In the electrochemical surface science during the past 20 years, in-situ electrochemical scanning tunneling microscopy (EC-STM) and atomic force microscopy (AFM) have made significant contribution to understand various electrochemical processes with atomic scale. For examples, the underpotential deposition of copper, silver, and other metal ions; the specific adsorption of anions such as iodine and sulfate/bisulfate ions; electrochemical etching processes of metals and semiconductors and the molecular assembly of many organic molecules, such as metalloporphyrins, and metallophthalocyanines. Furthermore, we have recently developed a high resolution laser confocal microscope, combined with a differential interference contrast microscope, which enables to follows fast dynamic electrochemical processes at atomic height resolution in relatively large areas. It has been shown for the first time that single atomic steps of metals can be successfully seen by the newly developed optical microscope. Surface imaging techniques provide local pictures of electrode processes on the atomic scale, not averaged information in large areas.
Electrochemical approaches for the fabrication of functional micro–nano structures and devices were comprehensively described primarily on the basis of the results obtained from previous studies conducted by the author’s group with the aim of demonstrating the potential for achieving further precise controllability. First, a theoretical study was conducted for investigating the processes, mainly focusing upon electroless deposition to present an approach for analyzing its reaction mechanism from the molecular level. These approaches could be powerful tools for elucidating the overall process and could contribute toward achieving the precise design of processes. Second, some experimental approaches for achieving the precise control of micro–nano fabrication of functional structures, such as maskless and electroless fabrication of metal nano-patterns, lateral enhanced electrodeposition to form ultrathin layers, as well as the nanostructures for various devices by through-mask electrochemical deposition, were introduced to demonstrate high capability of the processes for nanoscale fabrication in various applications.
Here, we present an overview of our recent research progress in development of electrochemical devices/systems for bioassays. These devices/systems are based on microchemistry and micro-electromechanical systems (MEMS) for sophisticated analytical and electrochemical measurements. In particular, we exploit the unique chemical reactions occurring in micrometer-size spaces and/or involving micrometer-size structures for bioassays, including cell analyses. This paper addresses five topics: probe-, chip-, large-scale-integration chip-, and dielectrophoresis-based devices, and electrodeposition of hydrogels for bioassays.
To improve the performance of electrochemical devices such as batteries and fuel cells, it is essential to understand reaction hierarchies over wide temporal and spatial ranges. To this end, operando measurement techniques have been developed that enable analysis of the electrode/electrolyte interface of the reaction site, phase transitions of active materials, and macro reactions within real electrodes over various spatial and temporal scales. These analytic techniques pioneer a new way of performing kinetic analysis by introducing axes of space and time into reaction analyses, and are applicable to various types of electrochemical devices. Moreover, a magnesium rechargeable battery featuring the merits of high theoretical energy density, high safety, and easily acquirable raw materials was developed by employing these operando analytic techniques.
Gaining a thorough understanding of the electrochemical interface in lithium ion batteries is essential for the development of a common strategy for the material design. This comprehensive paper presents the interfacial reaction analyses between intercalation electrodes and organic electrolytes using an epitaxial-film model electrode and in situ surface scattering techniques. The crystal structures of the intercalation electrodes drastically change in 10 nm-regions from the top of the electrode surface when soaked to the electrolyte and are reconstructed during the initial electrochemical reaction, which is accompanied with formation of a solid electrolyte interface layer. The reconstructed interfaces have a pronounced effect on the power characteristics and the stability at the subsequent electrochemical cycles.
Ionic liquids are of interest for application in electrolytes of lithium-ion batteries, because of their non-flammability, thermal stability, and non-volatility. Electrolytes containing ionic liquids have therefore been used to improve the safety of lithium-ion cells. Both the liquid electrolyte and the gelled electrolyte, which was composed of 1-ethyl-3-methyl-imidazolium tetrafluoroborate and LiBF4, were shown to have good thermal and electrochemical stability and to be applicable for use in lithium-ion cells with Li[Li1/3Ti5/3]O4 as the negative electrode active material. Electrolytes containing a mixture of organic solvents and N-methyl-N-propylpiperidinium bis (trifluoromethane-sulfonyl) imide were also found to exhibit good discharge performance for use in lithium-ion cells and non-flammability for use as an electrolyte. Furthermore, it was found that graphite was able to perform in the electrolyte containing the ionic liquid.
In this study, baddeleyite-structure NbON was investigated as new photocatalysts for solar hydrogen production devices. We deposited pure 90-nm-thick NbON films on quartz substrates under a fixed O2 and N2 ambient mixture by RF reactive sputtering. The NbON films showed semiconductive characteristics and a narrower band gap than that of TaON. The band gap of NbON was estimated to be 2.1 eV. We confirmed that the NbON film was very dense without distinct cracks and had an approximately stoichiometric and uniform composition. We prepared an NbON photoelectrode on a conducting substrate and clearly observed the photocurrent by 436-nm monochromatic light. NbON has potential as a photocatalyst for direct water splitting.
Electrochemical assembly of ZnO nanostructures in reverse micelle through the modification and influence of the soft template have been successfully performed. It has been found that the morphologies of ZnO are greatly influence by the added Li+ or K+ rather than current density. The reason is that alkali metal ions will accumulate at the interface of the cathode/solution and influence the flexibility of soft template. As can be seen, only random sheet can be obtained without alkali metal ions while different ZnO nanostructures can be obtained after the addition of alkali metal ions (Li+ or K+). After the addition of Li+, a diverse variety of nanostructures are obtained. This can be due to the existence of Li+ ions which makes the soft template more flexible and the ions easier to get through. Then higher nucleation rate is gained for the easier accumulation of ions which contributes to larger polarization over-potential. With the addition of K+, flower-like nanostructures are obtained.
Efficient generation of oxygen radicals and reactive oxygen was successfully performed at the dispersed-phasic interface between vapor-water and oxygen plasma in a reaction chamber having an internal atmosphere with a normal-pressure and temperature. In the space of the reactor chamber (radical vapor reactor [RVR]), the gas phase was strictly controlled in terms of vaporized water (small water mist), temperature, plasma conditions, and UV irradiation. According to spin-trapping electron spin resonance analysis, the RVR efficiently and quantitatively yielded two types of reactive oxygen species (1O2 and OH radical) with the atmosphere of the RVR chamber. This is the report of the efficient, quantitative production of reactive oxygen in an atmosphere. The reactivity of the produced 1O2 and OH radical may be applicable for various chemical processes, such as oxidation and electron absorption.
In this paper, we determined dopamine using screen-printed carbon electrodes (SPCEs) which was activated by 0.1 mol L−1 NaOH solution deposited on the electrode to improve the capabilities of detection. Cyclic voltammetry and differential pulse voltammetry were used to investigate the electrochemical behavior of dopamine. Cyclic voltammetry studies indicated that electrochemical oxidation of dopamine at the surface of SPCEs was decided by pH value. Different pulse voltammetry for dopamine oxidation at the SPCEs yielded a well-defined oxidation peak at 0.2 V in 0.1 mol L−1 phosphate buffer (pH 5.0). The proposed electrodes showed good selectivity for dopamine and a good linear relationship between dopamine concentration and oxidation current was obtained within the range of 2.0 × 10−7 mol L−1–300.0 × 10−6 mol L−1 with a detection limit of 6.7 × 10−8 mol L−1 (S/N = 3). In addition, the results showed that the precision in terms of reproducibility was 2.8% in the case of the activated SPCEs. The recovery rates of this technology were 95.40 to 103.4% with a relative standard deviation (RSD) was 2.7%–4.6%, indicating that this method can completely be used for detecting the practical dopamine injection sample.
As a part of studies for finding metal complexes as an active material in the redox-flow battery system using ionic liquids (ILs) as an electrolyte, we have measured cyclic voltammograms (CVs) of betainium bis(trifluoromethylsulfonyl)imide ([Hbet][Tf2N]) (H2O content: 11 wt%) dissolving Na[FeIII(edta)(H2O)] (edta = ethylenediamine-N,N,N′,N′-tetraacetate). Two peaks corresponding to one redox couple were observed around 50 and 220 mV vs. Ag/AgCl and assigned as a quasi-reversible redox reaction based on electrochemical data. Furthermore, the CVs were found to be cycled stably. From these results, the Na[FeIII(edta)(H2O)] is expected to be used as anode active material for the redox-flow batteries using [Hbet][Tf2N] containing 11 wt% H2O as the electrolyte.