Ar Atmosphere Research Articles

Direct TiH2 powder production by the reduction of TiO2 using Mg in Ar and H2 mixed gas atmosphere

To develop a direct production process for TiH2 powder from TiO2, the reduction of TiO2 using Mg in molten MgCl2 – KCl salt under a high hydrogen chemical potential was investigated. The reduction of nano-sized TiO2 powder was conducted at 973 – 1073 K under an Ar or Ar and 10% H2 mixed gas atmosphere when the mass ratios of Mg to feed and salt to feed were 1.14 – 2.86 and 0.87 – 3.48, respectively. The results showed that the oxygen concentration in the Ti product decreased as the mass ratio of salt to feed and temperature decreased. Furthermore, according to the variation in Mg amounts, the oxygen concentration was 0.350 – 0.441 mass%. In addition, employing hydrogen during the reduction enhances the capability to decrease the oxygen concentration in the Ti product. Moreover, the hydrogen concentration in the Ti product increased as the amount of molten salt decreased, thereby enabling pure TiH2 production. As a result, TiH2 powder with an oxygen concentration of 0.350 mass% was obtained under a certain condition. These results demonstrate the feasibility of the direct production of low-oxygen TiH2 powder from TiO2 via reduction at 973 K using Mg in an Ar and H2 mixed gas atmosphere.

The role of RF sputtering parameters on the uniformity and stability of Tb4O7 thin films on silicon substrates for passivation applications

Abstract In this study, the effects of different radio frequency (RF) parameters, were studied from the physical perspective of terbium oxide (Tb4O7) thin films deposited on silicon (Si) substrates, emphasizing their uniformity and stability for passivation applications. The findings for sample B, indicate that an optimal sputtering power of 110 W for 40 min enhances film uniformity while minimizing surface roughness, which is critical for achieving a stable passivation film. Notably, all the studied samples revealed a crystalline nature and maintained a stable phase, with no impurities detected from the grazing incident X-ray diffraction (GIXRD) patterns. Sample B revealed the highest value of crystallite size measured at 38 nm. Additionally, band gap energy (Eg) values between 2.19 and 2.78 eV were measured using the Kubelka-Munk (K-M) method. Photoluminescence (PL) analysis showed sample B achieved the highest peak intensity at 548 nm, corresponding to the 5D4 → 7F5 transition. Studies have been conducted on the formation of Tb4O7thin films deposited by RF sputtering on Si substrates, annealed in an argon (Ar) atmosphere. This study introduces a new approach to enhance film quality by adjusting the RF power during the sputtering process and subsequently annealing the sputtered samples. The aim was to investigate the benefits of nitrogen (N) annealing on the formation of a uniform passivation film of Tb4O7 material.

Recycling Nd Magnet Scraps to Synthesize Carbon‐Swaddled Fe3O4 Anode Material for Lithium‐Ion Battery

This study explores the innovative recycling of neodymium (Nd) permanent magnet scrap to synthesize Fe3O4, a high‐capacity anode material for secondary batteries, by leveraging the Fe oxalate solution produced during recycling. The traditional process of recovering Fe from permanent magnets in the form of oxides produces products with limited economic viability and usability. For the first time, we have successfully synthesized Fe3O4 as an anode material for lithium‐ion (Li‐ion) secondary batteries from scrap Nd magnets. We address the existing challenge by employing a novel approach: hydrothermal synthesis of crystalline FeC2O4·2H2O from the Fe leachate, extracted via oxalic acid leaching from a mixed phase of NdF3‐Fe2O3 controlled during fluorination heat treatment while recycling. The recovered FeC2O4·2H2O is subsequently phase‐transferred to Fe3O4 under an Ar atmosphere. To overcome the inherent low conductivity and rate capability of Fe3O4, a carbon‐coating process utilizing dopamine HCl is implemented. The developed C‐Fe3O4 anode material exhibits a significant capacity retention of 428 mAh/g after 500 cycles at 1C, showcasing its potential for use in high‐performance secondary batteries and contributing to the sustainable recycling of critical materials.

Impact of oxygen content on debinding of binder jetted 17-4 PH stainless steel: Part II – Sintering

Binder jetting requires the sintering of green parts to reach the properties of a metallic component. The sintering activity and sintered material properties of stainless steels are sensitive to powder oxidation and binder contamination, which are introduced by improper debinding. Air is often used during thermal debinding as oxygen aids binder removal, but the metal powder is oxidised being detrimental to sintering densification and final material properties. Hence, the impact of decreasing oxygen content in the debinding atmosphere on the sintering of 17-4 PH at 1300°C for 2 h in an inert argon atmosphere was investigated. Debinding in oxygen-containing atmospheres revealed the presence of δ-ferrite in the sintered microstructure, enhancing densification during sintering. Debinding in an inert Ar atmosphere resulted in low densification that was correlated to the absence of δ-ferrite due to the high amount of carbon in the sintered part. The high carbon content after debinding in Ar resulted in nearly complete oxygen removal by carbothermal reduction during sintering. Debinding in Ar + 1 vol.% O2 achieved the best combination of reducing final oxygen content by 46% via carbothermal reduction and the absence of carbon pickup during debinding and sintering. Debinding in processing atmospheres containing 3 vol.% O2 up to 20 vol.% O2, in contrast, led to a significant oxygen increase of 53 to 74% after sintering compared to the virgin powder.

Investigation of CuTi Alloy for Applications as Non-Sparking Material

A new non-sparking metallic material, Cu-Ti, with applications in potentially explosive environments is proposed as an alternative to CuBe, to reduce the processing and toxic effects of Be. Using high-purity Cu and Ti materials, a Cu (~3–4 wt%) Ti alloy with good chemical and structural homogeneity was fabricated in an induction furnace under an Ar atmosphere. The hot-rolled material was tested in an explosive gas mixture (10% H2 or 6.5% CH4) under extremely severe wear tests for 15,000 cycles, and no hot sparks were produced to ignite the medium. The material was investigated as hot-rolled plates (600 s at 950 °C and 10% reduction). The microstructures and surface of the wear test samples were investigated by light optical microscopy (LOM) and scanning electron microscopy (SEM). The chemical compositions were determined by energy dispersive spectrometry (EDS). The corrosion behavior was studied using electrochemical techniques: open-circuit, linear, and cyclic potentiometry in saline electrolyte solutions. The mechanical properties, such as microhardness and friction coefficient, were determined using UMT equipment. The results showed that the alloy is suitable for applications requiring non-ignition properties, with good hot rolling deformability and chemical composition homogeneity. Regarding the corrosion analysis and mechanical properties of the experimental CuTi alloy, minor differences were observed between the cast- and hot-rolled material.

Communication—Rotating Basket Cathode for High-Speed Electrolytic Reduction of TiO2 in Molten CaCl2-CaO

A rotating basket cathode improved the TiO2-reduction efficiency by 6.5-fold and accelerated the electrolysis of molten CaCl2-CaO at 1173 K in an Ar atmosphere. Promoting dissolution of the CaO byproduct and mass transfer near the cathode was effective for TiO2 reduction and α-Ti deoxidation. The reduction efficiency can be predicted by optimizing the rotational speed and pulse rotation.

Study on the reaction mechanism and kinetics of limestone hydrogenation by micro fluidized bed: Effect of H2 concentration and natural limestone

Limestone decomposition is the first step in cement production, which produces a significant amount of CO2 and poses a significant challenge to achieve carbon neutrality. Hydrogenation of limestone can produce CO or CH4 instead of CO2, which can be considered as a new way of carbon capture, making it a promising method for carbon emission reduction. In this work, pure CaCO3 and several natural limestone samples were hydrolyzed under varying H2 concentration using a micro fluidized bed (MFB) reactor combined with online mass spectrometry to reveal the mechanism and kinetics of limestone hydrogenation.The main gases produced by hydrogenation at 1 atm are CO and CO2. The CO2 comes from the calcination of CaCO3. The CO comes from 2 steps: the first step is the in-situ hydrogenation of CaCO3 and the second step is the Reverse Water Gas Shift (RWGS) reaction. The activation energy (Ea) of CO2 formation in H2 atmosphere is lower than in Ar atmosphere. However, there is no obvious effect of different H2 concentrations on the Ea of CO2 formation. The Ea of CO in situ formation is 72.70 KJ/mol, 54.53 KJ/mol, 71.34 KJ/mol and 60.29 KJ/mol in 10%, 30%, 50% and 70% H2 atmosphere, respectively. The H2 concentration also has no significant effect on the in-situ CO evolution. However, the H2 concentration can affect the Ea of CO produced by RWGS. The Ea is 75.67 KJ/mol, 167.59 KJ/mol and 221.47 KJ/mol in 10%, 30% and 50% H2 atmosphere, and this reaction doesn't occur in 70% H2 atmosphere. Compared with the pure CaCO3, the hydrogenation of limestone can produce more CO and less CO2. In limestone, impurity elements are the main factor affecting the reaction kinetics. Transition metals can increase the rate of CO2 production, but have no apparent effect on CO. The CO2 yield of high impurity limestone is higher than that of limestone with low impurities. Transition metals can also reduce the Ea of CO2 formation and the RWGS reaction. In the 50% H2 atmosphere, the Ea of CO2 formation is 88.87 KJ/mol and the Ea of CO from RWGS is 137.60 KJ/mol. However, under the same conditions, the Ea of pure CaCO3 is 126.91 KJ/mol and 221.47 KJ/mol.

Thermoelectric performance enhancement of Mg2Si-based silicides synthesized in nitrogen atmosphere

Abstract Thermoelectric materials are attractive for sustainable energy applications due to their ability to convert waste heat into electricity. However, one of the main hindrances to their widespread adoption is the stringent requirements during their synthesis and processing, and therefore affects their overall cost and sustainability. For instance, Mg-containing compounds generally requires processing in high vacuum or Argon protected atmosphere, which are less readily available. In this work, we demonstrate higher thermoelectric performance by synthesizing Mg2Si-based compounds in N2 compared to Ar atmosphere. The high performance originated from simultaneous improvement in electrical conductivity and reduced thermal conductivity. In addition, the introduction of Sn-alloying as well as Zn- and Bi- co-doping further improved both electronic and thermal transport properties, resulting in peak zT near 1.0 at 760 K for Mg1.9925Zn0.0075Si0.48Sn0.5Bi0.02. Owing to the much lower cost of N2 compared to Ar owing to their much higher relative abundance, such processing strategy is expected to reduce cost and improve sustainability. Furthermore, the insights derived from this work can potentially be applied to other compounds containing Mg- and other reactive elements. Fundamentally, this result will also motivate further studies on the intrinsic defect formation in N2 vs Ar atmosphere, which affects both electronic and thermal transports.

Fluoride Ion Conduction of BiSF with Distorted PbFCl-Type Structure

All-solid-state fluoride ion (F−) rechargeable batteries are expected to have a high energy density due to their wide potential window and the availability of multi-electron reactions at the electrodes. F− conductors used as solid electrolytes have lower conductivity at room temperature than cationic conductors, and the crystal structures studied are limited. We have previously discovered that an anion-ordered structure created by F− and S2− in sulfidefluoride has a F− conduction path that is not found in single anion compounds1), indicating that mixed-anion compound can be used to develop new F− conductors. In this study, we focused on BiSF, a fluorosulfide with distorted PbFCl-type structure. The 6s2 lone pair electrons (LPEs) around Bi3+ are expected to promote F− conductivity due to their high polarizability. In addition, the ionic conductivity of BiSF was compared with LaSF that has PbFCl-type structure but without LPEs. BiSF was obtained by mixing Bi2S3 and BiF3 in an Ar atmosphere, forming pellets, placing them in a cell for high-pressure synthesis, and performing high-pressure synthesis at 5 GPa and 650°C for 1 hour. LaSF was obtained by mixing La2S3 and LaF3 under an Ar atmosphere, pellet forming, vacuum sealing, and calcination at 800 °C for 24 hours. Powder X-ray diffraction measurements (XRD) were used to identify the experimental samples, while AC impedance methods were used to measure ionic conductivity. The XRD results confirmed that the synthesized sample contained few impurities and the target material BiSF was synthesized. AC impedance measurements of BiSF showed a rising behavior at the low frequency side, indicating that BiSF has ionic conduction. The ionic conductivity of BiSF at 30°C was 4.22 × 10−6 S cm−1. LaSF, which has similar PbFCl-type crystal structure as BiSF but without LPEs, did not exhibit F− conduction, suggesting that the F− conduction in BiSF is affected by LPEs present in Bi3+.【References】1) S. Tachibana, C. Zhong, K. Ide, H. Yamasaki, T. Tojigamori, H. Miki, T. Saito, T. Kamiyama, K. Shimoda,Y. Orikasa, Chem. Mater., 35, 4235-4242 (2023).

Electrochemical Impedance Spectroscopy of Bi-Based Cathode for Pellet-Type All Solid-State Fluoride Shuttle Battery

All solid-state fluoride shuttle battery (ASS-FSB) is one of the most promising rechargeable batteries due to its high energy density and cost effectiveness. The FSB operates based on conversion reactions with multi-electron transfers and does not require the use of high-cost metals like those used in lithium-ion batteries (LIBs). Therefore, the ASS-FSB is expanding research field for next generation batteries. Electrochemical impedance spectroscopy (EIS) is widely used for the analysis of energy devices such as LIB electrodes, as it can divide complicated electrochemical reactions into elemental processes based on their characteristic time constants without the need to disassemble batteries. We have reported that 3D structured electrodes can be analyzed by optimizing equivalent circuits 1–3. Although EIS is a powerful tool to understand electrochemical elemental processes in energy devices, detailed EIS analysis of ASS-FSB has not been reported. Here, we investigate the EIS analysis of a pellet-type ASS-FSB composed of a Bi-based cathode and a PbSnF4 anode, using it as an example of ASS-FSB.A Bi-based cathode cell for EIS is composed of Bi cathode (Bi/ Ce0.95Sr0.05F2.95/AB = 25/70/5 by weight), Pb0.58Sn0.42F2 anode (Pb0.58Sn0.42F2/AB = 70/5 by weight) and Ce0.95Sr0.05F2.95solid electrolyte. The loading amount of the Bi-based cathode was 10, 20, 30 mg and that of the Pb0.58Sn0.42F2 anode was fixed to be 20 mg. A three-layer pellet cell (φ10 mm) was prepared in Ar atmosphere by applying a pressure stepwise and finally reaching 740 MPa. The cell was held with 4 bolts, followed by keeping the cell under vacuum. Prior to conducting the EIS, the cells were charge with a CC (120 µA)-CV (cut off voltage of 0.9 V, down to 40 µA) mode. The EIS was carried out after 1st charge with a frequency range from 1 MHz to 100 mHz at SoC of 100% and 140 ℃.Figure 1 shows the charge and discharge curves of the pellet-type ASS-FSBs with different cathode amount measured at 140 ℃. The discharge capacity of the ASS-FSBs with 10, 20, 30 mg cathode loading was 323, 359, and 359 mAh/g-Bi, respectively. The discharge capacity was 84%, 93%, and 93% against the theoretical capacity of Bi, confirming that ASS-FSBs, especially those for 20 and 30 mg, were fabricated properly. Figure 2 represents Nyquist plots of pellet-type ASS-FSBs with different cathode amount measured at SoC 100% and 140℃. The Nyquist plots clearly show one semicircle in high-frequency region (see Fig.2 right) and a line with an angle of ~45゜ in middle-frequency region (see Fig.2 right) and a line with an angle of higher than 45゜ in low-frequency region (see Fig.2 left). Although the loading amount of the Bi cathode are different, the diameter of the semicircles is almost same, indicating that the semicircle is derived from a common element among the pellet-type ASS-FSBs. The length of the line with an angle of higher than 45゜ decreased with increase of the loading amount of the Bi cathode. The decrease is due to the increase of limiting capacitance 2. Meanwhile, the line with an angle of ~45゜ is characteristic feature of an ion transport property in depth direction. In addition, the length of the line increased proportionally to the loading amount of the Bi cathode, supporting that the line is derived from the reaction distribution. The results indicate necessity to adopt a transmission line model to analyze the pellet-type ASS-FSB by EIS.In the presentation, equivalent circuit design using a transmission line model and its attribution for the pellet-type ASSFSB with Bi-based cathode will be discussed with EIS data measured with various condition on SoC and temperature. References H. Nara, D. Mukoyama, T. Yokoshima, T. Momma, and T. Osaka, J. Electrochem. Soc., 163, A434–A441 (2016). H. Nara, K. Morita, D. Mukoyama, T. Yokoshima, T. Momma, and T. Osaka, Electrochim. Acta, 241, 323–330 (2017). H. Nara, D. Mukoyama, R. Shimizu, T. Momma, and T. Osaka, J. Power Sources, 409, 139–147 (2019). Acknowledgement This presentation is based on results obtained from a project, JPNP21006, commissioned by the New Energy and Industrial Technology Development Organization (NEDO). Figure 1

Effects of Electrolyte Salts on Ionic Transport in Solid Polymer Electrolytes Investigated by Operando Raman Spectroscopy

Introduction To achieve carbon-neutral society, battery technologies have been attracting attention in recent years owing to its potential for storing renewable energy and serving as a load leveling power sources. In particular, all-solid-state batteries (ASSBs) utilizing non-volatile and flame-resistant solid electrolytes are actively investigated worldwide for practical implementation, as they are expected to enhance safety. Among solid electrolytes, solid polymer electrolytes (SPEs), which exhibit high flexibility and formability, are expected for their application in electrochemical devices such as ASSBs. In SPEs, cations are solvated by the host polymer and occurs ionic conducte through cooperative transport associated with segmental motion. The ionic transport properties of SPE, affected by molecular structures of electrolyte salt, and are further influenced by processes solvation/desolvation of cation and decomposition reactions under electrochemical conditions, is considered different from static states. Therefore, we focused on applying [Li | SPE | Li] symmetric cells and evaluated the ionic transport processes within SPE under reaction conditions using concentration changes through operando Raman spectroscopy measurements. In this study, we applied the measurement approach for use on SPEs incorporating LiN(SO2F)2 (LiFSA), LiN(SO2CF3)2 (LiTFSA), and LiN(SO2C2F5)2 (LiBETI) as Li salts to investigate the impact of anion structure/molecular weight on ionic transport mechanisms under actual reaction conditions. Experiments Li-based solid polymer electrolytes were prepared by mixing cross-linked polyether-based macromonomer P(EO/PO) (EO: PO = 8:2), Li salts (LiFSA, LiTFSA, LiBETI), and photopolymerization initiator DMPA in acetonitrile under an Ar atmosphere within a glovebox. The resulting solution was vacuum-dried and filled between glass plates using a spacer (thickness: 0.5 mm). Each SPE film was then fabricated by UV irradiation. To investigate the solvation structure and salt dissociation characteristics of SPE (salt concentration: [Li]/[O] = 0.04-0.16) under static conditions, Raman spectroscopy measurements were performed (NRS-4500: Jasco). A 9 mm × 9 mm rectangular-shaped [Li | SPE([Li]/[O]=0.04, 0.16) | Li] symmetric cell was prepared for in situ monitoring of concentration variations into the SPE during electrochemical reactions. The symmetric cell was introduced into a sealed cell with a quartz glass having monitoring window and connected to a potentiostat (HZ-7000, Hokuto Denko). In o perando Raman spectroscopy, Raman spectra were obtained from the vicinity of the working electrode (W.E.) and the counter electrode (C.E.) within the SPE during voltage application. The W.E. and C.E. regions were measured at points approximately 10-30 µm from the electrode/electrolyte interface. Results & Discussion Raman spectrum of the P(EO/PO)-LiTFSA(1) and LiBETI(2) system exhibited the peak at approximately 740 cm-1 derived from SNS vibration of TFSA and BETI anion. This peak, which increases with salt concentration, can be utilized as an indicator to evaluate concentration changes within the SPE induced by electrode reactions. To evaluate the ionic transport properties, operand o Raman spectroscopy measurements were performed using [Li | SPE([Li]/[O]=0.04, 0.16)|Li] symmetry cells. The peak area change (A/A 0) from the initial state was calculated by using the obtained Raman spectra. Fig. 1 and 2 exhibited the relationship between A/A 0 and applied voltage time calculated from measured points near W.E. and C.E. in symmetrical cells using the LiTFSA and LiBETI systems. In both Fig. 1 and 2, the peak area changes (A/A 0) were observed that concentrations near W.E. and C.E. increased or decreased with voltage application. In particular, the peak area changes (A/A 0) of the LiTFSA system exhibited a rapid increase in W.E. and decrease in C.E. within the initial 1 h of measurement, followed by no significant changes over 5 h (Fig. 1). This result suggests that the SPE has reached a steady state within at the end of the experiment. And in Fig. 1, the area changes (A/A 0) of [Li]/[O]=0.04 was significantly higher than that of [Li]/[O]=0.16. This results suggests that the faster ionic transport characteristics of [Li]/[O]=0.04 compared to [Li]/[O]=0.16 can be attributed to the lower concentration of the former. No significant changes were observed both [Li]/[O]=0.04 and 0.16 owing to changes in A/A 0, similar to LiTFSA system (Fig. 2). The lower ionic transport properties of LiBETI can be attributed to the larger molecular weight of BETI anion. These results indicated that the ionic transport mechanisms under reaction conditions differ depending on the anion structure (molecular weight).(1) I. Rey, et al, J. Electrochem. Soc., 145, 3034 (1998).(2) C. Capiglia, et al., J. Electrochem. Soc., 150, A525 (2003). Figure 1

Carbothermal Shock Derived Electrochemical Regeneration of Spent Biochar for Remediation of Ciprofloxacine Contaminated Water

Biochar, derived from waste biomass, is a potent material for carbon dioxide sequestration, owing to its stable, non-degradable aromatic structure [1]. Biochar is found to have advantageous characteristics, such as a unique pore structure, large specific surface area, complex surface-active functional groups, and stable chemical properties. These properties make biochar as a high potential biosorbent for removal of pollutants from water [2]. Meanwhile, the escalating use of pharmaceuticals has led to pervasive environmental residues, posing public health risks. Specifically, antibiotic contamination risks augmenting antibiotic resistance, underscoring the need for efficient wastewater treatment methods [3]. However, current wastewater treatment plant(WWTP) based on biological treatment was not effectively eliminate this types of waste in the water and it is necessary to investigate efficient method for removal of antibiotics from wastewater.This study explores the use of biochar for ciprofloxacin (CIP) removal from water and introduces a novel electrochemical biochar regeneration technique. We utilized sludge from chemical plants to produce biochar through standard and alkali-activated pyrolysis, yielding CB (normal pyrolysis) and CAB (alkali activated pyrolysis) types with distinct physicochemical properties. CAB, with an exceptionally high surface area (~2330 m²/g) and carbon purity (95.4%), demonstrated superior CIP adsorption capacity (~550 mg/g). We investigated the CIP adsorption isotherm, kinetics and thermodynamics to elucidate the underlying mechanisms, which appear dominated by π-π and electrostatic interactions facilitated by the high pyrolysis temperatures reducing oxygen-containing groups on the biochar. After the biochar became saturated with CIP, we regenerated it using joule heating in Ar atmosphere, employing the carbothermal shock method for rapid, short-duration temperature increases [4]. In contrast to traditional CTS which can sometimes lead to structural damage by directly heating the material on the carbon substrate [5], we used radiant heat from the CTS process to ensure controlled temperature elevation. This modified approach maintains the structural integrity of the biochar by avoiding direct contact between the biochar and the carbon substrate while facilitating the regeneration process. Additionally, this method facilitates the physical separation of the biochar from the carbon substrate, enhancing the recovery and reuse of biochar. Such an approach contributes to the efficient regeneration of biochar and environmentally friendly processing. We examined parameters such as distance from the substrate and duration to optimize the regeneration conditions. Ultimately, we assessed the efficacy of the CIP adsorption by the regenerated biochar. Traditional thermal treatments for biochar regeneration are energy-intensive and time-consuming. We propose an innovative approach using joule heating under a nitrogen atmosphere, employing carbothermal shock for rapid, efficient regeneration. By optimizing parameters such as voltage and duration, we identified ideal conditions for regenerating biochar, significantly enhancing its CIP adsorption efficacy. This study not only highlights the potential of biochar in environmental remediation but also introduces an energy-efficient regeneration method, contributing to sustainable pollution management solutions.

Effects of Temperature and Different Electrolysis Processes on Mg Metal Deposition in Molten Salt Electrolysis

Metallic Mg has excellent mechanical properties, and its demand is growing worldwide. However, the supply risk and high greenhouse gas emission in its production became non-negligible nowadays. Our laboratory has been studying the Mg production process by molten salt electrolysis using the raw material extracted from seawater. In this study, Mg metal deposition was attempted by potentio-static and galvano-static electrolysis, and the influence of electrolysis temperature was discussed.Molten MgCl2-NaCl-CaCl2 was used as the electrolytic bath. Mo wire was used as the working electrode, and carbon rod was used as the counter electrode. The reference electrode was a Ag/AgCl couple in the same bath in a mullite tube, and its potential of the reference electrode was calibrated against the Mg deposition potential. Experiments were conducted in an Ar atmosphere, and the electrolysis temperature was 680°C~740°C. After observing the cathodic behavior by cyclic voltammetry, potentio-static electrolysis or galvano-static electrolysis was performed. The obtained electrodeposits were evaluated by XRD and XRF, and the cathodic current efficiency was calculated from the weight of the deposit and the quantity of electricity.The current in the potentio-static electrolysis became almost stable after the initial change in electrolysis. The stable current was 2.0A/cm2 at -0.2V (vs. Mg dept.), and depended on the applied potential. The potential in the galvano-static electrolysis also became stable after the initial change. The stable potential was -0.3V (vs. Mg dept.) at 1.0A/cm2. The stable potential was slightly affected by the applied current, but this potential was usually equivalent to that of Mg metal deposition. The values by the potentio-static electrolysis and those by the galvano-static electrolysis were almost consistent. Metallic Mg was obtained with either potentio-static or galvano-static electrolysis. The purity was generally higher than 99.9%, and rarely depended on the electrolysis method. The cathodic current efficiency was about 90% usually, and not influenced by the electrolysis method significantly.Figure 1 was shown the relationship between the electrolysis temperature and Mg purity of the electrodeposits. A clear dependence of the Mg purity on electrolysis temperature was not seen, and the purity was usually better than 99.8%. The current efficiency was not affected significantly by electrolysis temperature. In the case that the galvano-static electrolysis where the temperature changed during electrolysis was performed, the Mg purity and the current efficiency were not changed so much.The influences of electrolysis temperature and electrolysis method on the Mg purity and the current efficiency were studied in this study, and their influences were shown limited. Since the change in electrolytic current causes the change in the bath temperature in the actual Mg metal production by molten salt electrolysis, the results above indicate that the Mg deposition with variable temperature was possible under the actual electrolysis condition:1.0A/cm2 at 680~740°C.This work was performed under the support of the commissioned work (JPNP14004) of the New Energy and Industrial Technology Development Organization (NEDO). Figure 1

Fluoride Ion Conductor of Fluorosulfide with Double-Layer Honeycomb Structure

All-solid-state fluoride ion batteries (FIBs) have attracted considerable attention due to their high theoretical energy density and high safety compared with those of conventional lithium-ion batteries (LIBs) [1]. However, the practical application of FIB lacks suitable solid electrolyte with high ionic conductivity and wide electrochemical potential window at room temperature. In addition, most of the fluoride ionic conductors reported previously are limited to fluorides such as fluorite, tysonite-type, and perovskite-type structures [2]. Therefore, increasing the variations of crystal structures for fluoride ion conductors are expected.Fluorosulfides containing S2− and F− with largely different ionic radii are ideal for creating anion-ordered structures and expected to create fluoride ion conductors not found in reported fluoride[3]. In this study, we synthesized rare-earth fluorosulfides LaM 2F3S2 (M = Ba, Sr) and measured their ionic conductivity. Powder samples were weighed in stoichiometric ratio under an Ar atmosphere and pulverized by mortar mixing. The pelleted sample was placed in a Ta container, vacuum sealed using a quartz tube, and then calcined. The obtained samples were structurally evaluated by XRD measurement. For the evaluation of conductivity by the AC impedance method, the obtained powder was formed by isostatic pressing, sintered again, and Au electrodes were deposited on both sides as sintered specimens.In the crystal structure of these fluorosulfides, anion-ordered 2D crystal structures are formed, which cannot be achieved in a single anion compound. The F− conducting layer is a double-layer honeycomb structure, with F− conducting two-dimensionally via four-, six- and four-coordination sites. The conductivity at 100°C is in a order of 10-6 S cm-1, which is highest among mixed-anion compounds but is several orders of magnitude lower than previously reported single-anion compound. On the other hand, the activation energy was 0.50 eV, which is comparable to that of the fluorite-type structure Ba0.6La0.4F2.4. The material development of fluoride ion conductors using flurosulfide compounds is expected to increase crystal structure variations with fluoride-ion conduction pathways.

Construction of Perovskites Thin Films of Black Orthorhombic Phased Cesium Tin Iodide Using Pulsed Laser Deposition

Introduction: Perovskite solar cells have the potential to achieve higher efficiency than current mainstream silicon-based solar cells. Black orthorhombic (B-γ) phased cesium tin iodide (CsSnI3) perovskite, which contains no lead and organic content leading to be environmentally friendly and thermally stable, respectively, has attracted much more attention than methylammonium lead iodide (MAPbI3), which is the most commonly used photosensitive layer in the perovskite solar cells. However, its photoelectric efficiency is much lower than that of MAPbI3. This low efficiency is attributed to the high defect density in CsSnI3, such as Cs or Sn vacancies which have very low defect formation energies. Thus, it is essential to control the atomic arrangement at the interface and the crystal growth process. The CsSnI3 perovskite exists in two orthorhombic polymorphs at room temperature: one is a yellow 1D double-chain structure and the other is a black 3D perovskite structure (B-γ). The B-γ phase has a band gap of ca. 1.3 eV, which is desirable for the photosensitive layer of the solar cells, in contrast to the Y phase with ca. 2.6 eV band gap. However, the orthorhombic B-γ phase rapidly transitions to the Y phase when some external perturbation (oxygen, moisture, solvent) is applied, and subsequently transfers to photoinactive Cs2SnI6 because of self-doping from Sn2+ to form Sn4+ under ambient-air conditions [1]. Therefore, it is necessary to construct defect-free B-γ CsSnI3 layers on solid substrates. In this study, we attempted to construct defect-free CsSnI3 perovskite thin films on various solid substrates at room temperature using the pulsed laser deposition (PLD) method, which enables the control of crystal growth process at an atomic level. Experiment:To prepare the precursor target for the PLD, stoichiometric amounts of SnI2 and CsI powders were mixed and pressed to a tablet shape. Then it heated to 300ºC and held for 18 h under Ar atmosphere. The target was loaded into the PLD chamber, and CsSnI3 thin films were deposited onto n-typed Si(100), TiO2(100), (110), (001) single crystal and glass substrates at room temperature using a Nd:YAG laser. An Ar working pressure of 1.0 × 10-3 Torr was kept constant during deposition. Following CsSnI3 deposition, an amorphous Tin-doped Indium oxide (ITO) capping layer was applied by PLD to prevent the film oxidation. Result and Discussion: X-ray diffraction (XRD) analysis was conducted for the precursor target and the obtained thin films. It revealed that the precursor target contains only pure B-γ CsSnI3 polycrystals. For the obtained thin films, B-γ CsSnI3 was obtained and it oriented mainly in the [010] direction normal to the surface regardless of the substrate type. In addition, the 2D diffraction images indicated that the orientation ranged within ±10º, also regardless of the substrate type. In the previous study by Kiyek et al. [2], polycrystalline films were obtained by the PLD method with the precursor containing the mixture of the raw materials (CsI and SnI2). On the other hand, in this study, the oriented films were obtained with B-γ CsSnI3 precursor, suggesting that the precursor condition may affect the orientation because the laser plume constantly contains strictly Cs:Sn:I = 1:1:3 composition during ablation. We will discuss this phenomenon in detail.

Synthesis of Mesoporous Carbon Support Using Two Different Sizes of SiO2 Hard Templates

Introduction After 2030, extremely high cell performance is required for PEFCs used in fuel cell electric vehicles (FCEVs) in Japan [1]. For FCEVs, cost reduction is an urgent issue, and it is necessary to reduce the amount of Pt catalyst used in PEFCs by enhancing oxygen reduction reaction (ORR) activity. On the other hand, in order to improve cell performance, not only the ORR activity enhancement, but also suppression of ionomer poisoning and increase in oxygen diffusivity are required [2]. Therefore, development of a new carbon support is necessary for the latter. In this study, a mesoporous carbon (MPC) support was synthesized by using two different sizes of SiO2 hard templates. Porosity and morphology of the MPC support were characterized by N2 gas adsorption, SEM and TEM analyses and electrochemical properties of Pt/MPC catalyst were investigated. Experimental MPC support was synthesized by a SiO2 hard template method using resorcinol and formaldehyde as carbon sources [3]. In a mixture of 20 mL H2O and 80 mL EtOH, 150 mg of hexadecyltrimethylammonium bromide was added as a surfactant. The solution was stirred at 25℃ for 0.5 h. Subsequently, two kinds of SiO2 hard templates (5 nm: 600 mg and 50 nm: 300 mg) and 15 mg of 3-aminopropyltriethoxysilane as a silane coupling agent were added simultaneously to the solution and the solution was further stirred at 50℃ for 2.5 h. Then 650 mg resorcinol, 910 μL formaldehyde and 600 μL NH3 aq. (28%) were added to the solution, which was stirred at 25℃ for 24 h to cause polymerization reaction. After stirring, the solution was transferred to a 300 mL eggplant flask and the solvent was removed using an evaporator at 30 hPa and 30℃ for 3 h. The brown precipitate was dried in an oven at 60°C in air, and heat-treated at 850℃ for 3 h in Ar atmosphere. The obtained SiO2/MPC was dispersed in a HF solution (10%) to remove the SiO2 hard templates.The MPC support (300 mg) obtained was re-dispersed in a mixed solvent (37.5 mL EtOH/250 mL H2O) and Pt(NO2)2(NH3)2corresponding to 300 mg of metallic Pt was added. The solution was refluxed at about 90°C in N2 gas atmosphere for 4 h [4]. The resulting Pt/MPC catalyst was filtered, washed and dried at 60°C in air. The SiO2/MPC, MPC support and Pt/MPC catalyst were analyzed by N2 gas adsorption, TG-DTA, XRD, SEM, TEM and TEM-EDX. CV was recorded in Ar-saturated 0.1 M HClO4 at 25℃ at a scan rate of 50 mV/s and ORR activity was evaluated by LSV performed in O2-saturated 0.1 M HClO4 at 25℃ at a positive potential scan rate of 10 mV/s and at 1600 rpm. Results and Discussion TEM image and TEM-EDX compositional analysis of the SiO2/MPC are shown in Fig. 1. From the SEM images of Figure 2 and Figure 3, the primary particle size of MPC was about 60 nm and the secondary particle size was about 8 µm. Although presence of the 5-nm SiO2hard templates was not observed, the 50-nm ones were coexisted with carbon. Figure 2 depicts SEM and TEM images of the SiO2/MPC before and after HF treatment. The SiO2 templates were removed by the HF treatment and macropores about 50 nm in size were formed. Figure 4 demonstrates pore size distribution of MPC support after the HF treatment. The MPC had peak pore diameters of approximately 4 and 60 nm, reflecting the particle sizes of the SiO2 templates. The specific surface area of the SiO2/MPC was increased from 350 to 1170 m2/g after the HF treatment. The cross-sectional TEM images of Pt/MPC catalyst are shown in Fig. 5, indicating that Pt NPs are uniformly deposited throughout the MPC support. The Scherrer diameter of the Pt NPs was 2.6 nm. Electrochemical measurements revealed that electrochemical surface area and ORR mass activity were 84 m2/g and 350 A/g at 0.9 V vs. RHE, respectively. The low ORR mass activity of the Pt/MPC catalyst (350 A/g) can be attributed to the large secondary particle size of the MPC of 8 μm. At the conference, we will present the electrochemical properties and a single cell performance of the Pt/MPC catalyst synthesized by using pulverized MPC support.This study was partly supported by NEDO, Japan. Reference [1] M. Suzuki, https://www.nedo.go.jp/content/100895111.pdf, in Japanese.[2] V. Yarlagadda et al., ACS Energy Lett., 3, 618 (2018).[3] S. Li et al., Mater. Sci.-Poland, 37, 585 (2019).[4] M. M. Rahman et al., RSC Adv., 11, 20601 (2021). Figure 1

Development of Operando Bimodal Atomic Force Microscopy System for Real-Time Nanomechanical Mapping of Electrode Cross-Sections in All-Solid-State Lithium-Ion Battery Configuration

All-solid-state lithium-ion batteries (ASSLBs) have garnered considerable attention as the next-generation electrochemical energy storage systems due to their high chemical safety and wide electrochemical potential windows1. Among the available candidates for ASSLB negative electrodes, silicon is a promising material because of its extremely high theoretical capacity and low lithiation/delithiation potential2. However, Si is known to undergo severe structural changes during electrochemical lithiation/delithiation, as revealed by our previous operando studies using a laboratory-based X-ray photoelectron spectroscopy setup3,4. These dramatic structural changes may result in a significant volume expansion/contraction, leading to particle cracking, pulverization, and electrode failure. Hence, the understanding and control of such physicochemical phenomena are critical to prevent nanomechanical and electrochemical degradation of the electrode.In this talk, we will introduce our newly developed operando bimodal atomic force microscopy (AFM) system which enables real-time nanomechanical monitoring of an amorphous Si thin film electrode during electrochemical lithiation/delithiation, simultaneously with cross-sectional topography imaging5. An ASSLB cell composed of 3 µm-thick Si thin film/500 µm-thick Li6.6La3Zr1.6Ta0.4O12 (LLZT) solid electrolyte/50 µm-thick Li foil (Si/LLZT/Li) was fabricated, and its cross-section was smoothened by an Ar-ion beam prior to carrying out the nanomechanical mapping on the Si/LLZT interface. The nanomechanical mapping was performed during the first electrochemical lithiation and delithiation within a potential window of 0.01-1.20 V vs. Li+/Li under Ar atmosphere (H2O < 0.1 ppm, O2 < 0.1 ppm).Nanomechanical property maps of the Si electrode, in the form of Young’s modulus maps, were successfully acquired as a function of apparent Li content x in lithium silicide (Li x Si), together with real-time topography images. At the first lithiation, the average Young’s modulus drastically decreased due to the formation of Li x Si from pristine Si, followed by a moderate modulus reduction up to a capacity of 3300 mAh g-1 (x = 3.46 in Li x Si). Throughout the successive delithiation up to 1467 mAh g-1 (x = 1.54 in Li x Si), the average modulus was gradually recovered. The Li x Si moduli obtained from this study are consistent with the values from the first-principles calculations, showing the sensitivity and reliability of the technique6. The demonstrated technique can be implemented for a wide range of battery materials for both solid-state and liquid-electrolyte lithium battery systems.

Development of Fe/N/C Type Oxygen Reduction Catalysts Using Carbon Supports Derived from Cellulose Paper by a Microwave Method

Introduction Effective utilization of abundant forest resources is crucial in Japan, which has vast forest reserves. Cellulose, which constitutes half of plants, has recently garnered attention as a novel material, such as cellulose nanofiber. Kyotani et al. reported that high-yield carbon materials retaining the original shape can be obtained by high-temperature treatment of cellulose-based paper treated with methanesulfonic acid1.We have been preparing Fe/N/C oxygen reduction catalysts using the carbon materials prepared by the method as a support; however, the oxygen reduction activity was insufficient. This study aimed to enhance the oxygen reduction reaction (ORR) activity by employing the microwave method for the preparation of carbon supports, synthesis of catalyst precursors, and drying treatment. Experimental Cellulose paper (toilet paper (TP), Nippon Paper Crecia) was immersed in 1.0 M methanesulfonic acid and air-dried for more than two days in a container with a filter attached to the top. The air-dried sample was sandwiched between two carbon plates, placed in an electric furnace, and heat-treated at 800°C for 1 h under Ar atmosphere with a heating rate of 5.5°C/min to obtain a carbonized sample. The sample was heat-treated using microwave oven (ER-SS17A, TOSHIBA) (denoted as MWtre). The sample was pulverized into carbon powder, mixed with 1,10-phenanthroline monohydrate, zinc acetate dihydrate, iron(II) acetate, and Milli-Q water, and heated and stirred for 30 min. Subsequently, the catalyst precursor slurry was obtained by heating using a microwave oven (RE-S5C-W, SHARP) (denoted as MWref). The obtained catalyst precursor slurry was dried using a microwave oven (ER-SS17A, TOSHIBA) to obtain the catalyst precursor (denoted as MWdry). The heat treatment was carried out in two stages. In the first stage, the catalyst precursor was placed in a SUS316 sealed container, replaced with Ar, heated to 800°C at 14°C/min, and then quenched to room temperature to prepare an intermediate material. In the second stage, the intermediate material was placed on a quartz boat and heat-treated at 1050°C for 20 min under Ar flow to obtain the catalyst.The oxygen reduction activity of the prepared catalyst was evaluated using the rotating ring-disk electrode (RRDE) method. A 2.00 mg/mL catalyst-2-propanol suspension, prepared by sonication and shaking, was cast on the GC electrode of a Pt ring-glassy carbon (GC) disk electrode (φ 6 mm), air-dried, and then 0.1 wt% Nafion® was cast and air-dried to prepare a catalyst-modified electrode. The evaluation of ORR activity was performed in 0.1 M sulfuric acid using the modified electrode as the working electrode, a GC electrode as the counter electrode, and RHE as the reference electrode. Results and discussion Fig. 1 shows the polarization curve and the efficiency of four-electron reduction (%H2O) obtained by the RRDE method. For comparison, the results for the catalyst prepared using the conventional method (refluxing for 24 hours followed by drying using a rotary evaporator) are also shown in Fig. 1 (quoted as EVAdry). The onset potential (@0.1 mA mg−1) derived from the oxygen reduction reaction was improved by 0.012 V compared to the conventional method. The efficiency of 4-electron reduction (@0.6 V vs. RHE) was improved by 8.9 – 21.1% compared to the conventional method. References (1) M. Kyotani, K. Hiratani, T. Okada, S. Matsushita, and K. Akagi, Global Challenges, 1, 1700061 (2017). Figure 1

Formation of Crystalline Si Film Using Liquid Zn Electrode in Molten KF–KCl–K2SiF6

Introduction Recently, crystalline Si solar cells have been the mainstream in the solar cell market, and the demand for crystalline Si solar cells is expected to increase in the future. However, it is difficult to further improve productivity with the current manufacturing method. It is a multi-step process and includes processes with high energy consumption due to the inclusion of the Siemens method and a process with low yield due to kerf losses. As a new production method for crystalline Si solar cells, our research group has proposed direct electrodeposition of Si films in molten KF–KCl using SiCl4 as a Si source [1]. We have already reported electrodeposition of Si film with a dense and smooth surface in molten KF–KCl–K2SiF6, which is the same bath state as after SiCl4 introduction [2]. Although this method produced dense and smooth crystalline Si films, the grain size of electrodeposited Si was as small as 20 µm even at 1073 K. To fabricate Si solar cells with high efficiency, it is necessary to reduce the number of grain boundaries where electrons and holes generated by light recombine, which requires increasing the crystal size.Referring to a previous report of Si deposition using a liquid Ga electrode at 373 K [3], we focused on using a liquid metal electrode in high-temperature molten salt to increase the grain size. We have already reported the electrodeposition of Si using a liquid Zn electrode held in a BN crucible in molten KF–KCl–K2SiF6 at 923 K [4]. The maximum grain size of electrodeposited Si was approximately 2 mm. However, the obtained Si was not in film form.To obtain crystalline Si film with large grain size, we propose, in the present study, a direct film formation method using thin liquid Zn. Fig. 1 shows a schematic diagram of the proposed mechanism. In the initial stages, Si(IV) ions are electrochemically reduced to form Si–Zn liquid alloy on the liquid Zn electrode held on the substrate. As the electrodeposition progresses, Si forms a film on the substrate and crystals grow. Finally, Zn is removed to obtain a crystalline Si film with a large grain size on the substrate. The goal for this crystalline Si film is a grain size of at least 1 mm and a thickness of 50–100 µm. Experimental All electrodepositions were performed under an Ar atmosphere in a glove box. The electrodeposition process was carried out in two steps as shown in Fig. 2. Electrodeposition to prepare thin liquid Zn was performed in molten NaCl–KCl–ZnCl2 at 723 K using a Si substrate. After electrodeposition of Si in molten KF–KCl–K2SiF6, the samples were washed with water for salt removal, treated with HCl for Zn removal, and analyzed by SEM/EDX. Result and discussion Fig. 3(a) shows an SEM image of the sample after Zn deposition in molten NaCl–KCl–ZnCl2 at a current density of 50 mA cm–2 and charge density of 21 C cm–2. EDX analysis showed that the gray areas were Zn and the black areas were Si substrate. Si deposition was then performed using the obtained Zn deposit as a working electrode in molten KF–KCl–K2SiF6 at 923 K at a current density of 20 mA cm–2 and charge density of 90 C cm–2. Fig. 3(b) shows an SEM image of the sample after removal of Zn. Crystalline Si was observed over the entire surface, but the distribution was uneven for Si with large grain sizes. This was thought to be caused by the fact that the Zn film was not uniform.These results suggest that the preparation of uniform thin Zn is necessary to realize the proposed mechanism. The uniform Zn film may be achieved by adding ZnCl2 to molten KF–KCl–K2SiF6 to co-deposit Si and Zn. Since Zn has a more positive deposition potential than Si, Zn is preferentially deposited in co-deposition. Fig. 4 shows an optical image of the sample prepared at 150 mA cm–2 for 90 C cm–2 in molten KF–KCl–K2SiF6–ZnCl2 at 923 K. A film-like deposit with metallic luster was obtained. R eferences [1] K. Maeda, K. Yasuda, T. Nohira, R. Hagiwara, and T. Homma, J. Electrochem. Soc., 162, D444 (2015).[2] K. Yasuda, K. Saeki, T. Kato, R. Hagiwara, T. Nohira, J. Electrochem. Soc., 165, D825 (2018).[3] J. Gu, E. Fahrenkrug, and S. Maldonado, J Am Chem Soc, 135, 1684 (2013).[4] W. Moteki, Y. Norikawa, and T. Nohira, J. Electrochem. Soc., 170, 062506 (2023). Figure 1

Fluoride Ion Conductivity and Crystal Structure Analysis of Ba4Bi3F17 with Fluorite-Type Units

All-solid-state fluoride ion batteries are attracting attention as an innovative next-generation battery that can replace lithium-ion batteries due to their high energy density. For fluoride ion conductor, three main types of crystal structures have been reported: fluorite-type, tysonite-type, and perovskite-type. Among these, fluoride ionic conductors with fluorite-type structure show the best conductivity. In fluorite-type BaF2, 4-coordinated fluoride ions are difficult to move within the crystal structure, and it has been reported that the addition of La3+ with different valence improves conductivity by inserting fluoride ions into interstitial sites within certain solid solution regions.[1] The addition of Bi3+ results in the formation of a cation-ordered structure Ba4Bi3F17 in certain solid solution regions, which has fluorite-type structural units derived from BaF2 in the structure. Reports on Ba4Bi3F17 are limited to its crystal structure[2] and there are no studies on it as an ionic conductor. In this study, the fluoride ion conductivity and fluoride ion conduction pathway of Ba4Bi3F17 was evaluated and compared with those of BaF2 with fluorite-type structure.To synthesise Ba4Bi3F17, BaF2 and BiF3 were weighed in an Ar atmosphere, mixed for 10 min. After pressing into a φ10 pellet, it was wrapped in a Ta container and sealed in a quartz tube, following by calcining at 773 K for 24 hours. Samples were identified by powder X-ray diffraction and AC impedance measurements were performed to assess their conductivity.Powder X-ray diffraction results showed that Ba4Bi3F17 was successfully synthesized and exhibited Fluoride ion conductor of 1.63 × 10−6 S cm−1 at 473 K. Further analysis of the fluoride ion conductor pathways showed that fluoride ions in Ba4Bi3F17 conduct in a four-coordinate to four-coordinate conduction pathway, which is different from the conventional four-coordinate to six-coordinate conduction pathway in BaF2 with fluorite-type structure. These results indicate that even the same structural unit can change fluoride ion conductor pathways depending on the surrounding environment.[1] Kazuhiro Mori et. al., ACS Appl. Energy Mater., 2020, 3, 2873-2880[2] E.N. Dommbrovski et. al., Solid State Chemistry, 2004, 177, 312-318