Liana Anicai

Electrodeposition of Co and CoMo alloys coatings using choline chloride based ionic liquids - evaluation of corrosion behaviour

This study deals with the electrodeposition of Co and CoMo alloys from various ionic liquids based on choline chloride (ChCl) – urea and ChCl – ethylene glycol eutectic mixtures. The Co and Co–Mo (with 1–8 wt-% Mo content) deposits obtained were adherent, compact and uniform onto copper substrates. A decrease of the Mo content in the alloy has been shown as the applied current density increased in the range of 7–25 mA cm−2, at 90–100°C. Some peaks assigned to MoO3 or Co3Mo phases have been identified in the XRD patterns. The average size of crystallites has been estimated to be in the range of 7–9.2 nm (nanocrystalline deposits). Atomic Force Microscopy analysis gave evidence that Co deposits were formed by multiple compact almost rounded crystallites, while Co–Mo alloy ones consisted of multiple relatively compact grains with cylindrical shape. The coatings’ corrosion performance has been also measured by continuous immersion testing in 0.5M NaCl solution, and potentiodynamic polarisation and electrochemical impedance spectra.

Studies Regarding the Nickel Electrodeposition from Choline Chloride Based Ionic Liquids

The electrochemical technologies are extensively applied in a large range of industrial fields, from decorative/protective coatings in electrical engineering, electronics, automotive or machine building domains towards the manufacturing of microelectronic components, of micro-electro-mechanical systems (the so-called MEMS) or of the high precision microand nanostructures, including biological ones (Data & Landolt, 2000; Gurunathan et al., 1999). Due to the fact that electrochemical deposition is an atomic/molecular level process, the formed layer entirely takes the three-dimensional shape of the substrate with a very high accuracy. As a result of the last years scientific progress, the theoretical aspects of electrochemical engineering principles applicable for electrochemical micro-processing have significantly developed so that, associated with performance techniques and equipment lead to the new and innovative materials development having controlled microor nanostructures. In spite of a long history and experience, the metals surface finishing industry still has not been successful in extending the range of the metals able to be electrodeposited towards some of them with a promising technical potential, such as Al, W, Mo, Ti. Their capability to form stable oxides represents an obstacle against their application as coating layers, especially from classical aqueous electrolytes. Moreover, in the last decade sustained efforts have been made to preserve the environment and to minimize the toxic effects of certain electrochemical technologies on human health. Thus, certain metallic coatings have been and still are subjected to some use restrictions such as Cr, Ni, but Cu, Ag and Au as well, due to the involvement of aqueous cyanide electrolytes. Taking into account the above mentioned considerations, in the last 10 years investigations to develop and promote alternative more environmentally friendly electrochemical media have been reported, including the class of the so-called “ionic liquids”, defined as “ionic materials in liquid state for temperatures lower than 100oC” (Endres et al., 2008; Wasserscheid & Welton, 2007). The ionic liquids have some properties which make them adequate as metal electrodeposition electrolytes, such as:

Ni–Mo alloy nanostructures as cathodic materials for hydrogen evolution reaction during seawater electrolysis

In the case of hydrogen production involving seawater electrolysis, one of the main targets is to develop more active cathodic materials, to optimize the efficiency of hydrogen evolution reaction (HER) and, by doing so, enhance the overall energy efficiency of electrolysis. Thus, to develop suitable HER electrocatalysts either an increase of the electrode active surface area or a design of a material having high intrinsic catalytic activity should be taken into consideration, both of them decreasing the HER overpotential. In the present work, various Ni–Mo alloy nanostructures (10–40 wt% Mo) have been prepared involving electrochemical deposition from aqueous and deep eutectic solvent (DES)-based electrolytes as potential cathodic materials suitable for hydrogen evolution reaction during water electrolysis. The electrocatalytic activity of the obtained layers has been investigated using real seawater electrolyte. The determined Tafel slopes suggested that the electrodeposited Ni–Mo alloy coatings follow an HER mechanism controlled by the Volmer reaction step. The EIS results indicated that the use of choline chloride-based ionic liquids as electrolytes facilitated Ni–Mo alloy coatings showing a significant increase in surface roughness. Studies of the intrinsic activity showed that the main contribution towards the apparent activity comes from the increase of the real surface area, although a slight increase of the intrinsic electrocatalytic activity in the case of Ni–Mo alloy coatings electrodeposited on Ni foam was also noticed. These results showed that Ni–Mo alloy coatings electrodeposited from the novel electrolytes based on choline chloride–urea–citric acid ternary mixtures associated with a porous substrate may represent a promising technological approach to build cathodic materials suitable for seawater electrolysis.

Polypyrrole Films Doped with Phosphomolybdate Anions on Al Surfaces – Formation and Corrosion Protection Characterisation

Abstract The present paper deals with some preliminary experimental results regarding electrodeposition of polypyrrole films doped with phosphomolybdate anions onto Al substrates involving an initial anodizing in nitric acid electrolyte; early studies proved that this stage offers a very good adherence of the further layer on Al surfaces. The phosphomolybdate doped polypyrrole films have been formed both galvanostatically and involving cyclic voltammetry, in aqueous solutions containing phosphomolybdic acid and pyrrole. In several experiments Tiron (4,5-dihydroxy-1,3-benzenedisulfonic acid disodium salt) has been added, acting as mediator and improving the layer morphology and aspect. The films exhibited a very good adherence on the metallic substrate, with a uniform black color and showed classical cauliflower morphology, more dense and ordered in the presence of Tiron, according to SEM investigations. Raman spectroscopy and EDX analysis revealed the presence of doping anion within polypyrrole layer. Also EDX measurements suggested that the film incorporates a 1 : 9 ratio of phosphomolybdate anion to PPy units. When both Tiron and phosphomolybdate anions are present in the solution, phosphomolybdate and other related anions are preferentially incorporated within the layer. Based on the continuous immersion test in NaCl 0.5M solution for 240 h, the phosphomolybdate entrapping into the polymer matrix was shown to provide a better corrosion protection in chloride medium.