Tetrafluoroborate . electrodeposition

The electrodeposition of Ag has also been intensively investigated [41 3]. In the chloroaluminates - as in the case of Cu - it is only deposited from acidic solutions. The deposition occurs in one step from Ag(I). On glassy carbon and tungsten, three-dimensional nucleation was reported [41]. Quite recently it was reported that Ag can also be deposited in a one-electron step from tetrafluoroborate ionic liquids [43]. However, the charge-transfer reaction seems to play an important role in this medium and the deposition is not as reversible as in the chloroaluminate systems. 

Wilkes launched the field of air- and moisture-stable ionic liquids by introducing five new materials, each containing the Tethyl-3-methylimidazolium cation [EMIMJ+ with one of five anions nitrate [NC>3], nitrite [NO2]-, sulfate [SC>4]2, methyl carbonate [CH3CO2]- and tetrafluoroborate [BF [47]. Only the last two materials had melting points lower than room temperature, and the reactive nature of the methyl carbonate would make it unsuitable for many applications. This led to the early adoption of [EMIM][BF4] as a favored ionic liquid, which has since been the subject of over 350 scientific publications. One of the first appeared in 1997 [50], reporting the investigation of [EMIM][BF4] as the electrolyte system for a number of processes, including the electrodeposition of lithium (intended for use in lithium ion batteries). 

Palladium is employed in a number of industrial applications and fundamental studies because of its high catalytic activity for many chemical reactions, e.g. its ability to absorb hydrogen [41], On the other hand, due to hydrogen absorption, only brittle Pd deposits can be obtained in aqueous solutions. The advantage of performing electrodeposition of Pd in ionic liquids is that hydrogen evolution does not occur. Sun et al. demonstrated that Pd and some of its alloys, namely Pd-Ag [42], Pd-Au [43] and Pd-In [44], can be obtained from the basic l-ethyl-3-methylimidazolium chloride/tetrafluoroborate ionic liquid. Compact alloy deposits were obtained and the Pd content in the deposits increased with the increase in Pd mole fraction in the plating bath. 

The electrodeposition of silver from chloroaluminate ionic liquids has been studied by several authors [45-47], Katayama et al. [48] reported that the room-temperature ionic liquid l-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM]BF4) is applicable as an alternative electroplating bath for silver. The ionic liquid [EMIM]BF4 is superior to the chloroaluminate systems since the electrodeposition of silver can be performed without contamination of aluminum. Electrodeposition of silver in the ionic liquids 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4) and l-butyl-3-methylimidazoliumhexafluorophosphate was also reported [49], Recently we showed that isolated silver nanoparticles can be deposited on the surface of the ionic liquid Tbutyl-3-methylimidazolium trifluoromethylsulfonate ([BMIMJTfO) by electrochemical reduction with free electrons from low-temperature plasma [50] (see Chapter 10). This unusual reaction represents a novel electrochemical process, leading to the reproducible growth of nanoscale materials. In our experience silver is quite easy to deposit in many air- and water-stable ionic liquids. 

Antimony is a brittle silvery-white metal. Although the unalloyed form of antimony is not often used in industry, alloys of antimony have found wide commercial applications. The integration of antimony gives certain desirable properties, such as increased corrosion resistance and hardness. Moreover, antimony is also the component of some semiconductors such as InSb and InAsi %Sb%. Sb electrodeposits with good adherence were obtained in a water-stable l-ethyl-3-methylimidazolium chloride-tetrafluoroborate ([EMIM]C1-BF4) room-temperature ionicliquid [53]. Furthermore, it was stated that a crystalline InSb compound can be obtained through direct electrodeposition in the ionic liquid [EMIM]C1-BF4 containing In(III) and Sb(III) at 120 °C [54]. It is just a question of time until antimony electrodeposition is reported in the third generation of ionic liquids. 

CdTe, a II—VI compound semiconductor with a direct band gap of 1.44 eV at room temperature, is, from its physical properties, a promising photovoltaic material. The electrodeposition of CdTe in ionic liquid was published recently by Sun et al. [38]. They were able to show that the semiconductor can be electrodeposited at elevated temperature (above 120 °C) in the Lewis basic l-ethyl-3-methylimidazolium chloride/tetrafluoroborate ionic liquid containing CdCh and TeCU. CdTe films were obtained by the underpotential deposition (UPD) of Cd on the deposited Te. The deposit composition was independent of the deposition potential within the Cd UPD regime. The crystallinity of the deposits is improved by increasing the deposition temperature, which again demonstrates the high potential of the wide thermal windows of ionic liquids for compound electrodeposition. 

The electrodeposition of several metals and alloys has been investigated in tetrafluoroborate ionic liquids. In contrast to the chloroaluminate ionic liquids, the tetrafluoroborate ionic liquids are considerably more stable against moisture and are expected to be applicable to practical use. Moreover the co-deposition of... 

The electrodeposition of silver, Ag, has been reported in a neutral EMIBF4 ionic liquid [80]. Silver tetrafluoroborate, AgBp4, dissolves in the ionic liquid up to about... 

Hsiu SI, Tai CC, Sun IW (2006) Electrodeposition of paUadium-indium from l-ethyl-3-methylimidazoUum chloride tetrafluoroborate ionic liquid. Electrochim Acta 51 2607-2612... 

Tai CC, Su FY, Sun IW (2005) Electrodeposition of palladium-silver in a Lewis basic 1-ethyl-3-methyUmidazolium chloiide-tetrafluoroborate ionic liquid. Electrochim Acta 50 5504-5509... 

Yang MH, Yang MC, Sun IW (2003) Electrodeposition of indium antimonide from the water-stable l-ethyl-3-methylimidazolium chloride/tetrafluoroborate ionic liquid. J Electrochem Soc 150 C544-C550... 

Cd electrodeposition has been reported by Noel et al. and by Chen et al. [38,39]. CdCb was used to buffer neutral chloroaluminate liquids and the element could be deposited [38]. Chen et al. used a basic l-ethyl-3-methylimidazolium chloride/tetrafluoroborate ionic liquid to deposit Cd successfiiUy [39]. It is formed on platinum, tungsten and glassy carbon from CdCU in a quasi-reversible two-electron reduction process. This result is promising as Te could perhaps also be deposited from such an ionic liquid thus giving a system for direct CdTe electrodeposition. 

Jou LS, Chang JK, Twhang TJ, Sun fW (2009) Electrodeposition of palladium-copper films from 1-ethyl-3-methylimidazolium chloride-tetrafluoroborate ionic liquid on indium tin oxide electrodes. J Electrochem Soc 156(6) D193-D197... 

An important role is also played by the nature of the support electrolyte and, in particular, of the anion. As an example, tosylate greatly favors the electrodeposition of PP but is detrimental for PT for the latter, innocent anions, such as perchlorate, tetrafluoroborate, or hexafluorophosphate, are the best choice. 

Fu, Y.C., Su, Y.Z., Zhang, H.M. et al. (2010) An in situ scanning tunneling microscopic stndy of electrodeposition of bismuth on Au( 111) in a 1 -butyl-3-methylimidazolium tetrafluoroborate ionic liquid Precursor adsorption and underpotential deposition. ElectrochimicaActa, 55,8105-8110. 

Hsiu SI, Sun IW (2004) Electrodeposition behaviour of cadmium telluride from 1-ethyl-3-methylimi-dazolium chloride tetrafluoroborate ionic liquid. J Appl Electrochem 34 1057... 

Nonaqueous electrolyte solutions [5, 6]. The development of modem energy-storing devices (batteries and capacitors) is closely related to the utilization of nonaqueous electrolyte solu-tiiMis. Lithium tetrafluoroborate in propylene carbonate is a prominent example. Nonaqueous solutions play also a major role in other fields of electrochemistry such as electroplating, electrodeposition, or electrochemistry. 

From Molten Salts or Ionic Liquids Reports on the electrodeposition of CdTe from molten salts or ionic liquids are relatively rare. However, the electrodeposition of CdTe from the Lewis basic ionic liquid l-ethyl-3-methylimidazolium chloride/tetrafluoroborate (EMICI-BF4) has been achieved [96]. CdCl2 and TeCLt, used as the sources of Cd and Te, respectively, can dissolve in the Lewis basic ionic liquid via a complexing reaction with excess chloride ions in the ionic Uquid. Te(lV) can be reduced to Te through a four-electron step and CdTe electrodeposits can be obtained via the UPD of Cd on the deposited Te. 

The electrodeposition of InSb from a 1-ethyl-3-methyhmidazolium chloride/tetrafluoroborate room-temperature ionic liquid (molten salt) was investigated by Yang et al. [191] using SbCls and InCla as precursors. The composition of the In-Sb codeposits can be varied by the deposition potential and bath concentrations. At a potential at which the deposition of Sb and In is mass-transport limited, InSb compound can be obtained from solutions containing equal moles of Sb(lll) and In(ni). The electrodeposited InSb was a p-type semiconductor which exhibited a direct optical transition with an optical bandgap of 0.20 eV. 

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