The Electrochemical Society of Japan (ECSJ) has been publishing comprehensive papers related to the achievements of researchers who are awarded by ECSJ annually since 2014. The origin of the society awards, we can see that they began as Tanahashi Paper Award. In order to promote the use of this journal an academic and industrial outcomes from the activity of ECSJ members, the editorial board would like to introduce the society awards and the awardees’ achievements as an award-winning feature article.

Electrochemical capacitors are energy storage devices characterized by high power and long cycle life for charging/discharging. Carbon materials play a very key role as electrode active materials for the electrochemical capacitors. This comprehensive paper mainly covers the author’s research regarding the carbon materials as electrodes for the electric double layer capacitor used as an electrochemical capacitor. The importance of focusing on the pore structure, the surface chemistry, and the three-dimensional structure of the electrodes is stated from the viewpoint of improving the energy density and reliability, and the characteristic carbon materials that have a high capacitance even with a low microporosity are also reported. These research results indicate the potential of nano-sized carbons and classic carbons, such as activated carbon and graphite-related materials, to further develop the technologies of the capacitor electrodes.

ENE-FARM type S equipped with solid oxide fuel cell (SOFC) stack has been commercialized since 2012. To further expand the market of ENE-FARM type S, higher electrical efficiency, higher durability, and lower cost of SOFC stack are required. A coating on a SOFC metallic interconnector is the key technology for the long-term durability of SOFC. In this research, we achieved a significant reduction in resistance and improved durability by improving the highly mass-producible electrodeposition coating method, one of the ceramic coating methods for the SOFC metallic interconnector. Furthermore, the cost of metallic interconnector has been reduced using commodity stainless steel due to its high durability. The SOFC stack of the 2016 model equipped with the electrodeposition coating on the commodity ferritic stainless steel had higher performance and durability than the 2012 model, even if the current density was increased approximately 1.5 times. The electrodeposition coating on commodity ferritic stainless steel has been commercialized and installed in the 2016 and 2020 models of ENE-FARM type S.

For ensuring safety of lithium ion batteries (LIBs), we have extensively investigated the quasi-solid electrolyte where lithium ion conducive liquid is quasi-solidified at silica surfaces as thermally durable electrolyte, and applied it to high capacity and high energy density LIB. For the liquid phase, a solvate ionic liquid, which is an equimolar complex of lithium bis(trifluoromethanesulfonyl)amide (LiTFSA) and tetraethylene glycol dimethyl ether (G4), Li(G4)TFSA, was used. For enhancing discharge capability at a higher rate, Li(G4)TFSA was diluted by low viscos solvent such as propylene carbonate (PC). The developed electrolyte possessed a favorable volatilization temperature higher than 373 K. A 100-Wh-class laminated LIB with energy density of 363 Wh L⁻¹ was fabricated by employing the electrolyte to graphite-LiNi_xCo_yMn_zO₂ chemistry, and it generated neither fire nor smoke in a nail-penetration test. The result suggest that the developed LIB has high safety compared to a LIB comprised of a conventional organic liquid electrolyte. In addition, to enhance the cycle life of the LIB, the formation and growth mechanism of a solid-electrolyte interphase on a graphite-based negative electrode was investigated. Nuclear magnetic resonance and hard x-ray photoelectron spectroscopy revealed that the decompositions of LiTFSA, PC, and G4 contributed to the SEI formation at the initial charge, and that continuous decompositions of G4 and PC were a major reason for the SEI growth during charge-discharge cycles. Based on these analysis, we have substituted a highly concentrated sulfolane based liquid which exhibits a high Li ion conductivity with less amount of the low viscos solvent, for the G4 based liquid. The modification effectively improved the electrochemical durability of the electrolyte, leading to a higher capacity retention after charge-discharge cycle test.

Development of novel metal catalysts with high catalytic activity and selectivity is one of the most crucial research topics in the field of environmental and energy technologies. In general, the development of metal catalysts involves the addition of a second element to the active sites, such as Pt and Pd. Among the various metallic alloys, our focus has been specifically on a class of alloys, known as “intermetallic compounds,” which exhibit long range atomic order. This study aims to review the electrooxidation of formic acid, oxygen reduction reactions using atomically ordered intermetallic compounds such as Pd₃Pb and PdCu₃, high selectivity or catalytic reaction selectivity associated with additive element species, and CO₂ reduction reactions. Furthermore, various factors related to the electrocatalytic oxygen reduction reaction in acidic environments and electrooxidation of formic acid over Pd-based ordered intermetallic compounds have been discussed. The study also examines the photocatalytic activity of intermetallic co-catalysts toward the decomposition of volatile organic compounds using intermetallic co-catalysts. Finally, the electrocatalytic conversion of CO₂ over Sn- and Pd-based electrocatalysts has been discussed. The review and the ensuing discussions are presented in the backdrop of previous studies conducted in this field and is anticipated to provide important insights for the accelerated development of highly active advanced catalysts.

Control of the nanoscale interface leads to efficient electrochemical reactions and unique molecular behaviors. This paper reviews our recent investigations on understanding the unique property of the electrochemical reactions at nanostructured interfaces. We have focused on the control of chemical reactions in the vicinity of metal nanostructures to condense the energy perturbations of electrons, ions, and photons. We have established an electrochemical nanostructure control method to achieve ultimate energy condensation. In addition, we have revealed the unique molecular behaviors induced by the strong interaction between the target molecules and the nanostructured electrode, originating from the hybridization of the electronic states showing collective excitation modes especially under the light illumination. Furthermore, we have attempted to efficiently control the electrochemical reactions and observe the unique reaction selectivity on the nanostructured electrodes. Through these investigations, we have proposed advantages for the control of nanostructured interfaces to overcome the current limitation of electrochemical reactions.

Nonaqueous electrolytes are used in various electrochemical devices as their electrochemical potential window is wider than that of aqueous electrolytes. Electrochemical reactions significantly change depending on the combination of nonaqueous solvent and salt and the dissolved state of the metal ions or redox species in the solvent. Room-temperature ionic liquids (RTILs), a type of nonaqueous solvent, have unique physicochemical properties such as negligible vapor pressure and non-flammability. Their application as reaction media for a variety of reactions, including electrochemical reactions has attracted significant interest, as they enable reactions that cannot proceed in water or organic solvents. We have been researching materials synthesis and energy devices using RTILs and organic electrolytes. Herein, we comprehensively review our research on the electrodeposition of metals, preparation of metal nanoparticles, and secondary batteries using nonaqueous electrolytes.

In this research, organic–inorganic hybrid materials that enable the detection and manipulation of “invisible light” such as weak light, polarized light, and near-infrared (NIR) light are prepared and optoelectronic devices based on these materials are developed. The photoelectric conversion or energy transfer process resulting from light absorption is precisely controlled at the heterointerface of organic–inorganic hybrid structures, which enables the highly efficient amplification, conversion, and detection of invisible light under normal temperatures and pressures. Here, novel optical functions and devices based on organic–inorganic hybrid structures and interfaces are presented. For instance, in a hybrid structure in which organic molecules and inorganic semiconductors are chemically bonded, photocurrent was amplified more than 2000-fold at their heterointerface, resulting in highly sensitive photodetection at a low voltage (<1 V). As a novel device structure for the direct detection of circularly polarized light with high sensitivity, an inorganic crystal thin film with a one-dimensional helical structure was fabricated via interaction with organic chiral molecules. For NIR light, dye-sensitized up-conversion nanoparticles that can convert NIR light as weak as sunlight into visible light with high efficiency were developed and incorporated into a perovskite-based visible-light detector. This device detected light in the NIR region through energy conversion from NIR to visible light. And also, NIR light was promoted as ultra-bright luminescence by one-photon absorption two-photon emission (quantum-cutting) process in heterometal hybridized crystal thin films. The light-emitting diode was fabricated and demonstrated 6 % external conversion efficiency of field emission in the NIR region.

Detection methods for small biological molecules are needed to facilitate analysis of physiological and pathological mechanisms. We aimed to construct a 2-mercaptobenzimidazole modified gold nanoparticle electrode for detection of uremia-related substances, e.g. uric acid (UA) and indoxyl sulfate (IS), excreted via transporters expressed on cultured cells. This electrode detected the current changes in phosphate buffer at different potentials as the concentrations of ascorbic acid, UA, dopamine, and IS were linearly increased in 1 µg/mL increments. Real-time detection of IS excretion via ATP-binding cassette transporter G2 (ABCG2) expression was performed in a transcellular transport model with amperometric measurement. The electrode was highly sensitive to the current changes with IS even in a serum-free culture medium. We observed an increase in current of approximately 0.10 µA per mm² of polycrystalline electrode surface area with each 1 µg/mL increase in IS concentration. The current increased with time when the electrode was exposed to cells transfected with ABCG2 plasmid in tissue culture insert, indicating that IS excretion occurred via the transporter encoded by ABCG2. In conclusion, the electrode could be successfully used for the real-time detection of IS excreted via ABCG2 expressed on cultured cells.

Li–air batteries (LAB) have a theoretical energy density as high as 3500 Wh kg⁻¹; however, many problems remain to be addressed before their practical application. Introduction of a redox mediator (RM) is commonly applied to reduce the high overpotential of the air electrode (AE) during the charge process. We try to fix an RM on the AE by coating it with a slurry of carbon black and binder on a carbon paper substrate to enable us not only to suppress the shuttle effect but also to concentrate the RM on the surface of the AE where it works. We use LiBr as the RM in this study and compare two types of LAB cells: one with a LiBr-coated AE and the other with LiBr dissolved in the electrolyte solution. The cell with the LiBr-coated AE exhibits a better cell performance than that with the dissolved LiBr.

Benzofuro[2,3-c]carbazoloquinol derivatives, a new type of fluorescent dyes, were derived from the corresponding quinone, and their optical and electrochemical properties were investigated by photoabsorption and fluorescence spectroscopy, cyclic voltammetry (CV) and density functional theory (DFT) calculation. The quinol derivatives in 1,4-dioxane showed the photoabsorption band at around 435 nm (molar extinction coefficient (ε_max) = ca. 6000–8000 M⁻¹ cm⁻¹) and the fluorescence band at around 520 nm (fluorescence quantum yield (Φ_fl) = 0.24–0.28). The CV demonstrated that the quinol derivatives exhibit an irreversible oxidation wave at around −0.28 V versus Fc/Fc⁺. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels of the quinol derivatives which were calculated using DFT at the B3LYP/6-31G(d,p) level are in good agreement with the experimental results.

Combining highly concentrated electrolytes with a polymer network is a valid approach to simultaneously achieve fast Li⁺ ion transport, high thermal stability, and a wide electrochemical window in a quasi-solid-state form. In this work, flexible gel electrolytes comprising commercially available poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF–HFP) and highly concentrated electrolytes of Li salts/sulfolane (SL) were prepared by a simple solution casting method. The anionic effects of the gel electrolytes on the Li-ion conductivity and charge transfer kinetics at the gel/electrode interface were investigated. The SL-based gel electrolyte with lithium bis(fluorosulfonyl)amide (LiFSA) showed an ionic conductivity of 0.7 mS cm⁻¹ and a high Li transference number (>0.5) at 30 °C. The charge transfer resistance in a [Li/gel/LiCoO₂] cell with LiFSA was lower than that of the cells with lithium bis(trifluoromethanesulfonyl)amide (LiTFSA) or LiBF₄, indicating faster interfacial charge transfer kinetics in the gel electrolyte with FSA. The Li/LiCoO₂ cell with the LiFSA/SL gel electrolyte exhibited a higher capacity than that of the cells with the LiTFSA/SL and LiBF₄/SL gel electrolytes. Hence, rationally designed gel electrolytes containing highly concentrated SL-based electrolytes enable the high rate performance of Li batteries.

To improve the specific surface area (SSA) of steam activated carbon that has been prepared from spent coffee grounds (SCG), a demineralization of the SCG was conducted. As the ash content of the SCG decreased, fine micropores developed during the activation, leading to a significant increase in the SSA. An electric double layer capacitor was assembled and then evaluated, with the evaluation results indicating that the capacitance per electrode weight, the capacitance retention in relation to the current density, and the internal resistance were superior for activated carbon with a higher SSA. However, the capacitance per electrode volume had a maximum value under certain conditions, which were considered well balanced in terms of the SSA and electrode density.

It is very important to assess cell viability rapidly and sensitively for the cell biology research, medical and pharmaceutical application. Compared to conventional methods, we have established a new rapid and sensitive bio-electrochemical system using small screen-printed carbon electrode (SPCE) and 1-methoxy-5-methylphenazinium methyl sulfate (mPMS)/[Fe(CN)₆]³⁻(FeCN) as double electron mediators for monitoring cell viability through the measurement of intracellular NADH. A combination of 10 µmol L⁻¹ (µM) mPMS and 500 µM FeCN was the optimum concentration and, 10 minutes (min) incubation was enough to monitor intracellular NADH by chronoamperometry at +0.5 V applications. This mPMS/FeCN system works as useful as previously reported menadione (Mena)/FeCN system. We confirmed that the electron transfer from intracellular NADH to mPMS occurred non-enzymatically, though the electron transfer from intracellular NADH to Mena was catalyzed by cytosolic enzyme. We applied our system to count the three kinds of mammalian cells. The oxidation current in chronoamperometry after 10 min incubation showed a good linear relationship in two times wider of cell concentration as compared to the cell concentration detected with water soluble tetrazolium-1 (WST-1) assay. The results indicated that the metabolically active mammalian cells could be quickly quantified by our method. Furthermore, we have applied this method to evaluate the acute cytotoxicity of oxamic acid on cytoma cells. Only 10 min incubation and high sensitivity embellished this method. These results strongly supported that our electrochemical method might be potent to alternate to WST assay for cell viability and acute cytotoxicity test.

The mixing process of electrode-slurry plays an important role in the electrode performance of lithium-ion batteries (LIBs). The dispersion state of conductive materials, such as acetylene black (AB), in the electrode-slurry directly influences the electronic conductivity in the composite electrodes. In this study, the relation between the mixing process of electrode-slurry and the internal resistance of the composite electrode was investigated in combination with the characterization of the electrode-slurries by the rheological analysis and the alternating current (AC) impedance spectroscopy. Some of the electrode-slurries showed higher value and gentler slope of the dynamic storage modulus in the low-angular-frequency region and higher thixotropic index than the others depending on the way of the mixing process and the AB content, agreeing with the low electronic volume resistivities of the corresponding composite electrodes and the electrode-slurries, which indicates the AB network growth. The results suggested that the low-viscosity state when AB and active electrode material are mixed contributes to the dispersive AB network.

The performance of a sodium-ion (Na) battery is significantly influenced by its electrolyte characteristics. In particular, the transport properties of the electrolyte have considerable effects on the discharge rate capability. During discharging of a Na battery at high current densities, a concentration gradient of Na salt develops because both cations and anions are mobile in the liquid electrolyte. Concentration polarization can be suppressed by increasing the Na⁺ transference number (t_Na+) of the electrolyte. This study demonstrates that highly concentrated NaN(SO₂F)₂ dissolved in 3-methylsulfolane (MSL) exhibits a high t_Na+ value of >0.6 under anion-blocking conditions. Raman spectroscopy revealed that Na⁺ ions formed complexes with MSL and anions in the electrolyte. Na⁺ ions exchange ligands dynamically and move faster than the ligands, resulting in a high t_Na+. The high t_Na+ enables a high-rate discharge of the Na battery, despite the low ionic conductivity of the highly concentrated electrolyte.

For oxygen reduction reaction of an air battery which uses oxygen and water as reactants, it is important to control not only gas diffusivity but also hydrophilicity. In this study, the effect of hydrophilicity was investigated quantitatively. Various hydrophilic reaction layers were prepared with different amounts of Nafion as hydrophilic binder. The hydrophilicity was evaluated by measuring water vapor adsorption and nitrogen adsorption isotherms and calculating specific surface area by Brunauer-Emmett-Teller (BET) method. Polarization curves of oxygen reduction reaction revealed that the hydrophilicity effect differs between the reaction rate-determining range and the diffusion rate-determining range. In the reaction rate-determining range, the oxygen reduction current increased in proportion to the amount of water in the reaction layer, indicating the extension of the three-phase interface as the reaction field. In the diffusion rate-determining range, oxygen reduction current decreased with increasing the hydrophilicity, which demonstrates that high hydrophilicity suppressed oxygen diffusion.

In this work, cobalt electroplating from homogeneous oxidation of cobalt powder via iodine as a chemical oxidizing agent and from CoCl₂·6H₂O in choline chloride-ethylene glycol electrolytic bath was carried out at 90 °C. As relatively high temperature and corrosion resistive coating material, cobalt electroplating was performed. A number of electrochemical, spectroscopic and microscopic techniques, such as, cyclic voltammetry (CV), chronocoulometry, UV-visible spectroscopy and scanning electron microscopy (SEM) were used in fabrication and characterizations of the electroplated cobalt. The progressive nucleation mechanism is followed in case of cobalt electroplating using cobalt powder in the presence of iodine. The mirror-like surface (i.e., smooth surface) surface has been obtained when cobalt powder utilized with the aid of iodine as shown in the SEM images. The effectiveness of the existence of iodine and cobalt powder was evidenced from chronocoulometry in which huge number of charge was released during the electrochemical course.

The interplanetary spacecraft HAYABUSA returned to Earth on June 13, 2010, and a capsule containing an asteroid sample was released. The capsule deployed a parachute and transmitted a beacon signal indicating its position. The ground facilities successfully detected the beacon and determined the landing position of the capsule. For these actions, electricity was supplied by Li-CF_x cells installed in the electric unit of the capsule. These cells had to work after storage for 12 years, including 7 years of space flight. To confirm the performance of the flight cells, we prepared thermally degraded cells and tested their performance. We also discharged cells from the same lot as the flight cells. On the basis of the results, we expected proper performance of the cells up to landing of the capsule. These results were further compared with the discharge capability of the flight cells installed in the HAYABUSA capsule. Comparison of all these data enabled a reliable prediction of the performance of the Li-CF_x cells after an extended storage period, including a period in which the cells were subjected to space-flight conditions.