Details of a Researcher - Einaga, Yasuaki

Papers - Einaga, Yasuaki

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Metal modified carbon-based electrode for CO<inf>2</inf> electrochemical reduction: A review

Jiwanti P.K., Sultana S., Wicaksono W.P., Einaga Y.

Journal of Electroanalytical Chemistry (Journal of Electroanalytical Chemistry) 898 2021.10

ISSN 15726657

The carbon-based electrode has been widely used for electrochemical analysis and synthesis. It is relatively inert for hydrogen evolution in the negative potential range, which is suitable for CO2 electrochemical reduction. In improving the catalytic activity, a modification of metal particles is commonly used on its surface. Various metal particles have been reported with multiple modification methods, including electrochemical and physical methods. In this report, the utilization of different metal particles, including metal oxide, metal hydroxide, and metal complexes, which are modified on carbon-based electrodes for CO2 electrochemical reduction application is specifically reviewed. This review is expected to provide comprehensive information on related topics.

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Effect of Boron-Doping Level and Surface Termination in Diamond on Electrogenerated Chemiluminescence

Sakanoue K., Fiorani A., Irkham , Einaga Y.

ACS Applied Electronic Materials (ACS Applied Electronic Materials) 3 ( 9 ) 4180 - 4188 2021.09

Electrogenerated chemiluminescence (ECL) is a phenomenon of light emission from a molecular species that is triggered by an electrochemical reaction. As with many electrochemical systems, ECL is highly dependent on the electrode material and its surface state. Boron-doped diamond (BDD) has been applied for ECL, however, thoughtful investigation remains scarce. In particular, a peculiar feature of BDD is the tuning of its properties by changing the amount of boron doping which in turn affects the electrochemical response. Here, we summarize the results from the most important ECL systems, such as Ru(bpy)32+(bpy = 2,2′-bipyridine)/tri-n-propylamine (TPrA), Ru(bpy)32+/S2O82-, Ru(bpy)32+/SO42-, Ru(bpy)32+/CO32-, and the luminol/CO32-system, by using BDD and correlating the doping level to the ECL response. We showed that the most suitable boron doping level and surface state are highly dependent on the ECL system investigated, highlighting the importance of the right choice of the BDD electrode. While focused on ECL systems, these results offer a general interpretation and might be adapted to different electrochemical systems where BDD finds application.

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Unique properties of fine bubbles in the electrochemical reduction of carbon dioxide using boron-doped diamond electrodes

Tomisaki M., Natsui K., Fujioka S., Terasaka K., Einaga Y.

Electrochimica Acta (Electrochimica Acta) 389 2021.09

ISSN 00134686

The electrochemical CO2 reduction on boron-doped diamond (BDD) electrodes in an aqueous solution with fine bubbles was studied. The overpotential decreased and the production of carbon monoxide was promoted in the CO2 reduction with fine bubbles compared to that without fine bubbles. It is suggested that fine bubbles in solution could facilitate the mass transport and also act as the catalyst for producing carbon monoxide. Potential-dependent in-situ attenuated total reflectance-infrared (ATR-IR) measurements confirmed the catalytic activity, showing that in solutions with CO2 fine bubbles the CO2•– intermediate or the CO2 molecules themselves become stabilized near the electrode and these can be adsorbed on the electrode surface more easily compared to using solutions without CO2 fine bubbles. The reported work is a first step in understanding the effects of fine bubbles in CO2 reduction reactions.

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Boron position-dependent surface reconstruction and electronic states of boron-doped diamond(111) surfaces: An: ab initio study

The Anh L., Catalan F.C.I., Kim Y., Einaga Y., Tateyama Y.

Physical Chemistry Chemical Physics (Physical Chemistry Chemical Physics) 23 ( 29 ) 15628 - 15634 2021.08

ISSN 14639076

Boron-doped diamond (BDD) has attracted much attention in semi-/superconductor physics and electrochemistry, where the surface structures and electronic states play crucial roles. Herein, we systematically examine the structural and electronic properties of the unterminated and H-terminated diamond(111) surfaces by using density functional theory calculations, and the effect of the boron position on them. The surface energy increases compared to that of the undoped case when the boron is located at a deeper position in the diamond bulk, which indicates that boron near the surface can facilitate the surface stability of the BDD in addition to the H-termination. Moreover, the surface energy and projected density of state analyses suggest that the boron can enhance the graphitization of the pristine (ideal) unterminated (111) surface thanks to the alternative sp2-sp3 arrangement on that surface. Finally, we found that surface electronic states depend on the boron's position, i.e., the Fermi energy (EF) is located around the mid-gap position when the boron lies near the surface, instead of showing a p-type semiconductor behavior where the EF lies closer to the valence band maximum. This journal is

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An efficient, formic acid selective CO<inf>2</inf>electrolyzer with a boron-doped diamond cathode

Du J., Fiorani A., Einaga Y.

Sustainable Energy and Fuels (Sustainable Energy and Fuels) 5 ( 10 ) 2590 - 2594 2021.05

We fabricated a CO2 electrolyzer in order to investigate the energy requirements and the electrical-to-chemical energy conversion efficiency obtained when using boron-doped diamond as the cathode. The main product in the electrochemical reduction of CO2 using a boron-doped diamond electrode is formic acid, with a faradaic efficiency of 96%. The electrical-to-chemical energy conversion efficiency was investigated at various bias voltages, and it reached 43%, very close to the predicted maximum value, at a cell voltage of 3 V. If the secondary products, hydrogen and carbon monoxide, are also considered, the total electrical-to-chemical energy conversion efficiency was as much as 45%. This journal is

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Modification of boron-doped diamond electrodes with gold-palladium nanoparticles for an oxygen sensor

Ivandini T.A., Luhur M.S.P., Khalil M., Einaga Y.

Analyst (Analyst) 146 ( 9 ) 2842 - 2850 2021.05

ISSN 00032654

Modification of boron-doped diamond (BDD) with gold-palladium nanoparticles (Au@PdNPs) was successfully performed. Prior to the modification, BDD was modified with allylamine to provide active sites for the attachment of nanoparticles, while the synthesis of Au@PdNPs was performed by chemical reduction of a palladium salt solution in a colloidal solution of gold nanoparticles. Characterization using TEM images showed that by controlling the palladium concentration, flower and core-shell shaped Au@PdNPs can be prepared. XPS studies confirmed that the nanoparticles with a flower shape could be attached better on the BDD surface. The Au@PdNPs-modified BDD (Au@PdNPs-BDD) electrodes were then examined for the oxygen reduction reaction in comparison with gold and palladium-based electrodes. One order higher current response was observed at Au@PdNPs-BDD compared to AuNPs-BDD, indicating the contribution of palladium in the oxygen reduction reaction. Good linearity with comparable limits of detection suggested that Au@PdNPs-BDD electrodes are promising for use as oxygen sensors. Furthermore, their application as BOD sensors was demonstrated.

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Analysis of Pharmacokinetics in the Cochlea of the Inner Ear

Sawamura S., Ogata G., Asai K., Razvina O., Ota T., Zhang Q., Madhurantakam S., Akiyama K., Ino D., Kanzaki S., Saiki T., Matsumoto Y., Moriyama M., Saijo Y., Horii A., Einaga Y., Hibino H.

Frontiers in Pharmacology (Frontiers in Pharmacology) 12 2021.05

Hearing loss affects >5% of the global population and therefore, has a great social and clinical impact. Sensorineural hearing loss, which can be caused by different factors, such as acoustic trauma, aging, and administration of certain classes of drugs, stems primarily from a dysfunction of the cochlea in the inner ear. Few therapeutic strategies against sensorineural hearing loss are available. To develop effective treatments for this disease, it is crucial to precisely determine the behavior of ototoxic and therapeutic agents in the microenvironment of the cochlea in live animals. Since the 1980s, a number of studies have addressed this issue by different methodologies. However, there is much less information on pharmacokinetics in the cochlea than that in other organs; the delay in ontological pharmacology is likely due to technical difficulties with accessing the cochlea, a tiny organ that is encased with a bony wall and has a fine and complicated internal structure. In this review, we not only summarize the observations and insights obtained in classic and recent studies on pharmacokinetics in the cochlea but also describe relevant analytical techniques, with their strengths, limitations, and prospects.

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Enhancing the Electrochemical Reduction of CO<inf>2</inf>by Controlling the Flow Conditions: An Intermittent Flow Reduction System with a Boron-Doped Diamond Electrode

Irkham , Nagashima S., Tomisaki M., Einaga Y.

ACS Sustainable Chemistry and Engineering (ACS Sustainable Chemistry and Engineering) 9 ( 15 ) 5298 - 5303 2021.04

Electrochemical CO2 reduction using an intermittent flow cell system with boron-doped diamond (BDD) as the working electrode is presented. A stop-start motion of the flow conditions in the intermittent cell is created using a piston pump, and this considerably increases the rate of electrochemical conversion of CO2 to HCOOH compared to a continuous flow system. The system works by stopping the flow of the electrolytes at a controlled frequency, which allows for sufficient time for more CO2 anion radicals (intermediate species) to be reduced into HCOOH instead of being washed away from the surface of the electrode. The findings presented here provide an important basis from which the design of CO2 reduction systems for industrial-scale applications can be started.

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Fabrication and electrochemical properties of boron-doped SiC

Uchiyama K., Yamamoto T., Einaga Y.

Carbon (Carbon) 174 240 - 247 2021.04

ISSN 00086223

Silicon carbide (SiC) has excellent properties such as chemical and physical stability, biocompatibility, and high thermal conductivity. However, electrical conductivity of SiC is not high enough for electrochemical applications, which has been a major challenge. Here, in order to improve the conductivity, we prepared boron-doped SiC (SiC:B) and evaluated the electrochemical properties. SiC and SiC:B were fabricated by a microwave plasma chemical vapor deposition method. Structural characterization revealed that the main phase of SiC:B is 3C–SiC where the concentration of doped boron could be controlled by tuning the growth conditions. Electrochemical properties were evaluated by cyclic voltammetry measurements, indicating that the reactivity and sensitivity of the SiC:B electrode was comparable of that of the glassy carbon electrode.

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Annealing enhancement in stability and performance of copper modified boron-doped diamond (Cu-BDD) electrode for electrochemical nitrate reduction

Kuang P., Natsui K., Einaga Y., Feng C., Cui Y., Zhang W., Deng Y.

Diamond and Related Materials (Diamond and Related Materials) 114 2021.04

ISSN 09259635

Nitrate contamination in groundwater requires efficient remediation to prevent adverse environmental impacts. This study illustrates the improvement in nitrate reduction process using copper modified BDD (Cu-BDD) with higher stability after annealing treatment. The highest values for nitrate reduction and the selectivity of nitrogen gas were about 71% and 45%, respectively, which were obtained using annealed Cu-BDD electrode. Annealing process promoted the homogeneity of copper oxides that consolidated the electrodeposited copper oxides on the surface of Cu-BDD to enhance the stability of electrode. Meanwhile, annealed Cu-BDD exhibited higher conductivity to facilitate nitrate reduction initiating at a more positive potential. Furthermore, cuprous ions and metallic Cu were formed during the annealing treatment, and had active chemical reaction with nitrate and excellent catalytic capability for the reaction, which efficiently enhanced either the nitrate reduction efficiency or the selectivity of nitrogen gas. The findings advance the current understanding on the enhancement of electrochemical stability and nitrate reduction performance using Cu-BDD after the annealing treatment, and also offer a promising technology for remediation of nitrate-contaminated groundwater.

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Nickel hydroxide nanoparticles for application in immunochromatographic strip tests of melamine

Saepudin E., Yuliani T., Musyarofah N.R.R., Nasution M.A.F., Gunlazuardi J., Einaga Y., Ivandini T.A.

Sensors and Materials (Sensors and Materials) 33 ( 3-2 ) 1027 - 1036 2021.03

ISSN 09144935

Nickel hydroxide nanoparticles [Ni(OH)2-NPs] synthesized by a complexation-precipitation method under hydrothermal conditions were employed as a probe in immunochromatographic strip tests for the selective detection of melamine. The characterization of Ni(OH) -NPs and their conjugation to anti-melamine antibody (anti-MEL) were performed using a UV- visible spectrophotometer, Fourier transform infrared (FTIR) spectroscopy, and TEM. On the basis of the green line intensity, the strip test can selectively detect melamine at a minimum concentration of 25 ppm. Our results suggest that this system is promising for the quantitative detection of melamine. 2

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Nanodiamonds Inhibit Cancer Cell Migration by Strengthening Cell Adhesion: Implications for Cancer Treatment

Guo Q., Li L., Gao G., Liu R., Einaga Y., Zhi J.

ACS Applied Materials and Interfaces (ACS Applied Materials and Interfaces) 13 ( 8 ) 9620 - 9629 2021.03

ISSN 19448244

Nanodiamonds (NDs) are a type of biocompatible nanomaterial with easily modified surfaces and are considered as promising candidates in biomedicine. In this work, the inhibition of tumor cell migration by carboxylated nanodiamonds (cNDs) was investigated. AFM-based single cell adhesion and F-actin staining experiments demonstrated that cNDs treatment could enhance cell adhesion and impair assembly of the cytoskeleton. The mechanism analysis of the regulatory protein expression level also proved that cNDs could inhibit the migration of Hela cells by preventing the epithelial-mesenchymal transition (EMT) process through the transforming growth factor β (TGF-β) signaling pathway. The in vivo pulmonary metastasis model also showed that cNDs effectively reduced the metastasis of murine B16 melanoma cells. In summary, cNDs have been demonstrated to inhibit cancer cell migration in vitro and decrease tumor metastasis in vivo. Therefore, cNDs might have potential utility for specific cancer treatment.

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Electrogenerated Chemiluminescence of Luminol Mediated by Carbonate Electrochemical Oxidation at a Boron-Doped Diamond

Irkham , Rais R.R., Ivandini T.A., Fiorani A., Einaga Y.

Analytical Chemistry (Analytical Chemistry) 93 ( 4 ) 2336 - 2341 2021.02

ISSN 00032700

The electrogenerated chemiluminescence of luminol is a process by which light generation is triggered by adding hydrogen peroxide and then applying a suitable electrode potential. Here, we take this phenomenon one step forward by avoiding the addition of hydrogen peroxide using a smart combination of a boron-doped diamond electrode and a carbonate electrolyte to generate the hydrogen peroxide directly in situ. The reaction occurs because of the carbonate electrochemical oxidation to peroxydicarbonate and the following hydrolysis to hydrogen peroxide, which triggers the emission from luminol. The electrogenerated chemiluminescence emission has been optimized by an investigation of the applied potentials, the carbonate concentration, and the pH. Furthermore, these results have been used to shine a light on the reaction mechanisms. Because this method does not require the addition of hydrogen peroxide, it might find application in efforts to avoid instability of hydrogen peroxide or its interference with the analytes of interest.

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Recent progress in direct urea fuel cell

Putri Y.M.T.A., Gunlazuardi J., Yulizar Y., Wibowo R., Einaga Y., Ivandini T.A.

Open Chemistry (Open Chemistry) 19 ( 1 ) 1116 - 1133 2021.01

Direct urea fuel cell (DUFC) has attracted many researchers' attention due to the use of wastewater, for example urine, which contains urea for the fuel. The main factor to improve the electrochemical oxidation performance of urea and further enhance the performances of DUFC is the use of a good anode catalyst. Non-noble metal catalyst, such as nickel, is reported to have a good catalytic activity in alkaline medium towards urea electro-oxidation. Besides optimizing the anode catalyst, the use of supporting electrode which has a large surface area as well as the use of H2O2 as an oxidant to replace O2 could help to improve the performances. The recent progress in anode catalysts for DUFC is overviewed in this article. In addition, the advantages and disadvantages as well as the factors that could help to escalate the performance of DUFC are discussed together with the challenges and future perspectives.

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In situ infrared spectroscopy of dopamine oxidation/reduction reactions on a polycrystalline boron-doped diamond electrode

Hosoda R., Kamoshida N., Hoshi N., Einaga Y., Nakamura M.

Carbon (Carbon) 171 814 - 818 2021.01

ISSN 00086223

The oxidation of dopamine (DA) on a boron-doped diamond (BDD) electrode was investigated using in situ attenuated total reflection infrared spectroscopy (ATR-IR) and infrared reflection absorption spectroscopy (IRAS). Voltammogram showed multiple anodic/cathodic peaks for the oxidation/reduction of DA and its oxidized derivatives on the BDD electrode. The oxidation/reduction species on the surface and in solution were assigned using ATR-IR and IRAS, respectively. The anodic oxidation of DA promoted polymerization, and the polymerized DA (PDA) was continuously deposited on BDD without being reduced by potential cycles, which resulted in the irreversible behavior of the voltammogram. A decrease in the oxidation current of DA by potential cycles was due to the deposition of PDA. Some intermediate quinone species, such as dopaminequinone and dopaminechrome, were reversibly reduced to hydroquinone.

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Nanoscale Reactivity Mapping of a Single-Crystal Boron-Doped Diamond Particle

Ando T., Asai K., MacPherson J., Einaga Y., Fukuma T., Takahashi Y.

Analytical Chemistry (Analytical Chemistry) 93 ( 14 ) 5831 - 5838 2021

ISSN 00032700

Boron-doped diamond (BDD) is most often grown by chemical vapor deposition (CVD) in polycrystalline form, where the electrochemical response is averaged over the whole surface. Deconvoluting the impact of crystal orientation, surface termination, and boron-doped concentration on the electrochemical response is extremely challenging. To tackle this problem, we use CVD to grow isolated single-crystal microparticles of BDD with the crystal facets (100, square-shaped) and (111, triangle-shaped) exposed and combine with hopping mode scanning electrochemical cell microscopy (HM-SECCM) for electrochemical interrogation of the individual crystal faces (planar and nonplanar). Measurements are made on both hydrogen- (H-) and oxygen (O-)-terminated single-crystal facets with two different redox mediators, [Ru(NH3)6]3+/2+ and Fe(CN)64-/3-. Extraction of the half-wave potential from linear sweep and cyclic voltammetric experiments at all measurement (pixel) points shows unequivocally that electron transfer is faster at the H-terminated (111) surface than at the H-terminated (100) face, attributed to boron dopant differences. The most dramatic differences were seen for [Ru(NH3)6]3+/2+ when comparing the O-terminated (100) surface to the H-terminated (100) face. Removal of the H-surface conductivity layer and a potential-dependent density of states were thought to be responsible for the behavior observed. Finally, a bimodal distribution in the electrochemical activity on the as-grown H-terminated polycrystalline BDD electrode is attributed to the dominance of differently doped (100) and (111) facets in the material.

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Anodic Oxidation of Phenols: A Key Step for the Synthesis of Natural Products

Yamamoto T., Saitoh T., Einaga Y., Nishiyama S.

Chemical Record (Chemical Record) 21 ( 9 ) 2254 - 2268 2021

ISSN 15278999

Natural products have played a significant role not only in discovery of drugs but also in development of organic chemistry by providing the synthetic challenges. Inspired by biosynthesis where enzymes catalyze a multi-step reaction, we have investigated the natural product synthesis utilizing electrochemical reactions as the key step. Electrochemical organic synthesis, so-called electro-organic synthesis, enables to control the reactivity of substrates simply by tuning electrolysis conditions. In this Personal Account, we overview the recent progress of our research projects about natural product synthesis, in which anodic oxidation of phenol compounds affords the important frameworks such as diaryl ether, spirodienone, and spiroisoxazoline.

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Electrochemical Sensing Applications Using Diamond Microelectrodes

Ivandini T.A., Einaga Y.

Bulletin of the Chemical Society of Japan (Bulletin of the Chemical Society of Japan) 94 ( 12 ) 2838 - 2847 2021

ISSN 00092673

The miniaturization of boron-doped diamond (BDD) electrodes is an important requirement for application to the study of electrochemical processes in living beings. In this work, we describe the fabrication and characterization of BDD electrodes with micrometer dimensions, with a particular emphasis on micro needle electrodes. As a result of the combination of the microelectrode size effect and the intrinsic properties of the diamond films, these electrodes showed not only a significantly lower background current than diamond macroelectrodes, but also an ability for use in analytical sensing in low conductive media. Accordingly, a wider range of experiments including in vivo measurements could be performed.

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Micro-band Boron-doped Diamond Electrode in Capillary Electrophoresis for Simultaneous Detection of AMP, ADP, and ATP

Prayikaputri P.U., Jiwanti P.K., Nasution M.A.F., Gunlazuardi J., Saepudin E., Einaga Y., Ivandini T.A.

International Journal of Technology (International Journal of Technology) 12 ( 2 ) 252 - 262 2021

ISSN 20869614

A micro-band boron-doped diamond (BDD) electrode was prepared by sealing a piece of BDD film with an area of 1.11×10-7 m2 between two insulating plates, one Teflon and one silicon rubber, to form sandwich-like layers, so the surface area could be investigated. The micro-band BDD was combined with capillary zone electrophoresis as an electrode for the simultaneous detection of adenosine monophosphate (AMP), adenosine diphosphate (ADP), and adenosine triphosphate (ATP) in a solution. These adenosine phosphates can be separated with a 0.3 m-long fused silica capillary using Britton–Robinson buffers at pH 2.0. Current in the concentration range of 0.1 to 2.0 mM were linear with the limits of detection of 0.004 μM, 0.006 μM, and 0.011 μM for AMP, ADP, and ATP, respectively. A comparison with an unmodified BDD as the detector in the same electrophoresis system showed that the micro-band generated better limits of detection (LODs) than the macroelectrode. This method was successfully applied to human urine samples injected with three adenosine phosphates, as well as adenine and guanine, which can be well-separated with recovery percentages of adenine, guanine, AMP, ADP, and ATP of 99.2%, 102.5%, 107.4%, 107.7%, and 105.4%, respectively.

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Electrogenerated Chemiluminescence for Immunoassay Applications

Rahmawati I., Irkham I., Wibowo R., Gunlazuardi J., Einaga Y., Ivandini T.A.

Indonesian Journal of Chemistry (Indonesian Journal of Chemistry) 21 ( 6 ) 1599 - 1618 2021

ISSN 14119420

Electrogenerated chemiluminescence (ECL) has recently become one of the most prominent and well-established transducers for immunoassay techniques. ECL relates a luminophore concentration in solution with the emission of light triggered by an electrochemical stimulus. ECL immunoassay (ECLIA) performance depends on the parameters of its light generation, including the luminophore, the species that emit light called labels in ECLIA; co-reactants, which are added reagents that support the luminophore to undergo the excited state; electrodes, which are the place for the ECL reactions to take place; and the format of the immunoassay. This review discusses the behaviour of ECLIA parameters, the required instrumentations, and some important examples of detections based on ECLIA.

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