Porosity in anodic aluminum oxide (AAO) is one of the key structural features in the research and development of AAO-based nanostructured devices. Although surface image analysis (SIA) using scanning electron microscopy is commonly used to measure porosity, it tends to underestimate this value because of inherent systematic errors and transient surface structures. In addition, the tendency of pores to adopt a tapered shape during high-throughput, high-temperature anodization requires accurate structural measurements. In this study, we derived a theoretical formula for calculating the effective surface porosity P_top. We assessed its consistency by quantitatively comparing the apparent surface porosity from SIA and the pore-bottom porosity P_bottom measured using the pore-filling method. The formula proposed in this study enables a direct comparison of P_top and P_bottom on a unified scale. This achievement contributes to the efficient fabrication of samples through high-temperature anodization and improves the structural design of AAO-based research and application devices.

Lithium-ion batteries (LIBs) have high operating voltage, high energy density, and superior cycle performance, and are widely used in portable devices, electric vehicles, and stationary power sources. The further improvement of LIBs requires not only research on each component but also research based on their hierarchical structures. Carbonaceous materials play two important roles in LIBs: they act as negative electrode materials and as conductive materials for electron conduction networks in composite electrodes. In this comprehensive paper, research on LIBs based on carbonaceous materials is summarized. For the compatibility of propylene carbonate-based electrolyte solutions with graphite negative electrodes, the solvation structure of lithium ions and the SEI formation mechanism were controlled by the addition of Lewis acids and bases. In electrochemical analyses of solid electrolyte interphase (SEI) on graphite negative electrodes, the influence of SEI on interfacial lithium-ion transfer and the suppression of co-intercalation of solvated lithium ions was clarified. In addition, the negative electrode properties of graphitized carbon nanospheres, the electronic resistance of positive electrode slurries containing carbonaceous conductive materials, and interfacial reactions at graphite/sulfide solid electrolyte interfaces in all-solid-state lithium rechargeable batteries were investigated.

Electrocatalytic carbon dioxide reduction and oxygen evolution reactions are key reactions for renewable-energy-driven chemical conversion. The catalytic activity of electrocatalysts based on inorganic nanomaterials in these reactions is strongly governed by the coordination and electronic structures of the metal active centers. This paper summarizes the development of highly active electrocatalysts through structural control across multiple scales, including composition, electronic state, particle size and morphology. For electrochemical CO₂ reduction, control of composition and nanostructure was used to regulate product selectivity. For the oxygen evolution reaction, valence-state modulation, multi-element oxide design, and particle size control were employed to enhance catalytic activity. These studies demonstrate that precise structural control of inorganic nanomaterials provides an effective strategy for improving electrocatalytic activity and selectivity in CO₂ and water electrolysis.

Electrochemical self–assembly (ESA) by electrolysis in one–pot containing inorganic and organic ingredients results in hybrid materials to exert augmented functionalities due to strong coupling between the constituents in nanoscale. We have recently discovered ESA of redox active hybrid thin films by addition of 2,5-dihydroxy terephthalic acid (DHTPA) to the bath for cathodic electrodeposition of ZnO employing oxygen reduction reaction (ORR). As the process of ESA has been examined, we have unveiled electrocatalysis of ORR by the oxidized form of DHTPA, 2,5-dicarboxy benzoquinone (DCBQ), to promote the growth of ZnO. By contrast, DHTPA is not catalytic for ORR. This “turn-on and -off” of electrocatalysis by redox between DCBQ and DHTPA have nicely explained the peculiar S-shaped I-V curve measured during the electrodeposition by potential cycling (PC method) employing a rotating disk electrode (RDE). The hybrid thin film electrode obtained by the PC method showed fast and stable redox with increased capacities in a neutral Na₂SO₄ solution, superior to those previously achieved by the materials obtained by potentiostatic electrolysis (PS method). Owing to re-construction of hybrid nanostructure during repetitive DHTPA/DCBQ redox, smooth, flat, crack-free and yet highly porous hybrid thin film can be grown thicker by the PC method, while facilitating electronic and ionic transport for the redox reaction. The redox capacity determined in the galvanostatic charging/discharging test at 10C-rate has increased 23 times (6.24 µAh cm⁻²) as compared to that of the PS sample, indicating a large room of further improvements. The process of ESA can therefore be seen as a synthetic route to obtain novel materials for energy storage, out of earth-abundant, non-toxic elements with low process energy, to be combined with extremely safe neutral aqueous electrolyte, ideally suited as ubiquitous power source to back-up wearable electronic devices.

The practical application of graphite anodes in sulfide-based all-solid-state lithium-ion batteries is hindered by their poor charging rate capability and interfacial instability caused by the reductive decomposition of solid electrolytes. To address this, we systematically investigated the impact of ultra-thin surface modifications on graphite using atomic layer deposition. Four materials with distinct electronic and lithium-ion conductivities, LiF, Al₂O₃, TiO₂, and Li₃PO₄, were deposited on graphite powder. While all the modifying materials effectively reduced the initial irreversible capacity by suppressing solid electrolyte reduction, TiO₂ and Li₃PO₄ significantly improved the charging rate capability owing to their high lithium-ion conductivities. Furthermore, extended floating tests revealed that the Li₃PO₄ modification uniquely maintained its enhanced rate capability, whereas the TiO₂-modified graphite suffered from kinetic degradation. Because Li₃PO₄ is an electronic insulator, it effectively restricts the continuous reduction of the solid electrolyte compared to TiO₂, which becomes electronically conductive upon lithiation. This study demonstrates that surface modification with a material that is simultaneously an electronic insulator and lithium-ion conductor is crucial for achieving high rate capability and interfacial durability in all-solid-state batteries.

This work demonstrated the electrooxidation of cellulose dissolved in a highly alkaline aqueous solution using Pt nanoparticle electrocatalysts prepared via an ionic liquid/metal sputtering technique. The amount of Pt nanoparticles loaded onto a carbon black support and the quantity of the resulting Pt/C applied to a glassy carbon disk electrode were optimized so as to obtain the highest anodic current. The resulting material outperformed a planar Pt disk electrode and Pt nanoparticles synthesized via a conventional wet chemical reduction method when used to promote cellulose oxidation. This increased performance is attributed to the smaller particle sizes and higher dispersibility of the Pt nanoparticles synthesized through the sputtering method, which combined to increase the electrochemically active surface area.

The LaMgNi_3.9Co_0.1 hydrogen storage alloys were prepared by a vacuum powder sintering method, and the effects of sintering time (4–12 h) on their phase structures and electrochemical properties were systematically investigated. XRD analysis reveals that the alloys mainly consist of the Ce₂Ni₇ phase and PuNi₃ phase. With increasing sintering time, the phase evolution can be described as PuNi₃ → Ce₂Ni₇ → LaNi₅ (10 h). Electrochemical tests show that properly extending the sintering time can effectively improve the cycling stability and high-rate performance of the alloy. The alloy sintered for 10 h exhibits the optimal comprehensive electrochemical performance: C_max = 362.71 mAh g⁻¹, S₁₀₀ = 64.06 %, HRD₉₀₀ = 90.48 %. Electrochemical kinetic analysis reveals that the charge transfer rate plays a dominant role in controlling the electrochemical reaction.

The elucidation and quantification of individual resistance contributions in porous electrodes remain critical challenges in electrochemical energy-storage devices, particularly Li-ion batteries. To address this challenge, we propose an integrated analytical framework combining high-precision symmetric-cell electrochemical impedance spectroscopy (EIS) with equivalent circuit modeling based on a transmission-line model (TLM), enabling the systematic visualization and separation of these contributions. In conventional cell configurations with a counter electrode, the interfacial impedance responses of the working electrode are inherently affected by the opposing electrode, complicating the accurate interpretation of single-electrode behavior. In contrast, symmetric-cell EIS using thermodynamically identical electrodes enables the precise characterization of the intrinsic interfacial response of a single electrode. The integration of high-resolution measurements with TLM offers enhanced resolution and reproducibility, allowing the quantitative evaluation of resistance components that are otherwise difficult to resolve and providing deeper insight into electrochemical processes in porous electrodes. We comprehensively validated this unified measurement–modeling methodology across diverse porous electrode systems, demonstrating its applicability under various electrochemical conditions and electrode architectures and establishing it as a systematic and quantitative approach for resistance analysis in porous electrodes.

Ionic liquids show outstanding thermal stability, non-flammability, electrochemical stability, and high structural tunability. These characteristics make ionic liquids promising electrolytes for many types of secondary batteries, including alkali-ion batteries, metal-anode batteries, solid-state batteries (as additives), and dual-ion batteries. By selecting appropriate combinations of cations and anions, their properties can be tuned to suit specific electrochemical environments. For this reason, the coordination structures, ion–ion interactions, and the evolving interfacial behaviors of ionic liquids are considered especially important for the development of ionic liquid electrolytes. In this comprehensive paper, several strategies for ionic liquid utilization, developed primarily through the author’s research, are introduced. These strategies include cation- and anion-regulated ionic liquid systems, molten-salt-inspired formulations, hybrid electrolytes that combine ionic liquids with organic solvents, and solid-liquid composites to enhance interfacial properties. Overall, this comprehensive paper suggests that continued advances in ionic liquid research can contribute not only to the development of next-generation rechargeable batteries but also to a deeper understanding of the fundamental physicochemical properties that govern ionic liquid behavior.