Papers by Minoru Mizuhata
Electrochemistry, Oct 28, 2022
The signal detection of quantitative H nuclear magnetic resonance (1 H qNMR) for the amount of wa... more The signal detection of quantitative H nuclear magnetic resonance (1 H qNMR) for the amount of water in HCl and KOH aqueous solutions at low pH (pH −1.2) and high pH (pH 16) was discussed, and an "anomaly of decreasing 1 H NMR signal intensity" was observed. After adding significant amounts of acid (H +) or base (OH −) to the solution for pH regulation, the number of 1 H nuclei observed by 1 H NMR significantly decreased at pH : 2 and ; 13. The mobility and the activity coefficient of some or all the water molecules hydrated to H 3 O + significantly decreased; hence, they could not be detected by 1 H qNMR. The remarkably strong electrostatic interactions of the solvent with H 3 O + and OH − significantly reduce the activity coefficient of the solvent by restricting the solvent molecule to the vicinity of the ion. These results are comparable to those reported for vapor pressure measurements and can be attributed to a decrease in activity. H + (H 3 O +), which has a relatively small ionic radius, has a significant effect on the solvation structure and hydrogen-bond network owing to strong electrostatic interactions with the solvent. Subsequently, significant reduction in the 1 H NMR relaxation time of the water molecules and signal intensity, along with a low magnetic field shift in the 1 H NMR signal were also observed in the strongly acidic and strongly basic regions.
ECS transactions, Oct 25, 2017
Carbon coated porous silicon with various pore sizes as a model of porous electrode was prepared ... more Carbon coated porous silicon with various pore sizes as a model of porous electrode was prepared for Electric double layered capacitors (EDLCs). Each carbon coated PSi has a diameter ranged from 7 to 72 nm. The specific capacitance was influenced the diameter of main chain observed surface SEM images. The calculated capacity of each electrode depends on the pore distribution which showed the overlapping the electronic double layer.
ECS transactions, Oct 25, 2017
Electrical Conductivity of Ceria-Based Oxides/Alkali Carbonate Eutectic Nanocomposites
Journal of The Electrochemical Society, Apr 1, 2021
Differential thermal analysis (DTA) and electrical conductivity calculated from AC impedance meas... more Differential thermal analysis (DTA) and electrical conductivity calculated from AC impedance measurements are discussed for binary and ternary eutectics: (Li0.52Na0.48)2CO3 (LN) and (Li0.435Na0.315K0.25)2 CO3 (LNK), coexisting with nanosized CeO2 and ceria-based oxides such as CeO2:Sm3+(samarium doped ceria: SDC) particles prepared by the Pechini method. The influence of the surface properties of oxides with smooth surfaces, narrow particle size distributions, and large specific surface areas near the eutectic point is presented. The obtained DTA spectra indicate that the melting enthalpy disappeared in systems with a melt containing less than 30 vol% and 45 vol% LN and LNK eutectics, respectively. Sm3+ doping contributes to an increase in the electrical conductivity of the composites below the eutectic points of molten carbonate. The temperature dependence of the electrical conductivity for both binary and ternary eutectic carbonates coexisting with CeO2 and SDC at melt contents less than ca. 15 vol% does not indicate a remarkable change in conductivity in the temperature range near each eutectic point of molten carbonate. The low-temperature characteristics are significantly improved using nanosized ceria-based oxides because of non-frozen eutectics with a low molar enthalpy of fusion and limited solid-phase influence on ionic conduction.
Electrochemistry, 2015
The direct synthesis of an Ni-Al layered double hydroxide (LDH) as the active material in an Ni-m... more The direct synthesis of an Ni-Al layered double hydroxide (LDH) as the active material in an Ni-metal hydride secondary battery on an electron-conductive substrate was performed using liquid phase deposition method. A reduction in charge-transfer resistance was achieved by coating a Ni-Al LDH film on a Ni foam surface current collector, as a result of improved adhesion between the current collector and the active material.
Chemical Communications, 2020
LnNbO 4 (Ln = Y, Gd and Lu) is a type of material that can be used as both outstanding self-activ... more LnNbO 4 (Ln = Y, Gd and Lu) is a type of material that can be used as both outstanding self-activated phosphor and laser host has generated significant interests. However, their electronic structures and optical properties still require elucidation. To solve this intriguing problem, firstly, YNbO 4 and LuNbO 4 polycrystalline with monoclinic crystal structure were prepared by traditional high-temperature solid-state reaction method and their structure and luminescent properties were characterized in experiment. Additionally, their CIE chromaticity coordinate were presented to illustrate the luminescent color and the chromaticity coordinates for YNbO 4 and LuNbO 4 are x = 0.1581, y = 0.0725 and x = 0.1581, y = 0.0753, respectively. Secondly, systematic theoretical calculations based on density functional theory method were carried out on them and their band structures, density of states as well as optical properties were obtained in theoretical. The calculated band gap for YNbO 4 and LuNbO 4 are 4.101 and 4.214 eV, respectively. Lastly, a comparison between the experimental and calculated band gap and refractive index was conducted. The good coincident between them indicating the calculated results are reliable. Therefore, all of the obtained results could provide an essential understanding of LnNbO 4 materials.
Disproportionation Phenomenon at the Silica Interface of Propylene Carbonate–1,2-Dimethoxyethane Binary Solvent Containing Lithium Perchlorate
The Journal of Physical Chemistry C
Interionic interaction and hydration structure of high concentration aqueous electrolyte solution by quantitative NMR and activity measurement of the solvent
Yoyuen Oyobi Koon Kagaku, 2019
Journal of The Electrochemical Society, 2021
We investigated the suppressed capacity fading of a Ca-substituted P3-type NaxCoO2 during the cha... more We investigated the suppressed capacity fading of a Ca-substituted P3-type NaxCoO2 during the charge/discharge process. The Ca-substituted NaxCoO2 shows similar phase transition behavior to the Ca free one, with an expanded P′3 phase region. The capacity fading of the NaxCoO2 is highly correlated with the phase transition at 4.0 V of P′3–O3′ phase transition and at 2.7 V of O′3–P′3 phase transition. The amount of Co3O4 observed in the cycled electrodes corresponds to the capacity loss during the cycling test. Thus, the migration of the Co3+/4+ ions during the phase transition process causes the capacity fading. The decomposition of the electrolyte solution also accelerates the migration of the Co3+/4+ ions. Though the Ca-substitution does not prevent the phase transition, the Ca-substituted NaxCoO2 shows improved capacity retention.
Analysis of hydrolysis reaction of aluminum polynuclear complex with Cl− and SO42− anions by quantitative multinuclear NMR and evaluation of coagulation behavior of model sludge water
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2021
Dependence of Interlayer Distance on the Charge Transfer Reaction of Ni-Al Layered Double Hydroxides
ECS Transactions, 2017
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2015
g r a p h i c a l a b s t r a c t h i g h l i g h t s • Dependence of polyelectrolyte effects on ... more g r a p h i c a l a b s t r a c t h i g h l i g h t s • Dependence of polyelectrolyte effects on the number of ionic groups was revealed. • Polyelectrolyte effects increased non-monotonically with phosphate groups number. • These behaviors were observed not only electrochemical titration but also 23 Na NMR.
Electrochemistry, 2015
The direct synthesis of an Ni-Al layered double hydroxide (LDH) as the active material in an Ni-m... more The direct synthesis of an Ni-Al layered double hydroxide (LDH) as the active material in an Ni-metal hydride secondary battery on an electron-conductive substrate was performed using liquid phase deposition method. A reduction in charge-transfer resistance was achieved by coating a Ni-Al LDH film on a Ni foam surface current collector, as a result of improved adhesion between the current collector and the active material.
MRS Proceedings, 2011
We prepare Nd-Bi codoped zeolites by a method consisting of a simple ion-exchange process and sub... more We prepare Nd-Bi codoped zeolites by a method consisting of a simple ion-exchange process and subsequent high-temperature annealing. The emission covers the range of 970~1450 nm, corresponding to the electronic transitions of Nd 3+ ions and Bi-related active centers (BiRAC), respectively. The introduction of Bi distinctly broadens the excitation band of Nd 3+ in the visible region, and the lifetime of Nd 3+ reaches as long as 354 μs. In the zeolite matrix, Bi ions exist as BiRAC and Bi oxide agglomerates. The former one act as a sensitizer of Nd 3+ ions, and the latter one act as a blockage to avoid the quenching effect of coordinated water, which enable Nd 3+ ions to show efficient near-infrared (NIR) emission even the zeolites contain large amount of coordinated water. The excellent optical and structural properties make these NIR emitting nanoparticles promising in application as laser materials and biological probes.
Reply to Comment on ‘Europium doping induced symmetry deviation and its impact on the second harmonic generation of doped ZnO nanowires’
Nanotechnology, Oct 20, 2014
ABSTRACT In this work, we investigated the effects of europium doping on the second harmonic gene... more ABSTRACT In this work, we investigated the effects of europium doping on the second harmonic generation (SHG) of ZnO nanowires (NWs). A non-monotonic enhancement in the SHG is observed with the increase of the europium concentration. Maximum SHG is observed from the 1 at.% europium doped ZnO NWs with an enhancement factor of 4.5. To understand the underlying mechanism, the effective second order non–linear coefficient (deff) is calculated from the theoretical fitting with consideration of the absorption effect. Microstructural characterization reveals the structural deformation of the ZnO NWs caused by europium doping. We estimated the deviation in the crystal site symmetry around the Eu3+ ions (defined as the asymmetric factor) from photoluminescence measurement and it is found to be strongly correlated with the calculated deff value. A strong linear dependence between the magnitudes of deff and the asymmetric factor suggests that deviation in the local site symmetry of the ZnO crystal by europium doping could be the most probable origin of the observed large second order non-linearity.
In this work, we investigated the effect of Al doping and surface modification on a core-shell ty... more In this work, we investigated the effect of Al doping and surface modification on a core-shell type ZnO/ZnS NWs on the structural, electrical and PL properties. Doping and surface modification of the Al:ZnO NWs result in changes in the nature of PL spectra and electronic conductivity. Compared to the bare undoped ZnO NWs, a two times improvement in the electronic conductivity as well as five times enhancement in the UV PL intensity is obtained from the Al(2 at.%):ZnO/ZnS NWs. The UV PL enhancement factor is ~2.8 times higher than the case of undoped NWs coated with ZnS for same time duration. The observed changes are studied in details and origin of the enhancement is discussed.
Properties of CaCl<sub>2</sub>hydrate with an inorganic powder. Part 1.—Electrical conductivity of CaCl<sub>2</sub>·nH<sub>2</sub>O (n= 6.00–7.35) with α-Al<sub>2</sub>O<sub>3</sub>powder
Journal of the Chemical Society, Faraday Transactions, 1993
Electrical conductivity and its temperature dependence have been measured for mixtures of α-Al2O3... more Electrical conductivity and its temperature dependence have been measured for mixtures of α-Al2O3 powder and CaCl2·nH2O (n= 6.00–7.35) with liquid content 17.1–42.9 vol.%. The influence of the solid surface on electric conduction and phase transition in the liquid phase is discussed. Plots of the logarithm of the electrical conductivity, ln σ, vs. reciprocal temperature, 1/T, showed an abrupt change of slope at a temperature, Tt, the deflection point. The value of Tt appears to correspond to the end-point of the melting of the hydrate. The value of Tt decreased as the liquid phase decreased and as n increased. The activation energy for the electrical conductivity, ΔEa, decreased with increase in the apparent average thickness of the liquid phase up to 30–40 nm, after which ΔEa became constant. These results show that the thickness of the liquid layer which exists on, and is influenced by, the solid phase is ca. 30–40 nm. In this region, the melting point of the hydrate melt tends to be lowered and this change contributes to the electric conduction of hydrate at temperatures below the melting point.
Journal of The Electrochemical Society, Jun 1, 1992
Electrochemistry
The Editorial Board outlines the history of publication by the Electrochemical Society of Japan a... more The Editorial Board outlines the history of publication by the Electrochemical Society of Japan as it celebrates its 90th anniversary. The history of the journal is told by the Society's strong interest in publishing and its international development in line with current trends. The growing presence of the journal is described. This issue will also include the Comprehensive Papers by the winners of the ECSJ awards. The rationale for these awards will also be explained.
Electrochemistry
The Ni-Al layered double hydroxide materials with high crystallinity were synthesized by the room... more The Ni-Al layered double hydroxide materials with high crystallinity were synthesized by the room-temperature liquid process and applied as oxygen evolution reaction (OER) catalysts. It is interesting to note that the OER activity was found to be relatively high in comparison with the Ni-based materials. In addition, the structural analyses and the effects of interlayer anion specie on the OER activity were also evaluated. It was found that the changes in the interlayer anion species from F − to OH − resulted in the enhancement of the OER activity. The maintained chemical compositions and crystallinity after the electrochemical measurements were also observed through the X-ray analyses. The present work provides the insights about the possibility of the well-defined structures as the electrodes which were prepared by the unique liquid phase process.
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Papers by Minoru Mizuhata