Hideharu Niwa

Hideharu Niwa

University of Tsukuba

H-index: 24

Asia-Japan

About Hideharu Niwa

Hideharu Niwa, With an exceptional h-index of 24 and a recent h-index of 18 (since 2020), a distinguished researcher at University of Tsukuba,

His recent articles reflect a diverse array of research interests and contributions to the field:

Battery resistance and its effects on performance of laminate film type Co-PBA/Ni-PBA tertiary battery

Local structure of Fe2+ and Fe3+ in organic solvents

Coordination States of Fe3+ and Fe2+ Dissolved in Organic Solvents

Operando resonant soft X-ray emission spectroscopy of the LiMn 2 O 4 cathode using an aqueous electrolyte solution

Scaling Relation between Electrochemical Seebeck Coefficient for Fe2+/Fe3+ in Organic Solvent and Its Viscosity

In situ IR spectroscopy during oxidation process of cobalt Prussian blue analogues

Electronic surface reconstruction of TiO

Electronic surface reconstruction of TiO2 nanocrystals revealed by resonant inelastic x-ray scattering

Hideharu Niwa Information

University

University of Tsukuba

Position

Faculty of Pure and Applied Sciences

Citations(all)

2076

Citations(since 2020)

959

Cited By

1559

hIndex(all)

24

hIndex(since 2020)

18

i10Index(all)

35

i10Index(since 2020)

27

Email

University Profile Page

University of Tsukuba

Top articles of Hideharu Niwa

Battery resistance and its effects on performance of laminate film type Co-PBA/Ni-PBA tertiary battery

Authors

Kentaro Furuuchi,Yuga Taniguchi,Yicheng Bao,Hideharu Niwa,Yutaka Moritomo

Journal

Japanese Journal of Applied Physics

Published Date

2024/4/30

Tertiary battery (TB) can be charged by heating or cooling via difference in the electrochemical Seebeck coefficient α between cathode and anode. Here, we investigated battery resistance R and its effect on thermal cycle properties in laminate film type Na{1.48Co[Fe(CN)6]{0.87 (Co-PBA) / Na{1.76Ni[Fe(CN)6]{0.94} (Ni-PBA) TB. We found that charge-transfer resistance Rct and diffusion resistance Rdif are the dominant components of while solution resistance Rs has minor role. Regardless of the solute type, R varied inversely proportional to the Na+ concentration M. In high-R TB, the thermal voltage VTB and discharge capacity QTB per unit weight of the total active material is significantly suppressed, which is quantitatively explained in terms of the voltage drop (= IR; I is current) during the discharge process.

Local structure of Fe2+ and Fe3+ in organic solvents

Authors

Dai Inoue,Toshiki Komatsu,Hideharu Niwa,Hiroaki Nitani,Hitoshi Abe,Yutaka Moritomo

Journal

Japanese Journal of Applied Physics

Published Date

2022/10/18

We systematically investigated the local structure of Fe 2+ and Fe 3+ in 11 solvents by extended X-ray absorption fine structure (EXAFS) analysis and X-ray absorption near-edge structure (XANES). The EXAFS analyses with a one-shell model indicate that Fe 2+ and Fe 3+ are coordinated by six oxygen of the ligand molecules (L) and form a FeL 6-type complex in all solvents. The XANES suggests that the [FeL 6] 3+ complex shows noncentrosymmetric deformation in several solvents. In protic solvents, the EXAFS analyses with a two-shell model revealed that the coordination number (n C) of the second nearest carbon around Fe 3+ significantly depends on L. We interpreted the observation in terms of the distribution of the Fe-C distance.

Coordination States of Fe3+ and Fe2+ Dissolved in Organic Solvents

Authors

Dai Inoue,Toshiki Komatsu,Hideharu Niwa,Toshiaki Ina,Hiroaki Nitani,Hitoshi Abe,Yutaka Moritomo

Journal

Journal of the Physical Society of Japan

Published Date

2022/9/15

We spectroscopically investigated the coordination states of Fe2+ and Fe3+ dissolved in several organic solvents. Ultraviolet–visible (UV–vis) spectra and extended X-ray absorption fine structure (EXAFS) analyses revealed that Fe3+ forms [FeCl4]− complex in all the solutions. The EXAFS analysis suggests that Fe2+ forms [FeCl4]2− in N,N-dimethylformamide (DMF) and N-methylpyrrolidone (NMP) solutions while it forms [FeL6]2+ (L is solvent molecule) in ethylene glycol (EG) and methanol (MeOH) solutions. We interpreted the solvent dependence of the Fe2+ coordination state in terms of the L–Fe2+ interaction and Cl− solubility in solvent.

Operando resonant soft X-ray emission spectroscopy of the LiMn 2 O 4 cathode using an aqueous electrolyte solution

Authors

Daisuke Asakura,Yusuke Nanba,Hideharu Niwa,Hisao Kiuchi,Jun Miyawaki,Masashi Okubo,Hirofumi Matsuda,Yoshihisa Harada,Eiji Hosono

Journal

Physical Chemistry Chemical Physics

Published Date

2022

The Mn 3d electronic-structure change of the LiMn2O4 cathode during Li-ion extraction/insertion in an aqueous electrolyte solution was studied by operando resonant soft X-ray emission spectroscopy (RXES). The Mn L3 RXES spectra for the charged state revealed the Mn4+ state with strong charge-transfer from the O 2p to Mn 3d orbitals dominates, while for the open-circuit-voltage and discharged states it is ascribed to the mixture of sites with Mn3+ and Mn4+ states. The degree of charge transfer is significantly different between the Mn3+ and Mn4+ states, indicating that the redox reaction takes place on the strongly-hybridized Mn 3d–O 2p orbital rather than the localized Mn 3d orbital.

Scaling Relation between Electrochemical Seebeck Coefficient for Fe2+/Fe3+ in Organic Solvent and Its Viscosity

Authors

Dai Inoue,Hideharu Niwa,Hiroaki Nitani,Yutaka Moritomo

Journal

Journal of the Physical Society of Japan

Published Date

2021/3/15

The temperature coefficient α (= dV/dT) of the redox potential (V) in a redox system, or so-called electrochemical Seebeck coefficient, is a key parameter for thermal energy harvesting. We systematically investigated α for Fe2+/Fe3+ in 16 organic solvents, i.e., 8 protic and 8 aprotic solvents. We found that α shows remarkable solvent dependence and is distributed from 0.14 mV/K for glycerin to 3.60 mV/K for acetone. We further found a scaling relation between α and viscosity (η) of the solvent as α ∝ η−0.4. We will discuss solvent dependence of α and the scaling relation in terms of the configuration entropy of the solvent molecules.

In situ IR spectroscopy during oxidation process of cobalt Prussian blue analogues

Authors

Hideharu Niwa,Toshiaki Moriya,Takayuki Shibata,Yuya Fukuzumi,Yutaka Moritomo

Journal

Scientific Reports

Published Date

2021/2/18

Cobalt Prussian blue analogues (Co-PBA; NaxCo[Fe(CN)6]y), consisting of cyano-bridged transition metal network, –Fe–CN–Co–NC–Fe–, are promising cathode materials for Na-ion secondary batteries. In the oxidation process, oxidization of Fe and/or Co are compensated by Na+ deintercalation. Here, we investigated the oxidization process of three Co-PBAs by means of in situ infrared absorption (IR) spectroscopy. With use of an empirical rule of the frequencies of the CN− stretching mode in ferrocyanide ([FeII(CN)6]4−) and ferricyanide ([FeIII(CN)6]3−), the oxidation processes of Co-PBAs were determined against the Fe concentration (y) and temperature (T). We will discuss the interrelation between the oxidation processes and Fe concentration (y).

Electronic surface reconstruction of TiO

Authors

Cheng-Hao Chuang,Chieh-Ming Chen,Yu-Cheng Shao,Ping-Hung Yeh,Chih-Ming Chang,Way-Faung Pong,Mukes Kapilashrami,Per-Anders Glans,Sheraz Gul,Gongming Wang,Yat Li,Jin Zhang,Jun Miyawaki,Hideharu Niwa,Yoshihisa Harada,Jin-Ming Chen,Jinghua Guo

Published Date

2021

The identification of lattice multiphases in TiO2 nanocrystals is studied by high resolution transmission electron microscope and electron diffraction patterns. Based on the spectroscopic analysis using soft x-ray absorption and resonant inelastic soft x-ray scattering, it is believed that the oxygen vacancies at the interface exhibit structural distortion of the TiO8À

Electronic surface reconstruction of TiO2 nanocrystals revealed by resonant inelastic x-ray scattering

Authors

Cheng-Hao Chuang,Chieh-Ming Chen,Yu-Cheng Shao,Ping-Hung Yeh,Chih-Ming Chang,Way-Faung Pong,Mukes Kapilashrami,Per-Anders Glans,Sheraz Gul,Gongming Wang,Yat Li,Jin Zhang,Jun Miyawaki,Hideharu Niwa,Yoshihisa Harada,Jin-Ming Chen,Jinghua Guo

Journal

Journal of Vacuum Science & Technology A

Published Date

2021/12/1

The identification of lattice multiphases in TiO 2 nanocrystals is studied by high resolution transmission electron microscope and electron diffraction patterns. Based on the spectroscopic analysis using soft x-ray absorption and resonant inelastic soft x-ray scattering, it is believed that the oxygen vacancies at the interface exhibit structural distortion of the TiO 6 8− cluster around the defect site as for the multiphase lattice. We elucidate that the extra 3d electrons nearby induce the inelastic scattering features with the excitation energy dependence owing to different energy relaxation processes, a characteristic of the electron-phonon coupling or the nature of the electron-hole pair at the intermediate state. The manifold dd excitations driven by the strong interaction between Ti-3d and O-2p electrons are noticeably rich, coexisting on both Ti and O sites. This sophisticated experiment can advance the perspective of …

Extended charge-transfer model for Na x Co [Fe (CN) 6] 0.82

Authors

Yutaka Moritomo,Hiroki Tachihara,Hiroki Iwaizumi,Takayuki Shibata,Hideharu Niwa

Journal

Japanese Journal of Applied Physics

Published Date

2021/3/29

Cobalt Prussian blue analogues (Na x Co [Fe (CN) 6] y; ) whose valences are close to and show characteristic phase transitions triggered by cooperative charge transfer (CT) from to . Here, we extended the cooperative CT to the entire region of sodium concentration (). We systematically investigated (1) upper () and lower () critical temperature,(2) variation of the [(CN) 6] ([(CN) 6] ) concentration, and (3) spectral weight () due to electron transfer from to of thin films of Na x Co [Fe (CN) 6] 0.82 against x. In a wide x region from 0.00 to 0.57, we observed first-order phase transition triggered by the cooperative CT. The extended CT model reproduces the x-dependent behavior of the [Fe II (CN) 6] ([Fe III (CN) 6] ) concentration and , except for the high-x region above .

Aggregation tendency of guest Fe in NaCo1−xFexO2 (x < 0.1) as investigated by systematic EXAFS analysis

Authors

Toshiaki Moriya,Hideharu Niwa,Hiroaki Nitani,Yutaka Moritomo

Journal

Scientific Reports

Published Date

2020/7/9

In transition metal (M) compounds, the partial substitution of the host transition metal (Mh) to guest one (Mg) is effective to improve the functionality. To microscopically comprehend the substitution effect, degree of distribution of Mg is crucial. Here, we propose that a systematic EXAFS analysis against the Mg concentration can reveal the spatial distribution of Mg. We chose NaCo1−xFexO2 as a prototypical M compound and investigated the local intermetal distance around the guest Fe [dFe–M(x)] against Fe concentration (x). dFe–M(x) steeply increased with x, reflecting the larger ionic radius of high-spin Fe3+. The x-dependence of dFe–M(x) was analyzed by an empirical equation, , where dFe–Fe and dFe–Co are the Fe–Fe and Co–Fe distances, respectively. The parameter s represents degree of distribution of Fe; s = 1, > 1, < 1 are for random, attractive, and repulsive …

Persistence and amalgamation types of CN stretching mode in oxidation process of Prussian blue analogues

Authors

Toshiaki Moriya,Takayuki Shibata,Yuya Fukuzumi,Hideharu Niwa,Yutaka Moritomo

Journal

Journal of the Physical Society of Japan

Published Date

2020/6/15

Prussian blue analogues (PBAs) shows a cyano-bridged three-dimensional (3D) transition metal network, –M–NC–Fe–CN–M–NC–Fe–CN–M– (M = Co and Mn). Here, by in situ infrared (IR) spectroscopy, we investigated effect of the oxidation on the CN stretching mode. The CN stretching mode shows persistence or amalgamation behavior depending on the difference (Δ) in the phonon energies (ħωCN) between the reduced and oxidized states, e.g., M2+–NC–Fe2+ and M3+–NC–Fe2+. We found that the band width (W ≥ 39 cm−1) in ferrocyan ([Fe2+(CN)]4−) is larger than that (= 23 cm−1) in ferricyan ([Fe3+(CN)]3−). The larger W in ferrocyan is interpreted in terms of the stronger polarization of CN in ferrocyan.

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Hideharu Niwa FAQs

What is Hideharu Niwa's h-index at University of Tsukuba?

The h-index of Hideharu Niwa has been 18 since 2020 and 24 in total.

What are Hideharu Niwa's top articles?

The articles with the titles of

Battery resistance and its effects on performance of laminate film type Co-PBA/Ni-PBA tertiary battery

Local structure of Fe2+ and Fe3+ in organic solvents

Coordination States of Fe3+ and Fe2+ Dissolved in Organic Solvents

Operando resonant soft X-ray emission spectroscopy of the LiMn 2 O 4 cathode using an aqueous electrolyte solution

Scaling Relation between Electrochemical Seebeck Coefficient for Fe2+/Fe3+ in Organic Solvent and Its Viscosity

In situ IR spectroscopy during oxidation process of cobalt Prussian blue analogues

Electronic surface reconstruction of TiO

Electronic surface reconstruction of TiO2 nanocrystals revealed by resonant inelastic x-ray scattering

...

are the top articles of Hideharu Niwa at University of Tsukuba.

What is Hideharu Niwa's total number of citations?

Hideharu Niwa has 2,076 citations in total.

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