Xavier Alcobé

CHARACTERISATION OF ZINC+COBALT ALLOY PHASES OBTAINED BY ELECTRODEPOSITION

Abstract The anomalous codeposition of Zn+Co alloys on vitreous carbon, copper and nickel substrates in a chloride bath was studied. The results indicate that the substrate influences both the initial electrodeposition stages and the alloy formation. For the same electrodeposition conditions, vitreous carbon and copper substrates favour the formation of deposits richer in zinc than those obtained over a nickel substrate. In the stripping analysis of deposits obtained during anomalous codeposition, up to three major oxidation peaks were observed, the two corresponding to the more negative potentials are attributable to the zinc oxidation in the alloy and the more positive one to the oxidation of the remaining porous cobalt matrix of the alloy. Under our experimental conditions, two kinds of deposits have been analysed using X-ray diffraction (XRD). XRD analysis showed that deposits with very low cobalt percentage (less than 3%) and a hexagonal platelet structure had a distorted hcp zinc η-phase. Polyhedral-grained deposits with between 4 and 10% cobalt were made up of quasi-pure zinc and a Zn+Co γ-phase of bcc structure. A correlation between the stripping curve and the type of deposit has been found.

Alkali doping strategies for flexible and light-weight Cu2ZnSnSe4 solar cells

In this work we report on the effect of alkali doping via Na and/or K introduction into flexible and light-weight Cu2ZnSnSe4 (CZTSe) solar cells obtained using a sequential process based on the sputtering of metallic stacks and further reactive annealing. Different thicknesses of Cr diffusion barriers and 50 μm thick ferritic steel substrates were used. We compare different doping methods: Na-doped Mo targets (MoNa), SLG underneath the flexible substrates, NaF and KF pre-absorber synthesis evaporation (PAS) and post-deposition evaporation (PDT). Additionally, we report on the importance of the Cr barrier and back contact modification to improve solar cell performance. A remarkable enhancement in the absorber grain size and surface morphology occurred especially when using Na via MoNa and PAS. Nevertheless, preliminary experiments led to better results for MoNa doping due to a higher Na content confirmed by TOF-SIMS. K doping via PAS also showed promising results. An increase in the efficiency of solar cells from 2.2% to 4.3% was possible when using a MoNa layer sandwiched between regular Mo layers. The improvement is mainly related to a higher VOC and FF. After performing a detailed Cr and back contact optimization, a record value of 6.1% for flexible CZTSe solar cells was recently obtained using MoNa and a new surface Ge doping.

Electrodeposition of zinc+iron alloys: II. Relation between the stripping results and ex-situ characterization

Abstract Zn+Fe alloy electrodeposition under potentiostatic conditions was studied in chloride medium on vitreous carbon from solutions with relatively low metal concentrations. It has been demonstrated that electrochemical stripping techniques can be used to characterize the Zn+Fe alloy deposition process. Morphological and compositional studies, along with structural XRD analysis, enabled the electrodeposition conditions for obtaining a defined coating with defined characteristics to be specified. Anomalous codeposition of Zn+Fe alloy was maintained under gentle stirring conditions until zinc-rich deposits were obtained. In highly zinc-rich deposits, in which only the η-phase is present, a distorted platelet-like shape was seen. The zinc oxidation of these deposits took place in only one peak/plateau region in the electrochemical stripping curves. A slight increase in iron in the deposits (%Fe>4%) caused significant changes in both morphology and structure. For these deposits a second, more negative, peak/plateau region was recorded for the zinc oxidation in the stripping curves. Although the η-phase remains the phase mainly formed, the greater difficulty of zinc oxidation is interpreted as a consequence of the interactions between the η-phase and a new phase that probably has an fcc structure.

Tin-cobalt electrodeposition from sulfate-gluconate baths

The electrodeposition of tin + cobalt alloys from a slightly acidic sulfate–gluconate bath on both vitreous carbon and copper substrates has been studied for different [Sn(II)]/[Co(II)] ratios in the bath, varying between 1/10 and 1/2. A relationship between the electrochemical stripping analysis and the morphology of the deposits has been found. Two different types of deposit were obtained. At low [Sn(II)]/[Co(II)] ratios and relatively high deposition rates a nodular, cobalt-rich, nanocrystalline coating was obtained, while at high [Sn(II)]/[Co(II)] ratios and low deposition rates a new, well-defined tetragonal SnCo phase was obtained, with cell parameters of a = 3.087 Å and c = 5.849 Å. This structure favours hydrogen evolution.

Non Isomorphism and Miscibility in The Solid State: Determination of The Equilibrium Phase Diagram n-Octadecane C18H38 + n-Nonadecane C19H40

Abstract The phase diagram of the binary n-alkane system C18H38-C19H40 is determined by calorimetric and X-ray diffraction methods. The present experimental results and previous work on pure C18H38 and C19H40 paraffins allow us to identify all the phases of the binary system. The phase diagram exhibits no less than six distinct solid domains: three are one-phase regions, triclinic (T), orthorhombic (O) and face-centered orthorhombic, called rotator phase (RI), and three are two-phase equilibria [T + O], [T + RI] and [O + RI]. The two regions [O] and [RI] occur on large composition ranges (from the pure constituent C19H40). The solid-liquid equilibria are separated by a eutectic invariant. They can be explained in terms of crossed isodimorphism.

Highly efficient electrochemical and chemical hydrogenation of 4-nitrophenol using recyclable narrow mesoporous magnetic CoPt nanowires

Toxic nitro-compounds, such as 4-nitrophenol, are one of the most common wastewater industrial pollutants. Thus, efficient ways to neutralize them are actively pursued. Here novel procedures to degrade these types of compounds based on the use of mesoporous magnetic nanowires are demonstrated. Fully-mesoporous magnetic narrow (25 nm) CoPt nanowires with an extraordinary effective area are grown using ionic liquid-in-water microemulsions in alumina templates. These mesoporous nanowires are shown to be efficient catalysts for the hydrogenation of 4-nitrophenol by electrocatalysis. Additionally, these nanowires also present exceptional conventional catalytic activity when used in conjunction with NaBH4, particularly when magnetic stirring is utilized. In fact, magnetically actuated mesoporous CoPt nanowires drastically outperform all state-of-the-art 4-nitrophenol catalysts. Additionally, given their magnetic character, these nanowires can be easily recycled and reused. Thus, the outstanding catalytic performance of mesoporous CoPt nanowires makes them excellent candidates for wastewater treatment agents.

Cooperative induction in double H-bonding donor/acceptor compounds: Chains vs. ribbons

Two different types of monodimensional crystalline aggregates formed by squaramides, chains and ribbons, have been studied both in the solid state and ab initio with four model compounds. Although ribbons are a priori possible, only covalently forced syn conformations have been observed. Cooperative induction is postulated to explain the preference for chains instead of ribbons in squaramide crystals.

Nature of anode passivation in Zn-Ni electroplating baths

The behaviour of zinc anodes in two zinc-nickel electroplating baths (ammonium-containing and ammonium-free) was studied by recording changes in the anode potential and by analyzing the surface films formed at open-circuit and anodic polarization. The surface films were analyzed using XRD, SEM and XPS. The two baths gave films of similar composition but there were differences in their thickness and the zinc dissolution products. After various cycles of anodic polarization, the film formed in the ammonium bath contained nickel and zinc hydroxide and, although the oxidation process was more difficult, it was not completely hindered; in the ammonium-free bath the film was thicker and more compact and it was composed of nickel and the zinc hydroxichloride (simonkolleite), located in such a way that the zinc anode oxidation was completely blocked.

A cocrystal is the key intermediates for the production of a new polymorph of Vorinostat

A new kinetically stable polymorph of Vorinostat has been discovered as a result of a polymorph screening, however an impurity is always formed in its preparation by crystallization. The interaction of Vorinostat with ammonia yields a new cocrystal which transforms easily through thermal desorption into the new polymorph with a high degree of purity.

Magnetic Propulsion of Recyclable Catalytic Nanocleaners for Pollutant Degradation

Electrochemically fabricated magnetic mesoporous CoNi@Pt nanorods are excellent nanomotors with controlled magnetic propulsion and excellent catalytic properties. The core-shell structure allows a double functionality: (i) controlled motion of the nanorods by applying rotating magnetic fields at different frequencies and field strengths and (ii) effective catalytic activity of the platinum shell for reactions involving sodium borohydride. The structure and magnetic properties of the CoNi core are not modified by the presence of the Pt shell. Nanorods were propelled via a tumbling-like dynamic by a rotating magnetic field. While in absence of NaBH4, nanorods move at constant speed showing a linear path; in the presence of NaBH4, they showed an intermittent trajectory. These catalytic nanorods can be used as nanocleaners with controlled directionality for pollutants degradation in the presence of borohydride. Their magnetic character allows control of the velocity and the direction throughout the contaminated solution by degrading the different pollutants in their path. The magnetic character of nanorods also allows their easy recycling.