Ming-Jay Deng

An entirely electrochemical preparation of a nano-structured cobalt oxide electrode with superior redox activity

A nano-structured Co oxide electrode (with a Ni substrate) was successfully prepared using an entirely electrochemical process, which included the co-deposition of a Ni-Cu alloy film, selective etching of Cu from the film, and anodic deposition of Co oxide on the obtained nano-porous Ni substrate which had an average pore size of approximately 100 nm and a pore density of about 10(13) m(-2). The excellent electrochemical activity of the prepared electrode was demonstrated in terms of its pseudocapacitive performance, which was evaluated using cyclic voltammetry (CV) in 1 M KOH solution. The specific capacitance of the nano-structured Co oxide measured at a potential scan rate of 10 mV s(-1) was as high as 2200 F g(-1), which is over ten times higher than that of a flat oxide electrode (209 F g(-1)). The highly porous Co oxide also had superior kinetic performance as compared to a flat electrode. At a high CV scan rate of 50 mV s(-1), the two electrodes retained 94% and 59%, respectively, of their specific capacitances measured at 5 mV s(-1).

Electrochemical Study of Copper in the 1-Ethyl-3-Methylimidazolium Dicyanamide Room Temperature Ionic Liquid

The potential utility of the air- and water-stable ionic liquid l-ethyl-3-methylimidazolium dicyanamide (EMI-DCA) for electrochemical application was evaluated with copper(I) chloride. The temperature dependency of the density and absolute viscosity of EMI-DCA were measured over a temperature range from 297 to 343 K, and equations describing the dependencies are presented. Due to the ligand property of the DCA anion, both CuCl and CuCl 2 are soluble in EMI-DCA. Cyclic voltammograms of Cu(I) in EMI-DCA and other two ionic liquids were compared. Cu(I) can be oxidized to Cu(II) or reduced to Cu metal in these solutions. The electrodeposition of Cu on glassy carbon and nickel electrodes involves a three-dimensional progressive nucleation and growth process. Scanning electron microscopy and X-ray diffraction results indicate that the morphology of the copper electrodeposits is dependent on the deposition potential, and compact coatings containing nanocrystalline copper could be obtained by potentiostatic electrolysis at low overpotentials. The low viscosity of EMI-DCA and the high solubility of metal chlorides in it would facilitate the electrodeposition of metals using this ionic liquid.

Pseudocapacitive Mechanism of Manganese Oxide in 1-Ethyl-3-methylimidazolium Thiocyanate Ionic Liquid Electrolyte Studied Using X-ray Photoelectron Spectroscopy

The electrochemical behavior of anodically deposited manganese oxide was studied in pyrrolidinium formate (P-HCOO), 1-butyl-3-methylimidazolium hexafluorophosphate (BMI-PF6), and 1-ethyl-3-methylimidazolium thiocyanate (EMI-SCN) ionic liquids (ILs). The experimental data indicate that the Mn oxide electrode showed ideal pseudocapacitive performance in aprotic EMI-SCN IL. In a potential window of approximately 1.5 V, the oxide specific capacitance, evaluated using cyclic voltammetry and chronopotentiometry, was about 55 F/g. The electrochemical energy storage reaction was examined using X-ray photoelectron spectroscopy (XPS). It was confirmed that the SCN- anions, instead of the EMI+ cations, were the primary working species that can become incorporated into the oxide and thus compensate the Mn3+/Mn4+ valent state variation upon the charge-discharge process. According to the analytical results, a pseudocapacitive mechanism of Mn oxide in the SCN- based aprotic IL was proposed.

Improved Corrosion Resistance of Magnesium Alloy with a Surface Aluminum Coating Electrodeposited in Ionic Liquid

A metallic aluminum (Al) layer was successfully electrodeposited onto a magnesium (Mg) alloy in a Lewis acidic aluminum chloride-1-ethyl-3-methylimidazolium chloride (AlCl 3 -EMIC) ionic liquid under a galvanostatic condition at room temperature. Effects of deposition current density on material characteristics of the deposited layers were explored by means of a scanning electron microscope and an X-ray diffractometer. In addition, the improvement in corrosion resistance of the Mg alloy due to the Al coating was evaluated by electrochemical measurements and a salt spray test. The electrochemical impedance spectroscopic data indicated that a bare Mg alloy had a polarization resistance of only 470 Ω cm 2 in 3.5 wt % NaCl solution, whereas the Al-coated Mg sample showed its resistance as high as 8700 Ω cm 2 in the same environment. Moreover, it was also found that the Al layer deposited at a lower current density was more compact and uniform when compared to that deposited at a higher current density; consequently, this coating revealed a superior protection capability for the Mg substrate against corrosion.

Facile electrochemical synthesis of 3D nano-architectured CuO electrodes for high-performance supercapacitors

With a simple electrochemical process, we prepared nano-architectured CuO electrodes with a 3D hierarchically porous structure and an excellent supercapacitive performance. These nano-architectured CuO electrodes were processed through co-deposition of a Ni–Cu layer on Ni foam, selective etching of Cu from the Ni–Cu film (leaving tentacle-like nanoporous Ni), and anodic deposition of CuO nanoribbons (NRs) on the tentacle-like nanoporous Ni/Ni foam substrate. Because of its unique nano-architecture, the prepared CuO nanoribbon-on-Ni-nanoporous/Ni foam (CNRNP) electrode shows exceptional performance of energy storage relative to a conventional version of the electrode. The CNRNP electrode has also a superior kinetic performance relative to CuO nanoflake-on-Ni foam (CNFNF) and flake-like CuO (FLC) electrodes. Besides its excellent cyclic stability, an exceptionally large specific capacitance of 880 and 800 F g−1 (deducting the substrate capacitance from the total) for the CNRNP electrode is obtained at scan rates of 10 and 200 mV s−1, respectively. The excellent pseudocapacitive characteristics of CNRNP electrodes associated with the variation of the Cu oxidation state during charge and discharge cycles were elucidated with in situ X-ray absorption near-edge structure (XANES) spectra.

Fabrication of Mn/Mn oxide core–shell electrodes with three-dimensionally ordered macroporous structures for high-capacitance supercapacitors

Three-dimensionally ordered macroporous (3DOM) metallic Mn films have been prepared with ordered polystyrene (PS) templates on electrodeposition from an ionic liquid (IL). A 3DOM Mn core–Mn oxide shell film was prepared on anodizing a 3DOM Mn film in KCl aqueous solution. The varied anodization courses were confirmed to cause variations of the material characteristics of the prepared 3DOM Mn/Mn oxide electrodes and thereby in their pseudocapacitive performance. The 3DOM Mn/Mn oxide electrodes anodized with the cyclic voltammetric method showed the most promising specific capacitance, 1200 ± 60 F g−1 (based on the mass of 3DOM Mn/Mn oxides), with a satisfactory rate capability and cycling performance. Such electrodes can be potentially applied for lithium batteries and supercapacitors.

Pseudocapacitive behavior of Mn oxide in aprotic 1-ethyl-3-methylimidazolium–dicyanamide ionic liquid

The electrochemical behavior of anodically deposited Mn oxide was studied in three ionic liquids (ILs): 2-methylpyridine–trifluoroacetic acid (P–TFA), 1-ethyl-3-methylimidazolium–dicyanamide (EMI–DCA), and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI–BF4). In the aprotic and low-viscosity EMI–DCA IL, ideal pseudocapacitive behavior of the oxide electrode was observed; the specific capacitance, measured using cyclic voltammetry at a sweep rate of 5 mV/s, was 72 F/g. The operation potential window was as wide as 2 V, which is double that found in traditional aqueous electrolytes. Moreover, electrochemical stability of the Mn oxide electrode in EMI–DCA IL was excellent; after 600 redox cycles, the capacitance barely decayed. The charge storage mechanism of Mn oxide in the IL was examined using X-ray photoelectron spectroscopic (XPS) analyses. The results reveal that DCA−, instead of EMI+, is the primary working ion that penetrates into the oxide and compensates the Mn valent state variation. This is the first study that provides a detailed explanation of the pseudocapacitive properties of Mn oxide in IL.

Evaluation of Ionic Liquid Electrolytes for Use in Manganese Oxide Supercapacitors

Development of Mn oxide supercapacitors incorporating ionic liquid IL electrolytes was attempted. The experimental resultsindicate the possibility of achieving pseudocapacitive performance of Mn oxide in ILs without involving protons and alkalications, thus opening a route of developing electrolytes for oxide-based pseudocapacitors. In 1-ethyl-3-methylimidazolium-dicyanamide aprotic IL, Mn oxide can exhibit a specific capacitance of 72 F/g in a potential window of 2 V. Due to high ionicconductivity, large electrochemical windows, excellent thermal stability, and nonflammability of the IL, a high-voltage andlong-life energy storage system is successfully proposed.© 2008 The Electrochemical Society. DOI: 10.1149/1.3013028 All rights reserved.Manuscript submitted August 18, 2008; revised manuscript received October 3, 2008. Published November 6, 2008.

Electrochemistry of manganese in the hydrophilic N-butyl-N-methylpyrrolidinium dicyanamide room-temperature ionic liquid

The electrochemistry of manganese was studied at a polycrystalline platinum disk electrode in the hydrophilic ionic liquid N-butyl-N-methylpyrrolidinium dicyanamide (BMP-DCA). The density and absolute viscosity of BMP-DCA were determined over a temperature range from 299.0 to 343.0 K. A polynomial equation describing the temperature dependence of the density is provided. The viscosity obeys the Arrhenius temperature dependence. The dicyanamide anion exhibits a good complexing ability toward transition metal ions, and, therefore, Mn(II) species can be introduced into the ionic liquid either by anodic dissolution of a manganese electrode or by dissolution of manganese (II) chloride. Cyclic voltammograms indicated that the electrodeposition of Mn from Mn(II) was preceded by an overpotential-driven nucleation process. When the potential scan was reversed, the anodic stripping wave was fairly smaller than the cathodic wave, indicating that the oxidation of the Mn electrodeposits was kinetically hindered. However, this behavior was less noticeable for massive Mn electrodeposits. Manganese coatings were prepared at copper substrates by controlled-potential electrodeposition and characterized by scanning electron microscope, energy-dispersive spectrometer (EDS), and powder X-ray diffraction spectrometer (XRD). EDS analysis indicated that the purity of the Mn electrodeposits was good, although no crystal signal of Mn was observed in the XRD patterns.

Electrodeposition of Al coating on Mg alloy from Al chloride/1-ethyl-3-methylimidazolium chloride ionic liquids with different Lewis acidity

Abstract Electrodeposition of a metallic Al layer on a Mg alloy from a Lewis acidic Al chloride–1-ethyl-3-methylimidazolium chloride (EMIC) ionic liquid has been carried out at room temperature. The effects of the AlCl3 to EMIC molar ratio, in the range from 50%–50% to 60%–40%, on the electrodeposition characteristics were investigated. Scanning electron microscopy, X-ray energy dispersive spectroscopy, and X-ray diffractometry were used to examine the surface morphology, the chemical composition, and the crystal structure of the deposited layers prepared in the ionic liquids with different AlCl3 to EMIC ratios. The improvement of corrosion resistance of a Mg alloy to the Al surface coating was also evaluated by means of various electrochemical methods. The electrochemical impedance spectroscopic data indicated that while a bare Mg alloy had a polarisation resistance of only 470 Ω cm2 in 3˙5 wt-% NaCl solution, the Al coated sample deposited in the ionic liquid with 60%AlCl3 showed a resistance as high as 5200 Ω cm2 in the same environment.