I-Wen Sun

Nano-architectured Co(OH)2 electrodes constructed using an easily-manipulated electrochemical protocol for high-performance energy storage applications

A simple, low-cost, and efficient electrochemical strategy, which includes the co-deposition of a Ni–Cu layer, selective etching of Cu from the film (leaving nano-porous Ni), and electrodeposition of Co(OH)2 nano-whiskers on the obtained Ni substrate, is used to construct a nano-structured electrode. This process can be conducted on many conductive surfaces, which can be cheap, flexible, and wearable, and can be integrated into advanced mobile micro-power systems. Due to its unique nano-architecture, the prepared Co(OH)2 electrode shows exceptional energy storage performance as compared to that of the conventional version of the electrode. The optimum specific capacitance obtained in this study, evaluated using cyclic voltammetry (CV), was as high as 2800 F/g. When the CV scan rate was increased from 5 to 200 mV/s, only a 4% decay in the capacitance was found, indicating excellent high-power capability. These characteristics make the nano-structured Co(OH)2 electrode a promising candidate for supercapacitor applications.

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).

Electrodeposition of cobalt and zinccobalt alloys from a lewis acidic zinc chloride-1-ethyl-3-methylimidazolium chloride molten salt

Abstract The electrodeposition of cobalt and zinccobalt alloys on nickel, tungsten, copper, and glassy carbon electrodes was investigated in 40.0–60.0 mole percent (mol%) zinc chloride-1-ethyl-3-methylimidazolium chloride molten salt containing cobalt(II) at 80°C. At potentials positive of 0.15 V (vs. Zn), cobalt deposition on nickel occurs via three-dimensional instantaneous nucleation with diffusion controlled growth of the nuclei. At potentials between 0.1 and 0.0 V, underpotential deposition of zinc on cobalt occurs. At potentials more negative than −0.1 V, bulk zinc deposition takes place via three-dimensional instantaneous nucleation with mixed diffusion and kinetic controlled growth. The zinc content of the ZnCo alloys was found to vary nonlinearly with the deposition potential. X-ray diffraction measurements indicate that the ZnCo deposits with a low zinc content may be amorphous and the crystalline nature of the ZnCo electrodeposits increases as the zinc content of the deposits increases. Addition of propylene carbonate co-solvent to the melt solution decreases the melting temperature of the solution and enables the electrodeposition to be performed at 40°C.

Lewis acidity dependency of the electrochemical window of zinc chloride-1-ethyl-3-methylimidazolium chloride ionic liquids

Abstract Negative ion fast atom bombardment mass spectra (FAB-MS) recorded for ZnCl 2 –1-ethyl-3-methylimidazolium chloride (ZnCl 2 –EMIC) ionic liquids with various compositions indicate that various Lewis acidic chlorozincate clusters (ZnCl 3 − , Zn 2 Cl 5 − and Zn 3 Cl 7 − ) are present in ZnCl 2 –EMIC ionic liquids depending on the percentage of ZnCl 2 used in preparing the ionic liquids; higher ZnCl 2 percentage favors the larger clusters. Cyclic voltammetry reveals that the potential limits for a basic 1:3 ZnCl 2 –EMIC melt correspond to the cathodic reduction of EMI + and anodic oxidation of Cl − , giving an electrochemical window of approximately 3.0 V which is the same as that observed for basic AlCl 3 –EMIC ionic liquids. For acidic ionic liquids that have a ZnCl 2 /EMIC molar ratio higher than 0.5:1, the negative potential limit is due to the deposition of metallic zinc, and the positive potential limit is due to the oxidation of the chlorozincate complexes. All the acidic ionic liquids exhibit an electrochemical window of approximately 2 V, although the potential limits shifted in the positive direction with increasing ZnCl 2 mole ratio. Underpotential deposition of zinc was observed on Pt and Ni electrodes in the acidic ionic liquids. At proper temperatures and potentials, crystalline zinc electrodeposits were obtained from the acidic ionic liquids.

Electrochemical study of copper in a basic 1-ethyl-3-methylimidazolium tetrafluoroborate room temperature molten salt

Abstract The electrochemistry and electrodeposition of copper was investigated on polycrystalline tungsten, platinum and on glassy carbon electrodes in 1-ethyl-3-methylimidazolium tetrafluoroborate room temperature molten salt containing excess 1-ethyl-3-methylimidazolium chloride. Experiments performed in a N2-filled dry box show that Cu(I) can be oxidized to Cu(II) or reduced to Cu metal. The Cu(I)/Cu(II) redox couple exhibits a quasi-reversible charge-transfer behavior. The electrodeposition of copper on the platinum electrode was proceeded by underpotential deposition (UPD), whereas the electrodeposition of copper at glassy carbon and tungsten electrodes requires a nucleation overpotential. Although under ambient atmosphere, this melt absorbs some moisture, it is still stable because no significant difference was observed between the staircase cyclic voltammograms of the melt itself obtained in a N2-filled glove box and under ambient air. The electrochemical behavior of copper in this melt under the ambient atmosphere is very similar to that observed under the glove box atmosphere, except that Cu(I) spontaneously converts to Cu(II) in ambient air. Electrodeposits of Cu were obtained from experiments performed both in a glove box and under ambient atmosphere. Scanning electron microscope (SEM) results showed that the deposits were fairly dense.

Synthesis and Characterization of Organic Dyes Containing Various Donors and Acceptors

New organic dyes comprising carbazole, iminodibenzyl, or phenothiazine moieties, respectively, as the electron donors, and cyanoacetic acid or acrylic acid moieties as the electron acceptors/anchoring groups were synthesized and characterized. The influence of heteroatoms on carbazole, iminodibenzyl and phenothiazine donors, and cyano-substitution on the acid acceptor is evidenced by spectral, electrochemical, photovoltaic experiments, and density functional theory calculations. The phenothiazine dyes show solar-energy-to-electricity conversion efficiency (η) of 3.46–5.53%, whereas carbazole and iminodibenzyl dyes show η of 2.43% and 3.49%, respectively.

Electrochemistry of Cd(II) in the basic 1-ethyl-3-methylimidazolium chloride/tetrafluoroborate room temperature molten salt

Abstract The electrochemistry of cadmium species was investigated at glassy carbon, polycrystalline tungsten and platinum electrodes in a basic 1-ethyl-3-methylimidazolium chloride/tetrafluoroborate room temperature molten salt. Amperometric titration experiments suggest that Cd(II) chloride is complexed as [CdCl 4 ] 2− in this melt. [CdCl 4 ] 2− could be reduced to cadmium metal via a single-step quasi-reversible electron transfer process. On the other hand, effective dissolution of cadmium to Cd(II) is effected by the presence of sufficient chloride ions. The electrodeposition of cadmium proceeds via three-dimensional progressive nucleation with diffusion-controlled growth. The average Stokes–Einstein product for [CdCl 4 ] 2− is (2.3±0.1)×10 −10 g cm s −2 K −1 . The cadmium electrodeposits are found to be very pure and adhere well on the tungsten substrate.

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.

Electrodeposition of Cu‐Zn Alloy from a Lewis Acidic ZnCl2 ‐ EMIC Molten Salt

The electrodeposition of copper and copper-zinc alloys was investigated on tungsten and nickel electrodes in a Lewis acidic 50.0-50.0 mol % zinc chloride-1-ethyl-3-methylimidazolium chloride molten salt containing copper(I). The composition of the electrodeposited Cu-Zn alloys can be varied by deposition potential, temperature, and Cu(I) concentration of the plating bath. Analysis of the chronoamperometric transient behavior during electrodeposition suggests that pure copper electrodeposition proceeds via three-dimensional instantaneous nucleation with diffusion-controlled growth. However, as the deposition potential crosses from Cu metal into the alloy-forming range, the nucleation process changes to three-dimensional progressive nucleation with diffusion-controlled growth. Analysis of the X-ray diffraction patterns indicates that the electrodeposited Cu-Zn alloys exhibit a and β phases. The surface morphologies and the compositions of the electrodeposited Cu-Zn alloys were studied with scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS).

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.