New Energy And Industrial Technology Development Organization Research Articles

Factors Affecting ORR Activity of Nb-Added TiOx Catalyst Using Carbon Support for PEFC

1. IntroductionCarbon-supported platinum catalysts used for the cathode of present polymer electrolyte fuel cells (PEFCs) have some problems such as a large amount of platinum use and low durability under operation condition. Therefore, we have attempted to develop substitute of platinum based on group 4 and 5 transition metal oxides. We found that stable oxygen vacancies on the surface and lattice distortion of these metal oxides could act as active sites of oxygen reduction reaction (ORR)1). On the other hand, cup-stacked carbon nanotubes (CSCNTs) coated with TiO2 have been investigated as durable supports for a platinum-based catalysts2). We already revealed that Nb-added titanium oxide with lattice distortion showed some ORR activity1). Then, we thought that CSCNTs coated with Nb-added titanium oxide might show definite ORR activity. In this study, we prepared CSCNTs coated with Nb-added TiOx and evaluated their behavior to investigate the factors which affect the ORR activity.2. ExperimentalThe CSCNTs (GSI Creos) without amorphous carbon on the surface was added to 2-propanol and dispersed ultrasonically, then a desired amount of Ti isopropoxide and Nb ethoxide were added with stirring. A sufficient amount of water mixed with 2-propanol were added to proceed hydrolysis and stirred overnight. Suction filtration was performed to obtain a precursor. In this experiment, Nb was added into TiO2 with an atomic% of 10 against Ti, and a loading of oxide was adjusted to 30 wt% of total catalyst. The precursor was heat-treated under an Ar gas containing 4% hydrogen at desired temperature and time to obtain Nb-added TiOx catalysts, designated as Nb-added TiOx/CSCNTs.The Nb-added TiOx/CSCNT was supported on a glassy carbon rod to make a working electrode. Electrochemical measurements were carried out using a three-electrode cell at 30 ± 1 °C in 0.1 M H2SO4. Cyclic voltammetry was performed with 5 mV sec-1 in the potential range from 0.2 to 1.2 V in an oxygen and nitrogen atmosphere to obtain oxygen reduction current. ORR current based on oxides was obtained by subtracting the reduction current of carbon from the reduction current of the entire catalyst. The oxygen reduction current density, iORR, was normalized by the mass of the oxides.3. Results and discussionFigure 1 shows the dependence of iORR at 0.6 V of Nb-added TiOX/CSCNTs on heat treatment temperature. The results of Nb-added TiOx powders prepared without carbon were also plotted. Because the electro-conductivities of the Nb-added TiOx powders were very low, Ketjenblack was mixed as an electro-conductive material to evaluate the ORR activity. The current value of Nb-added TiOx/CSCNT is significantly improved compared to oxide powder. This is because the electron supply increased due to the deposition of oxides on the CSCNT. The highest ORR current density was observed at 800 oC.Figure 2 shows the SEM images of Nb-added TiOX/CSCNTs. Amorphous TiO2 covers with the surface of CSCNTs in the unheated catalyst. At 700 ° C and 800 ° C, the oxide particles of around 10 nanometers were supported with high dispersion. However, at 900 ° C, the particles aggregated to become larger.Figure 3 shows the Ti 2p XPS spectra of Nb-added TiOx/CSCNTs heat-treated at 600-1000 °C. Ti2p peak shifted to the lower binding energy from 600 ° C to 800 ° C and to the higher energy from 800 ° C to 1000 ° C. The proportion of low-valence state Ti3+ increased as the temperature increased from 600 to 800 ° C. The reason why the shift to the higher binding energy occurred above 800 ° C was that the oxide surface prepared at higher heat-treatment temperature was oxidized by exposure of the air.Figure 4 shows the relationship between ratio of Ti3+ / (Ti3+ + Ti4+) and ORR current density at 0.6 V. The ratio of Ti3+ was calculated from the Ti 2p XPS spectra. The iORR at 0.6 V increases as ratio of Ti3+ increases. The ratio of Ti3+ indicates the presence of oxygen vacancies on the surface of the oxide. Therefore, it is considered that the increase of oxygen vacancies on the oxide surface strongly affected the ORR activity.AcknowledgementThe authors wish to thank the supply of the CSCNT from GSI Creos and the support of the New Energy and Industrial Technology Development Organization (NEDO), JSPS grants-in-aid for scientific research, Suzuki Foundation, and Tonen General Sekiyu Research / Development Encouragement & Scholarship FoundationReferences1) A. Ishihara, et. al., Electrochim. Acta, 283,1779 (2018).2) F. Ando, et. al., Electrochim. Acta, 404, 232 (2010) Figure 1

Research on creation and practical application of high-value-added recycling technology for waste plastic

Professor Shigeru Yao and Dr Patchiya Phanthong are conducting highly collaborative research that is focused on improving mechanical technology for recycling plastics, as well as extending the shelf life of plastics, thus reducing plastic waste. The researchers are based at the Yao Laboratory, in the Department of Chemical Engineering, Fukuoka University, Japan. Phanthong is a Project Research Assistant Professor from the Research Institute for the Creation of Functional and Structural Materials working under the supervision of Yao. In addition to heading up the lab, Yao is also the lead for the NEDO (New Energy and Industrial Technology Development Organization) Advanced Research Program for Energy and Environmental Technologies. In their work, the researchers are collaborating with both industry and academia which is essential to its progression.

Demonstration Experiment and Numerical Simulation Analysis of Full-Scale Barge-Type Floating Offshore Wind Turbine

The development of Floating Offshore Wind Turbines (FOWT) has been progressing steadily. To utilize the moderate water depth of 50–100 m ocean space around Japan, a barge-type FOWT was installed in Kitakyushu as part of a demonstration project conducted by the New Energy and Industrial Technology Development Organization (NEDO) of Japan. The FOWT mounts a 3 MW two-bladed wind turbine with blade diameter of 100 m and hub height of 72 m. The barge-type floating support structure is equipped with a moonpool in the center and a skirt at its bottom and is moored with 9 lines of catenary chains. To investigate the dynamic behavior of the barge-type FOWT in extreme condition and the validity of the numerical simulation in modeling the effect of the complex flow around the floating structure to the FOWT’s motion response, the FOWT’s motion data during typhoon Tapah on 23 September 2019 were measured and compared with the simulation results. As the results, the simulation results showed a good agreement in general to the measurement data. However, some shifts in the peak frequency of the simulation’s motion spectrum and a disagreement in waves with shorter wave periods were also observed. The possible causes of these differences are discussed thoroughly in this paper.

Transition Analysis of Budgetary Allocation for Projects on Hydrogen-Related Technologies in Japan

Hydrogen technologies are promising candidates of new energy technologies for electric power load smoothing. However, regardless of long-term public investment, hydrogen economy has not been realized. In Japan, the National Research and Development Institute of New Energy and Industrial Technology Development Organization (NEDO), a public research-funding agency, has invested more than 200 billion yen in the technical development of hydrogen-related technologies. However, hydrogen technologies such as fuel cell vehicles (FCVs) have not been disseminated yet. Continuous and strategic research and development (R&D) are needed, but there is a lack of expertise in this field. In this study, the transition of the budgetary allocations by NEDO were analyzed by classifying NEDO projects along the hydrogen supply chain and research stage. We found a different R&D focus in different periods. From 2004 to 2007, empirical research on fuel cells increased with the majority of research focusing on standardization. From 2008 to 2011, investment in basic research of fuel cells increased again, the research for verification of fuel cells continued, and no allocation for research on hydrogen production was confirmed. Thereafter, the investment trend did not change until around 2013, when practical application of household fuel cells (ENE-FARM) started selling in 2009, in terms of hydrogen supply chain. Hydrogen economy requires a different hydrogen supply infrastructure, that is, an existing infrastructure of city gas for ENE-FARM and a dedicated infrastructure for FCVs (e.g., hydrogen stations). We discussed the possibility that structural inertia could prevent the transition to investing more in hydrogen infrastructure from hydrogen utilization technology. This work has significant implications for designing national research projects to realize hydrogen economy.

Selective Permeation of Neodymium Through an Alloy Diaphragm in Molten Chloride Systems

The authors have been investigating a new RE (RE=Dy and Nd) recycling process from Nd-Fe-B permanent magnets, which is characterized by the use of RE-IG (IG=Fe, Ni, Co) alloy diaphragms for separation of REs in molten salts (Fig. 1) [1, 2]. In this process, the RE-IG alloy diaphragm performs as a bipolar electrode and RE ions permeate via three steps: (1) reduction of RE ions to form alloy on the anolyte side of the diaphragm, (2) diffusion of RE atoms in the diaphragm, and (3) oxidation of RE atoms to dissolve into the catholyte as RE ions on the other side of the diaphragm. Because the reaction and diffusion rates depend on the kinds of RE elements and the electrolytic conditions, selective permeation of Dy and/or Nd is possible under an appropriate condition. Using this selective permeation phenomenon through the alloy diaphragms, Dy and Nd can be separately recovered from Nd-Fe-B permanent magnets only by molten salt electrolysis, as shown in Fig. 1.Recently, the authors reported selective Dy permeation through a RE-Ni alloy diaphragm in molten LiCl-KCl eutectic melts containing NdCl3 and DyCl3 at 450 ℃ [3]. Whereas, in the present study, selective permeation of Nd was examined using a similar experimental setup at the different electrolytic conditions. The obtained molar ratio of permeated Nd/Dy was around 6. Interestingly, EDX analysis revealed that the molar ratio of Nd/Dy in the alloy diaphragm was less than 0.05, which was two orders of magnitude lower than that of the permeated amount. These results suggested that the diffusion rate of Nd atoms in the alloy diaphragm was extremely high compared to that of Dy.AcknowledgementThis work was partly supported by the New Energy and Industrial Technology Development Organization (NEDO) of Japan.Reference[1] T. Oishi, H. Konishi, T. Nohira, M. Tanaka and T Usui, Kagaku Kogaku Ronbunshu, 36, 299–303 (2010).[2] T. Oishi, Molten Salts (Yoyuen Oyobi Koon Kagaku), 63, 78–83 (2020).[3] T. Oishi, M. Yaguchi, Y. Katasho and T. Nohira, Rare metal technology 2020, 151–156 (2020). Figure 1

Effects of Solvent Composition on Viscosity and Dispersion Structure of PEFC Catalyst Ink

A polymer electrolyte fuel cell (PEFC) is an energy device that generate electricity from the electrochemical reaction that produces water from hydrogen and oxygen. It has been expected to be used as a power source for automobiles that does not emit carbon dioxide. The catalyst layer of PEFC is nano-porous layer composed of platinum-supported carbon and ionomer. The catalyst layer is fabricated by coating and drying a catalyst ink in which these materials are dispersed in a solvent made of water and ethanol. At that time, the dispersion structure in the catalyst ink, that is, the dispersion state of the platinum-supported carbon and the ionomer affects the catalyst layer structure and the electrochemical surface area. Though the viscosity and dispersion structure of the ink changes depending on the ink composition and the shear rate during the mixing and coating process, the correlation between the viscosity and the dispersion state of the catalyst ink is not fully understood, and optimal control of dispersion structure is not established.The purpose of this study is to clarify the effect of the solvent composition, which affects the catalyst layer structure and the power generation characteristics of PEFC a lot [1], on the viscosity and dispersion structure of the catalyst ink. To achieve the purpose, the solvent composition was changed as a parameter, and the viscosity characteristics measurement and the particle size distribution measurement of the catalyst inks were carried out.For the catalyst ink, TEC10V30E (Tanaka Kikinzoku) was used as the platinum-supported carbon and DE1021 (Sigma-Aldrich) was used as the Nafion solution, and the water/ethanol ratio was changed so that the ionomer/carbon ratio and the solid content was kept 0.75 and 10%, respectively. The viscosity characteristics were measured at each shear rate in the range of 0.01 to 1000 1/s by a rotary rheometer (Anton-Paar, MCR302). The particle size distributions were measured to understand the dispersion structure of the undiluted catalyst ink, and the laser diffraction type particle size distribution meter (HORIBA, LA-960V2) made it possible by using the sample holder which seals the catalyst ink as a liquid film (thickness: 10 mm) to enhance light transmission.The viscosity characteristics of the catalyst inks were shown in Figure 1 (a). Regardless of the solvent composition, the catalyst ink showed shear-thinning behavior (higher viscosity at lower shear rate), and it was more remarkable for the ink with high ethanol ratio. The particle size distribution of the catalyst ink was shown in Figure 1 (b). The ink with an ethanol ratio of 46% had a larger particle size than the catalyst ink with an ethanol ratio of 20%, and the particle size larger than 10 mm was observed for the catalyst ink with an ethanol ratio of 60%. From the results of the particle size measurement, it was suggested that the aggregate structure of platinum-supported carbon was formed as the ethanol ratio increased. As a mechanism for a dispersion to exhibit shear-thinning behavior, it has been proposed that the aggregation structure in the liquid breaks and the viscosity decreases with the application of shear [2]. Since the difference in the aggregate particle size was observed from the particle size distribution measurement, it was suggested that the viscosity of the catalyst ink with high ethanol ratio increased in low shear rate region due to the formation of the aggregate structure and decreased in high shear rate region due to the breaking-up of the aggregate structure. Since the ink without platinum did not show shear thinning behavior, it was considered that the ethanol oxide generated by the decomposition of ethanol on the platinum catalyst caused the aggregation of the catalyst ink, and further understanding about the impacts of ethanol oxide is required to control the dispersion structure. Acknowledgment:This study is based on the results obtained from a project commissionedby the New Energy and Industrial Technology Development Organization (NEDO).Reference[1] M. Kishi, S. Moriyama, T. Mori, J.Soc. Powder Technol. Japan, 55, 366–374 (2018).[2] H. Nakamura, The Micromeritics, 62, 30-38 (2019). Figure 1

Investigation on Operating Conditions Influencing the Aluminum Electrolysis Using Chloroaluminate Ionic Liquids

Our group has focused on the Al electrolysis using room-temperature ionic liquids (RTILs). Al can be deposited from the chloroaluminate ILs, but a practical technology for depositing Al from even the ILs has not been established. There are several problems such as the low limiting current density and the deposition in a dendritic form. In particular, the surface smoothness of electrolytic Al foil is required for practical application. Many articles on the Al electrodeposition using the ILs have ever been reported. However, few articles systematically investigate the correlation between the Al electrodeposits and the operating conditions (parameters). Ueda and co-workers reported that the surface smoothness was improved by adding 1,10-phenanthroline anhydrate (OP) to a Lewis acidic AlCl3-EMIC (1-ethyl-3-methylimidazolium chloride) melt [1]. In order to effectively scale up from the laboratory level to the practical level, it is desirable to make the above correlation clear sufficiently. In this study, we investigated on the parameters influencing to obtain a smooth electrolytic Al foil.The chloroaluminate ionic liquids consisting of anhydrous AlCl3 and 1-ethyl-3-methylimidazolium chloride (EMIC) for 2:1 molar ratio were prepared as an electrolyte in an Ar-filled glove box. 20 mmol dm−3 OP (1,10-phenanthroline anhydrate) was added to the electrolyte as an additive. Galvanostatic electrolysis method was carried out in a conventional three-electrode cell with stirring at room temperature (RT) and 50 ℃. A Ti plate was employed as a cathode. The electricity was controlled to 30 C cm−2. Surface morphology was observed using a field-emission scanning electron microscope (FE-SEM). Arithmetic mean roughness (Sa) was observed using an atomic force microscope (AFM).The current efficiency of the resulting Al foil at the operating temperature of RT and 50 oC was 99.6% in the latter as compared to 84.8% in the former at a current density of 52.6 mA cm−2. The current efficiencies at the operating temperature of 50 oC were higher than those of RT also at other current densities. The Al foil was obtained without the reductive decomposition of EMI+ cation (-2.2 V vs. Al / Al (Ⅲ)) even at the high current density (63.2 mA cm−2) by increasing the operating temperature to 50 oC. Regardless of the addition of OP, the current efficiencies were more than 90% even at the current density of 50 mA cm-2.Fig. 1 shows the FE-SEM images of the Al foil obtained at the various operating conditions. The crystal grain shape was the same, like a texture, regardless of the operating conditions. In contrast, the crystal grain size became larger with increasing the operating temperature. Moreover, the addition of OP to the AlCl3-EMIC melt at 50 oC also affected the crystal grain size to be small while the addition of OP did not affect the overpotential for the electrolysis. The AEM images showed that the Sa value became larger with increasing the operating temperature. By adding OP to the melt, the Sa value became extremely smaller, indicating that the addition of OP strongly suppresses the roughness.These results indicate that the smooth electrolytic Al foil would be obtained even with high operating temperature and high current density by adding OP to the AlCl3-EMIC melt. Acknowledgements This work is based on results obtained from a project commissioned by the New Energy and Industrial Technology Development Organization (NEDO).

Electrochemical Reduction Behavior of Boron in Molten LiCl–KCl–KBF4

1. Introduction The consumption and demand of Nd-Fe-B magnets, so-called neodymium magnets, is increasing year by year. Since the rare earth elements such as Nd can be obtained from sparse mineral resources, the technology for the recycling system of Ne-Fe-B magnets are highly required. The authors have been developing a technique to separately recover Nd and Dy from used Ne-Fe-B magnets using alloy diaphragm and molten salt [1].Although the electrochemical behavior of Nd and Dy was intensively investigated, the Ne-Fe-B magnet contains B as well as Fe, and the behavior of B in molten salt has not been clarified yet. Therefore, in this study, we investigated the behavior of B in LiCl–KCl eutectic melts at 723 K. The LiCl–KCl eutectic melt was chosen because a high separation ratio of Nd and Dy was obtained in our past experiments [2]. 2. Experimental The experiments were conducted in LiCl–KCl (44:56 wt%) eutectic melt in a dry Ar atmosphere at 723 K inside a glove box with an electronic furnace. 300 g of LiCl–KCl was vacuum dried at 473 K for more than 24 hours before elevating the temperature. As working electrodes, Ni, and Ag wire (φ1 mm) electrodes were used for cyclic voltammetry. Ni and Ag plate electrodes (5 mm×15 mm×0.1 mm(t)) were used for electrodeposition. A glassy carbon rod was used as a counter electrode. A reference electrode was an Ag+/Ag electrode, which was prepared by immersing an Ag wire in a LiCl−KCl melt containing 1 mol% of AgCl set in a Pyrex glass tube. The potential of the reference electrode was calibrated by the Li+/Li potential obtained by open circuit potential measurement on a Mo wire (φ1 mm) electrode just after electrodepositing Li metal. All the potential hereafter is described in reference to this Li+/Li potential.Cyclic voltammetry was conducted at KBF4 concentrations of 0, 0.5 and 2.0 mol%. Potentiostatic and galvanostatic electrolysis was conducted at KBF4 concentrations of 2.0 mol%. After the electrolysis, the plate electrodes were rinsed by distilled water, and then characterized by SEM and XRD. 3. Results and Discussion 3-1. Cyclic Voltammetr y Cyclic voltammograms (CV) obtained by Ni and Ag electrodes are shown in Fig.1(a) and (b), respectively. In the case of Ni electrode, cathodic current was observed at around 1.2 V shown “a” in the figure. The couple of peaks “b” and “c” at around 0.0 V correspond to Li metal deposition and dissolution, respectively. In addition to current peak “a”, a small current peak “e” appeared at 1.8 V, which seems to correspond to a formation of Ni-B compounds. Except for the peak “e”, essentially the same results were obtained in the case of Ag electrode. In both cases, the peak current at around 1.2 V increased with the concentration of KBF4 (shown as “a” in the figures). This peak can correspond to the reduction of B(III) to B(0), although further investigation is needed to confirm it. 3-2. Characterization of Products Prepared by Potentiostatic and Galvanostatic Electrolysis Fig. 2 shows a microscope image and a surface SEM image of the deposit on the Ni plate electrode obtained by potentiostatic electrolysis at 1.2 V, Q= −50 C. The granules with a diameter of c.a. 1-2 μm were observed. From XRD measurement, the diffraction peaks coincided to Ni, Ni2B, and NiCl2 was confirmed. Weak peaks that might correspond to B were partially observed.Next, the galvanostatic electrolysis was conducted at −9.8 mA cm−2, Q= −15 C for a Ni and an Ag plate electrode, respectively. In the case of Ni electrode, Ni, Ni2B, NiCl2 and KCl were detected by XRD analysis. This is almost the same result as the potentiostatic electrolysis at 1.2 V. Ag was selected as the substrate because no alloys of Ag and B exist in phase diagram. From the XRD results, only clear diffraction peaks coincided to Ag was confirmed. Other peaks were also detected, but they did not correspond to elemental B or other expected compounds. From the observation by sight, some deposits were actually formed. Therefore, the deposit can be amorphous B. In the future, further analysis and experiments are needed to clarify the behavior of B on Ag electrode. Acknowledgement This work was partly supported by the New Energy and Industrial Technology Development Organization (NEDO) of Japan.

Development of a Half-Size 3 T REBCO Superconducting Magnet for MRI

We have been developing a liquid-helium-free 3T magnet for MRI using high-temperature superconducting (HTS) wires in a HTS application project supported by the New Energy and Industrial Technology Development Organization (NEDO). A half-size 3T-MRI magnet, which has 220 coils each of order meter size, has been manufactured in order to demonstrate MR imaging. 269 REBCO single-pancake coils were manufactured. We investigated the yield rate of meter-class REBCO coils by experiment and the degraded state of coils by calculation. It was found that the yield rate was 82 % and the degraded length was order millimeter size in total length of coil, which was several hundred meters. We will consider the factors of coil degradation and how to increase the yield rate of a REBCO coil.

Study on Influence of O2 Concentration in Wafer Cleaning Ambient for Smoothness of Silicon (110) Surface Appearing at Sidewall of Three-Dimensional Transistors

The Si(110) surface appears at the sidewall of 3D transistors such as FinFET [1,2]. The surface micro-roughness of Si(110) strongly affects to the device characteristics because the Si(110) sidewall surface have a higher proportion of channel region width the miniaturization of width of fin structure [1,2]. In this work, we investigated the ambient in the wafer cleaning process to keep the smoothness of Si(110) surface.The wafers used in this study were Cz p-type Si(110) substrates having nearly 10 Ωcm. The wet oxidation of these substrates was performed at 1000 °C to form 300nm-thick silicon oxide films. Just after this oxide films were removed by HF solution, the average surface microroughness (Ra) of Si(110) measured by atomic force microscopy (AFM) was about 0.073 nm. We evaluated the influence of O2 concentration during the immersion in ultra pure water (UPW) by using N2 sealed glove box. The N2 sealed glove box can be controlled O2 concentration from 20% to 30 ppm. After the removing the chemical oxide with a diluted HF (0.5wt %) solution in this glove box with O2 concentration of 100 ppm, the wafers were immersed in UPW. We also evaluated for SOI wafer (20nm-thick Si(110) layer / 400nm-thick BOX layer / 725μm-thick Si(110) substrate) in a similar way.Figure 1 shows AFM images of Si(110) surface (a) before and after immersion in UPW for 24 hour in (b) 20% O2 (atmosphere) and (c) N2 ambient with O2 concertation less than 100ppm by using glove box. Ra drastically increase in the case of 20% O2 concentration. On the other hand, the increase of Ra is suppressed in N2 ambient with O2 concertation less than 100ppm. This indicates that the controlling of O2 concertation of ambient during the immersion in UPW is very effective to suppress the increase of Ra of Si(110) surface. It has been reported that the increase of Ra is caused by Si dissolving in UPW and Si dissolving in UPW is caused by the local oxidation just on Si surface [3,4].Figure 2 shows AFM images of Si(110) surface after immersion in UPW for 1, 3 and 24 hour in N2 ambient with O2 concertation of 100ppm. During the immersion in UPW, the O2 concentration was held 100 ppm. Figure 3 shows Ra as a function of immersion time for Si(110) surface in N2 ambient with O2 concertation of 100ppm. As increasing immersion time, the Ra is increasing. In addition, the line-formed roughness to <110> direction and the local bumps are appeared on the Si(110) surface. However, the Ra of immersion for 1 hour is not almost change from the initial Ra. Moreover, Si atoms eluted in UPW for 24 hours calculated from the decrease of SOI thickness was less than 4.0×1014/cm2 per 1hour. This means that the amount of elution of Si atoms in UPW within 1 hour is less than 1 atomic layer because the areal density of Si(110) orientation substrate is 9.6×1014/cm2 [5]. In the actual wafer cleaning process, the time of UPW attaching to wafer surface is far shorter than 1 hour. Therefore, when the O2 concentration is controlled less than 100ppm in the wafer cleaning process, it can be expected that Si(110) surface of sidewall of 3D transistor is not roughened and the shape of Si fin structure is kept. Furthermore, we evaluate the O2 concentration by using the prototype 200mm single wafer cleaning chamber. We demonstrated that the O2 concentration in this chamber can be decreased less than 100ppm within 1 minute by N2 purge of 200 L/min.AcknowledgementsThis work is based on results obtained from a project commissioned by the New Energy and Industrial Technology Development Organization (NEDO) and was carried out at the Fluctuation Free Facility (FFF) of New Industry Creation Hatchery Center, Tohoku University.Reference[1] D. James, 27th Annual SEMI Advanced Semiconductor Manufacturing Conference (ASMC), pp. 324-329, May 2016.[2] A. Teramoto et al., IEEE Trans. Electron Devices, vol 54, No 6, pp. 1438-1443, 2007.[3] H. Morinaga, et al., Solid State Phenomena, Vol.134, pp.45-48, 2007.[4] K. Nii, et al., 206th Meeting of The Electrochemical Society, 2004.[5] M. Higuchi, et al., Appl. Phys. Lett. 90 Number 12, pp. 123114-1-123114-3, 2007. Figure 1

Redox Behavior of a CuF2/Cu Electrode for an All-Solid-State Fluoride Shuttle Battery

Introduction The popularization of electrified vehicles connected to the smart grid community systems with stationary energy storage has attracted much attention as one of the solutions to global environmental problems. The critical technologies for such systems are rechargeable batteries with energy densities higher than that of conventional Li-ion batteries (LIBs). Among various candidates, all-solid-state fluoride-ion batteries (FIBs) operated by fluoride-ion transport [1] are promising owing to an ultra-high theoretical energy density over 5000 Wh/L [2].The FIBs currently we refer to as Fluoride Shuttle Batteries (FSBs) [3] were previously reported as a primary battery [4]. For the development of rechargeable FSBs, both electrolytes with high fluoride-ion conductivity and active materials that undergo reversible fluorination/de-fluorination reactions are crucial. Fluorite- and tysonite-type fluorides have been investigated as potential solid electrolytes since around the 1970s [ 5 , 6]. Recently, our group reported a series of PbxSn2-xF4 (x = 0.96~1.52) compounds [7] with a unique structure consisting of two alternating layers; a double Pb layer and a triple-layer, each flanked by a single Sn layer. The highest conductivity of 1.1 × 10-1 S/cm at 140 °C was achieved for fluorite-type Pb1.2Sn0.8F4 (x = 1.2). As for tysonite-type fluoride, Reddy et al. reported a possible rechargeable FIB using a La0.9Ba0.1F2.9 solid electrolyte [1] in combination with the various metal fluoride active materials such as CuF2, BiF3, and KBiF4. Among many metal fluorides, CuF2/Cu is a fascinating redox couple as the cathode active material owing to its large theoretical capacity (843 mAh/g) and high electro-motive-force (3.5 V vs. Li/Li+) [8]. However, full utilization of their theoretical capacity has not yet been demonstrated. In this study, we investigated the possible rate-determining steps in the CuF2/Cu cathode reaction using Pb1.2Sn0.8F4 (x = 1.2) with a high fluoride-ion conductivity. Experimental The Pb1.2Sn0.8F4 electrolyte was prepared by solid-state reaction using a mixture of PbF2 and SnF2 powders [7]. The fluoride-ion conductivity was measured by electrochemical impedance spectroscopy. The electrochemical cells were prepared by pressing into a 10 mm diameter pellet. Here, the cathode material was assembled using Cu, Pb1.2Sn0.8F4, and C in a 25:70:5 wt% ratio to facilitate both electronic and ionic conduction. Charge/discharge measurements were performed at 140 °C. Structural and electrochemical characterizations were conducted using TEM/SAED and operando XAFS. Results and Discussion The initial charge/discharge curves at 140 °C for the Cu cathode versus the PbF2 anode are shown in Fig. 1. The Cu cathode with Pb1.2Sn0.8F4 electrolyte exhibited a large charge (discharge) capacity of 522 (342) mAh/g. This capacity corresponds to 62 (41) % of the theoretical specific capacity even though the ionic conductivity of Pb1.2Sn0.8F4 was approximately 1000 times higher than that of La0.9Ba0.1F2.9 [1]. The Cu K-edge XAFS measurements during the charging process revealed the oxidation of Cu from Cu0 to Cu2+, and vice versa during the discharging process. The isosbestic points observed for all the spectra indicated that the conversion reaction involved the two phases, in agreement with the results of our DFT calculations [9]. In the TEM/SAED patterns of the cathode after charge, the distinct diffraction spots related to the CuF2 phase were observed on the surface of the metallic Cu particle. The fluoride-ion conductivity of CuF2 was 10-11 S/cm at 140 °C, which was very low compared to Pb1.2Sn0.8F4 and La0.9Ba0.1F2.9. These results suggest that the solid electrolyte may not be a dominant factor in the reaction on the cathode side, and alternatively smooth fluoride-ion diffusion inside the Cu active material plays a key role for redox behavior. As a next step, it may be effective to make the Cu active material a nano-composite with other fluorides, which is currently underway. Acknowledgments This work was supported by the New Energy and Industrial Technology Development Organization (NEDO) of Japan under the RISING and RISING2 projects.

First-Principles Study for Fluorination/Defluorination Reaction Mechanism in Fluoride-Shuttle Batteries

INTRODUCTIONRechargeable batteries with energy densities higher than those of the present Li-ion batteries (LIBs) are required for electric vehicles. We focus on fluoride-ion (F−) transfer batteries whose electrodes are composed of metal/metal fluoride (M|MF n ) combinations. Electrochemical charge-transfer reactions occur during the discharge/charge processes at the two electrodes. Defluorination of the metal fluoride MF n and fluorination of another metal M’ occurs at the positive and negative electrodes, respectively, during the discharging process asM1/n F + e− → M1/n + F− (1),M’1/m + F− → M’1/m F + e− (2).This type of battery is called a fluoride-shuttle battery (FSB), which is expected to produce high voltage and have large capacity.1 In 2017, Okazaki et al. fabricated a Bi|BiF3 electrode with a liquid electrolyte prepared by dissolving an organic fluoride in an ionic liquids (ILs) at room temperature. 2 In 2018, Davis et al. reported another type of liquid electrolyte composed of a simple organic solvents (OSs) with F−conductivity greater than 1 mS/cm.3 From the development of these liquid electrolytes, the F− conductivity has been dramatically increased in recent years. After improvement of the electrolyte conductivity, the fluorination and defluorination reactions at the electrodes are considered to be the rate-determining steps in FSBs. However, the mechanism of the fluorination and defluorination reactions in FSBs has not been clarified in contrast to the well-investigated Li-intercalation reaction in LIBs.METHODSIn this study, we classify the fluorination and defluorination reactions into two possible reaction pathways from a thermodynamic point of view: reaction through the solid-solution state and reaction through the two-phase state. It is possible to find which reaction pathway is realized from the free energy difference. Selection of these reaction pathways can be determined from the enthalpies of all of the intermediate states, since the entropy term in the free energy is fairly cancelled when we consider the difference of free energies. Selection rule for the fluorination and defluorination reactions in FSBs is schematically illustrated in Figure 1. The solid-solution states of M1/n F x for x ≈ 0 and for x ≈ 1 are assumed to be formed by introducing an interstitial and a vacancy defect, respectively. In this case, the free energy relation for the selection can be described as G ss(x) < G tp(x) → H I(M1/n ) < H(M1/n F) or H(M1/n F) < −H V(M1/n F) (3),where G ss(x), G tp(x), H (M1/n F), H I(M1/n F) , H V(M1/n F) are the free energy of the solid-solution state of M1/n F x , that of two-phase state, the formation enthalpy of M1/n F, that of interstitial defect in M1/n , and that of vacancy defect in M1/n F, respectively. We use the energies from first-principles calculations for the enthalpy differences, whose accuracy is validated by comparing them with experimentally obtained thermodynamic enthalpy data.4 The first-principles calculations were performed with the configurations of the bulk crystal systems using Quantum Espresso package.5 The crystal data were taken from the AtomWork database.6 RESULTSThe relative formation enthalpies of typical, transition, and relativistic metal fluorides are well reproduced by first-principles calculations within 0.1, 0.2, and 0.4 eV, respectively. By comparing the formation enthalpies of H, H V, and H I, the relation H I > H > −H V is always satisfied in all of the calculated metal and metal-fluoride combinations (M = Li, Mg, Ca, Al, Co, Ni, Cu, Pb, Bi). Thus, the selection rule of eq. (3) strongly suggests that fluorination and defluorination in FSB electrodes occur by two-phase reaction.7 This fluorination and defluorination mechanism will be useful to clarify the rate-determining step in FSBs.AcknowledgmentsThis work was supported by the Research and Development Initiative for Scientific Innovation of New Generation Batteries 2 Project (RISING2) administrated by the New Energy and Industrial Technology Development Organization (NEDO).REFERENCES1) F. Gschwind, G. Rodriguez-Garcia, D. Sandbeck, A. Gross, M. Weil, M. Fichtner, N. Hörmann, J. Fluorine Chem. 182, 76 (2016).2) K.-I. Okazaki, Y. Uchimoto, T. Abe, Z. Ogumi, ACS Energy Lett. 2, 1460 (2017).3) V. K. Davis et al., Science 362, 1144 (2018).4) Handbook of Chemistry: Pure Chemistry, 5th ed.5) P. Giannozzi et al., J. Phys.: Condens. Matter. 29, 465901 (2017).6) National Institute for Materials Science (NIMS) AtomWork <http://crystdb.nims.go.jp/>7) J. Haruyama, K.-I. Okazaki, Y. Morita, H. Nakamoto, E. Matsubara, T. Ikeshoji, M. Otani, “Two-Phase Reaction Mechanism for Fluorination and Defluorination in Fluoride-Shuttle Batteries: A First-Principles Study” in revision. Figure 1. Two reaction pathways considered in this study. In the fluorination and defluorination reactions, the solid-solution (M1/n F x , 0 < x< 1) and two-phase (M1/n and M1/n F) states are considered to be possible intermediate states. Figure 1

Characterization of Carbon Properties Influencing on Lib Performance at Low Temperature

Introduction : In order to promote development of electric vehicle, it is required to improve the capacity density of a battery, the battery performance at a low temperature, and the high rate property of a battery. Characterization of the size distribution and the average size of carbon in the negative electrode significantly influence on the battery performance. We have studied clarification of graphitic carbon’s properties influencing on performance of LIB especially at low temperature. Firstly, the X-ray diffraction profiles of several graphitic carbons were analyzed by the fundamental parameter (FP) method. Further, the structure changes of lithium-intercalated graphite during the charge and discharge processes were investigated by operando measurement using synchrotron radiation at BL28XU of SPring-8 in Japan. The time resolution of the apparatus is the order of milliseconds for analyzing one diffraction pattern. Experimental : Crystallite size and its distribution of several graphitic carbons were analyzed by the fundamental parameter (FP) method using X-ray diffraction profiles. X-ray wavelength of 0.154 nm was used to obtain X-ray diffraction profiles. In order to analyze crystallite size and its distribution, X-ray diffraction profiles were calculated by using software called PDXL2 (Rigaku Corporation).Coin cells composed of carbon and NMC electrodes were prepared and subjected to the evaluation of the battery performances from the low temperature to the room temperature. Coin cells conditioned by several cycles were evaluated.Further, crystal structures of lithium-intercalated graphite during charge and discharge processes were investigated by operando analysis using synchrotron radiation diffraction at BL28XU beam line of SPring-8. Al-laminated half-cells composed of graphitic carbon and Li electrodes were prepared and subjected to the evaluation of operando measurement. The graphitic carbons of different crystallite sizes and their distributions were analysed. Al-laminated half-cells conditioned by several cycles were used for the measurement. Operando measurements were carried out during charge and discharge processes. X-ray of 25keV (its wavelength of 0.0496 nm) with a beam size of 0.2 mm ×0.5 mm was used to obtain diffraction patterns. The exposure time was set from 0.5 s to 10 s. The diffraction patterns were obtained by two-dimensional detector (Rigaku Corporation). Results and Discussion : The experimental X-ray diffraction profile of graphitic carbon and that calculated profile by the fundamental parameter (FP) method were obtained. The calculated profile showed a good fit with the measured one. The each plane of graphitic carbon was analyzed properly.The analysis of FP method revealed that crystallite sizes and their distributions of graphitic carbons influences on LIB performance especially at low temperature. The results indicate that the low temperature characteristics improve as the crystallite size and distribution of the graphite (102) plane decreases. The same results were also obtained for the relationship between the crystallite size distribution of the graphite (102) plane and the high-rate discharge characteristics of LIB. The crystallite size distribution of the graphite (102) plane is thought to express the Li diffusivity.Figure shows the result of synchrotron radiation diffraction pattern of lithium-intercalated graphite at the discharge process with current density of 0.2C. The stage change was analysed clearly as shown in Figure.The difference of stage change of each carbon was revealed in considerable detail by Operando measurement.The crystallite size and its distribution influencing on the battery performance at low temperature was examined in detail. The result showed that crystallite sizes and their distributions influence on the phase structure changes and give major effect on charge and discharge performances of graphite negative electrode at low temperature. Their battery reaction mechanism influenced by crystallite size distribution was elucidated by the Operando measurement. The detail results will be shown in the conference. Acknowledgment: This work was supported by the Research and Development Innovative for Scientific Innovation of New Generation Battery 2 (RISING2) project of the New Energy and Industrial Technology Development Organization (NEDO). Figure 1

Defluorination/Fluorination Reaction of BiF3 Nanoparticles Prepared Via Sol–Gel Method for Fluoride Shuttle Battery

Introduction Rechargeable batteries with high energy density have been required for recent applications such as hybrid electric vehicles and large-scale energy storage. Rechargeable batteries based on fluoride shuttle (FSBs) have attracted much attention as a candidate above, owing to their high theoretical energy density by selecting appropriate metal/metal fluoride couples as active materials of negative- and positive-electrode[1-3]. One of the important things of the battery is adoption of the good conductive media for fluoride species, that is, an electrolyte[4]. Another is reversible fluorination/defluorination of active materials at the interface with electrolyte. Previously, we have demonstrated archetypal reversible FSB using a liquid electrolyte containing organic fluoride at room temperature[3]. However, this battery needed to improve the utilization and cyclability of its active material. Since the common metal fluoride shows low electronic- and ionic-conductivity, the active materials should be minified for FSBs. In this study, metal fluoride nanoparticle, e.g. BiF3, was prepared via sol–gel method using a trifluoroacetate precursor for improvement of the charge/discharge reactions in FSB. Bismuth trifluoride having 302 mAh/g in theoretical capacity is considered as a candidate for positive active material[1-6]. Then, we studied reversible defluorination/fluorination reaction of thus prepared BiF3 nanoparticles in a liquid electrolyte of FSB at room temperature, and valence change of bismuth species in the consequent electrode was evaluated using synchrotron ex-situ XANES measurement.Experimental Bismuth trifluoride nanoparticle was prepared from bismuth trifluoroacetate precursor via decarboxylation at 453 K in an oleylamine solution under argon atmosphere. At that time, specific amount of trifluoroacetic acid and/or trifluoroacetic anhydride were added as a supplementary fluorine source. After the nanoparticles were precipitated via addition of toluene and ethanol sequentially, the resulting precipitation was centrifuged and then re-dispersed in toluene containing oleic acid as a dispersant. Finally, nanoparticles were obtained after stripping of ligand using a trimethyloxonium tetrafluoroborate. Size of the resulting nanoparticles can be controlled by precursor concentration, decarboxylation reaction time and its temperature. Electrochemical measurement was carried out using a three-electrode cell with a VSP-300 BioLogic potentiostat/galvanostat in an argon-filled glove box at room temperature. The cell was composed of a carbon cloth as a counter electrode, a silver wire as a quasi-reference electrode, and an ionic liquid containing an organic fluoride as a liquid electrolyte. The liquid electrolyte was prepared by dissolving N-methyl-N-propylpiperidinium fluoride (MPPF) or N,N,N-trimethyl-N-neopentylammonium fluoride (NpF) in N,N,N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)amide (TMPA-TFSA) with molar ratio of 1:10. Nanoparticles-supported carbon cloth electrode as a working electrode was prepared by soaking the cloth in BiF3-nanoparticles/acetonitrile dispersion. The prepared nanoparticles via the sol–gel method and the defluorination/fluorination products in electrochemical measurements were evaluated using XRD, XPS, SEM-EDS, and so on in our laboratory. Furthermore, valence change of bismuth species was evaluated using synchrotron ex-situ XANES measurement at SPring-8, Japan.Results and Discussion Thus obtained nanoparticles via above-mentioned procedure had a few tens of nanometers in diameter and showed low crystallinity. Moreover, it was suggested that small amount of oxygen would be doped into the nanoparticles according to elemental analyses. Then, non-doped BiF3 nanoparticles having hexagonal crystalline structure had been acquired after further fluorination-treatment. Consequent BiF3 nanoparticles-supported carbon cloth showed ca. 240 mAh/g (80%) as an initial discharge capacity, and retained ca. 100 mAh/g for more than five cycles at room temperature. Furthermore, in ex-situ bismuth L3-edge XANES spectra, valence of bismuth species changed from trivalent to zero (metal) during the defluorination reaction and similar reverse change was elucidated in fluorination reaction. In this way, the size of the active material was minified by the preparation method, thereby improving the utilization and cyclability in FSB. This method will be also applied for other positive- and negative-active material having high gravitational theoretical capacity.Acknowledgements This work was supported by the “Research and Development Initiative for Scientific Innovation of New Generation Batteries 2 (RISING2)” of the New Energy and Industrial Technology Development Organization (NEDO), Japan.

Reactivity and Mechanisms in Fluoride Shuttle Battery Reactions: Orthorhombic Vs Cubic BiF3 Single Microparticles

IntroductionFluoride shuttle batteries (FSBs) are attracting interest as candidates for a next generation battery with high energy density.[1-3]FSBs utilize the following redox reactions.MF x + xe- → M + xF- (at the positive electrode, M being metal) (1)M’ + yF- → M’Fy + ye- (at the negative electrode, M’ being metal) (2)To realize high battery performance, it is necessary to elucidate and control reactivity and mechanisms in FSB reactions.BiF3 is a strong candidate for a cathode material in FSBs. In the present work, structural transformation, reactivities and mechanisms in FSB reactions of BiF3 single microparticles were studied by insitu Raman microscopy. BiF3 microparticles were partly embedded in a gold plating film (BiF3/gold, orthorhombic BiF3 (o-BiF3) and cubic BiF3 (c-BiF3)). By using a Raman cell consisting a BiF3/gold cathode, a Pb wire anode and an ionic liquid-based electrolyte,[2] reactivities and mechanisms in defluorination were found to be different for o-BiF3 and c-BiF3.ExperimentalBiF3/gold was prepared by embedding o-BiF3 microparticles (Fluorochem Ltd.) in a gold plating film on a gold foil. [4,5] Briefly, a gold foil and gold plating solution for deposition of 24 K gold were put into a small vessel, and then a small amount of o-BiF3 powder was put in the solution. Then a platinum wire was placed in the solution and a current was applied between the wire and the gold foil. The amount of deposited gold corresponded to that of the gold plating film with a thickness of 1 μm without BiF3.An organic fluoride (1-methyl-1-propylpiperidinium fluoride: MPPF) was dissolved in an ionic liquid (N,N,N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)amide: TMPATFSA) at a molar ratio of 1:10 and the resultant solution was used as an electrolyte.[2]The electrochemical cell had a quartz window and a Pb wire as a counter electrode. The distance between BiF3/gold and the window was 30 μm to 4 μm, and the space between them was filled with the electrolyte. The cell was sealed with Kalrez and placed in flowing Ar during Raman microscopy measurements.Raman microscopy was conducted with an NRS-4500 Raman spectrometer (JASCO Corporation) and 532 nm laser light.ResultsAt OCV (0.7 V), o-BiF3 gradually transformed into cubic c-BiF3. When the voltage of the BiF3/gold cathode vs the Pb anode was decreased from OCV to 0.05 V step by step, direct defluorination (eq. (1)) of the surfaces of only o-BiF3 started from their contours at 0.45 V (Figs. 1a and 1b) and then extended to their center parts and was mostly completed at 0.2 V. The results suggest that the rate-limiting process of direct defluorination of o-BiF3 is electronic conduction at the surface of o-BiF3. Then defluorination of c-BiF3 started at a voltage below 0.2 V by both direct defluorination (eq. (1)) and dissolution-deposition mechanisms (BiF3 → Bi3 + + 3F− , Bi3 + + 3e− → Bi). In the direct mechanism, the nucleus of Bi first appeared near the edge of c-BiF3 microparticles, and the nucleus grew for defluorination to proceed over the whole surface, suggesting that the rate limiting process is formation of the nucleus of Bi. The direct defluorination of c-BiF3 was much slower than that of o-BiF3. Defluorination of c-BiF3 by the dissolution-deposition mechanism was fast and dominant at a high power of the excitation beam, probably due to a thermal effect.The results of the present work provide important implication for the development of electrodes and electrolytes with proper solubility of BiF3 and for better utilization of reactions by the two mechanisms in order to realize FSBs with high performance.ACKNOWLEDGMENTThis work was supported by the New Energy and Industrial Technology Development Organization (NEDO) under contract from the Research & Development Initiative for Scientific Innovation of New Generation Batteries 2 (RISING2).REFERENCES[1] F. Gschwind, G. Rodriguez-Garcia, D. Sandbeck, A. Gross, M. Weil, M. Fichtner, N. Hörmann, J. Fluorine Chem. 182, 76 (2016).[2] K.-I. Okazaki, Y. Uchimoto, T. Abe, Z. Ogumi, ACS Energy Lett. 2, 1460 (2017).[3] V. K. Davis et al., Science 362, 1144 (2018).[4] T. Yamanaka, K. Okazaki, T. Abe, K. Nishio, Z. Ogumi, ChemSusChem, 12, 527 – 534 (2019).[5] T. Yamanaka, T. Abe, K. Nishio, Z. Ogumi, J. Electrochem. Soc., 166, A635-A640 (2019). Figure 1. Results of Raman mapping of an area on a BiF3/gold sample in which both o-BiF3 and c-BiF3 particles were distributed. Only defluorination of o-BiF3 occurred at 0.45 V. The arrows in (b) indicate that defluorination started at the contours of o-BiF3 particles. Figure 1

Development of Cu-Based Positive Electrode for an All-Solid-State Fluoride Shuttle Battery

For the development of batteries with higher energy density, we have been developing all-solid-state fluoride shuttle batteries (FSBs) in RISING2 project of NEDO, Japan. Here we report the reversible electrochemical fluorination/de-fluorination of copper-based positive electrode using operando XAFS (X-ray absorption fine structure) measurement during charge/discharge processes. The Operando XAFS measurements were performed at the BL28XU of SPring-8, Japan. Based on the XAFS results, we have tried to improve the utilization of the active material by devising the electrode manufacturing method.The CeF3/Ce0.95Ba0.05F2.95/Cu cell showed 680 mAh/g(Cu) charge capacity and 593 mAh/g(Cu) discharge capacity, which was higher capacity than that of the previous works [1,2]. During the charge process, the operando XAFS spectra showed that pre-edge and white line peak intensity decreased and increased in proportion to the charge capacity, respectively, indicating that Cu converts to CuF2. On the other hand, the changes of XAFS spectra were opposite during the discharge process. These results indicate that this positive electrode is highly reversible for fluorination/de-fluorination reaction of Cu. However, some Cu metal remained at the full charge state because the charge capacity didn’t reach to the theoretical specific capacity (843 mAh/g), which was also confirmed from the XAFS spectrum.Other details will be shown in the conference. Acknowledgments This work was supported by the New Energy and Industrial Technology Development Organization (NEDO) of Japan under the Research and Development Initiative for Scientific Innovation of New Generation Battery (RISING2) project.

(Invited) Reverse Current Behavior and ADT Protocol for Start & Stop Operation of Bipolar Alkaline Water Electrolyzer

Introduction Water electrolysis is expected a key energy conversion system to introduce large-scale renewable electricity under power grid management. Here, less expensive large system is needed. Alkaline water electrolysis (AWE) systems are well-developed large system to combine hydropower generation, but fluctuated operation with start and stop operation is not considered for conventional systems. Therefore, improvement of durability to combine photovoltaic and/or wind turbine generation is significant issue. In this study, we have been investigated reverse current behavior of bipolar alkaline water electrolyzers and proposes accelerated durability test (ADT) protocol. Theoretical and Experimental Figure 1 shows configuration of bipolar alkaline water electrolyzer, principle of reverse current. An equivalent circuit to analyze reverse current is also shown in the figure. During electrolysis, surface Ni of anode oxidizes to Ni(III) and that of cathode reduces to Ni(0). They electronically connect on a bipolar plate and ionically connect through manifold to distribute electrolyte. In the equivalent circuit, electrochemical potential difference between anode and cathode on a bipolar plate correspond to electromotive force of Uk(t). The R 1 and R 2 correspond ionic resistances of branch and communicating tubes, respectively. Relationship among these parameters can describe as eq. 1 in Fig. 1 based on the Kirchhoff's laws, so reverse current would be estimated. In this study, we measured electrode potential and reverse current after 1 h water electrolysis at 0.6 Acm-2 for 2 to 4 cells stack bipolar electrolyzer using commercially available industrial anode and cathode (De Nora Permelec Ltd). The reverse current was measured ionic current through communicating tube with D. C. clamp meter.As bipolar electrolyzer evaluation, we measured electrode potential and reverse current after 1 h water electrolysis at 0.6 Acm-2 for 2 to 4 cells stack bipolar electrolyzer using the commercially available anode and cathode. Effective electrode size was 27 cm2. The reverse current was measured ionic current through communicating tube with D. C. clamp meter (KEW2510, Kyoritsu).As start & stop operation simulated ADT protocol, we propose the combination of constant current electrolysis, potential sweep, and chronoamperometry as the inset of illustration in Fig. 4, because constant current measurement is easier to get reproductivity in high current that need accurate iR correction for constant potential measurement and current control measurement never simulate stop operation. Results and discussion Figure 2 shows the setup of lab-scale electrolyzer and cell performances in the stacks. All cells showed almost the same performance. Figure 3 shows reverse currents and electrode potentials as a function of time for 2 to 4 cells stack electrolyzer. The longer cell stack had lager reverse current at initial period of stop operation. As the potential difference between anode and cathode decreased, the reverse current decreased. The anode potential significantly decreased certain time, and that for longer cell stack was shorter. For the 4 cells stack, the time for the BP2 was shorter than that for the BP1 and BP3. Simultaneously, the I 2 was larger than the I 1 and I 3. These behaviors could be explained with eq. 1 in the Fig. 1 with the same electromotive force of the U(t=0)s for initial period and time function of U(t)s with same surface condition for all cells at the end of electrolysis. Remarkable point is that the cathode potential of BP2 was higher than the anode, which is impossible with discharge of BP2 itself. This opposite potential of the BP2 would be forced by electromotive force of the BP1 and BP3.Figure 4 shows the anode potential at 10 mAcm-2 (E @10mAcm-2) of oxygen evolution reaction (OER) current during the ADT protocol with various minimum potential: E min. The all anodes significantly degraded for around 3-days test protocol, although DN851 was developed as an active and durable anode for conventional OER electrode. The degradation increased with decreases of the E min. Above 0 V vs. RHE of the E min, The E @10mAcm-2 increased after ca. 800 cycles of introduction period and reached around 1.69 V vs. RHE after 1900 cycles, although it increased from initial period and the increase continued around 2000 cycles for -0.3 V vs. RHE of the E min. From these experimental results, the E min of between 0 to 0.3 V vs. RHE might be suitable for the ADT protocol because of rapid degradation with robustness to the E min. Acknowledgements This study was based on results obtained from the Development of Fundamental Technology for Advancement of Water Electrolysis Hydrogen Production in Advancement of Hydrogen Technologies and Utilization Project commissioned by the New Energy and Industrial Technology Development Organization (NEDO). Figure 1

Corrosion Behavior of SUS304L Steel in High pH NaOH Solution

IntroductionRecently, interest in hydrogen energy has been increasing as it is an environmentally friendly energy source. Water electrolysis is one method to produce hydrogen and oxygen, and electrolysis of water can be achieved with little energy using renewable energy from sources such as wind and solar power.[1, 2] The AEM type water electrolysis using alkaline polymer electrolyte membranes (AEM) can be used with inexpensive metal oxides and catalysts such as metal and nitrogen-doped carbon and may be expected to be able to produce hydrogen at low cost. The electrolyte used in AEM type electrolysis is an alkaline solution with a high pH of 12 or 13. Titanium is currently used for electrolysis cells. However, because titanium is expensive, it is hoped that steel based materials could be used. In this study, SUS304L steel was used as a highly versatile commercially available steel, and electrochemical measurements were carried out in a NaOH solution with a pH of 12 or 13. After the electrochemical measurements, the steel electrode surface was analyzed.ExperimentalThe SUS304L (18%Cr-10%Ni-Fe alloy) was used as a sample for electrochemical measurements, polished with water-resistant polishing paper (# 400 to 2400) and further polished to a mirror surface using alumina powder. After the polishing, ultrasonic cleaning was performed in distilled water and acetone. As the electrolytic solution, an aqueous sodium hydroxide solution adjusted to pH = 12 and 13 were used. A potentiostat (Hokuto Denko Co, HZ-7000) was used for the electrochemical measurements. The experimental cell was a cylindrical PTFE cell with a working electrode, counter electrode, and reference electrode attached to the lid. The SUS304L was used for the working electrode, a platinum plate was used for the counter electrode, and Hg / HgO was used as the reference electrode. The temperature of the electrolytic solution was 25 and 60 ° C. Linear Sweep Voltammogram (LSV) measurements were performed from the open circuit potential to 1.2 V with a sweep rate of 5 mVs-1. Constant potential electrolysis was carried out at a potential of 1.0 V in the electrolytic solution at 60 ° C and with pH = 13 for 5, 10, or 20 hours. The surface roughness of the stainless steel before and after the controlled potential electrolysis were measured by an atomic force microscope (AFM) (Shimadzu Co: SPM-9700HT). The chemical states of Fe, Cr, and Ni on the surface of the specimens before and after the constant potential electrolysis were determined by XPS (JEOL: JPS-9200) measurements.Results and DiscussionIn the LSV results, an increase of anodic current was observed from 0.79 V at a temperature of 25 oC with the pH of 12. At pH of 13, the increase was from 0.71 V. At 60 oC, a current increase was observed from 0.75 V and 0.65 V at pH 12 and 13, respectively. From these results, the constant potential electrolysis was carried out at 1.0V, 60 oC, and in a pH 13 NaOH solution. Gas generation was confirmed on the surface of the SUS304L sample during the electrolysis, without any change in the observed color of the NaOH solution after the electrolysis.From the AFM measurements of the surface roughness before and after the constant potential electrolysis, the roughness was about 5 nm before the electrolysis, about 15 nm after electrolysis for 5 h and about 20 nm after 20 h of electrolysis. The XPS measurements of the sample surface detected Cr and Fe oxides before the electrolysis, and after electrolysis for 5 hours, the presence of CrOOH and FeOOH was confirmed, in addition to the oxides. These results suggest that the oxide film formed on the surface was dissolved by electrolysis, following this some Fe and Cr were also dissolved, and these formed the FeOOH and CrOOH via hydroxides on the surface.AcknowledgementPart of the experiments reported here are supported by the New Energy and Industrial Technology Development Organization(NEDO).[1]B. Pivovar, N. Rustagi, and S. Satyapal, Electrochem. Soc. Interface, vol. 27, 47–52, 2018.[2]P. Lettenmeier, R. Wang, R. Abouatallah, F. Burggraf, A. S. Gago, and K. A. Friedrich, J. Electrochem. Soc., vol. 163, No. 11, F3119–F3124, 2016.

(Invited) Highly Durable Platelet-Type Carbon Nanofibers for Oer in Alkaline Electrolyte

Porous anodic alumina films formed by anodizing of aluminum in acid electrolytes have a highly ordered, nanopore channels, which have attracted increased attention as template for various nanomaterials. Utilizing this template, platelet-type carbon nanofibers (pCNFs) have been successfully prepared by simply heating a mixture of the template and polymer powders, such as polyvinyl chloride and polyvinyl alcohol, in argon atmosphere via liquefied intermediate of the polymers (1, 2). The graphitization degree of pCNFs increases with annealing temperature, and interestingly, the neighboring reactive carbon edge sites at the sidewall of pCNFs form loops of several carbon layers at above 2000ºC. Here, we demonstrate that such pCNFs with high graphitization degree and loop structure exhibit extremely high oxidation resistance under oxygen evolution reaction (OER) conditions in highly alkaline electrolyte for a zinc-air secondary battery application.During galvanostatic OER on the state-of-the-art highly active Ca2FeCoO5 electrode with a conventional carbon black conductive agent in 4 mol dm-3 KOH electrolyte consumed the carbon black almost completely within a few days, whereas that with pCNFs annealed at 2400ºC exhibited almost no consumption of the pCNFs even after one month. The carbon nanofibers with platelet structure and high graphitization degree are promising for the air electrode materials in a zinc-air battery. Acknowledgment This work was supported in part by the RISING2 (Research and Development Initiative for Science Innovation of New Generation Batteries 2) of the New Energy and Industrial Technology Development Organization (NEDO), Japan. 1. H. Konno, S. Sato, H. Habazaki and M. Inagaki, Carbon, 42, 2756 (2004).2. H. Habazaki, M. Kiriu, M. Hayashi and H. Konno, Mater. Chem. Phys., 105, 367 (2007).

Visualization of Internal Potential Distribution in an All-Solid-State Fluoride Shuttle Battery Using Operando Hard X-Ray Photoelectron Spectroscopy

Introduction Fluoride shuttle battery (FSB), which uses fluoride ions as carrier ions, has attracted much attention as one of the innovative batteries that can theoretically exceed the energy density of conventional lithium-ion batteries. However, there are still few reports on charge/discharge reactions using fluoride ions as carriers[1, 2], and most of the electrode reactions are still unclear. Here we have applied the newly developed operando hard X-ray photoelectron spectroscopy (HAXPES) to a thin film Cu-based all-solid-state FSB, which allows us to observe the bulk-sensitive electronic structure changes in all the components (positive and negative active materials, a solid electrolyte and a current collector) during charge and discharge processes. Experimental A Cu positive electrode was deposited on a LaF3 substrate by a DC magnetron sputtering method, and an Au current collector was deposited thereon by the same method. A W current collector for the anode side was deposited on the back side of the LaF3 substrate by the same method. Electrochemical tests were performed with a constant current mode under potential rages from 3.6 V to 2.0 V at 140⁰C. The Au 4f, F 1s, La 3d, Cu 2p operando HAXPES measurements was performed at BL28XU in SPring-8 during the charge process. Results and Discussion Fig. 1 shows the Cu 2p 3/2, F 1s and La 3d 5/2 operando HAXPES spectra at each charge capacity. The Cu 2p 3/2 HAXPES spectra were normalized with a peak intensity of 932.5 eV derived from Cu metal. As charging progressed, new peaks derived from CuF2 appeared at 936.8 eV and 943.0 eV, indicating that Cu converts to CuF2. In the F 1s and La 3d 5/2 HAXPES spectra, a peak shift of approximately 1.4 eV toward the lower binding energy was observed at the beginning of charging. These peak shifts correspond to the sudden increase in the cell voltages at the beginning of charging, indicating that a potential difference is generated between the LaF3 solid electrolyte and Cu positive electrode. As the charging reaction further proceeds, the peak shifts to the lower binding energy as the cell voltage increases in the La 3d 5/2 region, however, a new peak appeared at 684.7 eV to the higher binding energy in the F 1s region, suggesting that F species of CuF2 have been detected. Therefore, we succeeded in capturing the fluorination process of Cu by both Cu 2p and F 1s HAXPES spectra changes and the potential distribution of the all-solid-state FSB using operando HAXPES. Acknowledgments This work was supported by the New Energy and Industrial Technology Development Organization (NEDO) under the “Research and Development Initiative for Scientific Innovation of New Generation Batteries 2 (RISING2)”.