Aoyama, Takahito; Sugawara, Yu*; Muto, Izumi*; Hara, Nobuyoshi*
Journal of the Electrochemical Society, 166(10), p.C250 - C260, 2019/01
The role of NO 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. NO 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 to ca. 5 A cm. After that, the current density suddenly decreased to less than 0.1 A cm. 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. It would appear that the generation of NH results in a pH increase and the further suppression of active dissolution, and then repassivation occurs.
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
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
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
The effects of surface coatings on LiMnO were investigated using LiMnO epitaxial thin films with a thickness of 30 nm. Bare and surface-coated LiMnO epitaxial thin films were synthesized on SrTiO(111) substrates using a pulsed laser deposition method. The surface coating, which was formed using the solid electrolyte LiPO and had a thickness of 3 nm, improved the reversibility of the electrochemical reactions undergone by the LiMnO epitaxial thin films. The changes induced in the surface structure were maintained during battery operation; in contrast, the bare LiMnO 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 LiPO coating and improved the electrochemical performance of the LiMnO thin-film electrode.
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
Graft-type anion-conducting electrolyte membranes (AEMs) with imidazolium cations on graft polymers were synthesized through radiation-induced graft polymerization of -vinylimidazole (NVIm) on poly(ethylene-co-tetrafluoroethylene) (ETFE) films, followed by -propylation and ion-exchange reactions. The -propylation proceeded quantitatively, whereas the ion-exchange reactions in 1 M KOH at 60C were accompanied by partial -elimination of the imidazolium cations(AEM2), which exhibited an ion-exchange capacity (IEC) of 0.85 mmol g and ionic conductivity of 10 mS cm. AEM2 showed alkaline stability at 60C but it gradually degraded at 80C for ca. 150 h. The copolymer-type AEM (AEM3) with an IEC of 1.20 mmol g was prepared through the copolymerization of NVIm with styrene on ETFE films, followed by the same -propylation and ion-exchange reactions. AEM3 was shown higher alkaline durability in 1 M KOH at 80C. As a result, it exhibited higher conductivity (10 mS cm) 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 is obtained for AEM3 in a direct hydrazine hydrate fuel cell.
Soma, Yasutaka; Kato, Chiaki; Yamamoto, Masahiro
Journal of the Electrochemical Society, 159(8), p.C334 - C340, 2012/07
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.
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
A manganese-based solid solution with the composition of LiMnCoO 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 LiMnO-type structure model with a space group symmetry of 2/. In cycling of the cell in the potential range from 2.0 to 4.8 V at current densities of 30 mAhg, the discharge capacity characteristically increases from 46.3 to 196.5 mAhg as the cycle increases from 1 to 11, and a discharge capacity above 175.5 mAhg 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.
Ben youcef, H.*; Gubler, L.*; Yamaki, Tetsuya; Sawada, Shinichi; Alkan Grsel, S.*; Wokaun, A.*; Scherer, G. G.*
Journal of the Electrochemical Society, 156(4), p.B532 - B539, 2009/02
The effect of cross-linker content on the chemical stability of poly(ethylene--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--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 V/h over the testing time at a current density of 500 mA/cm and a cell temperature of 80C, 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.
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
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 LiMnO. 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 LiMnO.
Kuznetsov, S. A.*; Hayashi, Hirokazu; Minato, Kazuo; Gaune-Escard, M.*
Journal of the Electrochemical Society, 152(4), p.C203 - C212, 2005/04
The electrochemical behavior of UCl and UCl 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 EU(IV)/U(III), EU(IV)/U, and EU(III)/U were determined and some thermodynamic properties of UCl and UCl dissolved in LiCl-KCl eutectic melt were calculated. Influence of oxide ions on electrochemical behavior was also studied.
Kawamura, Hiroyuki; Takahashi, Masamitsu; Mizuki, Junichiro
Journal of the Electrochemical Society, 149(11), p.C586 - C591, 2002/11
no abstracts in English
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
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 () R30 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.
Monguchi, Takuo*; Fujioka, Hiroshi*; Uragami, Takeshi*; Ono, Kanta*; Baba, Yuji; Oshima, Masaharu*
Journal of the Electrochemical Society, 147(2), p.741 - 743, 2000/02
no abstracts in English
Sakamura, Y.*; Shirai, Osamu; Iwai, Takashi; Suzuki, Yasufumi
Journal of the Electrochemical Society, 147(2), p.642 - 649, 2000/02
no abstracts in English