Synthesis of Silver Gallium Selenide (AgGaSe2) Nanotubes and Nanowires by Template-Based Electrodeposition.

In this work, a systematic investigation of the different parameters that control the electrodeposition processes was carried out at the aim to synthetizing AgGaSe2 nanostructures. We found that pH is a key parameter to control both the morphology and composition of the nanostructures. Low pH favours mainly the formation of Ag2Se nanotubes with a scarce mechanical stability, while multi-phase nanowires well anchored to the substrate were obtained at higher pH. We also found that it was necessary to increase dramatically the concentration of the gallium precursor into the deposition bath in order to obtain AgGaSe2 owing to lower redox potential of the Ga3+/Ga couple than Ag2+/Ag and Se4+/Se. Besides, the addition of specific complexing agents to deposition bath was necessary to better control the composition of the nanostructures. By increasing gallium precursor concentration and adding complexing agents, it was possible to obtain for the first time nanostructures of amorphous AgGaSe2 with different amount of Ga via one-step electrodeposition.

Behavior Modification of Nanostructured PbO2 Electrodes in Lead Acid Batteries Changing Electrolyte Concentration and Separator.

Currently, lead acid battery is extensively investigated owing to its prevalent use as a startinglighting and ignition device. An essential role for electrochemical reactions is played by the surface area available for conversion reactions and a possible approach is the use of nanostructured electrodes. In this work, lead dioxide nanostructured electrodes were tested in order to investigate the dependence of the charge and discharge behaviour on some parameters such as electrolyte concentration, and a new type of thin separator. In this last case, it is possible to reduce the size of the cell by using a very thin separator comparable to the nanostructured electrode thickness. Besides, a low concentration of electrolyte was also tested for studying its influence on the performance of a nanostructured electrode. Lead dioxide electrodes were cycled at 1C-rate and discharged to a cutoff voltage of 1.2 V up to 90% of the gravimetric capacity. Electrodes were assembled in a zero gap configuration using a commercial negative plate as counter-electrode with a large excess of active mass in comparison to the nanostructured one. Tests were conducted in very stressful conditions, in order to compare the behaviour of this new type of battery with that of the commercial one.

Pb-PbOHCl Composite Nanowires Synthesized by Galvanic Deposition in Template.

In this paper, we report a detailed study on the synthesis of composite nanowires of Pb-PbOHCl via galvanic deposition into the pores of a membrane acting as a template. PbOHCl deposition quantitatively occurs as the solution pH exceeds the value of about 4.12. Simultaneously, owing to the galvanic coupling, electro-deposition of lead occurs, so composite nanowires were formed. The role of different parameters controlling the kinetic evolution of the process, such as oxygen bubbling, solution pH, surface area and type of sacrificial anode were investigated one at a time. The results suggest that every modification accelerating the alkalization of the solution inside the template pores favors growth of composite nanowires richer in PbOHCl. Alumina and polycarbonate membranes were investigated as template, and the best results were obtained for polycarbonate membrane, which can be easily removed by dissolution in CHCl3 avoiding the collapse and successive loss of the nanowires.

Nanostructured Based Electrochemical Sensors.

In this work, we present some results concerning the electrochemical behavior of nanostructured-based electrochemical sensors. In particular, the attention has been focused on Pd and Cu nanowires for detection of hydrogen peroxide and NiO thin film or Ni@NiO core-shell nanowires for detection of mercury ions. Ordered array of Pd and Cu nanowires was obtained through displacement deposition reaction in a commercial polycarbonate membrane acting as a template. The method leads to stable nanostructured electrodes of Pd and Cu with high surface area. For the detection of mercury ions, we have fabricated a Ni/NiO electrochemical sensor, obtained by mild thermal oxidation of Ni-foil. Some results on Ni@NiO core-shell nanowires were also reported. The effect of oxidation time and temperature was studied in order to compare performances of the Ni@NiO nanowire array with those of NiO thin film. All samples were characterized by XRD, SEM and EDS analysis. Electrochemical tests have been conducted in order to characterize specific electrode performance such as sensibility, selectivity, and accuracy. Highly satisfying results have been obtained.

Chitosan-Coating Deposition via Galvanic Coupling.

A galvanic method to deposit chitosan coatings on stainless steel substrate is reported. Deposition of suitable coatings is desired to improve biocompatibility and corrosion resistance of metallic medical devices to be implanted in human body. In the present work, a thin hydrogel layer of chitosan was deposited on 304SS by a galvanic displacement reaction, which is advantageous first as it does not require external power supply. 304SS was immersed into an aqueous solution of chitosan/lactic acid and electrochemically coupled with magnesium acting as a sacrificial anode. SEM images showed the formation of a uniform layer of chitosan with a thickness controlled by deposition time. Corrosion tests in simulating body fluid showed that chitosan coatings shift the corrosion potential of 304 substrates toward nobler values. Finally, the cytotoxicity of the coating was investigated through cell viability assays with osteoblastic cell MC3T3-E1. The results revealed highly satisfying biocompatibility of the coating.

Galvanic deposition and characterization of brushite/hydroxyapatite coatings on 316L stainless steel.

In this work, brushite and brushite/hydroxyapatite (BS, CaHPO4·H2O; HA, Ca10(PO4)6(OH)2) coatings were deposited on 316L stainless steel (316LSS) from a solution containing Ca(NO3)2·4H2O and NH4H2PO4 by a displacement reaction based on a galvanic contact, where zinc acts as sacrificial anode. Driving force for the cementation reaction arises from the difference in the electrochemical standard potentials of two different metallic materials (316LSS and Zn) immersed in an electrolyte, so forming a galvanic contact leading to the deposition of BS/HA on nobler metal. We found that temperature and deposition time affect coating features (morphology, structure, and composition). Deposits were characterized by means of several techniques. The morphology was investigated by scanning electron microscopy, the elemental composition was obtained by X-ray energy dispersive spectroscopy, whilst the structure was identified by Raman spectroscopy and X-ray diffraction. BS was deposited at all investigated temperatures covering the 316LSS surface. At low and moderate temperature, BS coatings were compact, uniform and with good crystalline degree. On BS layers, HA crystals were obtained at 50°C for all deposition times, while at 25°C, its presence was revealed only after long deposition time. Electrochemical studies show remarkable improvement in corrosion resistance.