Charles L. Hussey

Electrochemistry of Titanium and the Electrodeposition of Al-Ti Alloys in the Lewis Acidic Aluminum Chloride–1-Ethyl-3-methylimidazolium Chloride Melt

The chemical and electrochemical behavior of titanium was examined in the Lewis acidic aluminum chloride-1-ethyl-3-methylimidazolium chloride (AlCl 3 -EtMeImCl, molten salt at 353.2 K. Dissolved Ti(II), as TiCl 2 , was stable in the 66.7-33.3% mole fraction ( m/o composition of this melt. but slowly disproportionated in the 60.0-40.0 m/o melt. At low current densities, the anodic oxidation of Ti(0)did not lead to dissolved Ti (II). but to an insoluble passivating film of TiCl 3 . At high current densities or very positive potentials, Ti (0) was oxidized directly to Ti(IV); however, the electrogenerated Ti (IV) vaporized from the melt as TiCl 4 (g). As found by other researchers working in Lewis acidic AlCl 3 -NaCl, Ti(II) tended to form polymers as its concentration in the AlCl 3 - EtMeImCl melt was increased. The electrodeposition of Al-Ti alloys was investigated at Cu rotating disk and wire electrodes. Al-Ti alloys containing up to ∼19% atomic fraction (a/o) titanium could be electrodeposited from saturated solutions of Ti (II) in the 66.7-33.3 m/o melt at low current densities, but the titanium content of these alloys decreased as the reduction current density was increased. The pitting potentials of these electrodeposited Al-Ti alloys exhibited a positive shift with increasing titanium content comparable to that observed for alloys prepared by sputter deposition.

Electrodeposition of Aluminum from the Aluminum Chloride‐1‐Methyl‐3‐ethylimidazolium Chloride Room Temperature Molten Salt + Benzene

The constant current electrodeposition of bulk aluminum on copper substrates was investigated in the Lewis acidic [> 50 mole percent (m/o) AlCl 3 ] aluminum chloride-1-methyl-3-ethylimidazolium chloride room temperature molten salt (AlCl 3 -MeEtimeCl). Although aluminum can be electroplated from the neat molten salt, we have found that the quality of the electrodeposit is greatly enhanced by the addition of benzene as a cosolvent. Electrodeposits produced in such melts exhibited a grain size on the order of 5 to 15 μm. The lattice parameters of these electrodeposits were slightly smaller than the Joint Committee on Powder Diffraction Standards (JCPDS) value; this was attributed to the presence of vacancies in the aluminum lattice that were present at concentrations ranging from about 0.1 to 0.5 atomic percent (a/o). The copper substrate was found to have a slight (311) texture as determined by x-ray diffraction; however, all of the electrodeposits exhibited a preferred (220) crystallographic orientation with the intensity of the (311) reflection being equal to that of a randomly oriented sample. The (200) and (111) reflections were relatively weak. The relative intensity of the (220) reflection increased and those for the (311), (200), and (111) orientations decreased as the benzene concentration was increased. A Williamson-Hall treatment indicated that microstrain in the electrodeposits was essentially nonexistent.

Electrodeposition of Al-Mo Alloys from the Lewis Acidic Aluminum Chloride-1-ethyl-3-methylimidazolium Chloride Molten Salt

The electrochemistry of Zr(IV) and Zr(II) and the electrodeposition of Al-Zr alloys were examined in the Lewis acidic 66.7-33.3 mol % aluminum chloride-1-ethyl-3-methylimidazolium chloride molten salt at 353 K. The electrochemical reduction of Zr(lV) to Zr(II) is complicated by the precipitation of ZrCl 3 ; however, solutions of Zr(II) can be prepared by reducing Zr(IV) with Al wire. Al-Zr alloys can be electrodeposited from plating baths containing either Zr(IV) or Zr(II), but for a given concentration and current density, baths containing Zr(IV) lead to Al-Zr alloys with the higher Zr content. This result was traced to the diminutive concentration-dependent diffusion coefficient for Zr(II). It was possible to prepare Al-Zr alloys containing up to ∼17% atomic fraction (atom %) Zr. The structure of these deposits depended on the Zr content. Alloys containing less than 5 atom % Zr could be indexed to a disordered face-centered cubic structure similar to pure Al, whereas alloys containing ∼17 atom % Zr were completely amorphous (metallic glass). The chloride pitting potentials of alloys with more than 8 atom % Zr were approximately +0.3 V relative to pure Al.

Electrodeposition of Cobalt and Cobalt‐Aluminum Alloys from a Room Temperature Chloroaluminate Molten Salt

The electrodeposition of magnetic cobalt-aluminum alloys was investigated in the Lewis acidic aluminum chloride-l-methyl-3-ethylimidazolium chloride [60.0-40.0 mole percent molten salt containing electrogenerated Co(II) at 25°C. Rotating disk electrode voltammetry indicated that it is possible to produce alloy deposits containing up to 62 atomic (a/o) aluminum at potentials positive of that for the bulk deposition of aluminum. The onset of the underpotential-driven aluminum codeposition process occurred at around 0.40 V vs. the Al/Al(III) couple in a 5.00 mmol liter -1 Co(II) solution but decreased as the Co(II) concentration increased. The Co-Al alloy composition displayed an inverse dependence on the Co(II) concentration but tended to become independent of concentration as the potential was decreased to 0 V. A rotating ring-disk electrode voltammetry technique was developed to analyze the composition and structure of the Co-Al alloy deposits. This technique takes advantage of the fact that the mass-transport-limited reduction of cobalt(II) occurs at potentials considerably more positive than that at which aluminum codeposition occurs. Scanning electron microscopy and energy dispersive x-ray analysis of bulk electrodeposits revealed that deposit morphology depends strongly upon aluminum content/deposition potential ; deposits produced at 0.40 V from 50.0 mmol liter -1 Co(II) solutions consisted of 10 to 20 μm diam multifaceted nodules of pure hcp cobalt, whereas those obtained at 0.20 V were dense and fine grained, containing about 4 a/o Al. Deposits produced at 0 V had the visual appearance of a loosely adherent black powder. x-ray diffraction measurements revealed a lattice expansion and a decrease in grain size as the hcp cobalt was alloyed with increasing amounts of aluminum.

Electrodeposition of Silver on Metallic and Nonmetallic Electrodes from the Acidic Aluminum Chloride‐1‐Methyl‐3‐Ethylimidazolium Chloride Molten Salt

The electrodeposition of silver was investigated at polycrystalline platinum, gold, and tungsten, and at glassy carbon in the 66.7-33.3 mole percent aluminium chloride-1-methyl-3-ethylimidazolium chloride room temperature molten salt at 40°C. Of the fourt materials studied, the silver deposition-stripping process seemed to be the least complex at platinum. In contrast, the bulk deposition of silver at gold appears to be preceded by an underpotential depostion process similar to that seen in aqueous solutions

Design, Synthesis, and Electrochemistry of Room‐Temperature Ionic Liquids Functionalized with Propylene Carbonate

Alkyl carbonates are often employed as solvents for the study of energy-storage devices (ESD), such as lithium secondary batteries (LSB) and electric double-layer capacitors. Some of these solvents, including propylene carbonate (PC) and diethyl carbonate, have already been put to practical use in modern electronics technology, such as in mobile phones and laptop computers. However, all of these organic solvents have potential safety drawbacks related to their flammable and volatile nature that can lead to explosions and/or fire accidents. Furthermore, lithium anodes with a high theoretical discharge capacity (3860 mAh g ) cannot be utilized in such solvents owing to dendritic lithium deposition during the charging cycle. However, room-temperature ionic liquids (RTILs) and RTIL-like solvents are expected to be a new class of solvents for next-generation rechargeable highenergy-density batteries because RTILs possess unique saltlike properties. Some of these properties, such as high electrochemical stability, negligible vapor pressure, and resistance to combustion, are highly advantageous in electrochemical applications. 7,8] Thus, we anticipated that chemically combining an appropriate carbonate and organic salt may remove some of the undesirable properties of alkyl carbonates and provide uniquely functionalized RTILs for ESDs, and particularly LSB systems (Figure 1).

The Electrochemistry of Tin in the Aluminum Chloride‐1‐methyl‐3‐ethylimidazolium Chloride Molten Salt

The electrochemistry of Sn(II) and Sn(IV) was studied with voltammetry and chronoamperometry at polycrystalline Pt and Au and at glassy carbon (GC) electrodes in the acidic and basic aluminum chloride-1-methyl-3-ethylimidazolium chloride (AlCl 3 -MeEtimCl) molten salt at 40 o C. The Sn(II) reduction process is uncomplicated at Pt. The underpotential deposition of a Sn monolayer is observed at Au; an additional UPD process is attributed to surface alloy formation. The deposition of Sn on GC is complicated by nucleation

Electrodeposition of Al–Mo–Ti Ternary Alloys in the Lewis Acidic Aluminum Chloride–1-Ethyl-3-methylimidazolium Chloride Room-Temperature Ionic Liquid

The electrodeposition of Al-Mo-Ti ternary alloys was examined in the Lewis acidic 66.7-33.3% mole fraction aluminum chloride-l-ethyl-3-methylimidazolium chloride (AlCl 3 -EtMelmCl) room-temperature ionic liquid containing (Mo 6 Cl 8 )Cl 4 and TiCl 2 . The Mo content in the alloys varied with the applied current density and the Mo(II)/Ti(II) concentration ratio. The Ti content was small and constant at 0.6 ± 0.2% atomic fraction (a/o) and was independent of the deposition conditions. All the electrodeposited Al-Mo-Ti alloys were dense and compact and adhered well to the copper substrate. The deposit surface morphology depended on the applied current density and the Mo content of the alloys, as reported previously for the amorphous binary Al-Mo alloys. However, no amorphous glass phase could be detected in the Al-Mo-Ti ternary alloy samples; this behavior may be related to the presence of Ti. In summary, the addition of a small amount of Ti (∼ 1 a/o) to the binary Al-Mo alloys resulted in a ternary alloy with a substantially improved chloride-induced pitting corrosion resistance compared to the related Al-Mo alloy.

The Electrochemistry of Gold at Glassy Carbon in the Basic Aluminum Chloride‐1‐Methyl‐3‐ethylimidazolium Chloride Molten Salt

Gold(III) is complexed as [AuCl 4 ] - in the basic aluminum chloride-1-methyl-3-ethylimidazolium chloride molten salt solvent. In contrast to the three-electron reduction process found at metal electrodes in molecular solvents, the voltammetric reduction of [AuCl 4 ] - at glassy carbon in this solvent occurs in two steps with the intermediate formation of a gold(I) complex, most likely [AuCl 2 ] -

Electrochemistry of Copper(I) Oxide in the 66.7–33.3 mol % Urea–Choline Chloride Room-Temperature Eutectic Melt

The electrochemistry of Cu(I) oxide (Cu 2 O) was examined in the 66.7-33.3% mole fraction (m/o) urea-choline chloride melt. Electrochemical parameters that were measured include the standard heterogeneous rate constant and transfer coefficient of the Cu(I)/Cu(II) reaction and the Cu(I) diffusion coefficient. Data about the density, equivalent conductance, and absolute viscosity of this melt were obtained over the temperature range of 298-353 K. The conductivity and viscosity exhibited the non-Arrhenius behavior typical of glass-forming liquids. Overall, the physicochemical properties of the urea-choline chloride melt are comparable to those of common room-temperature ionic liquids. The electrodeposition of Cu was examined on glassy carbon and platinum electrodes by using potential-step techniques. The critical number of atoms required for the formation of a stable nucleus on glassy carbon was ∼0, indicating that active sites on the electrode surface served as critical nuclei. Cu deposits on Ni substrates were dense, nodular, and compact.