425343 Electrodeposition of Chromium from Chromium(III)-Ionic Liquid Solutions

Monday, November 9, 2015: 6:50 PM
Exhibit Hall 1 (Salt Palace Convention Center)
Liyuan Sun and Joan F. Brennecke, Department of Chemical and Biomolecular Engineering, University of Notre Dame, Notre Dame, IN

Electrodeposition of Chromium from Chromium(III)-Ionic Liquid Solutions 

 

Liyuan Sun* and Joan F. Brennecke

Department of Chemical and Biomolecular Engineering, University of Notre Dame

Notre Dame, IN 46556, USA

lsun4@nd.edu

Electrodeposition of chromium (Cr) is indispensable for various industries, such as automotive, aerospace, electronics, optics, and sensors.  The most common industrial chromium coatings are usually electrodeposited from hexavalent chromium (Cr(VI)) aqueous solutions, which possesses severe concerns because Cr(VI) is highly toxic.  A straightforward alternative is less toxic trivalent chromium (Cr(III)) based solutions.  However, the high stability of the hexaaquochromium(III) complex formed in aqueous electrolyte solutions may obstruct or even prevent the electrodeposition of chromium from aqueous solutions.  Another considerable drawback of electrodeposition of chromium from aqueous solutions is hydrogen evolution, which results in safety issues and reduced current efficiency.  Using ionic liquids (ILs) for Cr(III) electrodeposition is a promising alternative that could address the above issues. So far, only a few limited examples of chromium electrodeposition from ILs have been reported (e.g., using a chromium chloride hexahydrate/choline chloride solution,1 or chromium chloride hexahydrate/1-buthyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) solution2).

In this work, we investigate new Cr(III)-IL solutions as potential candidates for chromium electrodeposition. To optimize the transport properties of the mixtures, different amounts of ultrapure water is added to the Cr(III) salt ĘC IL mixtures. The conductivity, viscosity, and 'ionicity' of the solutions are characterized over the temperature range from 283.15 K to 353.15K. Electrochemical reduction of Cr(III) is demonstrated by cyclic voltammetry and preliminary electrodeposition tests.  The physicochemical and electrochemical properties of the solutions depend heavily on the water content and the ion type.  The new Cr(III) salt ĘC IL mixtures are excellent candidates for chromium electrodeposition under carefully selected conditions where hydrogen evolution can be avoided or inhibited.

Reference:

1. Abbott, A. P.; Capper, G.; Davies, D. L.; Rasheed, R. K. Ionic liquid analogues formed from hydrated metal salts. Chemistry-a European Journal 2004, 10, 3769-3774.

2. Eugenio, S.; Rangel, C. M.; Vilar, R.; do Rego, A. M. B. Electrodeposition of black chromium spectrally selective coatings from a Cr(III)-ionic liquid solution. Thin Solid Films 2011, 519, 1845-1850.


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