Ionic nanocrystalline metal

The electrodeposition of metals from ionic liquids is a novel method for the production of nanocrystalline metals and alloys, because the grain size can be adjusted by varying the electrochemical parameters such as over-potential, current density, pulse parameters, bath composition and temperature and the liquids themselves. Recently, for the first time, nanocrystalline electrodeposition of Al, Fe and Al-Mn alloy has been demonstrated. 

Nanocrystalline Metals and Alloys from Chlorometallate-based Ionic Liquids... 

Nanocrystalline Metals from Air- and Water-stable Ionic Liquids I 227... 

Endres F, Bukowski M, Hempelmann R et al (2003) Electrodeposition of nanocrystalline metals and alloys from ionic liquids. Angew Chem Int Ed 42 3428-3432... 

Transition-metal nanoparticles in imidazolium ionic liquids recycable catalysts for biphasic hydrogenation reactions. Journal of the American Chemical Society, Vol.124, No.l6, (April 2002), pp. 4228-4229, ISSN 0002-7863 Endres, F. Bukowski, M. Hempelmann, R. Natter, H. (2003). Electrodeposition of nanocrystalline metals and alloys from ionic liquids. Angewandte Chemie, International Edition, Vol.42, No.29, 0uly 2003), pp., 3428-3430, ISSN 1521-37732003 Endres, F. Abedin, S. Z. (2002). Electrodeposition of stable and narrowly dispersed germanium nanoclusters from an ionic liquid. Chemical Commununication, No. 8, pp. 892 - 893, pp. 1359-7345, ISSN 1359-7345... 

Table 11.2 and assume A=100, which is rather conservative value, to compute J via Eq. (11.32) and O via Eq. (11.22). The results show t p 0.91 which implies that the O2 backspillover mechanism is fully operative under oxidation reaction conditions on nanoparticle metal crystallites supported on ionic or mixed ionic-electronic supports, such as YSZ, Ti02 and Ce02. This is quite reasonable in view of the fact that, as already mentioned an adsorbed O atom can migrate 1 pm per s on Pt at 400°C. So unless the oxidation reaction turnover frequency is higher than 103 s 1, which is practically never the case, the O8 backspillover double layer is present on the supported nanocrystalline catalyst particles. 

Cation Cationic structure and size will affect the viscosity and conductivity of the liquid and hence will control mass transport of metal ions to the electrode surface. They will also be adsorbed at the electrode surface at the deposition potential and hence the structure of the double layer is dominated by cations. Some studies have shown that changing the cationic component of the ionic liquid changes the structure of deposits from microcrystalline to nanocrystalline [27]. While these changes are undeniable more studies need to be carried out to confirm that it is a double layer effect. If this is in fact the case then the potential exists to use the cationic component in the liquid as a built-in brightener. 

In ionic liquids the situation seems to be totally different. It was surprising to us that the electrodeposition of metals and semiconductors in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide delivers nanocrystalline deposits with grain sizes varying from 10 to 200 nm for the different materials, like Si, Al, Cu, Ag and In, investigated to date. It was quite surprising in the case of Al deposition that temperature did not play a tremendous role. Between 25 and 125 °C we always got nanocrystalline Al with similar grain sizes. Similar results were obtained if the deposition was performed in tri-hexyl- tetradecylphos-phonium bis (trifluoromethylsulfonyl) amide. Maybe liquids with saturated nonaromatic cations deliver preferentially nanomaterials this is an aspect which, in our opinion, deserves further fundamental studies. 

Although the emphasis here will, by necessity, be placed on more recent data, several key reviews of transport in nanocrystalline ionic materials have been presented, the details of which will be outlined first. An international workshop on interfacially controlled functional materials was conducted in 2000, the proceedings of which were published in the journal Solid State Ionics (Volume 131), focusing on the topic of atomic transport. In this issue, Maier [29] considered point defect thermodynamics and particle size, and Tuller [239] critically reviewed the available transport data for three oxides, namely cubic zirconia, ceria, and titania. Subsequently, in 2003, Heitjans and Indris [210] reviewed the diffusion and ionic conductivity data in nanoionics, and included some useful tabulations of data. A review of nanocrystalline ceria and zirconia electrolytes was recently published [240], as have extensive reviews of the mechanical behavior (hardness and plasticity) of both metals and ceramics [13, 234]. 

Electrical transport measurements on layer-by-layer assemblies of nanocrystals on conducting substrates have been carried out with a sandwich configuration [691-693]. Nanocrystalline films with bulk metallic conductivity have been realized with Au nanocrystals of 5 and llnm diameter spaced with ionic and covalent spacers [692, 693]. The conductivity of monolayered two-dimensional arrays of metal nanocrystals has been examined with patterned electrodes [694-699], Structural disorder and interparticle separation distance are found to be key factors that determine the conductivity of such layers [694-697]. The conductivity of the layers can be enhanced by replacing the alkane thiol with an aromatic thiol in situ [698,699]. The interaction energy of nanocrystals in such organizations can be continually varied by changing the interparticle distance. 

Additive free electrodeposition of nanocrystalline aluminium in a water and air stable ionic liquid. Electrochem. Commun., 7,1111-1116 Zhong, C. Sasaki, T. Jimbo-Kobayashi, A. Fujiwara, E. Kobayashi, A. Tada, M. Iwasawa, Y. (2007). Syntheses, structures, and properties of a series of metal ion-containing dialkylimidazolium ionic liquids. Bull. Chem. Soc. fpn., 80, 2365-2374... 

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