Elucidation of the Electrochemical Oxidation Pathway of Ammonia in Dimethylformamide and the Room Temperature Ionic Liquid, 1‐Ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide

Abstract

The direct electrochemical oxidation of ammonia has been examined in both the organic solvent dimethylformamide (DMF) and the room temperature ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [EMIM][N(Tf) 2 ]. The corresponding voltammetric responses have been shown to be similar in each solvent with a broad oxidative wave occurring upon the introduction of ammonia to the solution and the appearance of a new reductive wave following the oxidation. The oxidative reaction process has been examined and a suitable reaction pathway has been deduced, corresponding to the formation of ammonium cations after oxidation of the ammonia. A linear response of limiting current against vol% ammonia was observed in both DMF and [EMIM][N(Tf) 2 ], suggesting potential application for analytical methods.

Electrochemical Ammonia Gas Sensing in Nonaqueous Systems: A Comparison of Propylene Carbonate with Room Temperature Ionic Liquids

“…is observed, and is attributed to the direct oxidation of ammonia at the electrode surface, consistent with the previous observation by Buzzeo et al [5] in the RTIL [C 2 mim] [NTf 2 ]. The peak potential of this wave becomes more negative when the scan rate is increased, indicating electrochemical irreversibility, as confirmed by Tafel analysis of the linear region between 10% and 90% of oxidation peak current.…”

“…From the voltammetry presented in Figure 3, it is suggested [5] that the electrochemical oxidation of ammonia likely proceeds via the following electrochemical step, which occurs at ca. þ 1.6 V at the GC electrode:…”

“…À 0.75 V vs. Ag (peak III) on the reverse scan, and a corresponding oxidative wave at À 0.35 V (peak IV). It is believed that peak III is the reduction of NH þ 4 , as indicated by the investigation of the voltammetry of NH 4 NO 3 [10] and by Buzzeo et al [5] in [C 2 mim] [NTf 2 ]. Since the appearance of peak IV has been reported previously, [5] but its identity is unconfirmed, a further experiment was then performed.…”

“…Note HA may in fact represent the interaction of H þ with one or more anions, e.g., homoconjugation. In the mechanism, ammonia is initially oxidized (with net three-quarters of a mole of electrons per mole NH 3 ) [5], producing nitrogen gas and three protons, which readily (probably instantaneously) protonate, or are solvated by the anion(s). The protonated anion(s) then reacts with another ammonia molecule to form an ammonium ion, which is in equilibrium with the protonated anion(s).…”

The electrochemistry of simple inorganic molecules in room temperature ionic liquids

“…Various studies have focussed on the electrochemical oxidation of ammonia in alkaline solutions, 39 and as a result, several protocols based on its determination via its direct oxidation have been developed. Mechanistic studies for the oxidation of ammonia have been reported in the aprotic solvents acetonitrile (MeCN), 40 dimethyl formamide (DMF), 41 propylene carbonate (PC), 42 Figure 8 shows the oxidation of ammonia (10% NH 3 , 90% N 2 ) on a Pt microdisk electrode (diameter = 10 m) in the RTIL [C 4 mim][BF 4 ] at a scan rate of 10 V s -1 . Peak I corresponds to the direct oxidation of ammonia, and peaks II, III and IV have been shown 18 to be due to the following electro-generated products; the solvated proton (H[BF 4 ] x ), ammonium ion (NH 4 + ) and adsorbed hydrogen (H 2 ) respectively.…”