Publications

Abstract <jats:p>The production of useful chemicals by electroreducing CO2 it is a promising approach to reduce the levels of this greenhouse gas in the atmosphere. This is not a straightforward process due to the high stability of the CO2 molecule and low selectivity however, these barriers can be overcome by using an appropriate catalyst. This research focus on the effect of pre-treating the carbon supports before incorporating the catalyst on the electroreduction of CO2. We found that the electrochemical behaviour of the carbon supports is modified by the nature of the pre-treatment used. From the structure perspective, the results showed partial destruction of the carbon structure mainly after the oxidative treatments nevertheless, the introduction of defect sites in the carbon structure contributed to catalyst performance. This improvement was proved by the LSV data that showed the reduction of the current associated with the hydrogen reduction reaction.</jats:p>

Abstract An alternative route is proposed for direct electrodeposition of TiO2 films. The electrochemical behaviour of Ti (IV) species in the deep eutectic solvent formed between choline chloride (ChCl) and ethylene glycol (EG) was studied by chronoamperometry and cyclic voltammetry. It was discussed that during the cathodic scan soluble subvalent TiCl chi species were formed using the eutectic system 1ChCl:2EG. Using ethylenediamine or LiF as additives it was possible to obtain a titanium dioxide thin film in the orthorhombic variant named brookite. Chronoamperometric investigations revealed a nucleation mechanism involving the simultaneous presence of 2D instantaneous nucleation process including lattice incorporation and a 3D diffusion-limited nucleation and growth process.

Abstract The effect of the addition of a group of organic additives on the electrodeposition behavior of zinc was investigated in choline chloride:ethylene glycol (ChC1:EG) eutectic mixture in the molar ratio of 1:2. Cyclic voltammograms recorded on steel electrode showed a cathodic peak is only observed after reversing of the scan. Chronoamperometric measurements indicated that the deposition of zinc occurs through 3D progressive nucleation mechanism. The morphology of the zinc deposits and was evident that additives influence the deposits morphologies. X-ray diffraction confirmed the presence of crystalline zinc and reveal the grain refinement effect obtained by using the additives selected where the smallest grain size of 31.7 nm was obtained in the presence of Dimethyl sulfoxide (DMSO). Moreover the XRD data showed that the addition of additives modified the preferential growth plane. The corrosion resistance properties of the electrodeposited Zn coatings were evaluated in 3% NaCI aqueous solution using potentiodynamic polarization. The results showed that the zinc film deposited with DMSO was the best corrosion resistant coating.

Abstract Co-Sn alloy films were electrodeposited from choline chloride (ChC1)-ethylene glycol (EG) and choline chloride (ChCl1)-urea (U) eutectic mixtures. The deposition of Co-Sn alloy on a copper electrode was studied by cyclic voltammetry, which demonstrates that the coelectrodeposition was achieved. For comparison of properties, Co-Sn alloys were deposited from electrolytes with different Co/Sn ratios. The X-ray diffraction patterns (XRD) showed that the phase structure was affected by the Co/Sn ratio; nevertheless, Co3Sn2 was always the predominant phase. Traces of metallic cobalt were also detected. The nature of the electrolyte used and the metallic composition affected the morphologies of the deposits and their corrosion resistance. The best corrosion resistant coating, with a corrosion potential of -617 mV, was composed by 44.4 wt % of Co and 55.6% of Sn, and it was obtained from the ChCl-EG electrolyte. The magnetic properties of the analyzed samples did not present an evident relationship with the metallic ions ratio in solution.

Abstract The paper presents experimental results regarding the electrodeposition and characterization of cobalt and cobalt composites with carbon nanotubes from a choline-chloride-based deep eutectic solvent. Dispersion stability of multi-walled carbon nanotubes (MWCNTs) was excellent in the eutectic solvent used. According to Raman and XRD analysis, the carbon nanotubes were successfully inserted into the metallic matrix. Furthermore, XRD results suggested that the incorporation of CNTs on the deposit promoted a preferred orientation of the Co crystallites on (220) plane. The Co and Co-composites coatings obtained onto a copper substrate are adherent and uniform. Pure Co deposit was formed by sharp edge grains, Co-composites appeared to be less compact and formed by relatively spherical particles connected by MWCNTS. Furthermore, it was found that the presence of MWCNTs contributed to decreasing the deposit's roughness. From corrosion tests, Co-composite films exhibit a comparable or slightly better corrosion performance as compared to pure Co films.

Abstract The deposition of Mn and Mn-Sn alloy from two deep eutectic solvents (DES) was investigated. Pure Mn deposits were powdery and amorphous regardless the DES used. In contrast, the manganese-tin deposits obtained from the two DES used were adherent. The morphology of the deposits obtained from the different DES was analyzed by SEM, which showed that pure Mn films were fibrous. The morphology of Mn-Sn deposits changed upon changing on the amount of tin in solution or the DES used. The phase composition of the Mn-Sn films were investigated by X-Ray diffraction, which showed that the deposits were formed by different MnxSny intermetallic phases. The metallic content in the deposit changed upon changing the bath composition or the DES used. Using the urea (U) based DES Mn-Sn deposits with a Sn content between 1.8 and 6.7 wt% were obtained. In contrast, using the ethylene glycol (EG) based DES the Sn content in the deposits varied between 33.2 and 59.0 wt%.

Abstract Zn alloys are considered an alternative to replace Cd in protective coatings. Among Zn alloys, Zn-Ni are those with the higher corrosion resistance and better mechanical characteristics. Although Zn-Ni alloy can be electrodeposited from eutectic-type ionic liquid the morphology of the deposits needs to be improved. The effect of ethylamine and ethylenediamine on the electrodeposition of Zn-Ni alloy was investigated from a eutectic-type ionic liquid (ethaline). The presence of the amines in the plating bath modified the CV and j-t profiles. The nucleation mechanism was also influenced by adding the amines to the solution and the deposition of Zn-Ni in the presence of ethylenediamine followed the 3D progressive mechanism. Electrodeposition of Zn-Ni alloy from ethaline gives origin to a deposit with small grain particles with partial coverage of the electrode. Using the same electrodeposition conditions, the addition of amines allowed the full coverage of the electrode surface. In the presence of ethylamine deposit was formed by globular particles and by hexagonal platelets for deposits obtained in the presence ethylenediamine. Corrosion of the Zn-Ni metallic films was evaluated by potentiodynamic polarization experiments. The lowest value for the corrosion potential was obtained for the deposit prepared in the presence of ethylenediamine.

Abstract In this work we present a fundamental study of the electrodeposition of tin from Deep Eutectic Solvents (DES) formed by a mixture of choline chloride and different hydrogen bond donors (HBD). Results shows that choline chloride based solvents can be successfully used for the electrodeposition of tin. Furthermore we demonstrate that the choice of hydrogen bond donor does not affect, significantly, the chemistry of tin in solution and we characterize the first stages of tin deposits at glassy-carbon (GC) electrode. The electrochemical characterization of tin deposits is carried out using cyclic voltammetry and chronoamperometry. The comparison of the theoretically and experimentally obtained current transients via dimensionless plots based on Bewick-Fleischman-Thirsk (BFT) theory, Scharifker and Hills (SH) and Scharifker and Mostany (SM) models and a non-linear fitting method showed that tin nucleation on GC surface occurs though a 3D instantaneous process with growth controlled by diffusion.

Abstract The use of deep eutectic solvents for metal electrodeposition has become an area of interest in the recent years. In this study, ethaline, propeline, and reline were used as solvents for the electrodeposition of Sn-Zn alloys. Ethaline, propeline, and reline displayed identical voltammetric profiles for the reduction of Zn(II) and Sn(II). Further studies were carried out in ethaline which is the liquid with lowest viscosity. To improve physical and morphological properties of the Sn-Zn deposits, additives were added to the ionic liquid solution. In this study, the addition of three chelators (EDTA, HEDTA, and Idranal VII) and their effects on the voltammetric behavior of zinc and tin and the resultant morphology was described. The structure and composition of the Zn-Sn deposit was largely affected by the additives with the largest effect being obtained in the presence of Idranal VII.

Abstract The use of additives for the electrodeposition from deep eutectic solvents is still an unexplored area however of the upmost importance to understand the role of additives in metal electrodeposition in new media such as DES. In this study we describe the effect of three additives with complexing properties and their effect on the voltammetric profile of tin and the deposit morphology. It is shown that EDTA and HEDTA do not alter the voltammetric profile of tin. In contrast the addition of Idranal VII has a pronounced effect the voltammetric behavior of tin and in the tin deposit morphology.