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Journal Articles

NH$$_4$$$$^+$$ generation; The Role of NO$$_3$$$$^-$$ in the crevice corrosion repassivation of type 316L stainless steel

Aoyama, Takahito; Sugawara, Yu*; Muto, Izumi*; Hara, Nobuyoshi*

Journal of the Electrochemical Society, 166(10), p.C250 - C260, 2019/01

 Times Cited Count:2 Percentile:13.91(Electrochemistry)

The role of NO$$_3$$$$^-$$ in the repassivation of crevice corrosion of Type 316L stainless steel was investigated. In crevice corrosion tests, the solution was changed from 1 M NaCl to NaCl-NaNO$$_3$$. NO$$_3$$$$^-$$ led to complete repassivation. Repassivation of the crevice corrosion was found to take place in two steps. In the first step, the estimated current density inside the crevice gradually decreased from ca. 5 mA cm$$^{-2}$$ to ca. 5 $$mu$$A cm$$^{-2}$$. After that, the current density suddenly decreased to less than 0.1 $$mu$$A cm$$^{-2}$$. From the potentiodynamic polarization in acidic solutions simulated inside the crevice (pH 0.2) and in situ observations of the crevice corrosion morphology, the first step was thought to be generated by the suppression of active dissolution by NO$$_3$$$$^{-}$$. It would appear that the generation of NH$$_{4}^{+}$$ results in a pH increase and the further suppression of active dissolution, and then repassivation occurs.

Journal Articles

NiO/Nb$$_{2}$$O$$_{5}$$/C hydrazine electrooxidation catalysts for anion exchange membrane fuel cells

Sakamoto, Tomokazu*; Masuda, Teruyuki*; Yoshimoto, Koji*; Kishi, Hirofumi*; Yamaguchi, Susumu*; Matsumura, Daiju; Tamura, Kazuhisa; Hori, Akihiro*; Horiuchi, Yosuke*; Serov, A.*; et al.

Journal of the Electrochemical Society, 164(4), p.F229 - F234, 2017/01

 Times Cited Count:11 Percentile:52.44(Electrochemistry)

Journal Articles

Mechanism study of hydrazine electrooxidation reaction on nickel oxide surface in alkaline electrolyte by in situ XAFS

Sakamoto, Tomokazu*; Kishi, Hirofumi*; Yamaguchi, Susumu*; Matsumura, Daiju; Tamura, Kazuhisa; Hori, Akihiro*; Horiuchi, Yosuke*; Serov, A.*; Artyushkova, K.*; Atanassov, P.*; et al.

Journal of the Electrochemical Society, 163(10), p.H951 - H957, 2016/08

 Times Cited Count:21 Percentile:75.3(Electrochemistry)

Journal Articles

Interfacial analysis of surface-coated LiMn$$_{2}$$O$$_{4}$$ epitaxial thin film electrode for lithium batteries

Suzuki, Kota*; Hirayama, Masaaki*; Kim, K.-S.*; Taminato, So*; Tamura, Kazuhisa; Son, J.-Y.*; Mizuki, Junichiro; Kanno, Ryoji*

Journal of the Electrochemical Society, 162(13), p.A7083 - A7090, 2015/08

 Times Cited Count:8 Percentile:33.81(Electrochemistry)

The effects of surface coatings on LiMn$$_{2}$$O$$_{4}$$ were investigated using LiMn$$_{2}$$O$$_{4}$$ epitaxial thin films with a thickness of 30 nm. Bare and surface-coated LiMn$$_{2}$$O$$_{4}$$ epitaxial thin films were synthesized on SrTiO$$_{3}$$(111) substrates using a pulsed laser deposition method. The surface coating, which was formed using the solid electrolyte Li$$_{3}$$PO$$_{4}$$ and had a thickness of 3 nm, improved the reversibility of the electrochemical reactions undergone by the LiMn$$_{2}$$O$$_{4}$$ epitaxial thin films. The changes induced in the surface structure were maintained during battery operation; in contrast, the bare LiMn$$_{2}$$O$$_{4}$$ thin film exhibited structural degradation and Mn dissolution. The structural changes induced in the coated electrode and the increase in its surface stability were intrinsic effects of the Li$$_{3}$$PO$$_{4}$$ coating and improved the electrochemical performance of the LiMn$$_{2}$$O$$_{4}$$ thin-film electrode.

Journal Articles

Imidazolium cation based anion-conducting electrolyte membranes prepared by radiation induced grafting for direct hydrazine hydrate fuel cells

Yoshimura, Kimio; Koshikawa, Hiroshi; Yamaki, Tetsuya; Shishitani, Hideyuki*; Yamamoto, Kazuya*; Yamaguchi, Susumu*; Tanaka, Hirohisa*; Maekawa, Yasunari

Journal of the Electrochemical Society, 161(9), p.F889 - F893, 2014/06

 Times Cited Count:20 Percentile:66.26(Electrochemistry)

Graft-type anion-conducting electrolyte membranes (AEMs) with imidazolium cations on graft polymers were synthesized through radiation-induced graft polymerization of ${it N}$-vinylimidazole (NVIm) on poly(ethylene-co-tetrafluoroethylene) (ETFE) films, followed by ${it N}$-propylation and ion-exchange reactions. The ${it N}$-propylation proceeded quantitatively, whereas the ion-exchange reactions in 1 M KOH at 60$$^{circ}$$C were accompanied by partial $$beta$$-elimination of the imidazolium cations(AEM2), which exhibited an ion-exchange capacity (IEC) of 0.85 mmol g$$^{-1}$$ and ionic conductivity of 10 mS cm$$^{-1}$$. AEM2 showed alkaline stability at 60$$^{circ}$$C but it gradually degraded at 80$$^{circ}$$C for ca. 150 h. The copolymer-type AEM (AEM3) with an IEC of 1.20 mmol g$$^{-1}$$ was prepared through the copolymerization of NVIm with styrene on ETFE films, followed by the same ${it N}$-propylation and ion-exchange reactions. AEM3 was shown higher alkaline durability in 1 M KOH at 80$$^{circ}$$C. As a result, it exhibited higher conductivity ($$>$$10 mS cm$$^{-1}$$) for 250 h. Therefore, alkylimidazolium cations in copolymer grafts are a promising anion conducting group for alkaline-durable AEMs. A maximum power density of 75 mW cm$$^{-2}$$ is obtained for AEM3 in a direct hydrazine hydrate fuel cell.

Journal Articles

Surface oxide layers on 316L stainless steel formed in 561 K pure water at different potentials

Soma, Yasutaka; Kato, Chiaki; Yamamoto, Masahiro

Journal of the Electrochemical Society, 159(8), p.C334 - C340, 2012/07

 Times Cited Count:7 Percentile:28.74(Electrochemistry)

Surface oxide layers on stainless steel were formed in 561 K pure water at different potentials. To understand the oxide's properties in terms of their potential dependence, cross-sectional views of the oxide layer were analyzed using an electron microprobe technique and potential-solubility (equilibrium concentration of ionic species) diagram. In the potential range investigated, duplex oxide layers composed of mono- and bimetallic oxide were formed. Both the structure and composition of the oxide layer were affected by solubility of oxides.

Journal Articles

Electrochemical characteristics of layered Li$$_{1.95}$$Mn$$_{0.9}$$Co$$_{0.15}$$O$$_{3}$$ (${it C}$2/${it m}$) as a lithium-battery cathode

Ozawa, Kiyoshi*; Nakao, Yasuhiro*; Mochiku, Takashi*; Cheng, Z.*; Wang, L.*; Iwai, Hideo*; Tsuchiya, Yoshinori*; Fujii, Hiroki*; Igawa, Naoki

Journal of the Electrochemical Society, 159(3), p.A300 - A304, 2012/01

 Times Cited Count:13 Percentile:49.71(Electrochemistry)

A manganese-based solid solution with the composition of Li$$_{1.95}$$Mn$$_{0.9}$$Co$$_{0.15}$$O$$_{3}$$ was synthesized by a simplified coprecipitation method, and its electrochemical characteristics as a lithium-battery cathode were investigated. Rietveld refinement based on neutron diffraction data revealed that the material is assigned to an Li$$_{2}$$MnO$$_{3}$$-type structure model with a space group symmetry of ${it C}$2/${it m}$. In cycling of the cell in the potential range from 2.0 to 4.8 V at current densities of 30 mAhg$$^{-1}$$, the discharge capacity characteristically increases from 46.3 to 196.5 mAhg$$^{-1}$$ as the cycle increases from 1 to 11, and a discharge capacity above 175.5 mAhg$$^{-1}$$ is obtained between the 23rd and 58th cycles. The cyclic voltammogram and X-ray photoelectron spectroscopy measurements showed that the manganese redox reaction is progressively activated during the first ten-odd cycles.

Journal Articles

Cross-linker effect in ETFE-based radiation-grafted proton-conducting membranes, 2; Extended fuel cell operation and degradation analysis

Ben youcef, H.*; Gubler, L.*; Yamaki, Tetsuya; Sawada, Shinichi; Alkan G$"u$rsel, S.*; Wokaun, A.*; Scherer, G. G.*

Journal of the Electrochemical Society, 156(4), p.B532 - B539, 2009/02

 Times Cited Count:16 Percentile:52.08(Electrochemistry)

The effect of cross-linker content on the chemical stability of poly(ethylene-${it alt}$-tetrafluoroethylene) (ETFE)-based radiation-grafted and sulfonated membranes was investigated. An ex situ degradation test in hydrogen peroxide solution showed a strong increase in stability of crosslinked membranes compared to uncrosslinked ones. Excessive crosslinking, however, is detrimental to the chemical and mechanical properties. Furthermore, the stability of grafted membranes based on ETFE was superior to those based on poly(tetrafluoroethylene-${it co}$-hexafluoropropylene) (FEP). An in situ long-term test in a hydrogen/oxygen single cell over 2180 h, using an ETFE-based grafted membrane optimized with respect to cross-linker content, with a graft level of 25% was carried out. The performance of the membrane electrode assembly exhibited a voltage decay rate of 13 $$mu$$V/h over the testing time at a current density of 500 mA/cm$$^{2}$$ and a cell temperature of 80$$^{circ}$$C, while the hydrogen permeation showed a steady increase over time. This indicates that, to some extent, changes in the membrane morphology occur over the operating period. Local postmortem analysis of the tested membrane reveals that high degradation was observed in areas adjacent to the oxygen inlet and in other areas nearby.

Journal Articles

Characterization of electrode/electrolyte interface with X-ray reflectometry and epitaxial-film LiMn$$_{2}$$O$$_{4}$$ electrode

Hirayama, Masaaki*; Sonoyama, Noriyuki*; Ito, Masumi*; Minoura, Machiko*; Mori, Daisuke*; Yamada, Atsuo*; Tamura, Kazuhisa; Mizuki, Junichiro; Kanno, Ryoji*

Journal of the Electrochemical Society, 154(11), p.A1065 - A1072, 2007/00

 Times Cited Count:80 Percentile:94.59(Electrochemistry)

Structural changes at electrode/electrolyte interface of a lithium cell were studied by X-ray reflectometry and two-dimensional model electrodes with a restricted lattice plane of LiMn$$_{2}$$O$$_{4}$$. The ex situ reflectometry indicated that a thin impurity layer covered the lattice plane of the as-grown film. The impurity layer was dissolved and a solid-electrolyte-interface-like phase appeared after the electrode was soaked into the electrolyte. The in situ observation clarified that the surface reactivity depended on the lattice planes of the spinel; the defect layer at the (111) plane was stable during the electrochemical reaction, whereas a slight decrease in the film thickness was observed for the (110) plane. Our surface characterization of the intercalation electrode indicated that the surface structure changes during the pristine stage of the change-discharge processes and these changes are dependent on the lattice orientation of LiMn$$_{2}$$O$$_{4}$$.

Journal Articles

Electrochemical behavior and some thermodynamic properties of UCl$$_4$$ and UCl$$_3$$ dissolved in a LiCl-KCl eutectic melt

Kuznetsov, S. A.*; Hayashi, Hirokazu; Minato, Kazuo; Gaune-Escard, M.*

Journal of the Electrochemical Society, 152(4), p.C203 - C212, 2005/04

 Times Cited Count:87 Percentile:93.34(Electrochemistry)

The electrochemical behavior of UCl$$_4$$ and UCl$$_3$$ dissolved in LiCl-KCl eutectic melt was studied at 723-823 K. Electroreduction of U(IV) in LiCl-KCl melt occurs via two successive steps involving transfer of one and three electrons. The diffusion coefficients of U(IV) and U(III) ions were determined by linear sweep voltammetry, chronopotentiometry, and chronoamperometry. The formal standard potential of E$$^*$$U(IV)/U(III), E$$^*$$U(IV)/U, and E$$^*$$U(III)/U were determined and some thermodynamic properties of UCl$$_4$$ and UCl$$_3$$ dissolved in LiCl-KCl eutectic melt were calculated. Influence of oxide ions on electrochemical behavior was also studied.

Journal Articles

Coverage of the Cd underpotential deposited layer formed on an Au(111) substrate; Effect of the electrolytic condition

Kawamura, Hiroyuki; Takahashi, Masamitsu; Mizuki, Junichiro

Journal of the Electrochemical Society, 149(11), p.C586 - C591, 2002/11

 Times Cited Count:14 Percentile:46.22(Electrochemistry)

no abstracts in English

Journal Articles

Evidence for the diffusion of Au atoms into the Te UPD layer formed on a Au(111) substrate

Kawamura, Hiroyuki; Takahashi, Masamitsu; Hojo, Nobuhiko*; Miyake, Masao*; Murase, Kuniaki*; Tamura, Kazuhisa*; Uosaki, Kohei*; Awakura, Yasuhiro*; Mizuki, Junichiro; Matsubara, Eiichiro*

Journal of the Electrochemical Society, 149(2), p.C83 - C88, 2002/02

 Times Cited Count:6 Percentile:22.56(Electrochemistry)

The structure of a Te layer formed on a Au(111) substrate by underpotential deposition (UPD) in an electrolytic solution has been studied using in-situ surface X-ray diffraction technique. The measurements were carried out for a series of samples which were kept at UPD potential for 4 to 59 hours. The results revealed that the Te UPD layer is unstable. The top layer is analyzed to consist of the UPD Te atoms and Au atoms which diffuse from the Au(111) substrate. Also, the Te UPD layer does not have the structure with periodicity reported in previous works, such as ($$sqrt{3}$$$$times$$$$sqrt{3}$$) R30$$^{circ}$$ after ample time elapses. Stripping voltammetry for the Te UPD layer shows that the interaction between Te and Au increases with time, supporting the finding that the top layer is a mixture of Te and Au.

Journal Articles

X-ray absorption studies of anodized monocrystalline 3C-SiC

Monguchi, Takuo*; Fujioka, Hiroshi*; Uragami, Takeshi*; Ono, Kanta*; Baba, Yuji; Oshima, Masaharu*

Journal of the Electrochemical Society, 147(2), p.741 - 743, 2000/02

 Times Cited Count:3 Percentile:15.14(Electrochemistry)

no abstracts in English

Journal Articles

Thermodynamics of neptunium in LiCl-KCl eutectic/liquid bismuth systems

Sakamura, Y.*; Shirai, Osamu; Iwai, Takashi; Suzuki, Yasufumi

Journal of the Electrochemical Society, 147(2), p.642 - 649, 2000/02

 Times Cited Count:17 Percentile:57.25(Electrochemistry)

no abstracts in English

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