Electrochemistry
Online ISSN : 2186-2451
Print ISSN : 1344-3542
ISSN-L : 1344-3542
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The 65th special feature “Fluorine Chemistry and Materials for Electrochemistry”
Article
  • Mikio HATA, Takaaki TANAKA, Daichi KATO, Jae-Ho KIM, Susumu YONEZAWA
    2021 Volume 89 Issue 3 Pages 223-229
    Published: May 05, 2021
    Released: May 05, 2021
    [Advance publication] Released: February 05, 2021
    JOURNALS OPEN ACCESS

    A Ni(OH)2 surface was fluorinated at 25 °C using F2 gas for 1 h under absolute pressure of 6.67 kPa. Some fluorides and oxyfluorides were detected only on the Ni(OH)2 particle surface, although most Ni(OH)2 remained inside of the particles. Fluorine-introduced NiO (NiO(F)) was obtained by heating the surface-fluorinated Ni(OH)2. After sintering at 750 °C for 6 h, the NiO(F) crystal size and surface area were, respectively, 0.6 times smaller and 4.7 times larger than those of NiO obtained from untreated Ni(OH)2. LiNiO2 samples were prepared via reaction between NiO(F) and Li2CO3 at 700 °C for 20 h and 30 h, respectively (LiNiO2 (20 h, F) and LiNiO2 (30 h, F)). The density of LiNiO2 (30 h, F) was 4.697, which was larger than the 4.556 of LiNiO2 prepared from NiO and Li2CO3 under the same conditions. The discharge capacity of LiNiO2 (30 h, F) was 202 mAh g−1, whereas the LiNiO2 prepared under the same condition from NiO and Li2CO3 was 172 mAh g−1. The discharge capacity of LiNiO2 as a cathode of LIB might be improved by introducing fluorine to its preparation process between NiO and Li2CO3.

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Articles
  • Yoshiyuki FURUSHO, Fumiaki AMANO
    2021 Volume 89 Issue 3 Pages 234-238
    Published: May 05, 2021
    Released: May 05, 2021
    [Advance publication] Released: February 05, 2021
    JOURNALS OPEN ACCESS
    Supplementary material

    We report amorphous iridium oxide (IrO2) and tantalum oxide (Ta2O5) electrocatalysts supported on titanium fiber felt as effective anodes for oxygen evolution reaction (OER). The IrO2-Ta2O5 electrode, prepared by thermal decomposition of the precursor added with polyethylene glycol (PEG), achieved a current density of 10 mA cm−2 at a low overpotential of 0.24 V in a sulfuric acidic solution. The high OER activity is because PEG generated mesopores in the amorphous IrO2-Ta2O5 layer after heating at 350 °C. The increase in the double-layer capacitance, proportional to the electrochemically active surface area (ECSA), was responsible for the high current density at low overpotentials. Furthermore, the addition of the polymer to the precursor suppressed the dissolution of Ir from the anode during the OER stability test and improved the durability of the IrO2-Ta2O5 electrocatalyst coated on the Ti felt.

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  • Kazuto KOGANEI, Atsushi SAKUDA, Tomonari TAKEUCHI, Hisao KIUCHI, Hikar ...
    2021 Volume 89 Issue 3 Pages 239-243
    Published: May 05, 2021
    Released: May 05, 2021
    [Advance publication] Released: February 06, 2021
    JOURNALS OPEN ACCESS

    Amorphous VS4 (a-VS4) electrode material was synthesized by mechanical milling of crystalline VS4 (c-VS4). The columbic efficiency of the a-VS4 cell was significantly improved (ca. 86 %) at the first cycle as compared with the c-VS4 cell (ca. 77 %), resulting in the improved capacity retention for prolonged cycling. Pair distribution function (PDF) analysis obtained from X-ray total scattering data, revealed that the radial atomic distribution of a-VS4 at initial stage was similar to that of the low-crystalline VS4 appeared after the first cycle of c-VS4. This is suggestive that the amorphization via mechanical milling process gave rise to the preparation of “first cycled VS4” which would contribute to the improved columbic efficiency at the first cycle and the resulting improved capacity retention for prolonged cycling. The structure of a-VS4 could be visualized by first-principles molecular dynamic calculation of “first-cycled VS4”.

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  • Akira NISHIO, Nobuaki SHIRAI, Hironari MINAMI, Hiroaki IZUMI, Atsushi ...
    2021 Volume 89 Issue 3 Pages 244-249
    Published: May 05, 2021
    Released: May 05, 2021
    [Advance publication] Released: February 10, 2021
    JOURNALS OPEN ACCESS
    Supplementary material

    To reduce the interfacial resistance between the electrodes and electrolyte in all solid-state battery, we have recently suggested the idea of a single-phase all-solid-state battery that is made from a single material with the three roles of electrolyte, positive electrode and negative electrode. In this research, the effects of Na3BO3 addition into Na3V2(PO4)3 were investigated with respect to the electrochemical properties. Na3BO3 addition improved the relative density of Na3V2(PO4)3 by acting as a flux to fill the voids of the sintered body, as confirmed by scanning electron microscopy (SEM) observations. The electrical conductivity is increased by the addition of Na3BO3, although the activation energy is also increased. Charge/discharge measurement revealed that Na3V2(PO4)3+Na3BO3 pellets exhibit improved cyclability and optical observation indicated a different mechanism for the in-situ formation of the electrode from a Na3V2(PO4)3 pellet.

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  • Shinsuke ANDOH, Akira FUJITA, Takeshi MIITSU, Yoshiyuki KURODA, Shigen ...
    2021 Volume 89 Issue 3 Pages 250-255
    Published: May 05, 2021
    Released: May 05, 2021
    [Advance publication] Released: February 20, 2021
    JOURNALS OPEN ACCESS

    An electrochemical methanol concentration sensor with practicality and reliability has been developed to apply for a direct methanol fuel cell (DMFC) system. The methanol concentration can be estimated simply by the original algorithm based on the Arrhenius law and diffusion limiting current, even though the complex oxidation current characteristics for the methanol concentration and temperature. The oxidation current of methanol shows linearity against the methanol concentration up to 10 wt% (15 mgPt cm−2 at anode) with quick response. The sensor also has a high durability for 6500 h in the simulated DMFC operating temperature.

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  • Chiaki ISHIBASHI, Mai ICHIYAMA, Naoya ISHIDA, Naoto KITAMURA, Yasushi ...
    2021 Volume 89 Issue 3 Pages 256-266
    Published: May 05, 2021
    Released: May 05, 2021
    [Advance publication] Released: February 26, 2021
    JOURNALS OPEN ACCESS
    Supplementary material

    In this study, the projected density of states (PDOS) of the stable normal-spinel structure and stable Mg/Co mixed-cation spinel structure of Mg1+yCo2−xMnxO4 (x = 0, 0.5; y = 0, 0.5, 1) in the pristine and discharged states are obtained using first-principles calculations. The spin state and the valence state of the transition metals are investigated. The overlaps of the d orbitals of the transition metals and the p orbitals of oxygen are large, and the covalency between the transition metal and oxygen is strong in the pristine MgCo2O4 and MgCo1.5Mn0.5O4. The M–O6 (M = Co, Mn) octahedra become stable as a host structure. From the PDOS spectra, Co atoms are in the trivalent low-spin state in pristine MgCo2O4 and MgCo1.5Mn0.5O4 and Mn atoms are nearly tetravalent in pristine MgCo1.5Mn0.5O4. In the discharge process, the overlap of the d orbitals of the transition metals and the p orbitals of oxygen becomes narrow and the valence of the transition metals decreases with increasing Mg insertion. The results of the first-principles calculations are consistent with those of X-ray absorption near edge structure spectra.

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  • Yu SHAO, Jiaojiao QI, Boyu YUAN, Liang LI, Chao WANG
    2021 Volume 89 Issue 3 Pages 267-272
    Published: May 05, 2021
    Released: May 05, 2021
    [Advance publication] Released: March 05, 2021
    JOURNALS OPEN ACCESS

    Electrochemical methods were used in conjunction with digital holography to study the effects of an environmentally friendly inhibitor, polyaspartic acid (PASP), on the anodic dissolution of Inconel® 600 in a 0.04 M HCl solution. The pitting inhibition ability was enhanced and the inhibition efficiency increased with the PASP concentration, reaching 84.13 % at 6.66 g L−1 PASP. A digital holograph was used to observe the in situ hydrolysis of M2+ (M = Ni and Fe) near the electrode surface during anodic dissolution and showed the formation of a surface film on the electrode. The inhibitory effects of PASP on Inconel® 600 may be caused by the adsorption of PASP and the formation of a PASP metal complex (PASP-M complex), which may seal defects in the surface film.

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  • Yuki UMEMURA, Tomonari TAKEUCHI, Hikari SAKAEBE, Hisao KIUCHI, Toyonar ...
    2021 Volume 89 Issue 3 Pages 273-278
    Published: May 05, 2021
    Released: May 05, 2021
    [Advance publication] Released: March 03, 2021
    JOURNALS OPEN ACCESS
    Supplementary material

    Vanadium tetrasulfide (VS4) have been attracting attention as the promising positive electrode material for next generation batteries because of its high theoretical capacity (1196 mAh g−1). In this study, a typical element (i.e., Phosphorus) was introduced into VS4 for an attempt to improve the electrochemical cycle performance of VS4. The prepared PxVSy showed significant increase in cycle capability; e.g., ca. 70 % after 50 cycles for P0.4VS5.0 sample cell, being much higher than that of pristine VS4 cell (ca. 10 %). The PDF (pair distribution function) analyses indicated that the structural reversibility of VS4 for Li insertion/extraction reactions was improved by the phosphorus addition.

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  • Liang HUANG, Yan CAO, Chunlei TIAN, Ruochen ZHAO, Jiang DU, Yuanfei WA ...
    2021 Volume 89 Issue 3 Pages 279-289
    Published: May 05, 2021
    Released: May 05, 2021
    [Advance publication] Released: March 10, 2021
    JOURNALS OPEN ACCESS
    Supplementary material

    To address the problems of serious tool loss and the easy deformation of aero-rotor blade profiles in NC milling technology, electrochemical machining can realize the processing of complex, specially structured products with advanced materials such as nickel alloy Inconel®718 by means of a non-contact electrochemical etching process. In this paper, by analysing the electrochemical reaction state of Inconel®718 alloy in vertical electrolytic processing, the electrolyte side flow of aero-blade electrochemical machining technology is innovatively transplanted to the traditional vertical single-axis feed machining tool, and the corresponding optimized flow channel structure that combines the characteristics of positive flow mode and side flow mode are proposed. Then, the verification test shows that the vertical machining of aero-blade with the characteristics of positive flow and side flow of electrolyte has high machining quality, and its surface error is in the range of 0.02–0.12 mm (the average surface error can reach 0.07 mm), the corresponding surface roughness is 1.16 µm. Therefore, the research foundation and technical potential are laid for the vertical electrochemical machining of the aero-rotor blades.

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  • Yu SUGIMOTO, Nobutaka FUJIEDA, Kenji KANO
    2021 Volume 89 Issue 3 Pages 290-295
    Published: May 05, 2021
    Released: May 05, 2021
    [Advance publication] Released: March 05, 2021
    JOURNALS OPEN ACCESS
    Supplementary material

    Electrostatic interactions greatly affect the interaction and activity of ions and charged molecules. In this study, electrochemical techniques were applied to evaluate the electrostatic interactions of zwitterions and proteins as charged molecules that have partially overlapped electric field. The formal potential of a probe redox couple, [Fe(CN)6]3−/4−, was used as a measure of the electrostatic interaction between the probe ions and linear amino acids as zwitterions. The zwitterions clearly showed electrostatic interaction with [Fe(CN)6]3−/4−, but the strength was weakened by the partial overlapping of the electric field of oppositely charged sites. Furthermore, we investigated the electrostatic interaction between proteins as multivalent polymeric ions using quinohemoprotein amine dehydrogenase and its electron accepter proteins (amicyanin, cytochrome c550, and horse heart cytochrome c). The second-order reaction rate constant (k) of the intermolecular electron transfer between the proteins was electrochemically determined in various ionic strengths (I). The I dependences of k were explained not by the net charges but by the local charges around the interaction interfaces of the proteins.

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  • Ruoyu QIU, Zhuangchun WU
    2021 Volume 89 Issue 3 Pages 296-302
    Published: May 05, 2021
    Released: May 05, 2021
    [Advance publication] Released: March 10, 2021
    JOURNALS OPEN ACCESS

    The high energy density of nickel-rich LiNi0.8Co0.1Mn0.1O2 (NCM811) was hindered the wide usage of this material, by the lack of interface stability which will reduce its long cycle electrochemical performance. In this paper, lithium fluoride nanoparticles were used as artificial cathode-electrolyte interphase to protect the NCM811 from vigorous SEI formation. Since the conductivity of lithium fluoride will reduce the electrode’s electron mobility, 1 wt% multi-wall carbon nanotubes were added to mitigate this issue. Scanning electron microscope and energy disperse spectroscopy represent that the lithium fluoride and multi-wall carbon nanotubes were both evenly dispersed throughout the electrode. After cycled at the same higher c-rates, the specific capacity retention at C/5-rate of the Pristine NCM811 decreased from 92.76 % to 86.55 % (158.7 mAh g−1) while the LiF 5 wt% + MWCNTs 1 wt% modified NCM811 decreased from 96.04 % to 91.77 % (182.6 mAh g−1). The outstanding electrochemical performance is mainly attribute to the artificial cathode-electrolyte interphase, which protects the cathode from side reactions and the consumption of electrolyte. The pulse measurements were also carried out after 50th cycle of 1 C-rate, and the total voltage change of the Pristine sample was up to 1.5336 V at maximum current rate of 10 C, while that of LiF 5 wt% + MWCNTs 1 wt% modified sample was only 0.3408 V, revealing that the artificial cathode-electrolyte interphase could reduce the polarization generated during cycles and the good conductivity by adding MWCNTs.

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Notes
  • Tsutomu HASHIMOTO, Hirokazu MUNAKATA, Kiyoshi KANAMURA
    2021 Volume 89 Issue 3 Pages 303-312
    Published: May 05, 2021
    Released: May 05, 2021
    [Advance publication] Released: January 30, 2021
    JOURNALS OPEN ACCESS
    Supplementary material

    The initial degradation behavior of lithium-ion batteries is complicated, and it has been difficult to construct a model that sufficiently matches the capacity change in cycle life tests and calendar life tests under different conditions. In this study, we measured the performance and lifetime of LiFePO4/Graphite lithium-ion battery and analyzed their electrochemical and degradation characteristics. As a result, we predicted the mechanism as follows. There are two or more phases of side reactions, including reversible reaction that forms the SEI layer and the sequential reaction that produces the non-rechargeable substance. These reactions proceed simultaneously, and each reaction rate changes depending on the electrode potential. In addition, the SEI layer is formed by the former reversible reaction and prevents the diffusion of the deteriorated substance. This model is able to fit to the complicated degrading behavior of the lithium-ion battery.

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  • Naoko SATO, Kouta TAKEDA, Nobuhumi NAKAMURA
    2021 Volume 89 Issue 3 Pages 313-316
    Published: May 05, 2021
    Released: May 05, 2021
    [Advance publication] Released: February 06, 2021
    JOURNALS OPEN ACCESS
    Supplementary material

    A copper-electrodeposited gold electrode that can quantitatively detect creatinine without being affected by urine components and can use collected urine as it is produced. In this study, the effect of interfering compounds was eliminated, and the linear range was expanded by increasing the concentration of Nafion covering the electrodes. Furthermore, by extending the electrodeposition time, the linear range was further expanded, and it was possible to measure concentrations up to 12.3 mM (M = mol dm−3), which is equivalent to the creatinine concentration range in the urine of healthy individuals.

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  • Yuto NAKAGAWA, Seiya TSUJIMURA
    2021 Volume 89 Issue 3 Pages 317-322
    Published: May 05, 2021
    Released: May 05, 2021
    [Advance publication] Released: February 09, 2021
    JOURNALS OPEN ACCESS
    Supplementary material

    Organic redox capacitors using neutral aqueous electrolyte solutions are environmentally friendly and safe. In this study, we report on the fabrication of an all-organic redox capacitor using NaCl solution. We used a 2,2,6,6-tetramethylpiperidinyl-N-oxyl (TEMPO) benzene derivative (4-hydroxy TEMPO benzoate, HTB) and 9,10-anthraquinone (AQ) as active materials for the positive electrode and negative electrode, respectively. The former has a positive redox potential, and the latter reacts with two electrons, which enhances the energy density. The capacitor fabricated with HTB and AQ has an energy density of 8.36 W h kg−1 at a rate of 10 C, which is nearly two times higher than that of the electric double-layer capacitor consisting of Ketjen black. The cycle test indicates that important factors affecting its performance are the ion diffusion and the dispersion of the active materials.

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  • Hiroshi YAMADA, Nobutaka YAMANAKA, Kenji YASUNAGA
    2021 Volume 89 Issue 3 Pages 323-327
    Published: May 05, 2021
    Released: May 05, 2021
    [Advance publication] Released: February 10, 2021
    JOURNALS OPEN ACCESS
    Supplementary material

    A conical-shaped Pt nanoelectrode whose tip apex features an effective electrode area was fabricated and used as a probe for scanning electrochemical microscopy (SECM). Nanoelectrodes were prepared by electroplating Pt in porous pyrolyzed polydimethylsiloxane filled into the tip of a quartz nanopipette. The current–distance curves were obtained by acquiring raw (without a low-pass filter) and low-pass-filtered (10 Hz) current simultaneously while a tip approached a flat Pt substrate. The raw-current approach curve showed the transition from faradaic feedback current to electron tunneling between the tip of the probe and the substrate. Alternatively, in the low-pass-filtered approach curve, a faradaic current with an improved signal-to-noise ratio was obtained without a transient increase of the tunneling current. From scanning electron microscopy observations, voltammograms, approach-curve measurements, and digital simulations of the response of a nanoelectrode, we deduced that only the apex of the conical-shaped electrode exhibited electrochemical activity and acted as an effective electrode. The constant-distance SECM imaging of an Au-sputtered polycarbonate membrane with sub-micrometer pores and Pt nanoparticles deposited on a highly oriented pyrolytic graphite (HOPG) was successfully demonstrated using the tunneling-current-based standing approach mode.

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