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The effects of nicotinic acid (NA), boric acid (BA) and benzoquinone (BQ) on the electrodeposition of Zn have been studied in a choline chloride (ChCl) ethylene glycol (EG) based deep eutectic solvent (DES), (1ChCl:2 EG), and for the first time a bright zinc coating has been achieved when NA was used. In metal electroplating processes, small-molecule additives are often included in the plating bath to improve properties of coating such as brightness, roughness, thickness, hardness and resistance to corrosion. The effects of additives on the electrodeposition of Zn from aqueous solution have been extensively investigated. However, very few studies have considered the effects of additives on the electrodeposition of Zn from ionic liquids or deep eutectic solvents. The electrochemical properties of the plating liquid have been studied here using cyclic voltammetry, chronocoulometry, chronoamperometry and microgravimetry (EQCM). Redox peak currents decrease when additives were included in the Zn solution and total charge was also reduced in experiments where additives were present. The Zn deposition in the absence of additive is in good agreement with an instantaneous growth mechanism at short experimental time scales (being indeterminate over longer periods), however, this changes to one of a progressive growth mechanism when additives were included in the coating bath. The current efficiency of zinc deposition in the DES without additives was 95%, which was reduced when additives were included. The resultant surface morphologies, thickness, topography, roughness and crystal structure of the Zn coating were revealed by scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD), demonstrating that those additives serve as effective brighteners that can produce highly uniform and smooth zinc deposits.

Electrodeposited conducting polymer films derived from aromatic monomers are known to possess properties that depend significantly on the deposition protocol, particularly the electrochemical control function employed. This study explores the underlying reasons for this common observation for the specific case of polypyrrole films deposited from aqueous media onto gold electrodes under potentiostatic, potentiodynamic and galvanostatic control. Although the control functions impose different conditions, the control parameters (potential, potential range and scan rate, and current) were selected so as generate films at comparable rates; this avoids inappropriate attribution of structural and compositional variations to different thickness regimes, irrespective of how they were generated. In each case, film deposition was periodically interrupted and the film characterised by specular neutron reflectivity measurements. By using d4-pyrrole monomer in H2O solvent, the isotopic selectivity of neutron reflectivity was used to extract polymer and solvent concentration profiles as a function of distance from the electrode/film interface. Spatial integration of these profiles was used to quantify total film solvent populations; these are expressed as solvent volume fractions. Films grown under the three different control regimes have measurably distinct solvent volume fraction profiles and there is evolution of these profiles with increasing thickness. Ultimately, for the conditions employed, the order of increasing porosity (i.e. solvent content) by control function was potentiostatic

Deep eutectic solvents (DESs) are mixtures of quaternary ammonium halides with hydrogen bond donors and are increasingly being used in applications where they are in contact with metals. This study investigates the corrosion of iron, nickel and aluminium in DESs. It shows that none of the metals show significant corrosion when glycerol is used as a hydrogen bond donor but when an acidic hydrogen bond donor such as oxalic acid is used, both iron and aluminium show catastrophic corrosion as may be expected. Surprisingly, however, nickel does not corrode in the acidic DES, Oxaline. The differences in corrosion observed for aluminium and iron are explained in terms of passivating films and the slowness of the oxygen reduction reaction despite the relatively high gas solubility. The high chloride ion content (roughly 4 mol dm−3) has a relatively small effect on the corrosion of the three metals. The formation of a passive layer as a result of hydrogen bond donor-metal ion complexes is shown to be more important. It is proposed that the low corrosion rates of some metals resulted from the slow rate of the cathodic reaction resulting from the high viscosity, low activity of water and low proton mobility.

The electropolymerisation of aniline is a well-studied and often used technology. While the mechanism has been investigated in a variety of media these have all concentrated on understanding the process on a molecular level. Anomalies in the electropolymerisation of aniline in four deep eutectic solvents, DESs, using urea, ethylene glycol, glycerol and oxalic acids as hydrogen bond donors with choline chloride led to an investigation of the aniline phase behaviour. It was only with oxalic acid that polymerisation was achieved and adjusting the pH of the other DESs using sulphuric acid did not enable polymer formation suggesting that pH was not the only factor enabling polymer growth. When 10 wt% water was added, polymers could be grown in all the DESs despite negligible change in solution pH. Dynamic light scattering showed that polymer only formed in systems where aniline formed an emulsion. Scanning electron microscopy, SEM and atomic force microscopy, AFM showed that the polyaniline films were formed of an agglomeration of small particles of the same dimensions as the dispersed monomer phase in solution. This suggests that the droplets of the monomer arrive at the electrode surface where they polymerise. This provides the first evidence that polyaniline grows by an emulsion polymerisation mechanism even in aqueous solutions.

Metal electrodeposition using ionic liquid electrolytes and deep eutectic solvents is now well known but to our knowledge for electrolytic deposition of metals such as nickel no direct comparison has thus far been drawn between deposition using aqueous solutions and DES under otherwise identical conditions. In the current study it is shown that nickel deposition can be carried out with similar deposition rates in aqueous and ionic media despite the significant differences in viscosity and conductivity. It is, however, shown that in ionic media the morphology of the deposits is markedly different from that achieved using a Watts nickel bath and that one aspect of these differences manifests itself in significant increase in the coating hardness. It is proposed that the observed morphology differences occur due to the variations of nickel speciation in each electrolyte environment.

The electrochemical quartz crystal microbalance (EQCM) and probe beam deflection (PBD) have been widely used to study interfacial processes in molecular solvent-based electrolytes. However, there has been limited use of the EQCM and none of PBD in room temperature ionic liquids, including deep eutectic solvents (DES). Here we explore the use of the combined EQCM/PBD technique to the study of Ag and Sn electrodeposition from a DES comprising a 1:2 mixture of choline chloride and ethylene glycol. While overcoming the effect of viscous loss in the acoustic wave (EQCM) part of the experiment is understood, the optical (PBD) technique fails to provide a meaningful response in slow scan rate voltammetric experiments; this contrasts sharply with the straightforward behaviour seen in aqueous media. Solution transport considerations reveal this to be a consequence of long surface-to-beam transit times in the viscous DES. The problem can be overcome by operating at scan rates 1-2 orders of magnitude slower, permitting application of this powerful technique to novel media of technological interest. The PBD responses reveal unanticipated chemical effects: multiple complexes in the Ag system and solubility limitations in the Sn system, neither of which is evident from the electrochemical or QCM responses.

Mechanistic studies are reported for redox switching (doping/undoping) of Au-supported poly(3,4-ethylenedioxythiophene) (PEDOT) films exposed to LiClO 4 /CH 3 CN (a conventional electrolyte based on a molecular solvent) and to Ethaline and Propaline (two choline chloride-based deep eutectic solvent (DES) media). A combination of electrochemical, acoustic (quartz crystal microbalance, QCM) and optical (probe beam deflection, PBD) methods was used to monitor the exchange of mobile species between the film and the bathing electrolyte. Qualitatively, film responses to a potentiodynamic control function showed that the redox switching mechanisms are quite different in all three media. When exposed to acetonitrile, anion transfer is dominant, with some accompanying solvent transfer but negligible cation transfer; application of the convolution protocol allowed these transfers to be quantified. Analogous observations in the DES media could be interpreted qualitatively in terms of dominant cation transfer, but the convolution protocol could not be used to quantify the contributions of individual species; in these viscous media, this is a consequence of the long transit times from the film/solution interface to the optical detection zone. Chronoamperometric experiments, in which the measurement time was an order of magnitude (or more) longer permitted the diffusional processes driven by the polymer/DES interfacial population changes to reach the optical detection zone.

The electrodeposition of metals using ionic liquids has received considerable attention during the last ten years. Recent developments have taken these novel electrolytes from laboratory to commercial scale. One of the factors limiting the development into practical plating systems is the understanding of how brighteners function. In this study we describe the addition of three polar additives and their effect upon the nucleation mechanism of zinc and the resultant morphology. It is shown that the structure of the zinc deposits is controlled by double layer properties and it is proposed that the brightening effect of ethylene diamine and ammonia are caused by their ability to inhibit the adsorption of chloride at the electrode surface. The deposition of most metals using ionic liquids results in apparently amorphous deposits, which tend to be actually nano-crystalline. The additives used in this study produce macro-crystalline deposits, which resemble those obtained from aqueous solutions.

Crown ether functionalised conducting polymer films were used to complex barium ions from acetonitrile solution. It was found that fully-functionalised N-derivatized polypyrrole films do not possess adequate mechanical stability, but dilution with unfunctionalised bithiophene co-monomer leads to a series of copolymer films with excellent stability. Film reactivity, composition and structure were investigated using electrochemical, nanogravimetric, FTIR, XPS and neutron reflectivity techniques. The first three of these provided spatially integrated barium populations and neutron reflectivity provided spatially resolved compositional profiles. Measurements at various stages of film fabrication yielded spatial distributions of co-monomer, crown ether, solvent and barium (as perchlorate) components. Critically, the amount of free volume to accommodate crown motifs and barium within the film was limited by the film's internal microstructure and solvent content; the low solvent volume fraction creates a different local environment to solution.

We demonstrate the first practical alternative to the use of phosphoric and sulphuric acid mixtures for the electropolishing of stainless steel. In this paper, efficient electropolishing of type 316 stainless steel is demonstrated in an ionic liquid composed of ethylene glycol (HOCH2CH2OH) and choline chloride (HOC2H4N(CH3)3+Cl−). Linear sweep voltammetry, chronoamperometry, scanning electron microscopy, atomic force microscopy and AC impedance methods were used to investigate the steel dissolution mechanism and the results are compared to polishing done in aqueous acidic solutions. It is shown that the quality of the polish is related to the breakdown of the oxide film and preliminary data suggest that the polishing process may be controlled by the diffusion of chloride ions. The dissolution is different from that found in aqueous acid solutions, and oxide breakdown is shown to be slower, which can lead to pitting at low current densities.