The Ni-Al layered double hydroxide materials with high crystallinity were synthesized by the room-temperature liquid process and applied as oxygen evolution reaction (OER) catalysts. It is interesting to note that the OER activity was found to be relatively high in comparison with the Ni-based materials. In addition, the structural analyses and the effects of interlayer anion specie on the OER activity were also evaluated. It was found that the changes in the interlayer anion species from F⁻ to OH⁻ resulted in the enhancement of the OER activity. The maintained crystallinity after the electrochemical measurements were also observed through the X-ray analyses. The present work provides the insights about the possibility of the well-defined structures as the electrodes which were prepared by the unique liquid phase process.

We have been developing sintered multilayer oxide-based all-solid-state batteries. Anode active material rutile-type TiO₂ was not reacted with amorphous Na superionic conductor (NASICON)-type solid electrolyte Li_1.5Al_0.5Ge_1.5(PO₄)₃ (LAGP) even after sintered at 600 °C in a nitrogen atmosphere from the XRD patterns. The charge/discharge behavior of the electrochemical measuring cell (when using a non-aqueous electrolyte) was not different from that of rutile-type TiO₂. However, anatase-type TiO₂ charge/discharge behavior changed after sintering process. Additionally, in the result of the input/output characteristics using multilayer oxide-based all-solid-state battery, rutile-type TiO₂ as anode material was 3 times higher discharge capacity than anatase-type TiO₂ at current value 25.6 µA mm⁻². Finally, we successfully measured the Raman spectroscopy of all-solid-battery and rutile-type TiO₂ Raman shift peaks were reversibility during charge/discharge. Based on these findings, we conclude that rutile-type TiO₂ maintained a strong crystalline structure and high Li diffusivity even when sintered with amorphous LAGP. It suggested that rutile-type TiO₂ is suitable as anode material for oxide-based all-solid-state batteries requiring the sintering process.

For lithium-sulfur (Li-S) batteries, high-concentration electrolyte that inhibits the dissolution of Li polysulfide has been widely studied; one such electrolyte contains sulfolane. This study investigates the conditions under which a microporous activated carbon cathode, derived from azurmic acid, operates stably in a sulfolane-based electrolyte. We expected this cathode to maintain a stable capacity in a sulfolane-based electrolyte because its micropores stabilize the S species. However, Li-S batteries containing this cathode and electrolyte exhibit significant capacity decay during cycling. The cutoff voltage during charge-discharge cycling is varied to suppress the capacity decay. At a discharge voltage of 1.4 V or lower, the cycle life of the Li-S batteries is significantly reduced. Conversely, increasing the cutoff voltage during discharge suppresses the capacity decay of Li-S batteries. On the other hand, increasing the upper voltage limit during charging increases the reversible capacity. Thus, the operating voltage range is optimized. This study indicates that the voltage range of Li-S batteries should be carefully determined depending on the type of cathode material and electrolyte.

Lithium/transition-metal polysulfide batteries are candidate materials for next-generation batteries with high energy densities. Transition metal polysulfides and lithium- or sodium-containing transition metal sulfides exhibit large reversible capacities based on multi-electron processes, owing to the redox reactions of S in addition to the transition metal. This comprehensive paper aims to address the idea, research, and development of transition metal polysulfide electrode active materials and summarizes the author’s views on the concept of transition metal polysulfide electrodes. Furthermore, the diversity of coordination structures and unique structural changes during charging and discharging will be discussed.

Electrode reactions in electrochemical devices often consist of charge transfer at electrode/electrolyte interface and charge compensation in electrode active material. Therefore, to design electrochemical devices with high electrochemical performance, it is important to understand electronic structures of the electrode/electrolyte interface and electrode bulk during electrochemical reactions, and to design electrode materials to control them. In this paper, certain phenomena at the electrode/electrolyte interface and electrode bulk in lithium-ion batteries are clarified by using synchrotron radiation X-ray analyses. The information obtained from those X-ray analyses are applied to control the structure of the electrode/electrolyte interface and electrode bulk. Moreover, new cathode materials for all-solid-state fluoride-ion with high power and cyclic performances have been developed, compared to simple metal/metal fluoride materials, by using the findings obtained from the synchrotron radiation X-ray analyses.

In this paper, we describe new strategies to reduce the resistances related to cathode reactions and interfacial proton transfer in protonic solid oxide fuel cells (H⁺-SOFCs) based on proton-conducting BaZr_xCe_0.8−xM_0.2O_3−δ (M = Y, Yb, Sc etc.) by means of material and cell-structure design changes. First, an extension of the effective cathode reaction areas by employing the H⁺/O²⁻/e⁻ triple-conducting cathode is described. Cubic La_0.7Sr_0.3Mn_1−xNi_xO_3−δ (x = 0–0.3) can be hydrated under fuel cell conditions due to its large hydration enthalpy (∼100 kJ mol⁻¹), whereas rhombohedral La_0.7Sr_0.3Mn_1−xNi_xO_3−δ does not exhibit hydration capabilities; hence, the porous anode cermet support fuel cells (PAFCs), which use the former as a cathode, possess significantly smaller cathode polarization resistances than the PAFCs that use the latter. Second, we describe a new thermodynamic mechanism for reducing the electrolyte and cathode reaction resistances in a hydrogen-permeable metal-support fuel cell (HMFC), which involves the blocking of the oxide ion minor conduction in the BaZr_xCe_0.8−xM_0.2O_3−δ electrolyte at metal/oxide heterointerfaces. The BaZr_xCe_0.8−xM_0.2O_3−δ membrane of HMFCs is forced to gain extra protons to compensate for the charge from the oxide ions accumulating near the heterointerfaces via blocking, resulting in extremely high proton conductivity. This promotes significant interfacial proton diffusion for cathode reactions.

A reactive π-conjugated polymer, bromo-substituted polythiophene, was synthesized by constant potential electrooxidative polymerization of 3-bromo-4-dodecylthiophene in an acetonitrile solution of Bu₄NPF₆. The resulting polymer was applied as a reactive precursor for functional polythiophenes. The protonation via lithiation of the polybromothiophene proceeded quantitatively. The phenylation of the polybromothiophene by the Kumada-Tamao coupling reaction also proceeded with a 70 % efficiency. The changes in optical and electronic properties of the polymers by their reactions are discussed by the results of UV-vis absorption spectroscopy, photoluminescence spectroscopy, and cyclic voltammetric analysis. The emission colors of the bromo-substituted, protonated, and phenylated polymers were green, yellow, and blue, respectively, demonstrating the tunability of this approach.

β-Scission from alkoxy radical enables selective C_sp3-C_sp3 bond cleavage under ambient conditions, offering a useful method for organic synthesis. Various photocatalytic systems for β-scission have been reported, where proton-coupled electron transfer (PCET) mechanism plays a key role in the generation of alkoxy radical and thus β-scission. Electrochemical β-scission has been mainly pioneered in the presence of mediator, and a direct electrochemical system has rarely been investigated. Here, we investigated the β-scission via direct electrochemical oxidation using a model compound with β-O-4 linkage. Synthetic experiments suggested smooth progress of β-scission in the presence of collidine as a base. Cyclic voltammetry measurement, voltammetric simulation, and quantum simulation suggested the PCET mechanism is responsible for the electrochemical reaction, which is followed by β-scission process. This report provides fundamental insights into the electrochemical β-scission via direct electron transfer on the electrode, which contribute to future applications such as biomass valorization.

Redox behavior is a fundamental and fascinating feature of polycyclic aromatic hydrocarbons (PAHs). Cyclic voltammetry (CV) measurements are commonly performed to estimate the electronic structure of PAHs and to determine the stability of their oxidation and reduction states. However, the influences of electrolytes on electrochemically oxidized/reduced PAHs have rarely been discussed. In this note, we report voltammetric analyses of five PAHs (anthracene, 9,10-dimethylanthracene, phenanthrene, pyrene, and perylene) in Bu₄NB(C₆F₅)₄/CH₂Cl₂ and Bu₄NTfO/CH₂Cl₂, respectively, to highlight how the electrolyte-coordination affects the oxidative voltammetric behavior of PAHs. In most cases, reversible voltammetric responses were obtained with Bu₄NB(C₆F₅)₄/CH₂Cl₂, suggesting that this electrolyte is enough weakly coordinating to investigate its intrinsic oxidation behavior. On the other hand, irreversible voltammetric responses were obtained with Bu₄NTfO/CH₂Cl₂, indicating that the presence of a relatively coordinating anion, TfO⁻, destabilizes the radical cation species and induces further chemical and electrochemical processes. This study provides hints for rational electrolyte design to properly understand the redox behavior of molecules and maximize the potential of functional molecules for applications related to redox chemistry.