• Title/Summary/Keyword: electrochemical absorption

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AC impedance study on the interface between organic electrolyte and amorphous $WO_3$ thin film relating to the electrochemical intercalation of lithium (비정질 $WO_3$ 박막과 전해질 계면에서의 리튬 층간 반응의 교류 임피던스 해석)

  • Kim Byoung-Chul;Ju Jeh-Beck;Sohn Tae-Won
    • Journal of the Korean Electrochemical Society
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    • v.1 no.1
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    • pp.33-39
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    • 1998
  • To AC impedance study was performed in this study on the interfacial reaction between organic electrolyte and amorphous tungsten oxides thin film, cathodically coloring oxide, prepared by e-beam evaporation method in the 1 M $LiClO_4/PC$ organic solution. The electrochemical reactions at the interface were analyzed by the transient method and the complex impedance spectroscopy. The impedance spectrums showed that the electro-chemical intercalation of lithium cations was consisted of the following three steps; the first step, the charge transfer reaction of lithium cation at the interface between amorphous tungsten oxides thin film and the organic electrolyte, the second step, the adsorption of lithium atom on the surface of amorphous tungsten oxides thin film, and then the third step, the absorption and the diffusion of lithium atom into amorphous tungsten oxides thin layer. The bleaching and the coloring characteristics of amorphous tungsten oxides thin film were explained in terms of thermodynamic and kinetic variables, the simulated $R_{ct},\;C_{dl},\;D$ and $\sigma_{Li}$ by CNLS fitting method. Especially it was found that the limiting values of electrochromic reaction were the molar ratio of lithium, y=0.167 and the electrode potential, E=2.245 V (vs. Li).

Photocurrent and Its Stability Enhancement of Dye-sensitized Nanoparticle $TiO_2$ Solar Cells (염료감응 나노입자 $TiO_2$ 태양전지의 광전류와 그 안정성 향상)

  • Chae Won-Weok;Kang Tae-Sik;Kim Kang-Jin
    • Journal of the Korean Electrochemical Society
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    • v.2 no.4
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    • pp.232-236
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    • 1999
  • A solar cell based on dye-sensitized photoelectric conversion was studied by electrochemical and spec-trofluorometric methods for the purposes of enhancing its efficiency and stability of $TiO_2$ solar cells. Nanocrystalline $TiO_2$ was used to prepare photoelectrodes, and photosensitizing dyes such as malachite green oxalate, basic blue3, rhodamine B, and bromocresol purple were chosen as sensitizers. Electrochemical oxidation potentials and absorption and emission wavelengths of dyes were used to determine energy levels of the dyes. By comparing excited energy levels of the dyes with the conduction band edge potential $(E_{c,s})\;of\;TiO_2$ calculated by using the flat-band potential $(E_{fb})\;of\;TiO_2$, properties of a dye required to fabricate a high efficient photosensitizing solar cell with high short-circuit current $(J_{sc})$ were suggested. Enhanced stability of photocurrent was obtained by coating a $TiO_2|ITO$ electrode with Polypyrrole that Possibly Prevented the recombination between the conduction band electrons and oxidized dyes and suppressed the direct electrode redox reactions of dyes on ITO.

Effects of Surface Characteristics of TiO2 Nanotublar Composite on Photocatalytic Activity (TiO2 복합 광촉매의 표면 특성과 광촉매 효율)

  • Lee, Jong-Ho;Youn, Jeong-Il;Kim, Young-Jig;Oh, Han-Jun
    • Korean Journal of Materials Research
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    • v.24 no.10
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    • pp.556-564
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    • 2014
  • To synthesize a high-performance photocatalyst, N doped $TiO_2$ nanotubes deposited with Ag nanoparticles were synthesized, and surface characteristics, electrochemical behaviors, and photocatalytic activity were investigated. The $TiO_2$ nanotubular photocatalyst was fabricated by anodization; the Ag nanoparticles on the $TiO_2$ nanotubes were synthesized by a reduction reaction in $AgNO_3$ solution under UV irradiation. The XPS results of the N doped $TiO_2$ nanotubes showed that the incorporated nitrogen ions were located in interstitial sites of the $TiO_2$ crystal structure. The N doped titania nanotubes exhibited a high dye degradation rate, which is effectively attributable to the increase of visible light absorption due to interstitial nitrogen ions in the crystalline $TiO_2$ structure. Moreover, the precipitated Ag particles on the titania nanotubes led to a decrease in the rate of electron-hole recombination; the photocurrent of this electrode was higher than that of the pure titania electrode. From electrochemical and dye degradation results, the photocurrent and photocatalytic efficiency were found to have been significantly affected by N doping and the deposition of Ag particles.

Evaluation of the inhibitive characteristics of 1,4-dihydropyridine derivatives for the corrosion of mild steel in 1M $H_2SO_4$

  • Sounthari, P.;Kiruthika, A.;Sai santhoshi, J.;Chitra, S.;Parameswari, K.;Selvaraj, A.
    • Corrosion Science and Technology
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    • v.12 no.2
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    • pp.65-78
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    • 2013
  • The present investigation deals with the corrosion inhibition of mild steel in 1M $H_2SO_4$ with 1, 4-dihydro pyridine and its derivatives prepared using microwave activation method. The synthesis of inhibitor was confirmed by IR spectra. The effect of 1, 4-dihydropyridine derivatives on the corrosion inhibition of mild steel in 1M $H_2SO_4$ was studied using weight loss and electrochemical polarization techniques. Influence of temperature (303-333K) and synergistic effect of halide ions ($I^-$, $Br^-$ and $Cl^-$) on the inhibition behaviour was also studied. Corrosion products on the metal surface were analyzed by scanning electron microscopy (SEM) and a possible mechanism of inhibition by the compounds is suggested. Thermodynamic parameters were calculated using weight loss data in order to elaborate the mechanism of corrosion inhibition. Polarization measurements revealed that the studied compounds acted as mixed type inhibitor but slightly anodic in nature. Electrochemical impedance measurements revealed that the compounds were adsorbed onto the carbon steel surface and the adsorption obeyed the Langmuir adsorption isotherm. The synergistic effect of halide ions on the IE increases with increase in concentration. The IE obtained from atomic absorption spectrophotometric studies was found to be in good agreement with that obtained from the conventional weight loss method. SEM revealed the information of a smooth, dense protective layer in presence of the inhibitors.

A Study on the Electronic Properties and Electrochemical Behavior of Transition Metal(Ⅳ) Complexes (Ⅳ) (전이금속(Ⅳ) 착물들의 전자적 성질과 전기 화학적 거동에 관한 연구(Ⅳ))

  • Choi, Chil Nam;Son, Hyo Youl
    • Journal of the Korean Chemical Society
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    • v.39 no.5
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    • pp.356-363
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    • 1995
  • The chemical behavior of the transition metal (Nb4+ and Mo4+) complexes with organoligand (dichloro-bis(η-cyclopentadienyl) has been investigated by the UV/vis-spectrophotometric, magnetic, and electrochemical method. The two or three energy absorption bands are observed by the spectra of these complexes. The magnitude of crystal field splitting energy, the spin pairing energy and bond strength was obtained from the spectra of the complexes. These are found to be delocalization, low-spin state, and strong bonding strength. The magnetic dipolemoment are found to be paramagnetic and diamagnetic complexes. The redox reaction processes of complexes were investigated by cyclic voltammetry in aprotic media. As a result the redox reaction proceses of Nb-C complex was couple-single reaction with diffusion and reaction current one electron process, and also Mo-C complex was couple-single reaction with reaction current of one electron process.

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Structural, Electrochemical, DNA Binding and Cleavage Properties of Nickel(II) Complex [Ni(H2biim)2(H2O)2]2+ of 2,2'-Biimidazole

  • Jayamani, Arumugam;Thamilarasan, Vijayan;Ganesan, Venketasan;Sengottuvelan, Nallathambi
    • Bulletin of the Korean Chemical Society
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    • v.34 no.12
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    • pp.3695-3702
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    • 2013
  • A nickel(II) complex $[Ni(H_2biim)_2(H_2O)_2](ClO_4)_2{\cdot}H_2O$ (1) of biimidazole ligand has been synthesized and characterized (Where $H_2biim$ = 2,2'-biimidazole). The single crystal X-ray diffraction of the complex shows a dimeric structure with six coordinated psudo-octahedral geometry. The cyclic voltammograms of complex exhibited one quasireversible reduction wave ($E_{pc}=-0.61V$) and an irreversible oxidation wave ($E_{pa}=1.28V$) in DMF solution. The interaction of the complex with Calf-Thymus DNA (CT-DNA) has been investigated by absorption and fluorescence spectroscopy. The complex is an avid DNA binder with a binding constant value of $1.03{\times}10^5M^{-1}$. The results suggest that the nickel(II) complex bind to CT-DNA via intercalative mode and can quench the fluorescence intensity of EB bind to CT-DNA with $K_{app}$ value of $3.2{\times}10^5M^{-1}$. The complex also shown efficient oxidative cleavage of supercoiled pBR322 DNA in the presence of hydrogen peroxide as oxidizing agent. The DNA cleavage by complex in presence of quenchers; viz. DMSO, KI, $NaN_3$ and EDTA reveals that hydroxyl radical or singlet oxygen mechanism is involved. The complex showed invitro antimicrobial activity against four bacteria and two fungi. The antimicrobial activity was nearer to that of standard drugs and greater than that of the free ligand.

Tuning Photophysical and Electrochemical Properties of Heteroleptic Cationic Iridium(III) Complexes Containing Substituted 2-Phenylquinoxaline and Biimidazole

  • Sengottuvelan, Nallathambi;Seo, Hoe-Joo;Kang, Sung-Kwon;Kim, Young-Inn
    • Bulletin of the Korean Chemical Society
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    • v.31 no.8
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    • pp.2309-2314
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    • 2010
  • Design and syntheses of four red phosphorescent heteroleptic cationic iridium(III) complexes containing two substituted phenylquinoxaline (pqx) or benzo[b]thiophen-2-yl-pyridin (btp) main ligands and one 2,2'-biimidazole (H2biim) ancillary ligand are reported: [$(pqx)_2$Ir(biim)]Cl (1), [$(dmpqx)_2$Ir(biim)]Cl (2), [$(dfpqx)_2$Ir(biim)]Cl (3), [$(btp)_2$Ir(biim)]Cl (4). Complex 1 showed a distorted octahedral geometry around the iridium(III) metal ion with cis metallated carbons and trans nitrogen atoms. The absorption, emission and electrochemical properties were systematically evaluated. The complexes exhibited red phosphorescence in the spectral range of 580 to 620 nm with high quantum efficiencies of 0.58 - 0.78 in both solution and solid-state at room temperature depending on the cyclometalated main ligands. The cyclic voltammetry of the complexes (1-3) showed a metal-centered irreversible oxidation in the range of 1.40 to 1.90 V as well as two quasi reversible reduction waves from -1.15 to -1.45 V attributed to the sequential addition of two electrons to the more electron accepting heterocyclic portion of two distinctive cyclometalated main ligands, whereas complex 4 showed a reversible oxidation potential at 1.24 V and irreversible reduction waves at -1.80 V.

Amorphous Vanadium Titanates as a Negative Electrode for Lithium-ion Batteries

  • Lee, Jeong Beom;Chae, Oh. B.;Chae, Seulki;Ryu, Ji Heon;Oh, Seung M.
    • Journal of Electrochemical Science and Technology
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    • v.7 no.4
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    • pp.306-315
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    • 2016
  • Amorphous vanadium titanates (aVTOs) are examined for use as a negative electrode in lithium-ion batteries. These amorphous mixed oxides are synthesized in nanosized particles (<100 nm) and flocculated to form secondary particles. The $V^{5+}$ ions in aVTO are found to occupy tetrahedral sites, whereas the $Ti^{4+}$ ions show fivefold coordination. Both are uniformly dispersed at the atomic scale in the amorphous oxide matrix, which has abundant structural defects. The first reversible capacity of an aVTO electrode ($295mAhg^{-1}$) is larger than that observed for a physically mixed electrode (1:2 $aV_2O_5$ | $aTiO_2$, $245mAhg^{-1}$). The discrepancy seems to be due to the unique four-coordinated $V^{5+}$ ions in aVTO, which either are more electron-accepting or generate more structural defects that serve as $Li^+$ storage sites. Coin-type Li/aVTO cells show a large irreversible capacity in the first cycle. When they are prepared under nitrogen (aVTO-N), the population of surface hydroxyl groups is greatly reduced. These groups irreversibly produce highly resistive inorganic compounds (LiOH and $Li_2O$), leading to increased irreversible capacity and electrode resistance. As a result, the material prepared under nitrogen shows higher Coulombic efficiency and rate capability.

Fabrication and (Photo)Electrochemical Properties of Fe2O3/Na2Ti6O13/FTO Films for Water Splitting Process (물분해용 Fe2O3/Na2Ti6O13/FTO 박막 제조 및 특성평가)

  • Yun, Kang-Seop;Ku, Hye-Kyung;Kang, Woo-Seung;Kim, Sun-Jae
    • Corrosion Science and Technology
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    • v.11 no.2
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    • pp.65-69
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    • 2012
  • One dimensional(1D) $Na_2Ti_6O_{13}$ nanorods with 70 nm in diameter was synthesized by a molten salt method. Using the synthesized nanorods, about 750 nm thick $Na_2Ti_6O_{13}$ film was coated on Fluorine-doped tin oxide(FTO) glasss substrate by the Layer-by-layer self-assembly(LBL-SA) method in which a repetitive self-assembling of ions containing an opposite electric charge in an aqueous solution was utilized. Using the Kubelka-Munk function, the band gap energy of the 1D-$Na_2Ti_6O_{13}$ nanorods was nalyzed to be 3.5 eV. On the other hand, the band gap energy of the $Na_2Ti_6O_{13}$ film coated on FTO was found to be a reduced value of 2.9 eV, resulting from the nano-scale and high porosity of the film processed by LBL-SA method, which was favorable for the photo absorption capability. A significant improvement of photocurrent and onset voltage was observed with the $Na_2Ti_6O_{13}$ film incorporated into the conventional $Fe_2O_3$ photoelectrode: the photocurrent increased from 0.25 to 0.82 mA/$cm^2$, the onset voltage decreased from 0.95 to 0.78 V.

A Study on the Anti-corrosion Properties of Organic and Inorganic Inhibitor by Electrochemical Evaluation Method in Saturated Aqueous Solution of Calcium Hydroxide (포화 수산화칼슘 수용액 내에서의 무기계 및 유기계 방청제의 전기화학적 방식 특성평가)

  • Kim, Soo-Young;Ryu, Hwa-Sung;Kim, Sung-Kil;Lee, Han-Seung
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.17 no.4
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    • pp.66-74
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    • 2013
  • In this study, corrosion potential ($E_{corr}$), corrosion rate, and polarization resistance were measured aimed at inorganic inhibitors (passive film type) and organic inhibitors (absorption type). The experiment was conducted using potentiostat for the variable molar ratio and chloride ion concentration of the components of inhibitors in an aqueous solution of saturated calcium hydroxide targeting corrosion. As a result, it was possible to ensure an anticorrosive performance of at least a 1.2 molar ratio of inorganic inhibitors. Also, the organic inhibitors ensured the prevention of the anticorrosive performance of at least about a 0.3 molar ratio. It also showed the tendency that between polarization resistance and corrosion rate, Ecorr and corrosion rate is inversely proportional to the linear. Conversely, the tendency between polarization resistance and Ecorr is proportional to the linear. Also, a distinct difference in organic and inorganic inhibitors' relationship to Ecorr, corrosion rate, and polarization resistance was not shown.