge associated with the combination of peaks A-C. On the other hand, the 2FΓ value corresponding to the fractional coverage, 3 / 7 , for the ( 7 × 7)R19°structure agrees satisfactorily with the charge associated with the sum of peaks A-D, thus suggesting a total electron transfer from sulfide ions to the metal over the range of stability of the latter structure.

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)).

We applied the electrochemical atomic layer epitaxy ͑ECALE͒ methodology to obtain deposits of CdS and ZnS on Ag͑111͒ 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.Recent work in our group is devoted to the growth of thin-film compound semiconductors on silver single crystals by electrochemical atomic layer epitaxy ͑ECALE͒. Stickney and co-workers developed this method to obtain structurally well-ordered II-VI and III-V compound semiconductors on gold at low cost. 1-3 The method is based on the alternate electrodeposition of atomic layers of the elements making up a compound, at underpotential. Underpotential deposition ͑UPD͒ is a surface-limited electrochemical phenomenon that results in the deposition of an atomic layer. A monolayer of the compound is obtained by alternating the UPD of the metallic element with the UPD of the nonmetallic element in a cycle. The ECALE cycle can be repeated as many times as necessary to obtain deposits of practical thickness, and the thickness of the deposit is determined by the number of cycles.The method requires the definition of precise experimental conditions, such as potentials, reactants, concentrations, supporting electrolytes, pH, deposition times, and the possible use of complexing agents. These conditions are strictly dependent on the compound one wants to form and on the substrate used. We found the conditions to grow practically all II-VI compound semiconductors and are now beginning to study the III-V compounds. The substrate that has been used up to now is Ag͑111͒, a single crystal to ensure the maximum probability for the epitaxial growth.In a previous paper we described the experimental conditions needed to obtain up to five sulfur layers and four cadmium layers of CdS. Sulfur layers were obtained by oxidative UPD from sulfide ion solutions, 4-6 whereas cadmium layers were obtained by reductive UPD from cadmium ion solutions. 7 Both precursors were dissolved in pyrophosphate plus sodium hydroxide of pH 12. The high pH was used to shift the hydrogen evolution toward very negative potentials in order to evidence the whole underpotential oxidation process of sulfide ions which takes place between Ϫ1.35 and Ϫ0.8 V/SCE. A strong complexing agent such as pyrophosphate was used to keep cadmium ions in solution at this high pH. This paper describes the growth of thicker deposits of CdS, up to 150 deposition cycles, obtained using an automated system. The deposit morphology was examined by scanning electron microscopy ͑SEM͒. This paper also describes conditions to form ZnS.The experimental conditions for CdS and ZnS growth on silver are different from those required on gold. 8-10 ExperimentalMerck analytical reagent-grade 3CdSO 4 •8H 2 O and Aldrich analytical reagent-grade Na 2 S were used ...

We report on the N-decoration of multiwalled carbon nanotubes (MWCNTs) via chemical functionalization under mild reaction conditions. The introduction of tailored pyridinic functionalities as N-containing edge-type group mimics generates effective catalysts for the oxygen reduction reaction (ORR) in an alkaline environment. The adopted methodology lists a number of remarkable technical advantages, among which is an easy tuning of the electronic properties of N-containing groups. The latter aspect further increases the level of complexity for the rationalization of the role of the N-functionalities on the ultimate electrochemical performance of the as-prepared metal-free catalysts. Electrochemical outcomes crossed with the computed electronic charge density distributions on each scrutinized pyridine group have evidenced the central role played by the N-chemical environment on the final catalyst performance. Notably, small variations of the atomic charges on the N-proximal carbon atoms of the chemically grafted heterocycles change the overpotential values at which the oxygen reduction reaction starts. The protocol described hereafter offers an excellent basis for the development of more active metal-free electrocatalysts for the ORR. Finally, the asprepared catalytically active materials represent a unique model for the in-depth understanding of the underlying ORR mechanism.

The electrosorption valency l B of an adsorbed species is usually obtained from the slope of plots of the charge density on the metal against the surface concentration of the given species, at constant applied potential. Herein, two alternative procedures for the estimate of l B are proposed and applied to the formation of ordered overlayers of chloride, bromide, iodide, and sulfide on Ag(111). One of these procedures applies to strongly adsorbing anions, whose incipient adsorption turns out to be diffusion controlled under limiting conditions when stepping from a potential negative enough to exclude their specific adsorption. This procedure allows l B to be estimated as a function of the applied potential. Partial charge-transfer coefficients λ estimated from l B values on the basis of some modelistic assumptions decrease in the order sulfide ≈ iodide > bromide > chloride, namely in the order of increasing Pauling's electronegativity. Some direct procedures for the estimate of λ, which avoid the intermediate estimate of l B, are shown to lead to erroneous results.

A straightforward, energy- and atom-saving process to the production of tailored N-doped and catalytically active metal-free carbon nanostructures, has been set up. Our ex situ approach to the N-decoration of the carbon nanotube sidewalls contributes to elucidate the complex structure–reactivity relationship of N-doped carbon nanomaterials in oxygen reduction reactions, providing fundamental insights on the nature of the N-active sites as well as on the role of neighboring carbons.

The study of aerosol composition and air–snow exchange processes is relevant to the reconstruction of past atmosphere composition from ice cores. For this purpose, aerosol samples, superficial snow layers and firn samples from snow pits were collected at Dome Concordia station, East Antarctica, during the 2000/01 summer field season. The aerosol was collected in a ‘coarse’ and a ‘fine’ fraction, roughly separated from each other by a stacked filter system (5.0 and 0.4 μm). Atomic Force Microscopy (AFM) direct measurements on the fine fraction showed that 72% of surface size distribution ranges from 1.0 x 105 to 1.2 x 106 nm2. Assuming a spherical model, the volume size distribution of particles smaller than 5.0 μm shows a mode in the radius range 0.2–0.6 μm. Ion chromatographic (IC) measurements of selected chemical components allowed calculation of the ionic balance of the two size fractions. The fine fraction is dominant, representing 86% of the total ionic budget, and it is characterized by high content of sulphate and acidity. Principal component analysis (PCA) identified sea-spray and biogenic aerosol sources and showed some particulars of the transport and depositional processes of some chemical components (Ca2+, MSA, nssSO42–). Comparative analysis of aerosol, surface hoar and superficial snow showed differences in chemical composition: nitrate and chloride exhibit very high concentrations in the uppermost snow layers and in the surface hoar, and low values in the aerosol. This evidence demonstrates that nitrate and chloride are mainly in gas phase at Dome C and they can be caught on the snow and hoar surface through dry deposition and adsorption processes.