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Journal Articles

Preparation of $$gamma$$-LiV$$_{2}$$O$$_{5}$$ from polyoxovanadate cluster Li$$_{7}$$[V$$_{15}$$O$$_{36}$$(CO$$_{3}$$)] as a high-performance cathode material and its reaction mechanism revealed by ${{it operando}}$ XAFS

Wang, H.*; Idobe, Jin*; Shimizu, Takeshi*; Matsumura, Daiju; Ina, Toshiaki*; Yoshikawa, Hirofumi*

Journal of Power Sources, 360, p.150 - 156, 2017/08

 Times Cited Count:9 Percentile:44.85(Chemistry, Physical)

Journal Articles

Study on the deterioration mechanism of layered rock-salt electrodes using epitaxial thin films; Li(Ni, Co, Mn)O$$_{2}$$ and their Zr-O surface modified electrodes

Abe, Machiko*; Iba, Hideki*; Suzuki, Kota*; Minamishima, Hiroaki*; Hirayama, Masaaki*; Tamura, Kazuhisa; Mizuki, Junichiro*; Saito, Tomohiro*; Ikuhara, Yuichi*; Kanno, Ryoji*

Journal of Power Sources, 345, p.108 - 119, 2017/03

 Times Cited Count:9 Percentile:44.85(Chemistry, Physical)

The surface structure of the Li(Ni, Co, Mn)O$$_{2}$$ electrode was studied during charge/discharge process using electrochemical methods and X-ray/Neutron scattering techniques. It was found that during charge/discharge process the coverage of spinel structure increased. The spinel structure has low electrochemical activity and is not involved in Li insertion/extraction. After the surface modification, it was found that the coverage of the spinel structure did not increase. Further, it was also found out that the Li concentration at the electrode/electrolyte interface increased.

Journal Articles

Lithium intercalation and structural changes at the LiCoO$$_{2}$$ surface under high voltage battery operation

Taminato, So*; Hirayama, Masaaki*; Suzuki, Kota*; Tamura, Kazuhisa; Minato, Taketoshi*; Arai, Hajime*; Uchimoto, Yoshiharu*; Ogumi, Zempachi*; Kanno, Ryoji*

Journal of Power Sources, 307, p.599 - 603, 2016/03

 Times Cited Count:26 Percentile:73.4(Chemistry, Physical)

An epitaxial-film model electrode of LiCoO$$_{2}$$(104) was fabricated on SrRuO$$_{3}$$(100)/Nb:SrTiO$$_{3}$$(100) using pulsed laser deposition. The 50 nm thick LiCoO$$_{2}$$(104) film exhibited lithium (de-)intercalation activity with a first discharge capacity of 119 mAh g$$^{-1}$$ between 3.0 and 4.4 V, followed by a gradual capacity fading with subsequent charge-discharge cycles. In contrast, a 3.2 nm thick Li$$_{3}$$PO$$_{4}$$-coated film exhibited a higher intercalation capacity of 148 mAh g$$^{-1}$$ with superior cycle retention than the uncoated film. In situ surface X-ray diffraction measurements revealed a small lattice change at the coated surface during the (de-)intercalation processes compared to the uncoated surface. The surface modification of LiCoO$$_{2}$$ by the Li$$_{3}$$PO$$_{4}$$ coating could lead to improvement of the structural stability at the surface region during lithium (de-)intercalation at high voltage.

Journal Articles

Electrooxidation of hydrazine hydrate using Ni-La catalyst for anion exchange membrane fuel cells

Sakamoto, Tomokazu*; Asazawa, Koichiro*; Martinez, U.*; Halevi, B.*; Suzuki, Toshiyuki*; Arai, Shigeo*; Matsumura, Daiju; Nishihata, Yasuo; Atanassov, P.*; Tanaka, Hirohisa*

Journal of Power Sources, 234, p.252 - 259, 2013/07

 Times Cited Count:61 Percentile:88.51(Chemistry, Physical)

Journal Articles

Probing carbon edge exposure of iron phthalocyanine-based oxygen reduction catalysts by soft X-ray absorption spectroscopy

Niwa, Hideharu*; Saito, Makoto*; Kobayashi, Masaki*; Harada, Yoshihisa*; Oshima, Masaharu*; Moriya, Shogo*; Matsubayashi, Katsuyuki*; Nabae, Yuta*; Kuroki, Shigeki*; Ikeda, Takashi; et al.

Journal of Power Sources, 223, p.30 - 35, 2013/02

 Times Cited Count:17 Percentile:54.86(Chemistry, Physical)

To design non-platinum, inexpensive, but high performance carbon-based cathode catalysts for polymer electrolyte fuel cells, it is important to elucidate the active site for oxygen reduction reaction (ORR). However, it is difficult to directly identify the active site by applying conventional structural or electronic probes to such complex systems. Here, we used C 1${it s}$ X-ray absorption spectroscopy (XAS) to observe electronic structure of carbon in iron phthalocyanine-based catalysts, and found a signature of edge exposure below the $$pi^{ast}$$ edge, whose intensity is well correlated with the ORR activity. These results demonstrate that C 1${it s}$ XAS can be used to characterize the ORR activity of carbon-based cathode catalysts in terms of the edge exposure.

Journal Articles

Role of residual transition-metal atoms in oxygen reduction reaction in cobalt phthalocyanine-based carbon cathode catalysts for polymer electrolyte fuel cell

Kobayashi, Masaki*; Niwa, Hideharu*; Harada, Yoshihisa*; Horiba, Koji*; Oshima, Masaharu*; Ofuchi, Hironori*; Terakura, Kiyoyuki*; Ikeda, Takashi; Koshigoe, Yuka*; Ozaki, Junichi*; et al.

Journal of Power Sources, 196(20), p.8346 - 8351, 2011/10

 Times Cited Count:32 Percentile:70.76(Chemistry, Physical)

The electronic structure of Co atoms in CoPc-based carbon catalysts, which were prepared by pyrolyzing a mixture of CoPc and phenol resin polymer up to 1000$$^circ$$C, has been investigated using XAFS analysis and HXPES. The Co K XAFS spectra show that most of the Co atoms are in the metallic state and small quantities of oxidized Co components are present in the samples even after acid washing to remove Co atoms. Based on the difference in probing depth between XAFS and HXPES, it was found that after acid washing, the surface region with the aggregated Co clusters is primarily composed of metallic Co. Since the electrochemical properties remain almost unchanged even after the acid washing process, the residual metallic and oxidized Co atoms themselves will hardly contribute to the ORR activity of the CoPc-based carbon cathode catalysts, implying that the active sites of the CoPc-based catalysts primarily consist of light elements such as C and N.

Journal Articles

X-ray photoemission spectroscopy analysis of N-containing carbon-based cathode catalysts for polymer electrolyte fuel cells

Niwa, Hideharu*; Kobayashi, Masaki*; Horiba, Koji*; Harada, Yoshihisa*; Oshima, Masaharu*; Terakura, Kiyoyuki*; Ikeda, Takashi; Koshigoe, Yuka*; Ozaki, Junichi*; Miyata, Seizo*; et al.

Journal of Power Sources, 196(3), p.1006 - 1011, 2011/02

 Times Cited Count:80 Percentile:92(Chemistry, Physical)

We report on the electronic structure of three different types of N-containing carbon-based cathode catalysts for polymer electrolyte fuel cells observed by hard X-ray photoemission spectroscopy. C 1s spectra show the importance of $$sp^{2}$$ carbon network formation for the oxygen reduction reaction (ORR) activity. Samples having high oxygen reduction reaction activity in terms of oxygen reduction potential contain high concentration of graphite-like nitrogen. Based on a quantitative analysis of our results, the oxygen reduction reaction activity of the carbon-based cathode catalysts will be improved by increasing concentration of graphite-like nitrogen in a developed $$sp^{2}$$ carbon network.

Journal Articles

Quantum-beam technology; A Versatile tool for developing polymer electrolyte fuel-cell membranes

Yamaki, Tetsuya

Journal of Power Sources, 195(18), p.5848 - 5855, 2010/09

 Times Cited Count:15 Percentile:46.99(Chemistry, Physical)

Fuel-cell application requires that the electrolyte membrane should meet the characteristics; for examples, proton conductivity, mechanical strength, swelling properties, chemical stability and hydrogen/methanol permeability. When higher proton conductivity is pursued for practical applications, at least one of the other membrane properties is usually reduced; these trade-offs must be assessed in the current stage of technology. My talk reviews briefly original techniques of Japan Atomic Energy Agency, which should break the above trade-off relationship in the development of the membranes. The main topic will be systematic utilization of quantum beam technology covering (1) radiation crosslinking and graft polymerization by using $$gamma$$-ray and electron beam, (2) preparation of nano-structure controlled membranes by ion track technology, and (3) use of neutron scattering for membrane analysis.

Journal Articles

X-ray absorption analysis of nitrogen contribution to oxygen reduction reaction in carbon alloy cathode catalysts for polymer electrolyte fuel cells

Niwa, Hideharu*; Horiba, Koji*; Harada, Yoshihisa*; Oshima, Masaharu*; Ikeda, Takashi; Terakura, Kiyoyuki*; Ozaki, Junichi*; Miyata, Seizo*

Journal of Power Sources, 187(1), p.93 - 97, 2009/02

 Times Cited Count:406 Percentile:99.83(Chemistry, Physical)

The electronic structure of nitrogens introduced in various carbon-based cathode catalysts for a polymer electrolyte fuel cell (PEFC) has been investigated using X-ray absorption spectroscopy (XAS). The profile of the $$pi^{ast}$$ peaks at the pre-edge of the N 1s XAS spectra is used to determine the chemical states of nitrogens, which can be a marker of the oxygen reduction reaction (ORR) activity; it is found that catalysts that have relatively high amount of graphite-like nitrogen exhibit higher ORR activity than those having relatively high amount of pyridine-like nitrogen. We propose that effective doping of graphite-like nitrogen is a practical guideline for the synthesis of active carbon alloy catalysts.

Journal Articles

Mechanistic study on lithium intercalation using a restricted reaction field in LiNi$$_{0.5}$$Mn$$_{0.5}$$O$$_{2}$$

Sakamoto, Kazuyuki*; Konishi, Hiroaki*; Sonoyama, Noriyuki*; Yamada, Atsuo*; Tamura, Kazuhisa; Mizuki, Junichiro; Kanno, Ryoji*

Journal of Power Sources, 174(2), p.678 - 682, 2007/12

 Times Cited Count:21 Percentile:58.03(Chemistry, Physical)

Structure changes of LiNi$$_{0.5}$$Mn$$_{0.5}$$O$$_{2}$$ were detected at the electrode/electrolyte interface of lithium cell using synchrotron X-ray scattering and two-dimensional model electrodes. The electrodes were constructed by an epitaxial film of LiNi$$_{0.5}$$Mn$$_{0.5}$$O$$_{2}$$ synthesized by pulsed laser deposition (PLD) method. The orientation of the film depends on the substrate plane; the 2D layer of LiNi$$_{0.5}$$Mn$$_{0.5}$$O$$_{2}$$ is parallel to the SrTiO$$_{3}$$(1 1 0) substrate ((1 1 0) LiNi$$_{0.5}$$Mn$$_{0.5}$$O$$_{2}$$//(1 1 0) SrTiO$$_{3}$$), while the 2D layer is perpendicular to the SrTiO$$_{3}$$(1 1 1) substrate ((0 0 3) LiNi$$_{0.5}$$Mn$$_{0.5}$$O$$_{2}$$//(1 1 1) SrTiO$$_{3}$$). The ${it in situ}$ X-ray diffraction of LiNi$$_{0.5}$$Mn$$_{0.5}$$O$$_{2}$$(0 0 3) confirmed three-dimensional lithium diffusion through the two-dimensional transition meal layers. The intercalation reaction of LiNi$$_{0.5}$$Mn$$_{0.5}$$O$$_{2}$$ will be discussed.

Journal Articles

Characterization of electrode/electrolyte interface for lithium batteries using ${it in situ}$ synchrotron X-ray reflectometry; A New experimental technique for LiCoO$$_{2}$$ model electrode

Hirayama, Masaaki*; Sonoyama, Noriyuki*; Abe, Takashi*; Minoura, Machiko*; Ito, Masumi*; Mori, Daisuke*; Yamada, Atsuo*; Kanno, Ryoji*; Terashima, Takahito*; Takano, Mikio*; et al.

Journal of Power Sources, 168(2), p.493 - 500, 2007/06

 Times Cited Count:80 Percentile:90.21(Chemistry, Physical)

A new experimental technique was developed for detecting structure changes at electrode/electrolyte interface of lithium cell using X-ray reflectometry and two-dimensional model electrodes with a restricted lattice-plane. The electrodes were constructed with an epitaxial film of LiCoO$$_{2}$$ synthesized by pulsed laser deposition method. The anisotropic properties were confirmed by electrochemical measurements. ${it Ex situ}$ X-ray reflectivity measurements indicated that the impurity layer existed on the as-grown LiCoO$$_{2}$$ was dissolved and a new SEI layer with lower density was formed after soaking into the electrolyte. ${it In situ}$ X-ray reflectivity measurements indicated that the surface roughness of the intercalation (1 1 0) plane increased with applying voltages, while no significant changes in surface morphology were observed for the intercalation non-active (0 0 3) plane during the pristine stage of the charge-discharge process.

Journal Articles

Chemical and radiation crosslinked polymer electrolyte membranes prepared from radiation-grafted ETFE films for DMFC applications

Chen, J.; Asano, Masaharu; Yamaki, Tetsuya; Yoshida, Masaru

Journal of Power Sources, 158(1), p.69 - 77, 2006/07

 Times Cited Count:100 Percentile:93.36(Chemistry, Physical)

To develop a highly chemically stable polymer electrolyte membrane for application in a direct methanol fuel cell(DMFC), doubly crosslinked membranes were prepared by chemical crosslinking using bifunctional monomers, such as divinylbenzene(DVB) and bis(p, p-vinyl phenyl) ethane(BVPE), and by radiation crosslinking. The membranes were prepared by grafting of m, p-methylstyrene(MeSt) and p-tert-butylstyrene(tBuSt) into poly(ethylene-co-tetrafluoroethylene)(ETFE) films and subsequent sulfonation. The effects of the DVB and BVPE crosslinkers on the grafting kinetics and the properties of the prepared membranes, such as water uptake, proton conductivity and chemical stability were investigated. Radiation crosslinking was introduced by irradiation of the ETFE base film, the grafted film or the sulfonated membrane. The membrane crosslinked by DVB and BVPE crosslinkers and post-crosslinked by $$gamma$$-ray irradiation of the corresponding grafted film possessed the highest chemical stability among the prepared membranes, a significantly lower methanol permeability compared to Nafion membranes, and a better DMFC performance for high methanol feed concentration. Therefore, this doubly crosslinked membrane was promising for application in a DMFC where relatively high methanol concentration could be fed.

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