The electrochemical oxidation and reduction of nitrate ions in the room temperature ionic liquid [C2mim][NTf2]; the latter behaves as a 'melt' rather than an 'organic solvent'
Journal
New Journal of Chemistry
Journal Volume
31
Journal Issue
6
Start Page
966
End Page
972
ISSN
11440546
Date Issued
2007
Author(s)
Broder, Tessa L.
Silvester, Debbie S.
Hardacre, Christopher
Crossley, Alison
Compton, Richard G.
Abstract
The electrochemical oxidation of 1-butyl-3-methylimidazolium nitrate [C4mim][NO3] was studied by cyclic voltammetry in the room temperature ionic liquid (RTIL) 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [C2mim][NTf2]. A sharp peak was observed on a Pt microelectrode (d = 10 μm), and a diffusion coefficient at infinite dilution of ca. 2.0 × 10-11 m 2 s-1 was obtained. Next, the cyclic voltammetry of sodium nitrate (NaNO3) and potassium nitrate (KNO3) was studied, by dissolving small amounts of solid into the RTIL [C2mim][NTf 2]. Similar oxidation peaks were observed, revealing diffusion coefficients of ca. 8.8 and 9.0 × 10-12 m2 s -1 and solubilities of 11.9 and 10.8 mM for NaNO3 and KNO3, respectively. The smaller diffusion coefficients for NaNO 3 and KNO3 (compared to [C4mim][NO 3]) may indicate that NO3- is ion-paired with Na+ or K+. This work may have applications in the electroanalytical determination of nitrate in RTIL solutions. Furthermore, a reduction feature was observed for both NaNO3 and KNO3, with additional anodic peaks indicating the formation of oxides, peroxides, superoxides and nitrites. This behaviour is surprisingly similar to that obtained from melts of NaNO3 and KNO3 at high temperatures (ca. 350-500°C), and this observation could significantly simplify experimental conditions required to investigate these compounds. We then used X-ray photoelectron spectroscopy (XPS) to suggest that disodium(i) oxide (Na2O), which has found use as a storage compound for hydrogen, was deposited on a Pt electrode surface following the reduction of NaNO3. © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.
Publisher
Royal Society of Chemistry
Type
journal article