Conversion reactions in lithium batteries have been proved for several classes of materials, such as oxides, fluorides, sulphides, nitrides, phosphides and recently for hydrides. Metal hydrides can be electrochemically reduced to a highly conductive composite material consisting of nanometric metallic particles dispersed in an amorphous LiH matrix. Magnesium hydride undergoes a reversible conversion reaction and it has very good theoretical performances, i.e. a theoretical specific capacity of 2038 mA h g -1 and a working potential of 0.5 V vs. Li +/Li. The purpose of our study is to investigate the MgH 2 redox activity by evaluating the effect of ball milling pre-treatments and by studying the conversion reaction mechanism. Three materials, prepared by submitting bulk MgH 2 to different ball milling procedures, are investigated. By coupling electrochemical tests, ex situ X-ray powder diffraction and transmission electron microscopy, we prove that the lithium incorporation does not follow a simple direct conversion path as it follows at least a sequence of four consecutive processes: (a) the hydride conversion reaction of MgH 2 to give Mg and LiH, (b) the alloying of Li in hcp Mg and (c and d) the formation and lithium enrichment of a bcc Li-Mg solid solution. Furthermore some experimental clues suggest that the mechanism is probably even more complex as it can imply the formation of other unknown intermediate Li-Mg-H phases. Moreover large morphological changes occur upon lithium incorporation in the electrodes: in particular an extended sintering of the metal nanoparticles occurs upon cycling. This effect leads to electrode pulverization and capacity fading. On the other hand MgH 2 shows a very limited potential hysteresis between discharge and charge and very promising kinetics at high current. © 2012 The Royal Society of Chemistry

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ionic Liquids are a promising alternative to water electrolytes for the electrodeposition of metals. these solvents have a much larger electrochemical window than water that expands the potential of electrodeposition. However, mass transport in Ionic Liquids is slow. The slow mass transport dramatically affects the rate of reactions at the solid-liquid interface, hampering the exploitation of Ionic Liquids in high-throughput electrodeposition processes. In this paper, we clarify the origin of such poor mass transport in the diffusion-advection (convection) regime. To determine the extent and the dynamics of the convection boundary layers, we performed Rotating Disk Electrode (RDE) experiments on model reactions along with the finite element simulation. Both the experiments and the finite element modelling showed the occurrence of peaks in the RDE curves even at relatively high rotation rates (up to 2000 rpm). The peak in the RDE is the fingerprint of partial diffusion control that happens for the relative extent of the diffusion and convection boundary layers. In looking for a close match between the experiments and the simulations, we found that the ohmic drop plays a critical role and must be considered in the calculation to find the best match with the experimental data. In the end, we have shown that the combined approach consisting of RDE experiments and finite elements modelling providing a tool to unravel of the structure of the diffusion and convection boundary layers both in dynamic and stationary conditions.

In order to substitute traditional cyanide-based baths and obtain a new eco-compatible route to synthesize via electrodeposition a CZTS (copper-zinc-tin sulfide) absorber films, this paper describes the development of a green electrodeposition bath for Cu–Sn alloys. CZTS, being a p-type semiconducting material could be used in novel and sustainable photovoltaic devices. In this work we analyzed the electrochemical behavior of different methanesulfonic acid-based prototype deposition bath containing tin methanesulfonate as tin precursor, copper sulfate or methanesulfonate as copper precursor, and hydroquinone, nitrilotriacetic acid and 2-picolinic acid as organic additives. Electrodeposition was conducted with different deposition parameters such as deposition potential, current density, potentiostatic or galvanostatic mode. Surface and cross-section morphology as well as composition of the films were characterized using SEM-EDS. The composition of the samples in terms of crystalline phases was analyzed using XRD, highlighting the information obtained by superlattice diffraction peaks based on the crystallography of Cu–Sn intermetallic phases. From prototype bath S4 a uniform composition around Cu:Sn = 2:1 was observed with η ′ phase as the dominant phase, which could possibly facilitate the synthesis of CZTS due to its aligned body-center vacancies that could serve as sulfur diffusion path during sulfurization within each η ′ crystal.

The role of thiourea as an organic additive in the nucleation and growth mechanism was studied for copper deposition and its application in the decorative electroplating and fashion accessory industries. The bath was designed to reduce the environmental and ecological impacts using methanesulfonic acid as electrolyte as an alternative to alkaline cyanide baths. We evaluated the nucleation and growth mechanism of copper exploiting voltametric and chronoamperometric measurements with a brightener concentration ranging from 0 to 90 ppm. We used the Scharifker–Hills model to estimate the type of nucleation mechanism after progressive addition of thiourea. Scanning electron microscope was employed for surface analysis and morphological characterisation of the nuclei. We verified that progressive nucleation is a key step in the obtainment of a shiny and homogeneous copper film, but an excess of thiourea could cause parasitic adsorption reactions on the surface of the substrate. X-ray fluorescence spectroscopy was used for the thickness determination of the copper deposits and the electrodeposition efficiency correlated to thiourea concentration. Finally, the optimal concentration of thiourea was assessed to be 60 ppm for the used formulation of copper plating.