Details of a Researcher - Einaga, Yasuaki

Papers - Einaga, Yasuaki

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Diamond Electrodes for Electrogenerated Chemiluminescence

Fiorani A., Irkham1 , Valenti G., Einaga Y., Paolucci F.

Nanocarbon Electrochemistry (Nanocarbon Electrochemistry) 285 - 321 2019.11

ISSN 9781119468233

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Electrochemical oxidation of palmitic acid solution using boron-doped diamond electrodes

Muharam S., Jiwanti P., Irkham, Gunlazuardi J., Einaga Y., Ivandini T.

Diamond and Related Materials (Diamond and Related Materials) 99 2019.11

ISSN 09259635

© 2019 Elsevier B.V. Palmitic acid, a model compound for palm oil mill effluent (POME), was eliminated from a water–ethanol solution using electrochemical oxidation with a boron-doped diamond (BDD) electrode. For a palmitic acid solution in a water–ethanol solution, chronoamperometry with a potential of +3.0 V (vs Ag/AgCl) showed a decrease in chemical oxygen demand (COD) of ~85.75% in 4 h, whereas at a higher potential (+10.0 V), the COD decreased to 75.76% in 1 h. It was noticed that the use of high potentials for up to 4 h caused the structure damaged of the BDD.

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Observation of Proton Transfer Coupled Spin Transition and Trapping of Photoinduced Metastable Proton Transfer State in an Fe(II) Complex

Nakanishi T., Hori Y., Sato H., Wu S., Okazawa A., Kojima N., Yamamoto T., Einaga Y., Hayami S., Horie Y., Okajima H., Sakamoto A., Shiota Y., Yoshizawa K., Sato O.

Journal of the American Chemical Society (Journal of the American Chemical Society) 141 ( 36 ) 14384 - 14393 2019.09

ISSN 00027863

Copyright © 2019 American Chemical Society. An important technique to realize novel electron- A nd/or proton-based functionalities is to use a proton-electron coupling mechanism. When either a proton or electron is excited, the other one is modulated, producing synergistic functions. However, although compounds with proton-coupled electron transfer have been synthesized, crystalline molecular compounds that exhibit proton-transfer-coupled spin-transition (PCST) behavior have not been reported. Here, we report the first example of a PCST Fe(II) complex, wherein the proton lies on the N of hydrazone and pyridine moieties in the ligand at high-spin and low-spin Fe(II), respectively. When the Fe(II) complex is irradiated with light, intramolecular proton transfer occurs from pyridine to hydrazone in conjunction with the photoinduced spin transition via the PCST mechanism. Because the light-induced excited high-spin state is trapped at low temperatures in the Fe(II) complex- A phenomenon known as the light-induced excited-spin-state trapping effect-the light-induced proton-transfer state, wherein the proton lies on the N of hydrazone, is also trapped as a metastable state. The proton transfer was accomplished within 50 ps at 190 K. The bistable nature of the proton position, where the position can be switched by light irradiation, is useful for modulating proton-based functionalities in molecular devices.

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Oxidation of hydroxide ions in weak basic solutions using boron-doped diamond electrodes: Effect of the buffer capacity

Irkham , Einaga Y.

Analyst (Analyst) 144 ( 15 ) 4499 - 4504 2019.08

ISSN 00032654

© 2019 The Royal Society of Chemistry. The electrochemical oxidation of hydroxide ions using boron-doped diamond (BDD) electrodes in weak basic solutions was examined. Using simple linear sweep voltammetry (LSV), a well-shaped peak originating from the oxidation of hydroxide ions involving a CE mechanism was observed at ∼1.30 V versus a Ag/AgCl reference electrode in 20 mM H3PO4 solutions with hydroxide ion concentrations ranging from 0.1 to 10 mM. Compared to a NaOH solution with the same hydroxide ion concentration, the peak current in the phosphate solution was found to be higher due to the buffering capability of the phosphate solution, which maintains the hydroxide ion concentration, making it possible to provide more hydroxide ions to the surface of the electrode. The peak was found to depend not only on the hydroxide ion concentration, but also on the phosphate concentration, confirming that the origin of the peak was due to oxidation of the hydroxide ions enhanced by the buffering capability of the weak basic solution. These results further promote the use of BDD electrodes for measuring hydroxide ion concentration, and offer the possibility of directly measuring the buffer capacity of a solution.

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Electrochemical mineralization of dimethyl sulfoxide on boron-doped diamond electrodes

Natsui K., Hosomi T., Ikemiya N., Einaga Y.

Environmental Technology and Innovation (Environmental Technology and Innovation) 15 2019.08

© 2019 Elsevier B.V. Dimethyl sulfoxide (DMSO) is an excellent organic solvent, and widely used in laboratories and industries. Therefore, plenty amount of wastewater containing DMSO have been discharged. As the DMSO is high resistant to biological process which is mostly used for wastewater treatments, other strong treatments are needed. Electrochemical oxidation using boron-doped diamond (BDD) anode is a promising method due to effective generation of free hydroxyl radicals which are quite strong oxidizing agents. In this work, a simulated wastewater containing DMSO was treated by the anodic oxidation using BDD electrodes. We found that BDD electrodes could oxidize and completely mineralize DMSO. Removal of total organic carbon was more than 99% after the electrolysis for 5 h using BDD electrodes. This is first observation for the electrochemical mineralization of persistent DMSO. Moreover, BDD electrodes enabled to mineralize DMSO without electrolytic corrosion at low current densities and high pH of the solution for the treatments.

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Influence of the Nature of Boron-Doped Diamond Anodes on the Dehydrogenative Phenol-Phenol Cross-Coupling

Gleede B., Yamamoto T., Nakahara K., Botz A., Graßl T., Neuber R., Matthée T., Einaga Y., Schuhmann W., Waldvogel S.

ChemElectroChem (ChemElectroChem) 6 ( 10 ) 2771 - 2776 2019.05

© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Boron-doped diamond (BDD) represents a powerful and innovative electrode material. In particular, in combination with fluorinated solvents such as 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), the system exhibits the largest known electrochemical window of approximately 5 V in protic media. Furthermore, the anodic treatment allows the direct formation of oxyl radicals, which are known to exhibit specific reactivity. The electrochemical dehydrogenative phenol-phenol cross-coupling is a versatile and useful transformation to non-symmetric biphenols. This electro-organic conversion can be divided into two regimes: initial oxidation at the anode and the electrolyte-controlled follow-up reaction. This work intends to provide an answer about the influence of BDD electrodes on oxidation reactions in electrosynthesis. Depending on the electro-organic transformation, the support material of BDD, its boron content, and its fabrication method have a significant influence on the electrosynthetic efficiency.

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Thermoresponsive, Freezing-Resistant Smart Windows with Adjustable Transition Temperature Made from Hydroxypropyl Cellulose and Glycerol

Nakamura C., Yamamoto T., Manabe K., Nakamura T., Einaga Y., Shiratori S.

Industrial and Engineering Chemistry Research (Industrial and Engineering Chemistry Research) 58 ( 16 ) 6424 - 6428 2019.04

ISSN 08885885

© 2019 American Chemical Society. A thermoresponsive smart window that can switch its transmittance to control heating from sunlight is attracting great attention. Such windows made from a hydrogel of a thermoresponsive polymer such as poly(N-isopropylacrylamide) (PNIPAm) or hydroxypropyl cellulose (HPC) have been successful and can switch their transmittance at room temperature. However, such hydrogels occasionally freeze in cold places, degrading their transmittance. Thus, a thermoresponsive hydrogel that can be used in various geographical regions is desired. Here, we produced a thermoresponsive smart window with freezing resistance made from HPC and glycerol. We could adjust its switching temperature by simply changing the amount of added glycerol, letting us easily change it to room temperature for practical use. These smart windows show high cyclic performance, freezing resistance, and heat shielding, demonstrating great potential.

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In Situ Spectroscopic Study on the Surface Hydroxylation of Diamond Electrodes

Kasahara S., Ogose T., Ikemiya N., Yamamoto T., Natsui K., Yokota Y., Wong R., Iizuka S., Hoshi N., Tateyama Y., Kim Y., Nakamura M., Einaga Y.

Analytical Chemistry (Analytical Chemistry) 91 ( 8 ) 4980 - 4986 2019.04

ISSN 00032700

Copyright © 2019 American Chemical Society. Carbon-based materials are regarded as an environmentally benign alternative to the conventional metal electrode used in electrochemistry from the viewpoint of sustainable chemistry. Among various carbon electrode materials, boron-doped diamond (BDD) exhibits superior electrochemical properties. However, it is still uncertain how surface chemical species of BDD influence the electrochemical performance, because of the difficulty in characterizing the surface species. Here, we have developed in situ spectroscopic measurement systems on BDD electrodes, i.e., in situ attenuated total reflection infrared spectroscopy (ATR-IR) and electrochemical X-ray photoelectron spectroscopy (EC-XPS). ATR-IR studies at a controlled electrode potential confirmed selective surface hydroxylation. EC-XPS studies confirmed deprotonation of C-OH groups at the BDD/electrolyte interface. These findings should be important not only for better understanding of BDD's fundamentals but also for a variety of applications.

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Switchable Product Selectivity in the Electrochemical Reduction of Carbon Dioxide Using Boron-Doped Diamond Electrodes

Tomisaki M., Kasahara S., Natsui K., Ikemiya N., Einaga Y.

Journal of the American Chemical Society (Journal of the American Chemical Society) 141 ( 18 ) 7414 - 7420 2019.04

ISSN 00027863

© 2019 American Chemical Society. The main product obtained by electrochemical reduction of CO 2 depends on the electrode material, and in many cases the Faradaic efficiency for this is determined by the electrolyte. Only a few investigations in which attempts to produce different products from the same electrode material have been done so far. In this work, we focus on boron-doped diamond (BDD) electrodes with which plentiful amounts of formic acid and small amounts of carbon monoxide have been produced. By optimizing certain parameters and conditions used in the electrochemical process with BDD electrodes, such as the electrolyte, the boron concentration of the BDD electrode, and the applied potential, we were able to control the selectivity and efficiency with which carbon monoxide is produced. On one hand, with a BDD electrode with 1% boron used for the cathode and KClO 4 for the catholyte, the selectivity for producing carbon monoxide was high. On the other hand, with a BDD electrode with 0.1% boron used for the cathode and KCl for the catholyte, the production of formic acid was the most evident. In situ attenuated total reflectance-infrared (ATR-IR) measurements during electrolysis showed that CO 2·- intermediates were adsorbed on the BDD surface in the KClO 4 aqueous solution. Here, switchable product selectivity was achieved when reducing CO 2 using BDD electrodes.

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Influence of Surface Orientation on Electrochemical Properties of Boron-Doped Diamond

Ivandini T., Watanabe T., Matsui T., Ootani Y., Iizuka S., Toyoshima R., Kodama H., Kondoh H., Tateyama Y., Einaga Y.

Journal of Physical Chemistry C (Journal of Physical Chemistry C) 123 ( 9 ) 5336 - 5344 2019.03

ISSN 19327447

© 2019 American Chemical Society. To study the influence of crystal orientation on the electrochemical properties of boron-doped diamond (BDD), electrodes comprising (100) and (111) homoepitaxial single-crystal layers of BDD were investigated and these were compared with a thin polycrystalline BDD electrode. The BDD samples with similar amounts of boron of around 1020 cm-3 and resistivity of around 6 × 10-3 ? cm were prepared. Evaluation of the electrochemical reactivity of each of the samples with both H- and O-terminated surfaces showed that polycrystalline BDD was the most reactive, whereas the (111) samples proved to be more reactive than the (100) ones for single-crystal BDD. Moreover, considering the results of first-principles molecular dynamics simulations, it is proposed that surface transfer doping is the dominating factor for H-terminated surfaces, whereas the degree of band bending and the thickness of the space-charge layer are the dominating factors for O-terminated surfaces.

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In situ ATR-IR study of Fe(CN) <inf>6</inf>3− /Fe(CN) <inf>6</inf>4− redox system on boron-doped diamond electrode

Kamoshida N., Kasahara S., Ikemiya N., Hoshi N., Nakamura M., Einaga Y.

Diamond and Related Materials (Diamond and Related Materials) 93 50 - 53 2019.03

ISSN 09259635

© 2019 Hexacyanoferrate redox couple is extensively used as a benchmark to evaluate electrode activity in aqueous electrochemistry. Interestingly, boron-doped diamond (BDD) electrode shows surface-dependent behaviors: fast electron transfer rate on hydrogen terminated surface and slow rate on oxygen terminated surface. On the other hand, origin of the surface-dependent response still remains unclear. In this study, we spectroscopically investigated the determinants of electrochemical activity of this system using in situ ATR-IR technique. Our experiment revealed that adsorbed intermediate species of this redox system exist on the hydrogen terminated BDD. On the oxygen terminated BDD, the bands of adsorbed species were weakened, indicating that the oxygen functional groups specifically inhibited the adsorption of the intermediate species.

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Conductive diamond: Synthesis, properties, and electrochemical applications

Yang N., Yu S., MacPherson J., Einaga Y., Zhao H., Zhao G., Swain G., Jiang X.

Chemical Society Reviews (Chemical Society Reviews) 48 ( 1 ) 157 - 204 2019.01

ISSN 03060012

© 2019 The Royal Society of Chemistry. Conductive diamond possesses unique features as compared to other solid electrodes, such as a wide electrochemical potential window, a low and stable background current, relatively rapid rates of electron-transfer for soluble redox systems without conventional pretreatment, long-term responses, stability, biocompatibility, and a rich surface chemistry. Conductive diamond microcrystalline and nanocrystalline films, structures and particles have been prepared using a variety of approaches. Given these highly desirable attributes, conductive diamond has found extensive use as an enabling electrode across a variety of fields encompassing chemical and biochemical sensing, environmental degradation, electrosynthesis, electrocatalysis, and energy storage and conversion. This review provides an overview of the fundamental properties and highlights recent progress and achievements in the growth of boron-doped (metal-like) and nitrogen and phosphorus-doped (semi-conducting) diamond and hydrogen-terminated undoped diamond electrodes. Applications in electroanalysis, environmental degradation, electrosynthesis electrocatalysis, and electrochemical energy storage are also discussed. Diamond electrochemical devices utilizing micro-scale, ultramicro-scale, and nano-scale electrodes as well as their counterpart arrays are viewed. The challenges and future research directions of conductive diamond are discussed and outlined. This review will be important and informative for chemists, biochemists, physicists, materials scientists, and engineers engaged in the use of these novel forms of carbon.

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The Utilization of Boron-doped Diamond Electrodes for the Electrochemical Reduction of CO <inf>2</inf> : Toward the production compounds with a high number of carbon atoms

Jiwanti P., Natsui K., Einaga Y.

Electrochemistry (Electrochemistry) 87 ( 2 ) 109 - 113 2019

ISSN 13443542

© The Electrochemical Society of Japan, All rights reserved. The utilization of boron doped diamond (BDD) as an electrode material for the electrochemical reduction of CO 2 has been studied in recent decades. Its stability and ability to suppress hydrogen evolution makes it an attractive choice for the electrochemical reduction of CO 2 . It has been confirmed that, when using a bare BDD electrode, very high selectivity and productivity can be achieved in the production of formic acid. Moreover, by modifying the surface of a BDD electrode with copper (Cu) particles, we have been able to produce compounds with a high number of carbon atoms. In this article, we summarize the results of our work on the electrochemical reduction of CO 2 using BDD electrodes, with the specific aim of the producing compounds with a high number of carbon atoms.

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Modification of boron-doped diamond electrodes with platinum to increase the stability and sensitivity of haemoglobin-based acrylamide sensors

Wulandari R., Ivandini T., Irkham, Saepudin E., Einaga Y.

Sensors and Materials (Sensors and Materials) 31 ( 4 ) 1105 - 1117 2019

ISSN 09144935

© MYU K.K. Boron-doped diamond (BDD) electrodes modified with platinum and haemoglobin (Hb) have been prepared for application as stable and sensitive acrylamide biosensors. The Platinum-modified BDD (Pt-BDD) was prepared in several steps, including the wet chemical seeding of Pt particles, the electrochemical overgrowth of Pt seeds, thermal annealing at 700 °C under N 2 atmosphere, as well as refresh and activation steps of Pt-BDD by cyclic voltammetry (CV). The characterization of the prepared Pt-BDD using scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS) and X-ray photoelectron spectroscopy (XPS) showed that the method can deposit Pt homogenously on the BDD surface with an average particle size of around 200 nm. The Raman results showed that the treatment steps during modification did not damage the sp 3 carbon in the BDD structure. After modification with Hb, the modified BDD was examined for acrylamide detection. CVs of Hb-Pt-modified BDD (Hb-Pt-BDD) in 0.2 M acetate buffer saline (ABS) (pH 4.8) containing acrylamide in the concentration range of 0.01 to 1 nM showed linear responses with a detection limit of 0.0085 nM and a quantification limit of 0.026 nM. The excellent stability of the prepared Pt-BDD was confirmed as it showed the reusability of Pt-BDD by removing the Hb adduct without removing Pt on the BDD surface.

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Increasing the electric double-layer capacitance in boron-doped diamond electrodes

Takagi K., Natsui K., Watanabe T., Einaga Y.

ChemElectroChem (ChemElectroChem) 6 ( 6 ) 1683 - 1687 2019

© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim. Highly boron-doped diamond (BDD) electrodes containing sp 2 carbon impurities exhibit an increase in the electric doublelayer capacitance (C dl ) after anodic oxidation. Although it is known that the electrochemical properties of BDD electrodes are affected by several factors, including the boron concentration, the amount of sp 2 carbon impurity, and the surface termination and orientation, clarification of the mechanism for the increase in C dl needs to be done. To this end, we prepared several BDD samples under various conditions and the properties of these samples, including C dl , were systematically investigated. The mechanism for the increase in C dl in particular, including the effect of the surface termination, is discussed.

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High-temperature cooperative spin crossover transitions and single-crystal reflection spectra of [Fe III (qsal) <inf>2</inf> ](CH <inf>3</inf> OSO <inf>3</inf> ) and related compounds

Takahashi K., Yamamoto K., Yamamoto T., Einaga Y., Shiota Y., Yoshizawa K., Mori H.

Crystals (Crystals) 9 ( 2 ) 2019

© 2019 by the authors. Licensee MDPI, Basel, Switzerland. New Fe(III) compounds from qsal ligand, [Fe(qsal) 2 ](CH 3 OSO 3 ) (1) and [Fe(qsal) 2 ](CH 3 SO 3 )·CH 3 OH (3), along with known compound, [Fe(qsal) 2 ](CF 3 SO 3 ) (2), were obtained as large well-shaped crystals (Hqsal = N-(8-quinolyl)salicylaldimine). The compounds 1 and 2 were in the low-spin (LS) state at 300 K and exhibited a cooperative spin crossover (SCO) transition with a thermal hysteresis loop at higher temperatures, whereas 3 was in the high-spin (HS) state below 300 K. The optical conductivity spectra for 1 and 3 were calculated from the single-crystal reflection spectra, which were, to the best of our knowledge, the first optical conductivity spectra of SCO compounds. The absorption bands for the LS and HS [Fe(qsal) 2 ] cations were assigned by time-dependent density functional theory calculations. The crystal structures of 1 and 2 consisted of a common one-dimensional (1D) array of the [Fe(qsal) 2 ] cation, whereas that of 3 had an unusual 1D arrangement by π-stacking interactions which has never been reported. The crystal structures in the high-temperature phases for 1 and 2 indicate that large structural changes were triggered by the motion of counter anions. The comparison of the crystal structures of the known [Fe(qsal) 2 ] compounds suggests the significant role of a large non-spherical counter-anion or solvate molecule for the total lattice energy gain in the crystal of a charged complex.

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Fabrication of an all-diamond microelectrode using a chromium mask

Asai K., Einaga Y.

Chemical Communications (Chemical Communications) 55 ( 7 ) 897 - 900 2019

ISSN 13597345

© 2019 The Royal Society of Chemistry. We have developed a new method for fabricating all-diamond microelectrodes. The process comprises three steps: masking the tip of an electrode by electroplating with chromium, depositing undoped diamond, which acts as an insulator on the sides of the electrode, and removing the chromium mask to expose the tip of the electrode. The active area of the electrode can be easily controlled in combination only with a conventional electroplating technique.

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Electrochemical Pinacol Coupling of Acetophenone Using Boron-Doped Diamond Electrode

Nakahara K., Naba K., Saitoh T., Sugai T., Obata R., Nishiyama S., Einaga Y., Yamamoto T.

ChemElectroChem (ChemElectroChem) 6 ( 16 ) 4153 - 4157 2019

© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim An electrochemical pinacol coupling reaction of acetophenone using a boron-doped diamond (BDD) electrode has been reported. This transformation is driven by the one-electron reduction of acetophenone on the BDD cathode, followed by an intermolecular radical coupling. Owing to the BDD's outstanding electrochemical properties, the pinacol-type compound has been obtained in good conversion yield. The roles of a supporting electrolyte and solvent were addressed; (1) lithium ions contribute to increase in the reactivity of the radical intermediate. (2) Addition of water promotes the electron transfer process at the BDD surface. The reaction is relatively tolerant to para-substituted acetophenone derivatives. Since electric current is directly employed as reducing reagents to generate a radical intermediate, the reaction is metal-free, sustainable, and inherently safe.

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CO<inf>2</inf> reduction to formic acid at low overpotential on BDD electrodes modified with nanostructured CeO<inf>2</inf>

Verlato E., Barison S., Einaga Y., Fasolin S., Musiani M., Nasi L., Natsui K., Paolucci F., Valenti G.

Journal of Materials Chemistry A (Journal of Materials Chemistry A) 7 ( 30 ) 17896 - 17905 2019

ISSN 20507488

© 2019 The Royal Society of Chemistry. Ceria was deposited onto boron doped polycrystalline diamond (BDD) cathodes, through electrochemically induced precipitation from nitrate-based solutions. The deposits were characterized using SEM-EDS, HRTEM, XRD and XPS. The morphology, thickness and composition of ceria films, which besides CeO2 contained Ce(OH)3 when prepared at very negative potential, were controlled by tuning the deposition parameters. Thin Ce(OH)3-free ceria films allowed CO2 electrochemical reduction at overpotentials below 50 mV, yielding formic acid with faradaic yield higher than 40% and stable performance for many hours. Ceria seemed to act as a co-catalyst that activated CO2 for reduction at the H-terminated BDD surface, because comparable results were not obtained with ceria-coated glassy carbon electrodes.

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Oxidative Cleavage of the Acyl-Carbon Bond in Phenylacetone with Electrogenerated Superoxide Anions

Zhang Y., Sugai T., Yamamoto T., Yamamoto N., Kutsumura N., Einaga Y., Nishiyama S., Saitoh T., Nagase H.

ChemElectroChem (ChemElectroChem) 6 ( 16 ) 4194 - 4198 2019

© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim An oxidative cleavage reaction of the acyl−carbon bond in phenylacetone derivatives under cathodic reduction is reported. This particular transformation is driven by the cathodic reduction of dissolved molecular oxygen to superoxide anions. Various cathode materials were examined, and we discovered that boron-doped diamond (BDD) enables highly efficient molecular conversion, owing to BDD's outstanding electrochemical property for utilizing the small amounts of molecular oxygen effectively. The scope of the reaction is broad and can be applied to a variety of substrates, ranging from ketones to esters and amides. As an electric current is directly employed to generate the superoxide anion, the reaction is metal- and catalyst-free. Electro-organic synthesis using the carbon-based BDD electrode thus provides access to sustainable molecular transformations.

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