No abstract

Electrochemical deposition was studied as a potentially scalable method for the preparation of Pt-rare earth alloys for application as cathode catalyst in proton exchange membrane fuel cells. For this purpose, experiments both on electrodeposition of platinum and of the rare earth elements yttrium and lanthanum were carried out in two different types of ionic liquid. While the electrodeposition of platinum was successful in both liquids, the deposition of the rare earth metals was more challenging. The deposition of Y in a TFSI based liquid was prevented by electrode passivation, while in a BF4 -liquid no passivation was seen, but also no clear indication of a deposition process was seen. For La, there was deposition using different precursors, but only at very low deposition rates. The nature of the deposit could not yet be unequivocally determined. Initial attempts in alloy deposition were not successful.

Ionic liquids have found widespread applications in electrochemistry, and are increasingly used in the field of electrochemical energy conversion and storage. In battery technology, the use of ionic liquids can increase the device safety significantly and help in enabling alternative technologies like Mg ion batteries. In fuel cell technology, new, water-free proton conducting membranes and new options for synthesis and improvement of catalysts are in the focus of research. In this paper some applications, advantages and drawbacks of ionic liquids in electrochemical energy technology are reviewed. Some examples from the authors' own work in batteries and electrocatalysis using standard electrolytes are presented, and the potential improvements by using ionic liquids in these studies are discussed.

In the electrochemical deposition of Tantalum from ionic liquids at moderate temperatures, the preparation of purely metallic coatings with thicknesses in the micrometer range and the accurate control of the crystallographic parameters remain challenging. In this work, preliminary experiments on the influence of fluid dynamics during the electrodeposition of tantalum in the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl) imide using ultrasound as an additional source of energy were carried out. This included a study on the influence of the ultrasound amplitude on the deposition rate of tantalum by using cyclic voltammetry and the in-situ electrochemical quartz crystal microbalance technique.

Platinum rare earth alloys show several times higher electrocatalytic activity for the oxygen reduction reaction than pure platinum while still maintaining an excellent stability. However, the high reactivity of rare earth elements makes the preparation of such alloys with scalable methods challenging. The electrodeposition from ionic liquids seems to be a possible route. In this work, we demonstrate the electrodeposition of the rare earth metal gadolinium from the ionic liquid butylmethylimidazolium dicyanamide at elevated temperatures. The deposition of Pt metal from this ionic liquid has been studied using several different precursors.

No abstract

This contribution discusses the application of ultrasound in ionic liquids (ILs) and its effect on refractory metal deposition as well as the particular electrochemistry of NbCl5 in TFSI based ILs. A systematic study was carried out studying electrochemical reactions and electrolyte decomposition in the presence of ultrasound. Extended application of ultrasound induced partial IL decomposition and formation of solid precipitates. Electrochemical reactions in ILs were enhanced by ultrasound application. Especially the application of short ultrasound pulses at elevated temperatures increased electrochemical reaction rates. The reduction of NbCl5 from BMP and OMP TFSI ILs is characterized by five separate distinct reduction and corresponding oxidation steps. This system was studied in depth using the electrochemical quartz crystal microbalance technique, revealing strong changes in the electrolyte properties close to the interface.

The deposition of platinum from precursors dissolved in the ionic liquid 1-methyl-1-octylpyrrolidinium bis(trifluoromethylsulfonyl) imide (OMP-TFSI) was the main scope of this study. Boron doped diamond (BDD) and Au electrodes on quartz resonators were used as the substrates. A typical Pt deposition on BDD and Au was accomplished by applying short electrical pulses followed by relaxation phases for different duration in order to find optimal deposition conditions. In order to prove whether Pt was deposited on the electrode, samples were cycled in 0.1 M H2SO4 after deposition. In addition to electrochemical parameters, in the experiments on Au, the electrochemical quartz crystal microbalance permitted to monitor directly changes in the resonance frequency and damping associated with the Pt ion reduction processes. The development of inexpensive fuel cells requires preparation of catalysts by scalable and inexpensive methods. For normal Pt-transition metal alloys, this can be accomplished