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A Pt/Pd/C core–shell-structured catalyst with an extraordinarily high activity of 3625 A g–1-Pt at 0.9 V versus a reversible hydrogen electrode (RHE) for the oxygen reduction reaction (ORR) was cre...

Enhancement of photovoltaic performance due to alkali-metal doping in various thin-film compound solar cells such as chalcogenide Cu(In,Ga)Se2 (CIGS), Cu2ZnSnS4 (CZTS), and organic–inorganic hybrid perovskite, is significant in the development of photovoltaic technologies. In this work, the effects of light Li- and heavy Cs-doping in ternary CuGaSe2 (CGS) and quaternary CIGS thin-films and devices are compared. The new findings are: (i) heavy alkali-metal halide CsF postdeposition treatment (PDT) modifies the CGS film surface morphology and increases the carrier density; however, the beneficial effects of Cs on the CGS photovoltaic performance are low when compared to the results observed from quaternary CIGS devices; (ii) LiF-PDT leads to no significant CGS and CIGS film surface (hetero p-n junction interface) modifications; thus, the use of a thin (approximately 30 nm) CdS buffer layer is not effective in enhancing photovoltaic performance; and (iii) the beneficial effects of either light Li or heavy Cs on ternary CGS devices are modest; nonetheless, Li may be more effective than Cs, unlike quaternary CIGS devices.

A designed two-compartment cell was applied to the degradation analysis of FeF3 having high theoretical energy density. Comparing with the result of the coin cell, the two-compartment cell gave us insight that the elution of Fe was responsible for the degradation of FeF3 and LiDFOB was found as an essentially effective additive for suppressing the degradation of FeF3.

Honeycomb layered oxides with monovalent or divalent, monolayered cationic lattices generally exhibit myriad crystalline features encompassing rich electrochemistry, geometries and disorders, which particularly places them as attractive material candidates for next-generation energy storage applications. Herein, we report global honeycomb layered oxide compositions, ${\rm Ag_2}M_2{\rm TeO_6}$ ($M = \rm Ni, Mg, \textit{etc}.$) exhibiting $\rm Ag$ atom bilayers with sub-valent states within Ag-rich crystalline domains of ${\rm Ag_6}M_2{\rm TeO_6}$ and $\rm Ag$-deficient domains of ${\rm Ag}_{2 - x}\rm Ni_2TeO_6$ ($0 < x < 2$). The $\rm Ag$-rich material characterised by aberration-corrected transmission electron microscopy reveals local atomic structural disorders characterised by aperiodic stacking and incoherency in the bilayer arrangement of $\rm Ag$ atoms. Meanwhile, the global material not only displays high ionic conductivity, but also manifests oxygen-hole electrochemistry during silver-ion extraction. Within the $\rm Ag$-rich domains, the bilayered structure, argentophilic interactions therein and the expected $\rm Ag$ sub-valent states ($1/2+, 2/3+, \textit{etc}.$) are theoretically understood via spontaneous symmetry breaking of SU($2$)$\times$U($1$) gauge symmetry interactions amongst $3$ degenerate mass-less chiral fermion states, justified by electron occupancy of silver $4d_{z^2}$ and $5s$ orbitals on a bifurcated honeycomb lattice. This implies that bilayered frameworks have research applications that go beyond the confines of energy storage., 67 pages, 5 figures, 1 cover art, 1 table

Hierarchical micro-/mesoporous carbons with abundant Fe-N-C sites were prepared through one-step carbonization of a metal-organic framework (MOF) with sodium iron ethylenediaminetetraacetic acid [NaFe(III)EDTA], which can facilitate the nucleation and growth of ultrafine (∼1.4 nm) and highly dispersed palladium nanoparticles (Pd NPs). Interfacing Pd NPs with Fe-N-C sites has been demonstrated for the first time to boost the heterogeneous catalysis of hydrogen production from formic acid, affording an ultrahigh turnover frequency (TOF) value of 7361 h-1 at 323 K. The robust synergistic interactions between Pd NPs and Fe-N-C sites together with the small size effects of Pd NPs are responsible for the enhanced catalytic activity.

Introduction Nanoparticles of Pt as well as Pt-based alloys are widely used as cathode catalyst materials for proton exchange membrane fuel cells (PEMFC). However, electrochemical stability of the materials is rather low under practical operating conditions of PEMFC cathode, resulting in severe deactivation of oxygen reduction reaction (ORR). Therefore, further material’s developments are required for next-generation PEMFC cathode catalysts, i.e., more enhanced ORR durability with low platinum group metal (PGM) usage. High entropy alloys (HEAs), defined as single phase solid solutions of five or more elements in equal composition ratios, are known as thermodynamically stable, in comparison to conventional binary alloys. Furthermore, complex atomic-level local structures bring about unique electronic as well as (electro-)chemical properties that originating from lattice strains induced by specific local structures and/or so-called sluggish diffusion of the constituent elements. [1] However, to our best knowledge, no study has been made for ORR properties of Pt alloying with non-PGM Cantor alloy (fcc structure HEA with equi-atomic ratio of Cr-Mn-Fe-Co-Ni [2]) elements in strong acid condition. In this study, we synthesized lattice stacking structures of Pt/HEA(hkl) (hkl = (111), (110), (100)) through arc-plasma deposition (APD) of the Cantor alloy layer on Pt(hkl) substrate surfaces, followed by deposition of the surface Pt layer in ~10-7 Pa. Then, we performed cross-sectional STEM-EDS observations for Pt/HEA/Pt(hkl) stacking structures with atomic-level resolution and evaluated the ORR properties (initial activity and structural stability). Experimental An APD target of Cr-Mn-Fe-Co-Ni (Cantor alloy) was fabricated by sintering of equal quantity corresponding elements. 10 ML(monolayer)-thick (1 ML = ca. 0.3 nm) Cantor alloy layer (as HEA) was vacuum-deposited by APD on surface cleaned Pt(hkl) substrate surfaces at 300 K, and subsequently annealed in vacuum at 773 K for 30 minutes. Then, 4ML-thick Pt layer was deposited on the pre-deposited Cantor alloy layer at 300 K and annealed at 623 K. The samples thus prepared are designated as Pt/HEA/Pt(hkl). The atomic-level micro-structures and chemical bonding states of Pt/HEA/Pt(hkl) surfaces were characterized by cross-sectional STEM-EDS, RHEED, XPS etc. CV and LSV with the RDE method were conducted in N2-purged and O2-saturated 0.1 M HClO4. ORR activity was evaluated from j k values at 0.9 V vs. RHE by using Koutecky-Levich equation and structural stability (ORR durability) was discussed based upon activity transitions during applying the potential cycles (PCs) of 0.6(3s)‐1.0(3s) V vs. RHE in O2 saturated 0.1 M HClO4 at room temperature. Results and Discussion Atomically-resolved, cross-sectional HAADF-STEM images for Pt/HEA/Pt(hkl) (a) and EDS line profiles of elemental distributions at corresponding yellow arrows (b) are presented in Figure 1. As clearly shown in (a), irrespective of the Pt surface indices, (hkl), HEA (Cantor alloy) and surface Pt layers are epitaxially grown on the substrates. By contrast, elemental distributions in each surface normal (b) seriously depend on the substrate Pt lattice indices. Notably, severe thermal diffusion of the constituent elements including Pt is confirmed by (a) and (b) for both Pt/HEA/Pt(110) and (100). Figure 2 summarizes electrochemical results. 4ML-thick-Pt/10ML-thick-Co/Pt(hkl) that prepared under the same preparation condition of Pt/HEA/Pt(hkl), and clean Pt(hkl) (light blue and gray, respectively) are also shown as references. As shown in the figure, the Pt/HEA and Pt/Co fabricated on Pt(111) substrate (top) show quite similar CV characteristics (shrink in hydrogen adsorption charges (0 – 0.3 V) and higher potential shifts in oxygen-related species adsorption (0.6 – 1.0 V)), in comparison to clean Pt(111), and almost the same initial ORR activity. Meanwhile, the Pt/HEA fabricated on Pt(110) and (100) substrates show more reduced hydrogen absorption charges, compared with corresponding Pt/Co samples. Particularly, distinctive redox features for clean Pt(110) at 0.12 V and for Pt(100) at 0.35 V are absent for corresponding CVs, suggesting specific topmost surface atomic-structures might be formed in the electrolyte, that probably resulting from significant electronic interactions between surface Pt and HEA constituent elements (Cr, Mn, Fe, Co, Ni) and/or local strain of the surface Pt layer induced by distorted Pt-HEA lattices located nearby. One might notice that Pt/HEA/Pt(110) reveals remarkable ORR activity enhancement compared with corresponding Pt/Co/Pt(110), while the activities for Pt/HEA and corresponding Pt/Co surfaces fabricated on Pt(100) are almost the same value. At the meeting, correlations between surface atomic-level micro-structures of Pt/HEA/Pt(hkl) and ORR properties will be discussed in detail. Acknowledgement This study was supported by new energy and industrial technology development organization (NEDO) of Japan and JST SPRING, Grant Number JPMJJSP2114. Reference [1] J. Yeh, JOM, 65, 1759 (2013). [2] B. Cantor et al., Mater. Sci. Eng. A, 375, 213 (2004). Figure 1

We have developed a method to obtain a data cube using a semi-parallel detection scheme and an electrostatic hemispherical analyzer (HSA) with multi-channel detection. By improving the Auger intensity map measurement scheme, the number of detector energy sweeps is reduced, and faster measurement is achieved. The gain differences among the detection channel are corrected by post-processing, and a data cube of Auger electron spectra is constructed. A data cube was obtained for an example of a sample with a non-flat surface, lead-free solder. It was demonstrated to be possible to extract spectra from any position within the measurement area and create the elemental distribution maps.

Both elemental Rb and Cs are known as effective dopants in enhancing Cu(In,Ga)Se2 (CIGS) thin-film photovoltaic device performance. It is, however, found that there are critical differences in the ...

We investigated the microstructures of Au-deposited PtCo@Pt core-shell nanoparticles (NPs) and discussed enhancement of the oxygen reduction reaction (ORR) properties by Au termination of low-coordination sites of the Pt-shell. The Au-deposited PtCo@Pt NPs showed an improved electrochemical structural stability, together with slight increment in increased initial, pristine area-specific activity relative to the non-Au-deposited PtCo@Pt NPs. Atomic-level microstructural characterization was performed by a back-side illumination fluorescence X-ray absorption fine structure (BI-FXAFS) method and scanning transmission electron microscopy with energy dispersive spectroscopy (STEM-EDS). The BI-FXAFS results indicated that compressive lattice strain in the Pt-shells of the PtCo@Pt NPs was almost unchanged by the subsequent Au deposition. Furthermore, STEM-EDS mapping of Pt, Co, and Au clearly showed that the deposited Au tended to localize at low-coordination sites of the Pt-shell surface, e.g., edges and corners. The atomic-level microstructural characterization conducted in this study demonstrated that effective Au surface terminations of the Pt-shell enhance the ORR durability of Pt-based core-shell type NP catalysts.

Li2MnO3, a layered lithium-rich manganese oxide, is one of the potential high-capacity positive electrode materials among the Li containing transition metal oxide materials but its low electrical conductivity restricts its electrochemical activity. In our previous study, Li–Mn cation disorder in Li2MnO3 resulting in the formation of a NaCl-type structure was found to improve its electrochemical activity, i.e., a high initial discharge capacity of 320 mA h g−1. However, it still suffered from a poor cycling performance probably due to another problem, e.g., its structural instability, i.e., oxygen emission during charging. In this study, we found that the structural stability of NaCl-type Li2MnO3 was significantly improved by forming a composite with spinel-type LiMn2O4 by mechanical milling. The initial discharge capacity of the composite was close to 400 mA h g−1 and its 15th discharge capacity still showed more than 80% of the initial one, while less than 50% for NaCl-type Li2MnO3. The oxide ions in the composite were found to be more stable than those of NaCl-type Li2MnO3 during the electrochemical redox reaction, which was confirmed by O K-edge XAS measurements, resulting in the higher reversible capacity and better cycling performance.

Typical electrodes for Li-ion batteries such as LiCoO2 operate via the insertion/de-insertion of Li ions; innovative electrodes that undergo conversion reactions have been developed to meet the requirement for greater capacities. However, batteries operating via a conversion process suffer from degradation over repeated cycles and from hysteresis in charge/discharge profiles, and their mechanism remains a topic of ongoing debate. We prepare the FeF3/C composite electrode as a model electrode to address the conversion mechanism. Magnetization measurements provide direct evidence of superparamagnetic behavior―Fe nanoparticles (NPs) are magnetized similarly to a paramagnet under an external field―after the discharge process. We quantify the size of the Fe NPs, and find a correlation between an increased Fe particle size and a decrease in discharge capacity. These findings would pave the strategy based on control of the size of Fe NPs for realizing a favorable cycling performance. Indeed, improvement of an electrolyte goes toward higher capacities after 30 cycles.

Replacing the scarce metal-based positive electrode materials currently used in rechargeable lithium ion batteries with organic compounds helps address environmental issues and might enhance gravimetric electrochemical capacity. The challenge has been to find organic materials with both high capacity and long-cycle life. Here, we study the naphthazarin (5,8-dihydroxy-1,4-naphthoquinone) skeleton as a high capacity candidate electrode for lithium-ion batteries, showing a multielectron-transfer type redox reaction. We also use electron energy-loss spectroscopy to reveal the reaction stoichiometry during charge/discharge processes. While the lithium salt of naphthazarin itself helped deliver a high initial capacity, its cycle-life was not satisfactory. Instead, a newly synthesized naphthazarin-dimer shows a lengthened cycle-life without sacrificing the initial high capacity of 416 mAh g−1 and energy density of 1.1 Wh g−1. Replacing metal electrodes in lithium-ion batteries with organic materials reduces environmental impact and might lead to high gravimetric capacity. Here, organic electrodes containing a naphthazarin-dimer skeleton achieve an initial capacity of 416 mAh g−1 and energy density of 1.1 Wh g−1 in a lithium-ion battery.

A designed two-compartment cell was applied to the degradation analysis of FeF3 having high theoretical energy density. Comparing with the result of the coin cell, the two-compartment cell gave us insight that the elution of Fe was responsible for the degradation of FeF3 and LiDFOB was found as an essentially effective additive for suppressing the degradation of FeF3.

Carbon-supported Pt, Pt-Cu, and Pt-Ru nanoparticles were prepared by an alcohol reduction method in the presence of carboxylates and phosphinate in order to investigate the role of these stabilizers in the nanoparticle formation process and the effect on catalytic properties in 2-propanol oxidation. For the Pt-Cu system, long chain carboxylate gave small dispersed particles even with high metal loading while phosphinate gave aggregated particles. For the Pt and Pt-Ru systems, fewer aggregates were observed and the particle size was independent of the chain length of carboxylate while much smaller and dispersed particles were obtained with phosphinate. Phosphinate mainly prevents metal crystal growth while carboxylates prevent both crystal growth and formation of aggregated particles. Although surface poisoning is severe on small dispersed particles in 2-propanol oxidation, dehydrogenation of 2-propanol at low potential is little affected. Phosphinate-protected catalysts were more tolerant to poisoning promoting 2-propanol electrooxidation at high potential range. The presence of Cu promoted 2-propanol electrooxidation at low potential range. These components made phosphinate-protected PtCu best perform in 2-propanol oxidation at 30 °C.

The structure of Fe-substituted Li 2 S-based positive electrode material Li 8 FeS 5 was analyzed using high-energy X-ray total scattering measurements. Pair distribution function (PDF) analyses indicated that the mechanically milled Li 8 FeS 5 sample could best be described as having an anti-fluorite structure in which Fe ions partially occupy Li sites in the Fm 3 ¯ m unit cell. The electrochemical properties of a cell utilizing Li 8 FeS 5 as the positive electrode were also consistent with this structural model.

To develop safe and low-cost Li-ion batteries (LIBs), recently, an aqueous-based electrolyte so-called “hydrate-melt” (HDM) electrolyte is proposed. Li4Ti5O12 is a promising negative electrode material for a LIB with such a HDM electrolyte because of its unexpected reversible Li insertion and extraction properties without usually inevitable water reduction. The solid-electrolyte interphase formation is one of the reasons for this stable reaction, although a detailed analysis is not yet performed. Here, a Li4Ti5O12 electrode surface reacted in a HDM electrolyte is investigated by scanning electron microscopy-based analysis. Surface reaction products are clearly observed on the Li4Ti5O12 surface after the Li insertion reaction in a HDM electrolyte. Energy-dispersive X-ray spectroscopy and Auger electron spectroscopy indicated that the products do not contain any components originated from Li salts, whereas anion-derived passivation films seem to cover a bare surface below the products. Further, the surface ...

The capability and reversibility of surface-coated LiCoO2 (LCO) during charge/discharge with a layered structure change between O3 and H1−3 phases was investigated. A compound oxide phase with a thickness of several nanometers and a LiMO2 structure (M: Co, Al, or Zr) formed on the surface of the coated LCO. The discharge capacity (Q D) and discharge energy density (E D) at a current-rate of 0.05 C in the initial charge/discharge voltage range of 2.5–4.6 V were 228 mAh g−1 and 936 Wh kg−1, respectively. The Q D at the 1st cycle at 1 C was 213 mAh g−1, and the retention at the 101st cycle was 88.8%. The Q D and E D at 6 C were 204 mAh g−1 and 778 Wh kg−1. Operando XRD and impedance analyses revealed that the decrease in capacity by cycling was mainly due to the increased polarization, which was caused by the increase in the Li-ion intercalation resistance at the electrode/electrolyte interface. The O3/H1−3 phase transition was reversible even after the cycle-test. Most of the capacity in the O3/H1−3 transition region could be reversibly charged/discharged up to 100 cycles. The transition from H1−3 to O3 during discharging was responsive up to a current-rate of 6 C.

We found that elemental Si-doped Cu(In,Ga)Se2 (CIGS) polycrystalline thin films exhibit a distinctive morphology due to the formation of grain boundary layers several tens of nanometers thick. The use of Si-doped CIGS films as the photoabsorber layer in simplified structure buffer-free solar cell devices is found to be effective in enhancing energy conversion efficiency. The grain boundary layers formed in Si-doped CIGS films are expected to play an important role in passivating CIGS grain interfaces and improving carrier transport. The simplified structure solar cells, which nominally consist of only a CIGS photoabsorber layer and a front transparent and a back metal electrode layer, demonstrate practical application level solar cell efficiencies exceeding 15%. To date, the cell efficiencies demonstrated from this type of device have remained relatively low, with values of about 10%. Also, Si-doped CIGS solar cell devices exhibit similar properties to those of CIGS devices fabricated with post deposition...

International audience; We report a scandium oxyhydride BaScO2H prepared by solid state reaction under high pressure. Rietveld refinements against powder synchrotron X-ray and neutron diffraction data revealed that BaScO2H adopts the ideal cubic perovskite structure (Pm3̅m), where oxide (O(2-)) and hydride (H(-)) anions are disordered. (1)H nuclear magnetic resonance (NMR) spectroscopy provides a positive chemical shift of about +4.4 ppm, which can be understood by the distance to the nearest (and possibly the next nearest) cation from the H nucleus. A further analysis of the NMR data and calculations based on ab initio random structure searches suggest a partial cis preference in ScO4H2 octahedra. The present oxyhydride, if compositionally or structurally tuned, may become a candidate for H(-) conductors.

Confirming the dopant site of In3+-doped SrTiO3 (In-STO) is essential to reveal the mechanism of its photocatalytic activity. In a previous study, x-ray absorption spectroscopic analysis and theoretical investigations were performed to discuss the dopant site, and In3+-Ti4+ substitution was proposed. However, direct confirmation of the In3+ dopant site has not yet been reported. Here, we performed direct atomic-scale imaging of In-STO crystals via analytical transmission electron microscopy and revealed the dopant site based on real-space elemental mapping. The Ti and Sr sites in the SrTiO3 crystal lattice were well identified by atomic column elemental mapping using energy dispersive x-ray spectroscopy (EDS). The EDS signal of indium has a stronger intensity at the Ti site than at the Sr site, based on the total analysis of each Ti and Sr atomic column. By applying principal component analysis on the raw EDS spectral imaging data cube, the indium site was clearly imaged; it completely fit into the Ti atomic column positions. These results provide direct evidence of In-Ti substitution in In-STO photocatalysts.

For large storage batteries, cost performance is more important than energy density. Iron-based conversion-type cathode active materials are promising because this material group satisfies both low-cost and high-capacity requirements. In particular, iron fluoride is notable for its relatively high discharge voltage. However, the electronic conductivity of FeF3 is poor and it has large discharge-charge overvoltage. To solve these issues, xFeF3-V2O5/C (9xFeF3-9V2O5–P2O5) was investigated and the composition with x = 2 was shown to be optimal. Furthermore, the cyclability of 2FeF3–V2O5/C was improved by changing the salt from LiPF6 to LiClO4 and changing the solvent from DMC to EMC. Although the V2O5 glass component showed irreversible capacity due to Li trapping in the glass matrix at the first cycle, the irreversible capacity at the first cycle was successfully compensated by the addition of LiF as a sacrificial salt.

This study aimed to reveal the electrical characteristics of the composite electrodes of Li-ion batteries. LiCoO2 electrodes were analyzed using atomic force microscopy, and three-dimensional datasets of current–voltage (I–V) curves (IV-datacubes) were obtained. The IV-datacubes were then analyzed using principal component analysis to determine the typical I–V curve corresponding to each LiCoO2 particle on a statistical basis. Detailed analysis based on the thermionic emission model with series resistance showed that some of the particles exhibited poor electrical contact in the electrode. Overall, the obtained results suggested that our IV-datacube analysis can reveal the characteristics of buried electrical contacts within electrodes, which is otherwise difficult to accomplish using alternative methods. We, therefore, believe that the method presented herein is a promising analytical method for composite electrodes.

In this study, we synthesized the solid solution system between La2Zr2O7 and La3TaO7 with a fluorite-type structure for the first time by the polymerized complex method and refined its crystal structural parameter using the Rietveld method. Furthermore, we synthesized a garnet-type Li-ion conductor by the precursor method which used a solid solution, La2+xZr2-2xTaxO7 (x = 0.4), as a precursor material. To investigate the reactivity between the Li oxides and the fluorite-type precursor oxide, we performed TG-DTA measurements. As a result, an exothermic peak was observed at 420 °C, indicating the phase formation of the garnet-type Li6.5La3Zr1.5Ta0.5O12 at low-temperature. In addition, we prepared the sintering body of the Li6.5La3Zr1.5Ta0.5O12 using the precursor method. The fabricated sample exhibits a bulk Li-ion conductivity of 9.4 × 10−4 S cm−1 at 25 °C.

The surfaces of LiCoO 2 particles were modified to improve the charge-discharge cycling properties of Li-ion batteries containing LiCoO 2 cathodes. The sol-gel technique was used to modify the surface of LiCoO 2 particles with magnesium oxide. Capacity retention during cycling of the magnesium oxide-coated LiCoO 2 cathode was superior to that of a cathode comprising pristine LiCoO 2 . Moreover, results obtained from TEM measurements indicate that the Li concentration was relatively homogeneous in the magnesium oxide-coated LiCoO 2 particles after cycling tests. The crystallographic planes of the coating were found to be coherently oriented with those of the substrate, MgO(111)[1−10]//LiCoO 2 (003)[100]. Therefore, we believe that a thin cover of Mg on the surface of LiCoO 2 stabilizes the surface, contributing to the homogeneity of charge and discharge reactions.

Au–Ag bimetallic catalysts on SiO2 were prepared using a simultaneous solid grinding (simul-SG) method, in which multiple kinds of organometallic complexes are ground with a support powder. After optimizing the Ag/Au ratio, the obtained catalysts exhibited remarkably high activity for low-temperature CO oxidation compared with that of Au/SiO2 or Ag/SiO2 catalysts. A detailed structural analysis using electron microscopy revealed that a higher ratio of Ag prevents growth of the particles via sintering and induces high densities of active Au–Ag contacts. Our simul-SG method is a promising tool for the easy preparation of multicomponent catalysts on various supports.

Li K-edge analysis obtained by scanning reflection energy loss spectroscopy (REELS) has been used to investigate the positive electrode of a Li-ion battery. Using spectral imaging data, Li mapping of a LiNi1/3Mn1/3Co1/3O2 electrode has been constructed. Inhomogeneous Li distributions are observed in LiNi1/3Mn1/3Co1/3O2 particles after cyclic electrode charging and discharging. The REELS results agree well with those obtained by scanning transmission electron microscopy-electron energy loss spectroscopy (STEM-EELS). Copyright © 2016 John Wiley & Sons, Ltd.

In this study, a new class of contenders for high-voltage and high-capacity positive electrode materials with the composition NaxLi0.7−xNi1−yMnyO2 (0.03 Na0.7Ni1−yMnyO2 (0.5 ≤ y ≤ 0.8) as the precursor exhibited a mixture of layered and spinel structures. The (dis)charge voltage-capacity curve of materials with these compositions significantly varied according to the residual Na and Mn content. Notably, HT-NaxLi0.7−xNi1−yMnyO2 (x = 0.093, y = 0.67) exhibited a maximum discharge capacity of 261 mA h g−1 at an average voltage of 3.36 V at 25 °C (between 2.0 and 4.8 V), which translates to an energy density of 943 W h kg−1. The obtained electrochemical performance is rationalized by the phase fractions of layered and spinel structures, which is triggered by the residual Na and Mn content in NaxLi0.7−xNi1−yMnyO2.

Iron trifluoride (FeF3) has been attracted as one of the promising candidates for the positive electrode material of lithium secondary batteries due to their high theoretical capacity (712 mA g–1) and high energy density (1949 Wh kg–1). However, its poor cyclability and a large hysteresis of the voltage during charge and discharge still remain the problem to solve for the commercialization. The cycling performance of FeF3-based lithium secondary battery has been improved by various strategies, such as the addition of anion receptor, coating by other metals and tuning of electrolyte composition so far [1-3], but the suppression of degradation and the elucidation of its mechanism have not accomplished completely. In the present study, we investigated the charge and discharge behavior of the FeF3 positive electrode using a designed two-compartment type cell which has lithium ion-conducting ceramics as a separator to prevent the cross-talk of the electrolyte between the positive and negative electrode. A charge/discharge test was performed using a coin cell and two-compartment type cell using 1.0 mol dm–3 LiPF6 in 1:1 ratio of ethylene carbonate (EC) and dimethyl carbonate (DMC) as the electrolyte. Disassembling analysis of both cells including SEM observation and X-ray fluorescence analysis revealed that the elution of Fe is more responsible for the degradation of the FeF3 electrode than a thick film formation on the electrode due to the cross-talk in the coin cell. Furthermore, the cyclability was improved using the electrolyte with LiDFOB as an additive for only the positive electrode side of the two-compartment type cell, whereas the improvement of the cyclability was not found when the additive was applied to a coin cell. After the cycling tests, various analyses, such as electrochemical impedance, X-ray photoelectron spectroscopy, and transmission electron microscopy, were also conducted for the electrode with and without additives in the electrolyte to examine the degradation mechanism of FeF3 positive electrode. The obtained results were considered useful for the improvement of the cycling performance of FeF3-based lithium ion batteries. References [1] K. Kumagae, K.-I. Okazaki, K. Matsui, H. Horino, T. Hirai, J.-I. Yamaki and Z. Ogumi, J. Electrochem. Soc., 163, A1633 (2016). [2] Y. Li, X. Zhou, Y. Bai, G. Chen, Z. Wang, H. Li, F. Wu and C. Wu, ACS Appl. Mater. Interfaces, 9, 19852 (2017). [3] H. Senoh, K. Matsui, M. Shikano, T. Okumura, H. Kiuchi, K. Shimoda, K. Yamanaka, T. Ohta, T. Fukunaga, H. Sakaebe and E. Matsubara, ACS Appl. Mater. Interfaces, 11, 30959 (2019). Acknowledgement 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)”

An electron-conducting mixed oxide, Co-Pt bronze was synthesized and examined as a candidate for a highly durable electrocatalyst for both the polymer electrolyte fuel cells and electrolyzers. The motivation of this study comes from the fact that this material has not been studied as an electrocatalyst in acidic media, although past studies showed a high electronic conductivity and a high corrosion resistance. Co-Pt bronze without metallic Pt was obtained by solid-state synthesis and hot aqua regia rinsing. The OER activity was found to be among the highest as a material without Ir and Ru in acidic media, and it showed extremely high electrochemical stability in the OER potential range. Its oxygen reduction reaction (ORR) was obtained after potential cycles down to the hydrogen region, which formed a thin Pt metallic layer over the oxide. While its specific activity was not more than that of pure platinum nanoparticles, its durability against the potential cycles was much higher.

To develop safe and low-cost Li-ion batteries (LIBs), recently, an aqueous-based electrolyte so-called "hydrate-melt" (HDM) electrolyte is proposed. Li