Rechargeable aluminum batteries utilizing a chloroaluminate inorganic ionic liquid electrolyte.

Rechargeable aluminum batteries composed of an aluminum anode, an expanded graphite cathode, and an inorganic chloroaluminate ionic liquid electrolyte show remarkably improved capacity, reversibility, and rate capability at 393 K compared to cells based on a common organic salt based ionic liquid, AlCl3-1-ethyl-3-methylimidazolium chloride.

Anodic Dissolution of Aluminum in the Aluminum Chloride-1-Ethyl-3-methylimidazolium Chloride Ionic Liquid.

The anodic dissolution of aluminum metal was investigated in the Lewis acidic chloroaluminate ionic liquid, aluminum chloride-1-ethyl-3-methylimidazolium chloride. The investigation was conducted on aluminum rotating disk electrodes as a function of potential, ionic liquid composition, and temperature. Two different dissolution mechanisms were realized. At modest overpotentials, dissolution takes place under mixed kinetic-mass transport control. However, as the overpotential is increased to induce higher dissolution rates and/or the ionic liquid is made more acidic, the dissolution reaction transitions to a potential-independent passivation-like process ascribed to the formation of a porous solid layer of AlCl3(s). At a fixed temperature and composition, the limiting passivation current density displays Levich behavior and also scales linearly with the concentration of AlCl4 - in the ionic liquid. The heterogeneous kinetics of the Al dissolution reaction were measured in the active dissolution potential regime. The exchange current densities were independent of the composition of the ionic liquid, and the anodic transfer coefficients were close to zero and seemed to be independent of the Al grain size.

An electrochemical and spectroscopic study of Nd(III) and Pr(III) coordination in the 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ionic liquid containing chloride ion.

The coordination and accessible oxidation states of Nd and Pr were investigated in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BuMePyroTf2N) by using electronic absorption spectroscopy, cyclic staircase voltammetry, and controlled potential coulometry. These experiments were carried out in the neat ionic liquid (IL) and in the IL containing free Cl(-) from the dissolution of BuMePyroCl. The electrolytic dissolution of Ln = Nd and Pr metal in this IL produces only the respective Ln(3+) ions. These trivalent species can be reduced to Ln(2+), but the resulting divalent species exhibit only transient stability, undergoing rapid disproportionation to Ln(3+) and Ln(0). The intensity of the hypersensitive (4)G5/2 ← (4)I9/2 electronic transition for Nd(3+) dissolved in the IL was substantially larger than it was in noncoordinating solvents such as aqueous HClO4, indicating moderate interactions between Nd(3+) and Tf2N(-) ions, probably resulting in anionic species such as [Nd(Tf2N)x]((x-3)-). The addition of Cl(-) to [Ln(Tf2N)x]((x-3)-) solutions results in the precipitation of LnCl3(s) (s = solid). The LnCl3(s) redissolves to give the octahedral complex [LnCl6](3-) as the Cl(-) concentration is raised further. In the IL containing excess chloride, the (3)P0 ← (3)H4 transition for [PrCl6](3-) exhibits ligand-mediated pseudohypersensitive behavior.

Electrochemical and spectroscopic investigation of Ln3+ (Ln = Sm, Eu, and Yb) solvation in bis(trifluoromethylsulfonyl)imide-based ionic liquids and coordination by N,N,N',N'-tetraoctyl-3-oxa-pentane diamide (TODGA) and chloride.

The electrochemistry and electronic absorption spectroscopy of samarium, europium, and ytterbium were investigated in the 1-(1-butyl)trimethylammonium bis(trifluoromethylsulfonyl)imide (BuMe3NTf2N) and 1-butyl-3-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BuMePyroTf2N) ionic liquids and in these solvents containing the neutral tridentate ligand N,N,N',N'-tetraoctyl-3-oxo-pentane diamide (TODGA) and the anionic hard ligand chloride. Lanthanide ions were introduced into the ionic liquids by controlled potential oxidation of the respective metals to yield solutions containing Eu(2+), Sm(3+), and Yb(3+), and it was possible to cycle between Eu(2+) and Eu(3+) as well as Yb(3+) and Yb(2+) using controlled potential electrolysis. Electronic absorption spectroscopy suggested that the Ln(3+) species are weakly solvated by Tf2N(-) anions as [Ln(Tf2N)x]((x-3)-) in the neat ILs. The quasireversible Ln(3+/2+) couples of all three elements were readily accessible in these ILs, but Sm(2+) was only stable on the voltammetric time scale. Addition of TODGA to [Ln(Tf2N)x]((x-3)-) solutions produces 3:1 complexes with Eu(3+) and Sm(3+) but only a 2:1 complex with the smaller Yb(3+) ion. Depending on the temperature, addition of Cl(-) to solutions of [Ln(Tf2N)x]((x-3)-) induces precipitation of LnCl3(s) when the mole ratio mCl(-)/mLn(3+) ≈ 3. However, when mCl(-)/mLn(3+) > 3, these precipitates redissolve to form the octahedral chloride complexes, [LnCl6](3-).

Electrochemical and spectroscopic study of Ce(III) coordination in the 1-butyl-3-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ionic liquid containing chloride ion.

Cyclic staircase voltammetry, controlled potential coulometry, and electronic absorption spectroscopy were used to probe the coordination and accessible oxidation states of Ce(3+) dissolved in the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BuMePyroTf(2)N) before and after the addition of chloride ion as BuMePyroCl. Controlled potential coulometry indicated that the oxidation of Ce metal in this ionic liquid produces only Ce(3+). Spectroscopic examination of the resulting solutions indicated that Ce(3+) was weakly solvated by Tf(2)N(-) ions as [Ce(Tf(2)N)(x)]((x-3)-), x ≥ 3. This species can be reduced at negative potentials, probably to a related Ce(2+) species, but the latter is unstable and quickly disproportionates to Ce(3+) and Ce(0); the latter appears to react with the ionic liquid. The addition of Cl(-) to solutions of [Ce(Tf(2)N)(x)]((x-3)-) causes the precipitation of CeCl(3)(s), providing a convenient route to the nondestructive recovery of Ce(3+) from the ionic liquid. However, as the Cl(-) concentration is further increased, the CeCl(3)(s) redissolves as the octahedral complex, [CeCl(6)](3-), and the voltammetric and spectroscopic signature for [Ce(Tf(2)N)(x)]((x-3)-) disappears. Absorption spectroscopy indicated that the bulk controlled potential oxidation of solutions containing [CeCl(6)](3-) produces [CeCl(6)](2-). Although stable on the time scale of voltammetry, this species slowly reacts with the ionic liquid and is converted back to [CeCl(6)](3-).

Physicochemical properties of highly conductive urea-EtMeImCl melts.

Urea-EtMeImCl mixtures have melting points from 333 to 363 K at 10-80 mol% urea, and, at temperatures >343 K, these melts show the highest conductivity reported to date for urea-based binary melts.

Uranium halide complexes in ionic liquids: an electrochemical and structural study.

The electrochemistry of the salts, [emim]2[UBr6] and [emim]2[UO2Br4] ([emim] = 1-ethyl-3-methylimidazolium), has been investigated in both a basic and an acidic bromoaluminate(III) ionic liquid. In the basic ionic liquid, the hexabromo salt undergoes a one-electron reversible reduction process at a stationary glassy carbon disc electrode, while the tetrabromodioxo salt was reduced to a uranium(IV) species by an irreversible two-electron process with the simultaneous transfer of oxide to the ionic liquid. On the other hand, dissolution of either of the salts in an acidic bromoaluminate(III) ionic liquid resulted in the formation of the same electroactive species. The solid state structures of the uranium chloride salts, [emim]2[UCl6] and [emim]2[UO2Cl4], have previously been reported, but have now been re-evaluated using a new statistical model developed in our group, to determine the presence or absence of weak hydrogen bonding interactions in the crystalline state.

Electrochemistry in ultrahigh vacuum: underpotential deposition of Al on polycrystalline W and Au from room temperature AlCl(3)/1-ethyl-3-methylimidazolium chloride melts.

The voltammetric characteristics of polycrystalline Au and W electrodes cleaned (thermal annealing at 1100 K) and characterized (Auger electron spectroscopy) in ultrahigh vacuum (UHV) have been examined in ultrapure AlCl(3)/1-ethyl-3-methylimidazolium chloride (EtMeImCl) melts in UHV. These experiments were performed using a custom-designed transfer system that allows for the all-Al electrochemical cell to be filled with EtMeImCl in an auxiliary UHV chamber and later transferred under UHV to the main UHV chamber that houses the Auger electron spectrometer. The results obtained for the underpotential (UPD) and bulk deposition of Al on Au were found to be very similar to those reported in the literature for measurements carried out under 1 atm of an inert gas in a glovebox. For the far more reactive W surfaces, voltammetric features ascribed to the stripping of underpotential-deposited Al could be observed following a single scan from 1.0 V vs Al(3+)/Al to a potential negative enough for bulk deposition of Al to ensue. This behavior is unlike that reported in the literature for experiments performed in a glovebox, which required either extensive potential cycling in the Al bulk deposition and stripping region or excursions to potentials positive enough for chlorine evolution to ensue for Al UPD features to be clearly discerned. These observations open new prospects for fundamental electrochemical studies of well-characterized, highly reactive metals, including single crystals, in a variety of low vapor pressure ionic liquids.