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Atsuki TABO, Hisayoshi MATSUSHIMA, Takahiro OHKUBO, Kei NISHIKAWA, Mik ...
2024 Volume 92 Issue 4 Pages
043011
Published: April 01, 2024
Released on J-STAGE: April 01, 2024
Advance online publication: January 17, 2024
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The arrangement of ions at the interface between highly oriented pyrolytic graphite (HOPG) and Aluminum chloride–1-ehtyl-3-methylimidazolium chloride (AlCl3–EmImCl) ionic liquid was evaluated using Atomic Force Microscopy (AFM) force curve measurements. In the force curve measurements, three steps were observed towards the HOPG electrode. The width of each step was 0.3, 0.4, and 0.5 nm in order from the final arrival point. Their step widths were regarded as the thicknesses of EmIm+, Al2Cl7−, or their mixed layers. The force curve measurements at each potential demonstrated that the width of the first layer close to the HOPG tended to decrease as the potential shifted towards the less noble side.
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Yuya UEMURA, Tetsuya TSUDA, Hajime MATSUMOTO, Rina MIYAJIMA, Susumu KU ...
2024 Volume 92 Issue 4 Pages
043012
Published: April 01, 2024
Released on J-STAGE: April 01, 2024
Advance online publication: February 15, 2024
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In this article, electrode behavior of commercially available exfoliated graphite material, GRAFOIL®, was examined in Lewis acidic AlCl3–1-ethyl-3-methylimidazolium chloride ([C2mim]Cl) ionic liquid electrolytes (AlCl3 molar fraction: >50 mol%). Cyclic voltammograms and chronopotentiograms recorded at the GRAFOIL® electrode strongly suggested that the electrode behavior is very similar to that for the graphite cathode active materials employed for the Al metal anode rechargeable batteries and that the intercalation reaction of the [AlCl4]− into the GRAFOIL® proceeds electrochemically. From XRD data of the [AlCl4]−-intercalated GRAFOIL® obtained, a lot of information was obtained about its crystal structure. Relatively high discharge capacity over 80 mAh g−1 of GRAFOIL® cathode would be due to the formation of graphite intercalation compound with stage 3 structure. The laminate-type Al metal anode–GRAFOIL® cathode rechargeable batteries created based on the obtained knowledge showed a favorable battery performance, if the appropriate charging condition that suppress Cl2 generation was applied.
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Tsuyoshi MURAKAMI, Yoshiharu SAKAMURA, Koichi UOZUMI, Masatoshi IIZUKA
2024 Volume 92 Issue 4 Pages
043013
Published: April 01, 2024
Released on J-STAGE: April 01, 2024
Advance online publication: February 21, 2024
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During the electrorefining of spent nuclear metallic fuels for recycling actinides, fission products of rare-earths, alkaline-earths and alkalis accumulate in LiCl–KCl melt in the form of their chlorides. For the purpose of periodically removing the accumulated fission product chlorides from the melt and stabilizing them in a waste form, a novel used-salt treatment process was proposed wherein electrochemical rare-earth silicide formation on a Si cathode was used as one of the main reactions. In this study, electrochemical measurements using a Si plate electrode were performed in LiCl–KCl melt containing lanthanide chlorides at 723 K to obtain basic knowledge of designing the Si cathode configuration and evaluating the composition of the recovered fission products in the proposed used-salt treatment process. A linear relationship between the thickness of the dense silicide layer and the square root of the electrolysis time in potentiostatic electrolysis at −1.5 V vs. Ag/AgCl was seen, which suggested the dense silicide layer growth governed by a diffusion in the layer. We also found a dependence of the distribution of lanthanides between the silicides and the melt on the applied cathodic current density during galvanostatic electrolysis for their recovery as silicides from the melt containing multi-lanthanide chlorides.
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Sondre G. IVELAND, Alexander WESTBYE, Jorge M. MARCHETTI, Espen OLSEN, ...
2024 Volume 92 Issue 4 Pages
043014
Published: April 01, 2024
Released on J-STAGE: April 01, 2024
Advance online publication: February 22, 2024
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Post-combustion CO2 capture is a promising method for removing CO2 from processes where emissions cannot be mitigated by renewable energy input and where the chemical reactions required for production emit CO2, e.g. calcination of calcium carbonate (CaCO3) for cement production. One promising capture method is carbon capture in molten salts (CCMS). CCMS is a thermal swing gas-liquid process that utilizes CaO carbonation to absorb CO2. The molten salt used in this work is 15 wt% CaO in eutectic CaCl2-CaF2 (86.2 : 13.8 wt%). The CaCl2-CaF2-CaO system has been found to have high cyclic absorption capacity (0.6 g CO2/g CaO), though reaction kinetics has yet to be studied. By utilizing a novel experimental setup, data is collected, and a kinetic model is developed, which can be used in a techno-economic evaluation. The model proposes a simplified description of the CaCl2-CaF2-CaO system, with the assumption that the reaction is a first order elementary reaction where CaO and CO2 react to form CaCO3 without any solubility of CO2 in the molten salt. CO2 concentration, temperature, wt% CaO and surface area of molten salt are parameters in the proposed kinetic model. The result is a kinetic model that accurately fits the experimental data with an R2 value above 0.98. It has been found that increasing the CO2 concentration and decreasing the temperature yield a higher CaO to CaCO3 equilibrium conversion.
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Yuxiang ZHONG, Yuanjia MA, Yangzhou HE, Xiao YANG
2024 Volume 92 Issue 4 Pages
043015
Published: April 01, 2024
Released on J-STAGE: April 01, 2024
Advance online publication: February 28, 2024
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The authors focus on the development of a molten salt processing technology for extracting white phosphorus (P4) from sewage sludge ash, which is recognized as a potential secondary P source due to its composition of various metal phosphates. This work offers insights into the interaction between solid AlPO4 and molten CaCl2. The results show that solid AlPO4 exhibits favorable solubility in molten CaCl2, although at a slower rate compared to solid Ca3(PO4)2 due to the presence of stable Al–O bonds. The study also demonstrates the feasibility of extracting high-purity P4 from the molten mixture through electrolysis. The purity of the obtained electrolyzed P4 from AlPO4 is comparable to the commercially available high-purity-grade product. These findings underscore the potential of sewage sludge ash containing AlPO4 as a viable source for extracting high-purity P4. This research contributes to the advancement of sustainable P utilization technologies from secondary sources.
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Tetsuo OISHI, Miki YAGUCHI, Yumi KATASHO, Hirokazu KONISHI
2024 Volume 92 Issue 4 Pages
043016
Published: April 01, 2024
Released on J-STAGE: April 01, 2024
Advance online publication: February 16, 2024
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The permeation tendency of La, Ce, Pr, Nd, Gd, and Tb was examined using a rare earth (RE)–Ni alloy diaphragm in LiCl–KCl eutectic melts at 450 °C. This experiment was conducted as a part of an ongoing study on a new recycling process for Nd–Fe–B permanent magnets, because wasted magnets may contain La, Ce, Pr, Gd, and Tb as RE impurities. The permeation experiments were performed under two conditions that were expected to enable the selective permeation of Nd and Dy, respectively, which were determined on the basis of our previous studies confirming the selective permeation of Nd and Dy. As a result, Gd and Tb showed a similar permeation tendency to Dy, whereas Ce and Pr behaved like Nd. Under both experimental conditions, La hardly permeated. These tendencies are discussed on the basis of the applied potential and the equilibrium potential for RENi2/RENi3 (RE = Ce, Pr, Nd, Gd, Tb, and Dy) and La7Ni16/LaNi3. The cross sections of the alloy diaphragm after the permeation experiments were analyzed via scanning electron microscopy/energy-dispersive X-ray spectroscopy. Relatively high concentrations of Gd, Tb, and Dy were detected in the alloy diaphragm, whereas the concentrations of La, Ce, Pr, and Nd were low in both experiments.
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Yoshifumi ISHIO, Takayuki YAMAMOTO, Koki MANABE, Toshiyuki NOHIRA
2024 Volume 92 Issue 4 Pages
043017
Published: April 01, 2024
Released on J-STAGE: April 01, 2024
Advance online publication: February 22, 2024
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Na-ion batteries (NIBs) with ionic liquid (IL) electrolytes are promising candidates for large-scale energy storage devices owing to the abundance of Na resources and the safety of ILs. In our previous study, we have demonstrated the improved rate capability of NIBs consisting of a hard carbon negative electrode, an NaCrO2 positive electrode, and an FSA-based IL electrolyte (FSA = bis(fluorosulfonyl)amide) by increasing the Na+ ion concentration in the IL. However, this phenomenon is not consistent with the trend observed for the ionic conductivities of bulk ILs. In this study, to clarify the unexplained behavior particularly for electrolytes with high Na+ concentrations, we performed in-situ Raman spectroscopic analysis in the vicinity of the electrode/electrolyte interface. The results of discharge rate capability tests indicated that a rate-determining step existed in the reaction at the positive electrode, where Na+ insertion occurred during discharge. In-situ Raman spectroscopy for Na/NaCrO2 half-cells using an IL electrolyte of low Na+ concentration (∼1 mol dm−3) revealed that the Na+ ion concentration at the interface (inside the NaCrO2 composite electrode) locally decreased as the discharging proceeded. In contrast, a high Na+ concentration electrolyte (∼2.2 mol dm−3) considerably suppressed the decrease in the Na+ ion concentration at the interface. Therefore, the improved performance of the electrolyte with a high Na+ concentration can be explained by the local Na+ ion concentration near the electrode/electrolyte interface, rather than by the bulk properties of the IL electrolytes.
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Junji NUNOMURA, Hisayoshi MATSUSHIMA, Yoshihiko KYO, Yoichi KOJIMA, Mi ...
2024 Volume 92 Issue 4 Pages
043018
Published: April 05, 2024
Released on J-STAGE: April 05, 2024
Advance online publication: February 28, 2024
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The anodic dissolution reaction of Al–Zn alloys containing a Zn solid solution in Lewis acidic AlCl3–1-ethyl-3-methyl-imidazolium chloride (EmImCl) ionic liquids at various potentials is investigated herein. An enrichment layer was formed on the anode surface after applying constant potentials of 0.3 and 0.7 V in the 60 mol%AlCl3–40 %EmImCl (60 % AlCl3) electrolyte and 0.2 V in the 67 mol%AlCl3–33 %EmImCl (67 %AlCl3) electrolyte. Consequently, metallic Zn was detected in the enriched layer using X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Notably, in the 60 %AlCl3 electrolyte, high-purity Al was obtained at a much nobler potential than the dissolution potential of pure Zn, suggesting that the anodic dissolution of Zn from the Al–Zn alloy into the electrolyte was difficult. When electrorefining Al–Zn alloy anodes containing a Zn solid solution using 60 %AlCl3, which has lower acidity than the 67 %AlCl3 electrolyte, it is possible to increase the anodic potential from 0.2 to 0.7 V. At this higher potential, high-purity Al is obtained at the cathode.
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Yuri YAMAMOTO, Kazuki MINOWA, Youko TAKAHATAKE, Sou WATANABE, Masahiro ...
2024 Volume 92 Issue 4 Pages
043019
Published: April 05, 2024
Released on J-STAGE: April 05, 2024
Advance online publication: March 01, 2024
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In the pyro-reprocessing of spent nuclear fuel, salt bath is normally used in several times, but at final moment, spent salt containing small amount of chloride nuclear fuel material is generated. In terms of managing nuclear fuel materials, it is desirable that the nuclear fuel materials should be recovered from the spent salt. We are proposing methods for recovering nuclear fuel materials using precipitation by oxide addition and distillation for reducing pressure techniques. In this study, we have focused on the behavior of manganese(II), which is one of the radioactivated products. As a result of experiments and thermodynamic simulation, it was found that manganese(II) is likely to be entrained in nuclear fuel materials. Therefore, it is necessary to add a step to separate manganese(II) from nuclear fuel materials.
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Hirokazu HAYASHI, Kazuo MINATO
2024 Volume 92 Issue 4 Pages
043020
Published: April 05, 2024
Released on J-STAGE: April 05, 2024
Advance online publication: March 01, 2024
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The electrochemical behavior of neptunium in NaCl–2CsCl melt at 823–923 K was investigated by cyclic voltammetry, differential pulse voltammetry, and open-circuit chronopotentiometry after polarization. The results show that Np4+ ions are reduced to Np metal by a two-step mechanism via Np3+ ions in the NaCl–2CsCl melt. The diffusion coefficients of Np3+ and Np4+ ions were determined from cyclic voltammograms. The apparent standard potentials of Np3+/Np0 and Np4+/Np3+ redox couples have been determined to be E*(Np3+/Np0) = −3.353 + 7.67 × 10−4 T and E*(Np4+/Np3+) = −1.175 + 4.99 × 10−4 T vs. Cl2/Cl− (V), respectively. The activity coefficients of Np3+ and Np4+ ions were also determined using the reported data on the Gibbs free energy of formation for NpCl3 and NpCl4 in a supercooled liquid state.
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Keita GOTO, Kenji KAWAGUCHI, Toshiyuki NOHIRA
2024 Volume 92 Issue 4 Pages
043021
Published: April 06, 2024
Released on J-STAGE: April 06, 2024
Advance online publication: February 28, 2024
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To enhance the efficiency of water electrolysis, this study focuses on the NaOH–KOH hydrate melt (NaOH : KOH : H2O = 9 : 61 : 30 mol%) at temperatures ranging from 100 to 200 °C. We examined the behaviors of hydrogen and oxygen evolution reactions (HER and OER) on a Ni electrode at atmospheric pressure. In the Tafel plots, the upper limit of the Tafel region for both HER and OER expanded with increasing temperature, especially at 200 °C. Additionally, changes in the rate-determining step for HER and OER were observed compared to a 30 wt% KOH aqueous solution at 80 °C. The total overpotential for HER and OER was compared to the value of 1133 mV obtained in the 30 wt% KOH aqueous solution (80 °C, 500 mA cm−2). The total overpotentials in the NaOH–KOH hydrate melt at 200 °C and 500, 1000, and 2000 mA cm−2 were 545, 619, and 714 mV, respectively. The reduction in overpotentials was 52 %, 45 %, and 37 %, respectively. Water electrolysis utilizing the NaOH–KOH hydrate melt shows promising potential for significantly enhancing energy efficiency even at higher current densities relative to traditional alkaline water electrolysis.
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Koya YAMAZAKI, Naoki TARUMI, Isamu SATO, Haruka TADA, Haruaki MATSUURA
2024 Volume 92 Issue 4 Pages
043022
Published: April 16, 2024
Released on J-STAGE: April 16, 2024
Advance online publication: March 19, 2024
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The composition of platinum group alloys in insoluble residue liquid waste produced during spent nuclear fuel reprocessing depends on the type of fuel and the degree of burn-up. Consequently, for disposal of this waste by its vitrification in borosilicate glass, robustness of the vitrification process is necessary. It is very important in this process whether the platinum group alloy contained in the undissolved residue remains as a metal or blends into the glass. In this paper, the local structure and chemical state of each type of atom in borosilicate glass have been analyzed by SEM-EDS and EXAFS to evaluate the behavior of platinum group alloys in the glass. The SEM-EDS results showed that molybdenum migrate into the glass phase easily, while ruthenium, rhodium, and palladium atoms tend to stay in the alloy phase. The EXAFS showed that molybdenum (VI), ruthenium (IV), and palladium (0) were present in the same chemical form regardless of compositional change, while rhodium (III or IV) varied depending on the composition of the alloy.
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Ana Maria MARTINEZ, Anne STØRE, Karen OSEN
2024 Volume 92 Issue 4 Pages
043023
Published: April 22, 2024
Released on J-STAGE: April 22, 2024
Advance online publication: March 16, 2024
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Tungsten is a basic metal commodity that is classified as critical raw material (CRM) by the European Commission (EC) with the highest economical importance compared to other CRM. Thanks to its unique properties, secure W supply is critical to all industrial applications involving cutting or component wear, such as mining, machining, construction, tools and dies. Other important uses are in high-strength steels and high-temperature alloys, chemicals, mill products and lighting filaments. The production of W metal or carbide to be used in end products, requires a reduction process of the oxide which has been previously extracted from the primary (ores) resources by complex and energy intensive hydrometallurgical processes.
In the frame of the EC-funded TARANTULA project (GA 821159), innovative methods to obtain W metal directly from scheelite raw material have been investigated. The process comprises two steps, i.e., selective chlorination of the W ore in a molten chloride media using gaseous reactants, and subsequent electrolysis of the dissolved W electroactive species from the same reaction media. The chlorination of natural scheelite in a molten chloride has been demonstrated in the equimolar NaCl-KCl mixture at a working temperature of 727 °C, using both Cl2 (g) and HCl (g). The dissolved W species in the molten chloride were found to be tri-tungstate: W3O102− and/or the chloro-complex, as e.g., W3O10Cl24−. Subsequent electrolysis trials demonstrated the recovery of WC2 deposits on a carbonaceous cathode, while the anode reaction was evidenced to include the discharge of the oxide ions from the dissolved tri-tungstate species.
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Yoshiki ISHII, Sataro KIKO, Norikazu OHTORI
2024 Volume 92 Issue 4 Pages
043024
Published: April 25, 2024
Released on J-STAGE: April 25, 2024
Advance online publication: March 22, 2024
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A polarizable ion model was applied to the solid and molten alkaline-earth halide MX2, the parameters of which were determined by using first-principles calculations based on density functional theory, where M = Ca, Sr, Ba, and X = F, Cl, Br. The obtained parameters were used to evaluate the ionic conductivity, shear viscosity, and thermal conductivity in the molten and solid states by molecular dynamics simulations using the Green-Kubo relations. The calculated results were in good agreement with the experimental ionic conductivities and shear viscosities. The behaviors of all the calculated properties were well accounted for by ionic mass, number density, and packing fraction. Especially, the calculated thermal conductivities were well expressed by the empirical formula obtained for molten alkali halides. In addition, it was revealed that the reversal of cationic dependence in ionic conductivity of fluorides between solids and melts is due to the mass effects of carrier ions.
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Takanori OSANAI, Hidehiro SEKIMOTO
2024 Volume 92 Issue 4 Pages
043025
Published: April 30, 2024
Released on J-STAGE: April 30, 2024
Advance online publication: April 06, 2024
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Titanium (Ti) is widely desired in various industries because of its excellent properties. However, use of Ti is limited owing to the high costs associated with the extraction, melting, and rolling processes. In this study, we present a novel Ti film production process that does not require melting of Ti. To improve the practicality of the process, Ti films were formed through the reaction of Li2TiF6 with Ce and subsequent segregation in a Mo crucible. A Ti film with a thickness of 10 µm was obtained when 0.7 g of Li2TiF6 was added to 1.3 g of LiF molten salt on 8 g of liquid Ce in a Mo crucible, which reacted at 1000 °C for 9 h to form a Ce-Ti alloy. The alloy was maintained at 900 °C for 9 h to promote segregation. The thickness of the Ti film increased up to 90 µm when the segregation time was increased to 18 h, whereas an increase in the reaction time did not significantly affect the thickness of the Ti film. However, a decrease in the reaction time to 4.5 h inhibited the formation of the Ti film. When the Ce-Ti alloy with excess Ti at the bottom of the Mo crucible was segregated, a Ti film did not form on the Ce/molten salt interface. Furthermore, an increase in the amount of Li2TiF6 added to the molten LiF inhibited the formation of the Ti films as the Ce surface was covered with precipitates of CeOxFy. The mechanism of the formation of the Ti film via the segregation of the Ce-Ti alloy coexisting with LiF-based molten salts was explored based on these results.
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Karen OSEN, Ana Maria MARTINEZ, Anne STØRE, Cathrine K. W. SOLEM, Zhao ...
2024 Volume 92 Issue 4 Pages
043026
Published: April 30, 2024
Released on J-STAGE: April 30, 2024
Advance online publication: April 06, 2024
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The recent exponential growth in the Li ion batteries (LIB) market, is largely driven by the demand for electric vehicles and the general transition to a green and digital economy. It is therefore imperative to develop more effective and economic processes for recovering battery raw materials such as Li, Co, Cu and Ni. Moreover, these materials are all classified as critical or strategic (Cu, Ni) raw materials by the European Commission, and for Europe, it is of great importance to build a sustainable European supply chain for Li and other battery raw materials to decrease its dependency on import. In this work, we have studied the possibility to recover Li, Ni, Cu and Co from secondary raw materials like black mass (cathode and anode fraction from shredded end- of-life Li ion batteries), as well as Li from spodumene concentrate, spodumene being an important and available Li mineral. The approach has been to convert the metals in the raw materials to metal chlorides, by chlorination in LiCl-KCl (58 : 42) melts at 470 °C and CaCl2-NaCl-KCl (35 : 30 : 30) at 727 °C. With this method, the metals could potentially be reduced from the chloride matrix by subsequent sequential electrodeposition, utilizing their difference in nobility. Regarding black mass, the highest chlorination yields were obtained from uncalcined material (Li 64 %, Co and Ni 22–24 %, Cu 83 %, and Mn 49 %) in LiCl-KCl at 470 °C, the carbon in the black mass probably enhancing the chlorination rate. For spodumene concentrate, a high yield for Li (100 %) was obtained with Cl2 in CaCl2-NaCl-KCl at 727 °C, this melt composition being more oxoacidic and the higher temperature helping the chlorination kinetics.
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Chengqi FENG, Zhiyuan CHEN, Haoyong YIN, Jianying GONG, Hui WANG, Canc ...
2024 Volume 92 Issue 4 Pages
047001
Published: April 06, 2024
Released on J-STAGE: April 06, 2024
Advance online publication: March 07, 2024
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Eectrochemical glucose sensors is crucial for both environmental and human health, requiring rational nanoarchitectures with high electrochemical performance for glucose oxidation. Ni(OH)2/Ni(DMG)2 composite nanotubes were synthesized by etching nickel-dimethylglyoxime (DMG) nanorods with OH−, using Ni(DMG)2 as a partially sacrificial template. The optimal Ni(OH)2/Ni(DMG)2 nonenzymatic glucose sensor was evaluated on both conventional and portable electrochemical workstations, showing high sensitivity and a low detection limit. The optimal Ni(OH)2/Ni(DMG)2 glucose sensors integrated into smartphones demonstrated a low detection limit of 3.3 µM (M = mol L−1), a wide linear range (10 µM–8 mM), and a sensitivity of 262.80 µA mM−1 cm−2 for glucose detection. The sensors also exhibited favorable stability and reproducibility, along with preferable resistance to interference in the presence of uric acid, gluconate, proline, NaCl, valine, and lysine. Moreover, the portable sensor also demonstrated satisfactory glucose recovery (97.25–104 %) in serum samples, indicating its potential for future applications in real samples analysis.
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Yusuke MORINO, Misae OTOYAMA, Toyoki OKUMURA, Kentaro KURATANI, Naoya ...
2024 Volume 92 Issue 4 Pages
047002
Published: April 12, 2024
Released on J-STAGE: April 12, 2024
Advance online publication: March 19, 2024
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The sulfide solid electrolyte Li4SnS4 has gained attention owing to its high moisture durability. In this study, we quantitatively investigated the changes in the electrochemical properties and chemical/physical states of Li4SnS4 resulted from moisture exposure using the XRD, Raman spectroscopy, and high-frequency electrochemical impedance spectroscopy (HF-EIS). Li4SnS4 was subjected to Ar gas flow at a dew point ranging from −20 °C to 0 °C for 1 h, and sulfide hydrolysis generated only a minute amount of H2S. The XRD patterns and Raman spectra revealed the formation of Li4SnS4·4H2O with increasing dew point. The HF-EIS analysis, which was conducted to clarify the spatial distribution of the hydrate within the particle, revealed a significant decrease in the ionic conductivity of Li4SnS4; this result can be attributed to the increased grain-boundary (SE/SE particle contact) resistance due to the formation of Li4SnS4·4H2O at the particle surface, despite the generation of a minute amount of H2S. By combining these multifaceted analytical methods, we demonstrated that the thermodynamically stable surface hydrate Li4SnS4·4H2O reduced the lithium-ion conductivity without H2S generation owing to the hydrolysis of sulfide. Thus, we chemically, spatially, and quantitatively verified the mechanism underlying the observed decrease in the ionic conductivity.
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Fumisato OZAWA, Kazuki KOYAMA, Daiki IWASAKI, Shota AZUMA, Akihiro NOM ...
2024 Volume 92 Issue 4 Pages
047003
Published: April 20, 2024
Released on J-STAGE: April 20, 2024
Advance online publication: March 22, 2024
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Although Li-air batteries (LAB) have a high theoretical energy density (3500 Wh kg−1), further developments are required to overcome their practical limitations. Regarding the Li-metal negative electrode (NE), we have previously reported on the reversibility of the Li dissolution/deposition reaction by using Li|Li symmetric cells with a tetraglyme (G4)-based electrolytic solution. Particularly, in the 1.0 M (= mol L−1) LiNO3/G4 electrolyte under an O2 atmosphere, a Li2O protective layer is efficiently formed on the Li-metal electrode at a current density of 0.40 mA cm−2, and Li dendrite formation is suppressed. In the present study, we expanded the test conditions (current densities up to 2.0 mA cm−2 and temperatures of 10 to 50 °C) to clarify the dissolution/deposition behavior of the Li-metal NE. The effects of two electrolyte solutions, namely LiTFSI/G4 and LiNO3/G4, on the Li-metal NE were evaluated based on cyclical testing using Li|Li symmetric cells under an O2 atmosphere. The NEs were also examined by scanning electron microscopy and X-ray photoelectron spectroscopy. The results indicated that not only LiNO3 salt but also the supply of Li and nitrate ions at the Li electrode surface are critical factors in LAB performance.
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Mariko MATSUNAGA, Yuehai YU, Kensei TAKAHASHI
2024 Volume 92 Issue 4 Pages
047004
Published: April 25, 2024
Released on J-STAGE: April 25, 2024
Advance online publication: March 22, 2024
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Photoelectrodes have attracted significant attention in green hydrogen production via water electrolysis. Among others, titanium oxide (TiO2) is a representative photoelectrode for the conversion of solar energy in the ultravisible region into electrical and chemical energies. However, the poor solar adsorption of this material and the low anode reaction rate have limited the efficiency of hydrogen production via water electrolysis. In addition, there is an urgent need for more ecofriendly hydrogen production systems. The composite films of TiO2 and electronically conductive materials with various structures have been investigated to improve the photoelectrochemical activity of TiO2 by increasing the effective surface area of TiO2 and electronic conductivity of the films, which suppress the electron–hole pair combination. Herein, TiO2 and multiwalled carbon nanotube (MWCNT) composite films with various structures are prepared using the sol–gel method and electrophoretic deposition simultaneously, i.e., sol–gel electrophoretic deposition, under different solution conditions. Scanning electron microscopy (SEM)/energy dispersive X-ray spectroscopy (EDS) results reveals that additives and the mixing ratio of TiO2 sol and MWCNT dispersion solution in the electrophoresis bath affect film structure. Thin-film electrodes with different structures show different photoelectrochemical activities. Most as-fabricated TiO2/MWCNT composite thin-film electrodes outperform pristine TiO2 thin-film electrodes. TiO2 deposition on the MWCNT network surface with an antenna-like shape yields the best photoelectrochemical activity, achieving a low film resistance and ∼80 % anatase/rutile ratio.
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