研究者詳細 - 栄長　泰明

論文 - 栄長　泰明

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Fabrication of three-dimensional boron-doped diamond electrodes on SiC scaffolds

Otake A., Diaz-Herrezuelo I., Uchiyama K., Fiorani A., Belmonte M., Einaga Y.

Diamond and Related Materials （Diamond and Related Materials） 146 2024年06月

ISSN 09259635

Three-dimensional (3D) architected electrode materials are expected to exhibit advantageous properties such as enlarged surface area, increased mass transfer, enhanced adsorption and more active sites exposed. In this paper, boron-doped diamond (BDD) electrodes on 3D printed patterned silicon carbide (SiC) scaffolds have been fabricated using chemical vapor deposition (CVD). The stabilization of the plasma sphere by using clamshell type CVD reactor, introducing the outer protecting plate, the optimization of CVD parameters, and the design of 3D-SiC scaffolds improved the sp3/sp2 ratio, uniformity and growth rate of BDD. 3D-BDD electrodes exhibit enough electrical conductivity for electrochemical applications. The preliminary test for electrochemical carbon dioxide reduction (CO2R) has showed the potential advantages of this type of 3D structured BDD electrodes.

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Fabrication of polycrystalline phosphorus-doped diamond electrodes from red phosphorus

Moriguchi T., Tomisaki M., Sato S., Nakamura J., Yamada H., Einaga Y.

Physical Chemistry Chemical Physics （Physical Chemistry Chemical Physics） 26 （ 20 ） 14825 - 14831 2024年05月

ISSN 14639076

Polycrystalline phosphorus-doped diamond was fabricated by the quartz-tube-type microwave plasma-assisted chemical vapor deposition method. Significantly, red phosphorus was used as a source of phosphorous, instead of PH3. Phosphorus-doped diamond electrodes with hydrogen-terminated and oxygen-terminated surfaces were investigated for the redox reactions of K3[Fe(CN)6] and [Ru(NH3)6]Cl3. The carrier concentration was estimated as 2.1-5.3 × 1018 cm−3 from electrochemical impedance measurements. Polycrystalline phosphorus-doped diamond shows great promise as chemical electrode materials.

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Green Synthesis of Ceria Nanoparticles from Cassava Tubers for Electrochemical Aptasensor Detection of SARS-CoV-2 on a Screen-Printed Carbon Electrode

Zakiyyah S.N., Irkham N., Einaga Y., Gultom N.S., Fauzia R.P., Kadja G.T.M., Gaffar S., Ozsoz M., Hartati Y.W.

ACS Applied Bio Materials （ACS Applied Bio Materials） 7 （ 4 ） 2488 - 2498 2024年04月

Green synthesis approaches for making nanosized ceria using starch from cassava as template molecules to control the particle size are reported. The results of the green synthesis of ceria with an optimum calcination temperature of 800 °C shows a size distribution of each particle of less than 30 nm with an average size of 9.68 nm, while the ratio of Ce3+ to Ce4+ was 25.6%. The green-synthesized nanoceria are applied to increase the sensitivity and attach biomolecules to the electrode surface of the electrochemical aptasensor system for coronavirus disease (COVID-19). The response of the aptasensor to the receptor binding domain of the virus was determined with the potassium ferricyanide redox system. The screen-printed carbon electrode that has been modified with green-synthesized nanoceria shows 1.43 times higher conductivity than the bare electrode, while those modified with commercial ceria increase only 1.18 times. Using an optimized parameter for preparing the aptasensors, the detection and quantification limits were 1.94 and 5.87 ng·mL-1, and the accuracy and precision values were 98.5 and 89.1%. These results show that green-synthesized ceria could be a promising approach for fabricating an electrochemical aptasensor.

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Modification of boron-doped diamond electrode with polyaniline and gold particles to enhance the electrochemiluminescence of luminol for the detection of reactive oxygen species (hydrogen peroxide and hypochlorite)

Rahmawati I., Fiorani A., Sanjaya A.R., Irkham , Du J., Saepudin E., Einaga Y., Ivandini T.A.

Diamond and Related Materials （Diamond and Related Materials） 144 2024年04月

ISSN 09259635

A luminol electrochemiluminescence (ECL)-based sensor for reactive oxygen species (ROS), including H2O2 and hypochlorite was developed using gold particles-modified on polyaniline‑boron doped diamond electrode (Au-PANI/BDD). The gold particles were incorporated onto the surface of boron-doped diamond (BDD) electrode to enhance the electrochemiluminescence of luminol, while the polyaniline was used to provide better attachment of the gold particles on the surface of BDD electrode. The uniform distribution of gold particles on the PANI/BDD surface was verified through FE-SEM EDX analysis with an approximately weight percentage of 45.6 % (w/w). The modified electrode exhibited a remarkable five-fold increase in ECL intensity compared to the unmodified BDD, resulting in higher sensitivity. Furthermore, the sensor's performance was successfully demonstrated for H2O2 concentrations ranged linearly from 1 to 100 μM (R2 ≥ 0.99) with a low detection limit of 0.81 μM, and for hypochlorite concentrations from 1 to 20 μM (R2 ≥ 0.99) with a detection limit as low as 0.51 μM. Additionally, excellent repeatability and stability of the signals was also observed over 7 days. Furthermore, successful application in detecting H2O2 and hypochlorite in real sample highlights its promising potential as an ROS sensor.

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Sluggish Electron Transfer of Oxygen-Terminated Moderately Boron-Doped Diamond Electrode Induced by Large Interfacial Capacitance between a Diamond and Silicon Interface

Otake A., Nishida T., Ohmagari S., Einaga Y.

JACS Au （JACS Au） 4 （ 3 ） 1184 - 1193 2024年03月

Boron-doped diamond (BDD) has tremendous potential for use as an electrode material with outstanding characteristics. The substrate material of BDD can affect the electrochemical properties of BDD electrodes due to the different junction structures of BDD and the substrate materials. However, the BDD/substrate interfacial properties have not been clarified. In this study, the electrochemical behavior of BDD electrodes with different boron-doping levels (0.1% and 1.0% B/C ratios) synthesized on Si, W, Nb, and Mo substrates was investigated. Potential band diagrams of the BDD/substrate interface were proposed to explain different junction structures and electrochemical behaviors. Oxygen-terminated BDD with moderate boron-doping levels exhibited sluggish electron transfer induced by the large capacitance generated at the BDD/Si interface. These findings provide a fundamental understanding of diamond electrochemistry and insight into the selection of suitable substrate materials for practical applications of BDD electrodes.

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Designing Molecularly Imprinted Polymer-Modified Boron-Doped Diamond Electrodes for Highly Selective Electrochemical Drug Sensors

Ishii K., Ogata G., Yamamoto T., Sun S., Shiigi H., Einaga Y.

ACS Sensors （ACS Sensors） 9 （ 3 ） 1611 - 1619 2024年03月

Drug detection in biological solutions is essential in studying the pharmacokinetics of the body. Electrochemical detection is an accurate and rapid method, but measuring multiple drugs that react at similar potentials is challenging. Herein, we developed an electrochemical sensor using a boron-doped diamond (BDD) electrode modified with a molecularly imprinted polymer (MIP) to provide specificity in drug sensing. The MIP is a polymer material designed to recognize and capture template molecules, enabling the selective detection of target molecules. In this study, we selected the anticancer drug doxorubicin (DOX) as the template molecule. In the electrochemical measurements using an unmodified BDD, the DOX reduction was observed at approximately −0.5 V (vs Ag/AgCl). Other drugs, i.e., mitomycin C or clonazepam (CZP), also underwent a reduction reaction at a similar potential to that of DOX, when using the unmodified BDD, which rendered the accurate quantification of DOX in a mixture challenging. Similar measurements conducted in PBS using the MIP-BDD only resulted in a DOX reduction current, with no reduction reaction observed in the presence of mitomycin C and CZP. These results suggest that the MIP, whose template molecule is DOX, inhibits the reduction of other drugs on the electrode surface. Selective DOX measurement using the MIP-BDD was also possible in human plasma, and the respective limits of detection of DOX in PBS and human plasma were 32.10 and 16.61 nM. The MIP-BDD was durable for use in six repeated measurements, and MIP-BDD may be applicable as an electrochemical sensor for application in therapeutic drug monitoring.

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Impact of gate electrode on free chlorine sensing performance in solution-gated graphene field-effect transistors

Sugawara M., Watanabe T., Einaga Y., Koh S.

RSC Advances （RSC Advances） 14 （ 11 ） 7867 - 7876 2024年03月

Free chlorine is widely used to disinfect water used for drinking and food processing. This requires highly sensitive, simple, and capable continuous-measurement sensors to enable the concentration of free chlorine in water to be monitored and controlled. Free chlorine sensors based on solution-gated graphene field-effect transistors (GFETs) are a suitable platform for highly sensitive and continuous measurements. However, their sensing mechanisms require further elucidation to improve their performance. In this study, we focused on the gate electrode and investigated its influence on the sensing performance. Using the free chlorine sensor based on the solution-gate GFET, we showed that the Dirac point voltage in the transfer curve changed significantly as the free chlorine concentration changed, and the electric double-layer capacitance of the gate electrode decreased. Furthermore, we demonstrated that a solution-gated GFET using graphene or boron-doped diamond as the gate electrode could be used to detect changes in the free chlorine concentration in the concentration range of tap water. The sensing performance in the low concentration range benefits from the wide potential window of carbon-based electrodes, which do not have electrochemically active sites. Using these carbon-based materials as gate electrodes, GFETs have the potential to be used as durable sensors that are resistant to surface fouling and oxidation.

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Real-Time Measurement of Antiglaucoma Drugs in Porcine Eyes Using Boron-Doped Diamond Microelectrodes

Ogata G., Yoneda M., Ogawa R., Hanawa A., Asai K., Yamagishi R., Honjo M., Aihara M., Einaga Y.

ACS Sensors （ACS Sensors） 9 （ 2 ） 781 - 788 2024年02月

The primary treatment for glaucoma, the most common cause of intermediate vision impairment, involves administering ocular hypotensive drugs in the form of topical eye drops. Observing real-time changes in the drugs that pass through the cornea and reach the anterior chamber of the eye is crucial for improving and developing safe, reliable, and effective medical treatments. Traditional methods for measuring temporal changes in drug concentrations in the aqueous humor employ separation analyzers such as LC-MS/MS. However, this technique requires multiple measurements on the eyes of various test subjects to track changes over time with a high temporal resolution. To address this issue, we have developed a measurement method that employs boron-doped diamond (BDD) microelectrodes to monitor real-time drug concentrations in the anterior chamber of the eye. First, we confirmed the electrochemical reactivity of 13 antiglaucoma drugs in a phosphate buffer solution with a pH of 7.4. Next, we optimized the method for continuous measurement of timolol maleate (TIM), a sympathetic beta-receptor antagonist, and generated calibration curves for each BDD microelectrode using aqueous humor collected from enucleated porcine eyes. We successfully demonstrated the continuous ex vivo monitoring of TIM concentrations in the anterior chambers of these enucleated porcine eyes. The results indicate that changes in intracameral TIM concentrations can be monitored through electrochemical measurements using BDD microelectrodes. This technique holds promise for future advancements in optimizing glaucoma treatment and drug administration strategies.

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Hydroxyapatite-Gold Modified Screen-Printed Carbon Electrode for Selective SARS-CoV‑2 Antibody Immunosensor

Syafira R.S., Devi M.J., Gaffar S., Irkham , Kurnia I., Arnafia W., Einaga Y., Syakir N., Noviyanti A.R., Hartati Y.W.

ACS Applied Bio Materials （ACS Applied Bio Materials） 7 （ 2 ） 950 - 960 2024年02月

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), or coronavirus disease 2019 (COVID-19), is still spreading worldwide; therefore, the need for rapid and accurate detection methods remains relevant to maintain the spread of this infectious disease. Electrochemical immunosensors are an alternative method for the rapid detection of the SARS-CoV-2 virus. Herein, we report the development of a screen-printed carbon electrode immunosensor using a hydroxyapatite-gold nanocomposite (SPCE/HA-Au) directly spray-coated with the immobilization receptor binding domain (RBD) Spike to increase the conductivity and surface electrode area. The HA-Au composite synthesis was optimized using the Box−Behnken method, and the resulting composite was characterized by UV−vis spectrophotometry, TEM-EDX, and XRD analysis. The specific interaction of RBD Spike with immunoglobulin G (IgG) antibodies was evaluated by differential pulse voltammetry and electrochemical impedance spectroscopy methods in a [Fe(CN)6]4−/3− solution redox system. The IgG was detected with a detection limit of 0.0561 pg mL−1, and the immunosensor had selectivity and stability of 103−122% and was stable until week 7 with the influence of storage conditions. Also, the immunosensor was tested using real samples from human serum, where the results were confirmed using the chemiluminescent microparticle immunoassay (CMIA) method and showed satisfactory results. Therefore, the developed electrochemical immunosensor can rapidly and accurately detect SARS-CoV-2 antibodies.

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Anode Reaction Control for a Single-Compartment Electrochemical CO<inf>2</inf> Reduction Reactor with a Surface-Activated Diamond Cathode

Otake A., Asai K., Einaga Y.

Chemistry - A European Journal （Chemistry - A European Journal） 30 （ 9 ） 2024年02月

ISSN 09476539

The electrochemical reaction of carbon dioxide (CO2) in aqueous electrolyte solutions is attracting increasing attention for sustainable chemical production. Boron-doped diamond (BDD) electrodes have been previously shown to be very effective for the stable electrochemical production of formic acid from CO2. Typically, the electrochemical production of formic acid by CO2 reduction (CO2R) reaction is performed with a dual-compartment flow reactor equipped with a membrane separator. The problems caused by the membrane separator, such as scaling-up, complicated operational control and materials costs can be solved using a membrane free single-compartment reactor. Here we demonstrate anode reaction control for a single-compartment CO2R flow reactor using a surface-activated BDD cathode and achieve a Faradaic efficiency for formic acid production of over 70 %.

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Electrochemical CO<inf>2</inf> reduction properties of boron-doped diamond powder

Miyake Y., Kondo T., Otake A., Einaga Y., Tojo T., Yuasa M.

Diamond and Related Materials （Diamond and Related Materials） 142 2024年02月

ISSN 09259635

The electrochemical CO2 reduction reaction (CO2RR) properties of boron-doped diamond powder (BDDP) were investigated. A BDDP-painted electrode was prepared by casting BDDP ink on the surface of a BDD thin-film electrode as a current collector. The CO2RR properties of the BDDP-painted electrode were compared to those of conventional BDD thin-film electrodes, which were prepared directly on a conductive silicon wafer substrate by the microwave plasma-assisted chemical vapor deposition method. The result of the electrolysis at −1.8 V vs. Ag/AgCl in 0.5 M KCl catholyte showed that the BDDP-painted electrode was superior to the BDD thin-film electrode because it produced a large amount of products (formic acid and carbon monoxide) at a low overpotential. The highest performance of the CO2RR in the BDDP-painted electrode was achieved with the BDDP with high boron doping and high sp2 carbon content. We considered that structural defects, boron doping level, and sp2 carbon content influenced the reactivity for CO2 reduction. Therefore, the BDDP-painted electrodes should be useful not only for the production of a large-size electrode but also for efficient CO2RR.

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Cu, Fe, N-doped Carbon Nanotubes Prepared through Silica Coating for Selective Oxygen Reduction to Water in Acidic Media

Kato M., Abe D., Xie S., Sato S., Fujibayashi N., Matsumoto K., Onoda A., Hayashi T., Mitsui T., Fujiwara K., Yamamoto T., Einaga Y., Tadgell C.A., Kato Y., Asakura K., Yagi I.

ChemCatChem （ChemCatChem） 2024年

ISSN 18673880

We report Cu, Fe, N-doped carbon nanotubes, (Cu,Fe)−N−CNT, as electrocatalysts for the oxygen reduction reaction (ORR) in acidic media. (Cu,Fe)−N−CNT was prepared using a silica coating method in pyrolysis to minimize the formation of carbon-coated metal oxide or carbide nanoparticles, which are known to be inactive for the H2O2 reduction. (Cu,Fe)−N−CNT shows a turnover frequency of 0.66 e− site−1 s−1 at +0.8 V vs. RHE and H2O2 yields of <1 % for the ORR with a utilization factor of active sites of 82 %. Kinetic analysis reveals that 4e− transfer rates for (Cu,Fe)−N−CNT are higher than those of a monometallic counterpart of Fe−N−CNT. In situ X-ray absorption spectroscopy enables us to determine redox potentials: E°’(FeIII/FeII)=0.65 V vs. RHE and E°’(CuII/CuI)=0.45 V for (Cu,Fe)−N−CNT, and E°’(FeIII/FeII)=0.65 V for Fe−N−CNT. These results indicate that bimetallic doping into carbon nanotubes gives the effect on kinetic parameters but not on thermodynamic ones. In other words, there is no direct electronic interactions between the Cu and Fe active sites for (Cu,Fe)-N-CNT because such interactions should modulate their redox potentials.

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Measuring the Permittivity of Liposome and Yeast Using a 3D-printed Electrode-replaceable Measuring Cell

Kageyama Y., Sueoka H., Kimura A., Sato M., Ito A., Horie T., Ogata G., Einaga Y., Suzuki H., Murakami S.

Advanced Biomedical Engineering （Advanced Biomedical Engineering） 13 90 - 99 2024年

The lipid bilayer membrane of microorganisms exhibits capacitance that can be used to assess the proliferation, reduction, or transformation of these microorganisms by evaluating the permittivity of their lipid bilay-er membrane. Traditionally, the effects of pharmacological substances on viruses have been measured indirectly by observing cytopathic effects on cultured cells. Nevertheless, the novel approach that depends on permittivity is antic-ipated to provide an innovative assay for preliminary screening of potential drugs against microorganisms. In an ef-fort to quantify directly the pharmacological effects of compounds on microorganisms, we devised a method that avoids the indirect pharmacological effects on cultured cells. Instead, this method measures the direct effect by as-sessing the permittivity induced by the lipid bilayer membrane itself. To validate the effectiveness of our approach, and to demonstrate the feasibility of permittivity measurements in microorganisms, we designed an electrode-re-placeable measuring cell using 3D printing technology. Using this measuring cell, we measured permittivity of egg phosphatidylcholine liposomes and yeast cells, both of which exhibit lipid bilayers and are suitable for experimental purposes. We measured the permittivity of a KCl solution, as well as suspension of liposomes or yeast cells in KCl solution. We observed an increase in permittivity within a frequency range of 104–108 Hz, which can be ascribed to the lipid bilayers of the liposomes and yeast cells. Following lysis of liposomes by adding Triton-X 100, we observed a reduction in the enhanced permittivity. Furthermore, when the yeast cell count was reduced by dilution, there was a corresponding decrease in the enhanced permittivity. A decrease in permittivity was also noted in a suspension of yeast cells in KCl solution following heat and enzyme treatments. These results suggest that the permittivity of lipid bilayer membrane can be measured and harnessed to estimate the concentration of microorganisms in a solution. Consequently, we anticipate that this method will be developed as a pioneering assay for early drug screening, given its capacity to evaluate the pharmacological effects of compounds on viruses, without the necessity for cultured cells.

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Effect of the Substrate Materials in the Fabrication of an Electrode Based on Mixed Nickel-Iron Oxide Electrocatalyst

Tsuji Y., Fiorani A., Einaga Y.

Advanced Sustainable Systems （Advanced Sustainable Systems） 2024年

The effect of different substrate materials in the fabrication of an electrode intended for use in the water oxidation reaction is investigated. The electrocatalyst is nickel-iron oxide (NiFeOx) which is deposited by chronoamperometry on nickel, iron, titanium, and stainless steel substrates. The process of electrodeposition is optimized to achieve the lowest overpotential for the water oxidation reaction. The four electrodes are characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and glow-discharge optical emission spectroscopy (GDOES) to describe the effect of the substrate on the nature of the electrocatalyst layer. Electrochemical tests in 1 m NaOH are applied on the four electrodes to assess the stability and the retention of the electrocatalytic properties of the whole electrode. All electrodes show similar overpotential of ≈0.3 V at 10 mA cm−2 implying that the substrate do not affect the electrocatalytic activity of the NiFeOx. After use, the overpotential increases in a range of 30–50 mV for nickel, iron, and titanium substrates, while stainless steel retains the lowest overpotential with an increase of 10 mV. This limited variation can be the effect of smaller NiFeOx nanoparticles compared to other substrates. XPS analysis reveals that after galvanostatic electrolysis, the oxidation state of Fe shifts slightly from Fe(II) to Fe(III), likely Fe3O4 and Fe2O3, while NiO/Ni2O3 change partially to Ni(OH)2.

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Electrochemical Diagnosis of Urinary Tract Infection Using Boron-Doped Diamond Electrodes

Zhang Z., Ogata G., Asai K., Yamamoto T., Einaga Y.

ACS Sensors （ACS Sensors） 8 （ 11 ） 4245 - 4252 2023年11月

Efficient detection of sodium nitrite in human urine could be used to diagnose urinary tract infections rapidly. Here, we demonstrate a fast and novel method for the selective detection of sodium nitrite in different human urine samples using electrolysis with a bare boron-doped diamond electrode. The measurement is performed without adding any other species, such as enzymes, and uses a simple electrochemical approach with an oxidation step followed by reduction. In the present study, we pay attention to the reduction potential range for the measurement, which is substantially different from many previous literature reports that focus on the oxidation reaction. The determination of added sodium nitrite based on cyclic voltammetry or differential pulse voltammetry is employed for two pooled urine samples and three individual urine matrices. From this, the linear response ranges for sodium nitrite detection are 0.5-10 mg/L (7.2-140 μmol/L) and 10-400 mg/L (140-5800 μmol/L). The results from these urine samples convert well to the calibration curve, with a limit of detection established as 0.82 mg/L (R2 = 0.9914), which is clinically relevant.

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Molybdenum oxide electrodeposition on boron-doped diamond: Investigation of valence state and application in electrochemical nitrogen reduction to ammonia

Kuramochi S., Fiorani A., Einaga Y.

Diamond and Related Materials （Diamond and Related Materials） 139 2023年11月

ISSN 09259635

In this study, molybdenum-modified boron-doped diamond (MoBDD) was prepared by electrodeposition from a molybdate precursor, and the molybdenum oxide valence state was investigated by XPS analysis. The molybdenum oxide was used as an electrocatalyst in electrochemical nitrogen reduction for ammonia synthesis at room temperature and atmospheric pressure. MoBDD could produce ammonia at 1.26 nmol h−1 cm−2 with a faradaic efficiency of 9.15 % which was higher than a pure Mo plate set as a comparison. The XRD spectroscopy analysis suggests that high state Mo oxides are responsible for the electrocatalytic activity.

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Surface morphology-assisted electrochemical conversion of carbon dioxide to formic acid via nanocrystalline boron-doped diamond electrodes

Ashcheulov P., Otake A., Akai K., Taylor A., Klimša L., Hubík P., More-Chevalier J., Einaga Y.

Chemical Engineering Journal （Chemical Engineering Journal） 473 2023年10月

ISSN 13858947

Due to its unmatched corrosion stability and overall versatility, boron-doped diamond (BDD) has superb potential as an electrode material for the production of valuable chemicals via electrochemical reduction of carbon dioxide (CO2). To advance its practical application, it is necessary to explore ways to achieve cost-effective fabrication of BDD electrodes, which can enable significant selectivity for product formation during CO2 electroreduction. Here, BDD electrodes of nanocrystalline form were fabricated employing two distinct chemical vapor deposition (CVD) techniques, which allow for substantial upscaling of electrode dimensions to match industrial/wafer-size standards. Thin (<400 nm) nanocrystalline BDD layers were fabricated at various synthesis temperatures to investigate its effect on the electrical, structural, and electrochemical characteristics. Furthermore, modification of the BDD layer crystallinity and morphology has been performed to significantly alter the overall electrode structure and sp3/sp2-carbon phase-composition. Finally, when employed as cathodes in electrochemical CO2 reduction, nanocrystalline BDD electrodes of modified structure demonstrated enhanced values of faradaic efficiency (FE) towards production of formic acid (HCOOH), surpassing FEHCOOH values observed for microcrystalline form of BDD cathodes. Reported findings present a basis for further development of BDD cathodes, including their design, structure, and composition, which leverages the advantages of scalable and cost-effective synthesis of BDD electrodes.

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Morphology modulation on boron-doped diamond electrodes and its effect on boosting the conversion of CO<inf>2</inf>-to-CO

Peng Z., Fiorani A., Tomisaki M., Nishide Y., Hagiwara M., Fujihara S., Einaga Y.

Diamond and Related Materials （Diamond and Related Materials） 138 2023年10月

ISSN 09259635

Boron-doped diamond (BDD) electrodes have achieved excellent selectivity and switchable product formation for electrochemical CO2 reduction reaction (eCO2RR), although the current should be improved. Surface morphology modulation is a promising approach for improving it by exposing a larger electroactive area. Herein, we fabricated a porous 1 % BDD film (p-BDD) and a rough-surfaced 1 % BDD film (r-BDD) by modifying the surface of a flat 1 % BDD film (f-BDD). Fundamental electrochemical properties, including potential window, differential capacitance, and active area were examined, followed by eCO2RR activity evaluation. The synthetic r-BDD electrode enabled approximately 1.7-fold increases in current density and yield rate (17.6 μmol h−1) toward CO production compared to f-BDD (10.3 μmol h−1). This improvement in eCO2RR is ascribed to the larger electroactive area with a comparable kinetic performance, in comparison to f-BDD. On the other hand, p-BDD possesses the largest real area, but showed the lowest activity for eCO2RR (1.2 μmol h−1 for CO), which could result from hindered diffusion of CO2 inside the pores. X-rays photoelectron spectroscopy and electrochemical impedance spectroscopy were employed to disentangle the morphological structure effect from the chemical reactivity of the electrode surface.

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Urine protein quantification in human urine on boron-doped diamond electrodes based on the electrochemical reaction of Coomassie brilliant blue

Aoki H., Miyazaki R., Ohama M., Murata M., Asai K., Ogata G., Einaga Y.

Analyst （Analyst） 148 （ 18 ） 4396 - 4405 2023年08月

ISSN 00032654

Urinalysis is attracting interest in personal healthcare management as part of a general move to improve quality of life. Urine contains various metabolites and the protein level in urine is an indicator of kidney function. In this study, a novel electrochemical sensing system based on boron-doped diamond (BDD) electrodes was developed for the detection of protein concentrations in human urine. BDD electrodes have the advantages of a wide electrochemical potential window and low non-specific adsorption, making them ideal for simple, rapid, and compact devices for home detection of bio-relevant substances. Coomassie brilliant blue (CBB), a dye that selectively and strongly binds to urine proteins, was found to be a redox-active indicator to show a decrease in its redox currents in relation to the concentration of protein in urine samples. Our detailed studies of BDD electrodes showed their limit of detection to be 2.57 μg mL−1 and that they have a linear response that ranges from 0 to 400 μg mL−1 in urine samples. We also investigated the detection of urine protein in different urine samples. Our results agreed with those obtained using conventional colorimetric analysis. We believe this to be the first study of electrochemical detection of urine protein in urine samples on BDD electrodes, which is of great significance to be able to obtain results with electrical signals rapidly compared to conventional colorimetric analysis. This CBB-BDD technique has the potential to assist healthcare management in the form of a rapid daily diagnostic test to judge whether a more detailed examination is needed.

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Electrochemical reduction of carbon dioxide to acetic acid on a Cu-Au modified boron-doped diamond electrode with a flow-cell system

Saprudin M.H., Jiwanti P.K., Saprudin D., Sanjaya A.R., Putri Y.M.T.A., Einaga Y., Ivandini T.A.

RSC Advances （RSC Advances） 13 （ 32 ） 22061 - 22069 2023年07月

Boron-doped diamond (BDD) was modified with copper and gold particles by using an electrodeposition technique to improve its catalytic effect on CO2 reduction in a flow system. The system was optimized based on the production of formic acid by the electroreduction process. At the optimum applied potential of −1.0 V (vs. Ag/AgCl) and flow rate of 50 mL min−1, the copper-gold-modified BDD produced formic acid at the highest rate of 4.88 mol m−2 s−1 and a concentration of 15.93 ppm, while acetic acid was produced with a rate of 0.11 mol m−2 s−1 and a concentration of 0.47 ppm. An advantage of the flow system using the modified BDD was that it was found to accelerate the production rate of acetic acid as well as to decrease the reduction potential of CO2. Furthermore, better stability of the metal particles was observed when using mixed copper-gold modification on the BDD surface than single modification by either metal. The results indicated that a flow system is suitable to be employed for electroreduction of CO2 using the bimetal-modified BDD electrodes, especially with copper and gold as the modifying particles.

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