This study focuses on electrochemical potential control and fabrication methods for various metal complexes and polycyclic aromatic hydrocarbons at solid–liquid interfaces, particularly using electrochemical scanning tunneling microscopy (EC-STM) and atomic force microscopy (AFM). The in situ observation of molecular assemblies and understanding of the phase transition dynamics and ligand exchange reactions at the molecular and/or submolecular levels provide information on functional molecular design and surface engineering. In addition, ionic liquids electrochemistry is summarized from the viewpoint of single-crystal electrochemistry.

The design of high-performance electrochemical devices requires a profound understanding of the mechanisms governing the electrochemical reactions within the device, ranging from microscopic one involving atoms and molecules to macroscopic one observed in cells/stacks of practical devices. While extensive efforts have been made to understand the microscopic and macroscopic electrochemical phenomena in these devices, understanding the interplay between micro- and macro-scale electrochemical phenomena has not necessarily been sufficient. One reason is that what connects the macroscopic and microscopic electrochemical phenomena is a complex electrochemical phenomenon involving the collective behavior of a large population of particles within an electrode under the influence of external fields such as stress. This comprehensive paper presents the research conducted by the authors to develop novel techniques for understanding the intricate electrochemical phenomena that bridge the micro and macro scales. The first part of this paper presents our work on the development of a technique to perform three-dimensional operando observation of heterogeneous electrochemical reactions occurring in a particle ensemble within solid state battery electrodes using computed-tomography with X-ray absorption near edge structure spectroscopy (CT-XANES). The latter part focuses on the development of a method to quantitatively evaluate stress-induced modulation of material properties of battery electrode materials (chemo-mechanical coupling phenomena).

Cathodic reduction efficiently cleaved N–O bonds. The simple cathodic reduction of Weinreb amides in a divided cell afforded the corresponding amide in good yields. Cyclic voltammetry experiments and density functional theory calculations suggested that the direct reduction of the N-methoxy amide generates the methoxy radical and amide anion. The release of methanol derived from methoxy radical would be the driving force of the N–O bond cleavage.

The development of new materials leads to the invention of new devices. The exploitation of high ionic conductivity materials has facilitated the emergence of a new category of energy storage devices, including the all-solid-state battery. This paper reviews the history of the development of lithium solid electrolytes and their application in all-solid-state batteries. Particular focus is given to the development process of Li₁₀GeP₂S₁₂, which surpasses the conductivity characteristics of liquid-electrolyte systems targeted by lithium-ion conductors, and its application to solid-state batteries is described. Furthermore, this review describes new science that will be born when batteries become solid-state.

The influence of nano- and micro-structures on various physicochemical phenomena is a subject of interest to many researchers. Physicochemical reactions at solid/electrolyte interfaces, such as crystallization, metal complex formation, adsorption, and electrochemical reactions are influenced by surface modifications with organic thin films. In this study, we review and generalize the findings of our research on the application of organic thin films with or without three-dimensional structures to chiral sensors, interactive motions of nano/micro materials, and electrodes for electrochemical energy devices.

There is growing demand for the energy storage devices with superior energy density than that of conventional lithium-ion batteries. Lithium-air batteries (LABs) are promising candidates for next-generation rechargeable batteries due to their extremely high theoretical energy density. In recent several years, there are many research progress for LABs mainly in the field of academia. However, in most of the studies, the performance evaluation of LABs is performed under inappropriate technological parameters from the viewpoint of the high energy density cell design. As results, the cell-level energy density of LABs is lower than conventional lithium-ion batteries. For realizing the cell-level high energy density LABs, such as 500 Wh/kg class LABs, the cell should be operated under lean electrolyte and high areal capacity condition and the suitable electrode materials and electrolyte should be developed. This article over-views the recent research progress of LABs, from the viewpoint of practical cell design and material development. In addition, the perspective for future research direction for realizing LABs with practically high energy density and long cycle life is also described.

The quest to design active and stable electrochemical interface hinges on unequivocally identifying the active site(s) and reaction mechanism under realistic operating conditions. This comprehensive paper summarizes the most recent understanding of the electrochemical interface during energy conversion and storage reactions probed by operando surface-enhanced infrared spectroscopy (SEIRAS), operando attenuated total reflection infrared spectroscopy (ATR-IR), and operando synchrotron surface X-ray scattering, coupled with density functional theory (DFT) calculations. The paper also demonstrates that the holistic information about the complex interaction in the electrochemical interface can alter the reaction energetics/kinetics in a way incapable of electrode-centered design strategy. This work shed light on the significance of advanced operando techniques to accelerate the design of electrochemical interfaces by providing additional knobs to tune the reaction energetics/kinetics, leading further improvements in electrocatalytic activity for energy conversion and storage reactions.

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.