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The mechanism of the electrochemical intercalation of LiNiO2 (LNO) electrodes in an aqueous LiNO3 electrolyte was investigated with special focus on the electrode/electrolyte interfacial reaction including the hydration state of Li+ ions. Electrochemical measurements, the Nernst equation, and in situ X-ray diffraction analysis revealed that lithium ion was main intercalation species, instead of proton, into LNO in aqueous electrolytes. In addition, calculation of the lattice parameters of LNO during charge/discharge processes indicated the co-intercalation of Li+ ions with H2O molecules, supported by the activation energy of Li+ ions estimated for the intercalation. Furthermore, in situ Raman spectra showed that partially hydrated Li+ ions were co-intercalated into LNO.

Invited for this month's cover are the groups of Shih-kang Lin at the National Cheng Kung University and Takeshi Abe at Kyoto University. The image shows how interfacial chemistry design can play a role in unlocking higher-energy-density and fast-charging Li4 Ti5 O12 -based lithium-ion batteries for electric vehicle applications. The Full Paper itself is available at 10.1002/cssc.202001086.

We investigated the influence of the surface orientation of La0.8Sr0.2CoO3 (LSCO) on the catalytic activities for oxygen evolution and reduction reactions in alkaline solutions when using single crystals of LSCO. When LSCO single-crystal rods are sliced along the (001), (110), and (111) planes of a high-temperature cubic structure, we obtain crystal electrodes that can be denoted (001)C, (110)C, and (111)C, respectively. The catalytic activities for oxygen evolution occur in the order (110)C> (001)C≈(111)C. Although the currents for oxygen reduction on LSCO single crystals are hardly observed, their activities are enhanced when carbon is placed on the crystal surfaces. These results clearly show that the oxygen evolution activities of LSCO electrodes are dependent on their crystal planes, whereas their oxygen reduction activities rely on the interplay between carbon and LSCO. These findings may contribute toward the development of an effective electrocatalyst for rechargeable air electrodes.

Cobalt-based layered perovskite oxychlorides Sr2CoO3Cl and Sr3Co2O5Cl2 exhibit high oxygen electrocatalytic activity compared to conventional lanthanum cobalt-based perovskite oxides. The enhanced oxygen electrocatalytic activity can be attributed to the upshifted O p-band center relative to the Fermi level caused by the incorporation of chloride anion into oxygen sites.

For the fast charge of lithium-ion batteries, internal resistances must be decreased. Among the internal resistances, charge (lithium-ion) transfer resistances and ion transport resistances inside the composite electrode are the major ones. Charge transfer resistance of R ct can be expressed by 1/R ct = A/T exp(-E a/RT). Here, A, T, E a, and R are pre-exponential factor, absolute temperature, activation energy, and gas constant, respectively. We have extensively studied the activation energies for the charge transfer reactions, and concluded that de-solvation process is responsible for the activation energies. Then, we have tried to understand the pre-exponential factor of A. This factor corresponds to the reaction sites of insertion active materials. Here we evaluated the reaction sites of high oriented pyrolytic graphite by several methods, and the charge transfer resistances of graphite electrode were correlated with the reaction sites.

The electrochemical stability of an electrolyte solution, its so-called "potential window", is simply determined by the oxidative potential and reductive potential of the solvent, if solutes dissolved in the electrolyte solution are electrochemically stable within the potential window of the solvent. Water is the most conventional solvent in the field of electrochemistry, and its potential window is as narrow as 1.23 V, thermodynamically. Practically, however, the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) need certain overpotentials, which extends the potential windows of aqueous solutions. Besides the catalytic activities of the electrode materials, the properties of aqueous solutions such as hydration structures and salt concentrations also affect the potential window.Recently, aqueous rechargeable lithium batteries (ARLBs) have attracted much attention due to their low cost and safety. However, the working voltage of ARLBs is limited to below 1.5 V due to the narrow potential window of water. Recently, a few papers have discussed the potential window of concentrated aqueous solutions with neutral pH. However, there are still fundamental unanswered questions regarding the pH-dependence of the potential window of water. In this study, the potential window of concentrated electrolyte solutions with neutral pH and the expansion of the potential window were investigated from the viewpoint of the local pH change and water concentration. Here, we shed light on the dependence of the potential window of water on local pH changes and water concentrations. Next, we focused on the water concentration, since the potential windows are determined by the water electrolysis reactions (OER and HER). The potential windows are shown in Fig. 1 as a function of the water concentrations. In this study, the onset potential of the OER/HER was defined when the current density was ± 0.1 mA cm-2 in CVs at 1 mV s-1. There are two clear tendencies in Fig. 1. First, the windows in neutral pH electrolyte solutions (closed symbols in Fig. 1) were obviously wider than those in acidic/alkaline electrolyte solutions (open symbols in Fig. 1), even at a dilute salt concentration (ca. 55 M water concentration). Second, the windows in neutral pH electrolyte solution (closed symbols in Fig. 1) were not affected by the kind of the electrolyte salt, but depended linearly on the water concentration. The windows were expanded when the water concentration decreased, i.e., the electrolyte salt concentrations increased. Potential windows of aqueous solutions were investigated systematically using various salts at different concentrations. Cyclic voltammetry measurements of Pt electrodes revealed two important points. First, the potential window in unbuffered neutral pH solution was broader than that in acidic/alkaline solutions. This expansion of potential windows can be explained by the shift in the reaction potential with local pH changes in the vicinity of the electrode. Second, the potential windows were not affected by electrolyte salts, but rather depended linearly on the water concentration. The difference for OER overpotentials was much larger than that for HER overpotentials. While HER overpotentials were derived from a local pH change, OER overpotentials were derived from both a reduced water concentration and local pH change. This study highlights the importance of these two main factors (water concentration and local pH change) in determining the potential windows of concentrated electrolyte solutions. Figure 1

Dynamics of deuterium recycling, including retention and sputtering behaviors was studied for C+ implanted tungsten. The amount of deuterium trapped by irradiation damages was clearly increased in the C+ implantation sample because the irradiation damages in the C+ implanted sample were formed more than those in the only D 2 + implanted one. In addition, the deuterium diffusion toward the bulk would be refrained by the formation of W–C mixed layer, which would work as the deuterium diffusion barrier. The in situ sputtered particle measurement system has been established and revealed that the formation of hydrocarbons such as CD4 was directly observed during D 2 + implantation into the C+ implanted tungsten. In the lower deuterium fluence, the CD4 sputtering rate was enhanced with increasing the deuterium fluence. It was considered that the sputtering rate of CD4 would be controlled by the concentration of deuterium on the top surface of the W–C mixed layer.

Tritium release kinetics for Li 2+ x TiO 3 , the lithium-enriched Li 2 TiO 3 , was investigated by isochronal and isothermal annealing experiments. Tritium release by isochronal annealing showed that the dominant release stage was found at around 600 K. An additional release stage at lower temperature side was appeared with increasing excess lithium, which was attributed to the release of tritium trapped in Li 4 TiO 4 structure. The dominant release stage was considered to a release of tritium trapped by irradiation defects. Isothermal annealing experiments indicated that tritium releases were controlled by diffusion process. The diffusion coefficient of Li 2.0 TiO 3 was one order of magnitude as large as those of Li 2.2 TiO 3 and Li 2.4 TiO 3 , although their activation energies were almost the same. These results showed that rate-determining step was the diffusion process of tritium in Li 2 TiO 3 structure for Li 2+ x TiO 3 and excess lithium would make diffusion coefficient smaller. Simulation of tritium-TDS spectra for Li 2.0 TiO 3 has clarified that the TDS spectrum forLi 2.0 TiO 3 can be demonstrated by using Arrhenius diffusion parameters obtained by isothermal annealing experiment in the present study.

Present LIBs for EV-use possess large power densities by the sacrifice of energy densities in order to shorten the charging time. In the practical LIBs for portable devices, dense and thick composite electrodes are used. In this case, the ion transport of electrolyte solution through the pores in the composite electrodes becomes a slow process. In order to enhance the energy densities with remaining high power densities, the ion transport rate should be increased for the dense and thick composite electrodes. Unfortunately, to develop dense and thick electrodes with high power densities, fundamental understanding of the ion transport in composite electrodes has not been clear. In this study, ion transportation behavior was investigated with ac impedance spectroscopy. To focus on the impedance of ion transportation of electrolyte through the pores in composite electrode, we prepared anodic aluminum membranes with homogeneous macro- and meso- pores. In addition, graphite composite electrodes were also used. As a result, we obtained semi-circles, and this semi-circle was assigned to the ion transport process through the graphite composite electrode. The detail analysis will be presented at the meeting.

Introduction There has been increasing attention to electrochemical energy conversion devices using oxygen electrodes in alkaline media such as fuel cells, metal−air rechargeable batteries, and water-splitting devices. Because of the sluggish kinetics of the oxygen electrode reactions, many researchers have been exploring cost-effective materials which can catalyze both/either oxygen reduction reaction (ORR) and/or oxygen evolution reaction (OER). Among various kinds of catalysts, a family of perovskite-type compounds have been extensively studied because of its structural and compositional flexibility. In order to enhance the catalytic activity of perovskites, researches based on the choice of cation elements and their compositions has been extensively conducted.1 On the other hand, those based on the choice of anion elements and their compositions has been rarely conducted. These days, some research groups report that mixed-anion catalysts exhibit ORR and/or OER activities,2,3 suggesting that “anion blending” can be a great tool for enhancing catalytic activity of perovskites. Therefore, the present work focuses on the measurement of ORR and OER activities for mixed-anion perovskites. Herein we used Sr2CoO3Cl and its related materials.4 Experimental Sr2CoO3Cl and Sr3Co2O5Cl2 were synthesized by a solid-state method. Sr2Co2O5 precursor was firstly prepared by heating a stoichiometric mixture of SrCO3 and Co3O4 at 1273 K in air followed by quenching in liquid N2. Next, stoichiometric amounts of Sr2Co2O5, SrCO3, and SrCl2·6H2O were mixed and heated at 1123 K in air. For benchmarking catalysts, LaSrCoO4, which has the same crystal structure and valence state of cobalt ion, LaCoO3, which is a well-known single-perovskite catalyst with the same valence state of cobalt ion, and Ba0.5Sr0.5Co0.8Fe0.2O3 -d (BSCF), which is known as a highly-active OER electrocatalyst, were used. ORR and OER activities of the samples were carried out by using three-electrode electrochemical cell with rotating disk electrode (RDE) setup. Composite electrodes consisting of perovskites, Vulcan XC-72 (Cabot), and AS-4 (Tokuyama) were formed on a glassy carbon RDE and were used as the working electrode. Pt wire, reversible hydrogen electrode (RHE), and 1.0 mol dm-3 KOH solution were used as the counter electrode, the reference electrode, and the electrolyte, respectively. Results and discussions From scanning electron microscope-energy dispersive X-ray spectroscopy, the oxychlorides had a particle size of 1-10 μm with almost ideal atomic concentrations. X-ray diffraction patterns of the oxychlorides were almost identical to those in ICSD database. While the ORR activity of LaSrCoO4 was negligible, that of the oxychlorides was as high as that of LaCoO3, indicating that the mixing of oxide and chloride ions was effective to add the ORR activity. Fig. 1 shows OER polarization curves of perovskite catalysts. Surprisingly, the OER activity of Sr2CoO3Cl was as high as that of BSCF, proving that “anion blending” is a powerful tool to enhance the OER activity. Roles of chloride ion in improving ORR and OER activities will be discussed in the conference. Fig. 1. OER polarization curves of (solid line) Sr2CoO3Cl, (dashed line) LaSrCoO4, and (dotted line) Ba0.5Sr0.5Co0.8Fe0.2O3 -d in 1 mol dm-3 KOH solution. References 1. D. Chen, C. Chen, Z. M. Baiyee, Z. Shao, and F. Ciucci, Chem. Rev., 115, 9869 (2015). 2. A. Miura, C. Rosero-Navarro, Y. Masubuchi, M. Higuchi, S. Kikkawa, and K. Tadanaga, Angew. Chem. Int. Ed., 55, 7963 (2016). 3. M. A. Ghanem, P. Arunachalam, A. Almayouf, and M. T. Weller, J. Electrochem. Soc., 163 H450 (2016). 4. Y. Miyahara, K. Miyazaki, T. Fukutsuka, and T. Abe, Chem. Comm., 53 2713 (2017). Figure 1

Introduction Much attention has been paid to oxygen electrochemical reactions in alkaline electrolytes such as alkaline fuel cell, alkaline rechargeable metal-air battery and water-splitting devices. Many researchers have been exploring highly-active and cost-effective oxygen electrode catalysts, and one example of good oxygen electrocatalysts is perovskite-type oxide with the general formula of ABO3. Our group focuses on observing intrinsic electrochemical properties of perovskite when used as an oxygen electrode catalyst, using a carbon-free and binder-free perovskite electrode.1, 2 One of our research findings was that whereas oxygen evolution reaction activity of model electrodes were as high as that of composite electrodes consisting of perovskite powder, carbon and binder, oxygen reduction reaction activity of model electrodes was much lower than that of composite electrodes. This contrasting behavior motivated us to conduct further experiments such as hydrogen peroxide reduction reaction activity and cyclic characteristics of oxygen electrochemical reactions by using the model electrode and the composite electrode in terms of surface oxygen non-stoichiometry, which is our present research topic. Experimental section Synthesis and fabrication of La0.8Sr0.2CoO3 (LSCO) crystal electrodes were described in our previous literature.2 Perovskite powders were also synthesized by hydroxide-acid aided process3 and solid state process. The resultant oxide crystals and powders were characterized by using X-ray diffraction (XRD), energy-dispersive X-ray (EDX) spectroscopy, Brunauer-Emmett-Teller for oxide powders, and iodometry for oxide powders. Electrochemical measurements were conducted by using a rotating disk electrode (RDE) in a three-electrode cell. For a working electrode, RDE of LSCO crystal electrodes were assembled by mounting a LSCO crystal in a Teflon disk holder. As for composite electrodes, a catalyst layer consisting of 250 μg cm-2 perovskite powder, 50 μg cm-2 Vulcan XC-72 (Cabot), and 50 μg cm-2 anion conductive ionomer (AS-4, Tokuyama) was formed on glassy carbon (GC) RDE. 50 μg cm-2 Pt(40wt%)/Vulcan (E-TEK) and 50 μg cm-2 anion conductive ionomer on GC RDE was also used as benchmarking of oxygen electrochemical reactions. Pt wire and reversible hydrogen electrode (RHE) were used as counter and reference electrodes, respectively. Oxygen electrochemical activity measurements were conducted using a solution of oxygen-saturated 1.0 mol dm-3 KOH for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), and argon-purged 1 mol dm-3 KOH containing ca. 5 mmol dm-3 H2O2 for hydrogen peroxide reduction reaction (PRR). For qualitative electronic conductivity measurement, ferricyanide reduction reaction (FRR) was observed in a solution of argon-purged 1.0 mol dm-3 KOH containing 20 mmol dm-3 K3[Fe(CN)6]. Results and discussions XRD and EDX measurements confirmed that resultant LSCO crystals and perovskite powders had perovskite structure and the atomic compositions were quite similar as the desired composition. Figure 1 shows PRR activity on LSCO crystal. In the initial cycles, it shows clear rotation dependence indicating that LSCO crystal was active toward PRR. However, as the cycle number of cyclic voltammetry increased, reduction currents were decreased and finally showed no dependence on rotation. Similar results were observed for solid-state-synthesized LSCO composite electrode suggesting that obtained results by model electrodes were universal for practical electrodes. The decrease in activities was also observed for ORR, while the decrease in OER activity on LSCO crystal was not observed. FRR after PRR and ORR showed that electronic conductivity of LSCO crystal was decreased. The reason of activity decrease in ORR and PRR, and the influence of B-site cation in ORR and PRR in terms of surface oxygen non-stoichiometry will be discussed in the conference. References 1. Y. Miyahara, K. Miyazaki, T. Fukutsuka, and T. Abe, J. Electrochem. Soc., 161(6), F694 (2014). 2. Y. Miyahara, K. Miyazaki, T. Fukutsuka, and T. Abe, ChemElectroChem, 3, 214 (2016). 3. Y. Teraoka, H. Kakebayashi, I. Moriguchi, and S. Kagawa, J. Alloys Compd., 193, 70 (1993). Figure 1

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