Details of a Researcher - Einaga, Yasuaki

Papers - Einaga, Yasuaki

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Electrochemical investigation of hydroxyapatite-lanthanum strontium cobalt ferrite composites (HA-LSCF) for SARS-CoV-2 aptasensors

Hartati Y.W., Devi M.J., Irkham N., Zulqaidah S., Noviyanti A.R., Rochani S., Topkaya S.N., Einaga Y.

RSC Advances (RSC Advances) 13 ( 29 ) 20209 - 20216 2023.07

The hydroxyapatite-lanthanum strontium cobalt ferrite (HA-LSCF) composite showed a good response on a screen-printed carbon electrode (SPCE) electrochemical aptasensor to detect SARS-CoV-2. SPCE/HA-LSCF with a thiolated aptamer has a strong affinity for the SARS-CoV-2 spike RBD protein. This occurs due to the binding of -SH to the HA-positive region. In the presence of LSCF, which is conductive, an increase in electron transfer from the redox system [Fe(CN)6]3−/4− occurs. The interaction of the aptamer with the RBD protein can be observed based on the decrease in the electron transfer process. As a result, the developed biosensor is highly sensitive to the SARS-CoV-2 spike RBD protein with a linear range of 0.125 to 2.0 ng mL−1, a detection limit of 0.012 ng mL−1, and a quantification limit of 0.040 ng mL−1. The analytical application of the aptasensor demonstrates its feasibility in the analysis of saliva or swab samples.

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Boron- and Nitrogen-Codoped Diamond Electrodes for the Improved Reactivity of Electrochemical CO<inf>2</inf> Reduction Reaction

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

ACS Sustainable Chemistry and Engineering (ACS Sustainable Chemistry and Engineering) 11 ( 23 ) 8495 - 8502 2023.06

We investigated the electrochemical CO2 reduction reaction (CO2RR) properties of boron- and nitrogen-codoped diamond (BNDD) electrodes. The BNDD electrodes exhibited higher CO2RR performance than boron-doped diamond (BDD) electrodes, indicating that the nitrogen doping can promote CO2RR reactivity. In particular, the faradaic efficiencies of the CO2RR products, obtained at a relatively low negative potential (−2.0 V vs Ag/AgCl) in this study, were significantly higher using BNDD electrodes with high nitrogen-doping levels. At this potential, it should be difficult to generate CO2•- as an initial intermediate of CO2RR; therefore, nitrogen doping promoted the generation of the intermediate through another reaction pathway. Linear sweep voltammetry revealed that nitrogen doping could promote the generation of adsorbed hydrogen atoms on the electrode surface by proton reduction. Thus, we concluded that nitrogen doping promoted the initial step of CO2RR through the adsorption of hydrogen atoms on the electrode surface. In addition, electrolysis using various electrolyte solutions confirmed that the influence of dopants on the BNDD electrode surface was significant for CO2RR, particularly at low overpotentials.

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Enhancement of the Catalytic Effect on the Electrochemical Conversion of CO<inf>2</inf> to Formic Acid Using MXene (Ti<inf>3</inf>C<inf>2</inf>T<inf>x</inf>)-Modified Boron-Doped Diamond Electrode

Jiwanti P.K., Alfaza A.M., Kadja G.T.M., Natalya S.A.C., Sagita F., Einaga Y., Purwaningsih A., Amalina I., Rizki I.N.

Energies (Energies) 16 ( 12 ) 2023.06

The rising concentration of carbon dioxide (CO2) as one of the greenhouse gases in the atmosphere is a major source of worry. Electrochemical reduction of CO2 is one of many ways to convert CO2 gas into usable compounds. An electrochemical technique was applied in this study to reduce CO2 using a boron-doped diamond (BDD) working electrode modified with MXene (Ti3C2Tx) material to improve electrode performance. MXene concentrations of 0.5 mg/mL (MXene-BDD 0.5), 1.0 mg/mL (MXene-BDD 1.0), and 2.0 mg/mL (MXene-BDD 2.0) were drop-casted onto the BDD surface. MXene was effectively deposited on top of the BDD surface, with Ti weight loads of 0.12%, 4.06%, and 7.14% on MXene-BDD 0.5, MXene-BDD 1.0, and MXene-BDD 2.0, respectively. The modified working electrode was employed for CO2 electroreduction with optimal CO2 gas aeration. The existence of the MXene substance in BDD reduced the electroreduction overpotential of CO2. For the final result, we found that the MXene-BDD 2.0 electrode effectively generated the most formic acid product with a maximum reduction potential as low as −1.3 V (vs. Ag/AgCl).

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Electrogenerated chemiluminescence at boron-doped diamond electrodes

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

Chemical Communications (Chemical Communications) 59 ( 51 ) 7900 - 7910 2023.05

ISSN 13597345

Electrogenerated chemiluminescence (ECL) refers to the phenomenon of light emission from molecular species which is triggered by an electrochemical reaction. Therefore, like most electrochemical systems, the electrode material plays a pivotal role and much effort has been made in order to find the best material for ECL, in terms of light signal intensity and long-term stability, especially after the development of ECL for analytical applications. In this article, we will introduce and highlight the distinctive features of boron-doped diamond (BDD) as an electrode material for ECL which has complementary properties compared to the most common metals (e.g., Au or Pt) and carbon materials (e.g., glassy carbon, carbon nanotubes and graphene). Boron-doped diamond electrodes emerged as novel electrodes, gaining more and more interest from the electrochemical community for their peculiar characteristics such as a wide solvent window, low capacitance, resistance to fouling and mechanical robustness. Furthermore, compared to metal electrodes, BDD does not form an oxide layer in aqueous solutions, and the sp3 carbon hybridization gives BDD the ability to enable peculiar electrochemical reactions that are not possible on sp2 carbon materials. Electrogenerated chemiluminescence investigations with boron-doped diamond electrodes have been reported for common ECL systems (luminophores and co-reactants), and special ECL that is only possible on BDD which includes the in situ electrochemical generation of the co-reactant.

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A strategy for low-cost portable monitoring of plasma drug concentrations using a sustainable boron-doped-diamond chip

Saiki T., Ogata G., Sawamura S., Asai K., Razvina O., Watanabe K., Kato R., Zhang Q., Akiyama K., Madhurantakam S., Ahmad N.B., Ino D., Nashimoto H., Matsumoto Y., Moriyama M., Horii A., Kondo C., Ochiai R., Kusuhara H., Saijo Y., Einaga Y., Hibino H.

Heliyon (Heliyon) 9 ( 5 ) 2023.05

ISSN 24058440

On-site monitoring of plasma drug concentrations is required for effective therapies. Recently developed handy biosensors are not yet popular owing to insufficient evaluation of accuracy on clinical samples and the necessity of complicated costly fabrication processes. Here, we approached these bottlenecks via a strategy involving engineeringly unmodified boron-doped diamond (BDD), a sustainable electrochemical material. A sensing system based on a ∼1 cm2 BDD chip, when analysing rat plasma spiked with a molecular-targeting anticancer drug, pazopanib, detected clinically relevant concentrations. The response was stable in 60 sequential measurements on the same chip. In a clinical study, data obtained with a BDD chip were consistent with liquid chromatography–mass spectrometry results. Finally, the portable system with a palm-sized sensor containing the chip analysed ∼40 μL of whole blood from dosed rats within ∼10 min. This approach with the ‘reusable’ sensor may improve point-of-monitoring systems and personalised medicine while reducing medical costs.

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Electrochemical CO<inf>2</inf> reduction to CO facilitated by reduced boron-doped diamond

Du J., Fiorani A., Einaga Y.

Diamond and Related Materials (Diamond and Related Materials) 135 2023.05

ISSN 09259635

In the mechanistic investigations of electrochemical CO2 reduction reaction (eCO2RR), the undercoordinated site and oxidized metals are generally considered the most likely sources of catalytic sites. However, in the eCO2RR on boron-doped diamond (BDD) electrodes, metal centers are not available, and undercoordinated sites from boron doping did not demonstrated a favorable effect on the catalytic activity. By means of electrochemical activation, we found that when the surface of BDD electrodes is in a stable reduced state, the catalytic activity of eCO2RR for CO production is optimal. The Faradaic efficiency for CO production was increased up to 64 %, and the corresponding production rate reached 23 μmol cm−2 h−1, which was more than three times of the non-activated BDD set as comparison. This work demonstrates that the catalytic activity for eCO2RR can also originate from a reduced surface of BDD electrode.

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Development of an Acrylamide Biosensor Using Guanine and Adenine as Biomarkers at Boron-Doped Diamond Electrodes: Integrated Molecular Docking and Experimental Studies

Anggraini L.E., Rahmawati I., Nasution M.A.F., Jiwanti P.K., Einaga Y., Ivandini T.A.

Bulletin of the Chemical Society of Japan (Bulletin of the Chemical Society of Japan) 96 ( 5 ) 420 - 428 2023.05

ISSN 00092673

An acrylamide biosensor was developed by utilizing purine bases, i.e. guanine and adenine, through computational and electrochemical approaches. The molecular docking simulation proved that interaction of double-stranded DNA with the purine bases has the lowest Gibbs binding free energy compared to other biomolecules with a ΔGbinding of -4.2759 kcal/mol. Meanwhile, cyclic voltammetry of both guanine and adenine in 0.1M phosphate buffer solution at pH 7.4 using a boron-doped diamond electrode showed an irreversible oxidation peak in the potential range of 0 to +1.8V (vs. Ag/AgCl), confirming that the oxidation reaction was irreversible. The current of these peaks decreased linearly with the concentration of acrylamide due to the adduct formation between the purine bases and acrylamide. The formation of acrylamide adducts between acrylamide and purine bases was confirmed by the shift of the peak wavelength of the UV spectrum from 260 to 257 nm. The use of guanine for acrylamide sensing showed a linear calibration curve in the concentration range of 0.20-1.00 μM (R2 = 0.99) with a limit of detection and limit of quantification attained at 0.11 and 0.36 μM, respectively. In the case of adenine, a linear calibration curve was observed in the concentration range of 0.14-1.00 μM (R2 = 0.99) with a limit of detection and limit of quantification of 0.10 and 0.34 μM, respectively. The developed method was successfully performed for the acrylamide determination in coffee samples and was validated by HPLC.

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Spin Manipulation in a Metal–Organic Layer through Mechanical Exfoliation for Highly Selective CO<inf>2</inf> Photoreduction

Wu D., Yin H.Q., Wang Z., Zhou M., Yu C., Wu J., Miao H., Yamamoto T., Zhaxi W., Huang Z., Liu L., Huang W., Zhong W., Einaga Y., Jiang J., Zhang Z.M.

Angewandte Chemie - International Edition (Angewandte Chemie - International Edition) 62 ( 18 ) 2023.04

ISSN 14337851

Spin manipulation of transition-metal catalysts has great potential in mimicking enzyme electronic structures to improve activity and/or selectivity. However, it remains a great challenge to manipulate room-temperature spin state of catalytic centers. Herein, we report a mechanical exfoliation strategy to in situ induce partial spin crossover from high-spin (s=5/2) to low-spin (s=1/2) of the ferric center. Due to spin transition of catalytic center, mixed-spin catalyst exhibits a high CO yield of 19.7 mmol g−1 with selectivity of 91.6 %, much superior to that of high-spin bulk counterpart (50 % selectivity). Density functional theory calculations reveal that low-spin 3d-orbital electronic configuration performs a key function in promoting CO2 adsorption and reducing activation barrier. Hence, the spin manipulation highlights a new insight into designing highly efficient biomimetic catalysts via optimizing spin state.

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Development of Ofloxacin Electrochemical Sensor in Milk Sample using Boron-doped Diamond Electrode Decorated by Zinc Nanoparticles

Jiwanti P.K., Hendri M., Wafiroh S., Einaga Y.

Analytical and Bioanalytical Electrochemistry (Analytical and Bioanalytical Electrochemistry) 15 ( 4 ) 280 - 293 2023.04

The study of Ofloxacin (OFL) electrochemical sensor on the surface of zinc modified boron-doped diamond (Zn-BDD) electrode is reported. OFL has been known as one of the fluoroquinolone antibiotics which is used in treating infectious diseases and also in animal agriculture. Despite its effectiveness, long-term consumption could promote antimicrobial resistance. Therefore, a sensitive and selective detection method is important. Meanwhile, BDD has been known for its low background current and high stability, in which, it is necessary for sensor application. Besides, Zn nanoparticles have been widely used for sensor applications due to their low toxicity and low cost. In this work, Zn-BDD electrode was prepared through electrodeposition. The S/B value and sensitivity for OFL analysis were 9.5 and 0.42 respectively on Zn-BDD, in which, it is higher compared to the use of a bare BDD electrode. The analysis in milk was possible with the recovery of 83.05% and 101.20% for BDD and Zn-BDD electrodes respectively. It is suggested that Zn-BDD electrode could be applied for OFL analysis for further real application.

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Low-interference norepinephrine signal on dopamine detection using nafion-coated boron doped diamond electrodes

Irkham , Nasa K., Kurnia I., Hartati Y.W., Einaga Y.

Biosensors and Bioelectronics (Biosensors and Bioelectronics) 220 2023.01

ISSN 09565663

The detection of dopamine in the presence of norepinephrine using nafion-coated boron doped diamond (Nafion-BDD) electrodes was presented. An increase current signal for dopamine could be observed at around 0.75 V using Nafion-BDD, while a change in the current signal of norepinephrine that appears at similar potential was not observed. This might be due to electronegativity of the norepinephrine that is not positive enough to be attracted towards the nafion membrane, albeit neutral enough to pass through the membrane and undergo electrochemical oxidation. An optimization process including accumulation time of dopamine inside the nafion layer, solution of the pH, and nafion thickness was conducted to exploit the difference electrochemical behavior between those two catecholamines at the Nafion-BDD. Using an accumulation time of 300 s, solution pH of 7, and nafion thickness of 1.1 μm, dopamine's LOD was found to be 0.966 μM. Low-interference signal of norepinephrine to the dopamine could be observed with an excellent %recovery of dopamine in 5% range when the concentration of norepinephrine was 10 times lower compared to dopamine concentration.

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Selective electro-oxidation of cumene utilizing a flow reactor equipped with diamond electrodes

Nihongi S., Matsuoka R., Saitoh T., Einaga Y., Yamamoto T.

Current Research in Green and Sustainable Chemistry (Current Research in Green and Sustainable Chemistry) 7 2023.01

Although oxidation of benzylic C(sp3)−H bonds is an important process for synthesizing biologically active compounds, the reactions generically require hazardous reagents, catalysts, and harsh conditions. Since electro-organic synthesis utilizes electricity itself as a reagent, reactions can proceed well even under ambient conditions. Herein, we report a selective oxidation of cumene in an electrochemical flow reactor. Cumyl alcohol was selectively obtained under optimum amount of charge and current density. The selective oxidation of cumene to cumyl alcohol was achieved because overoxidation of cumyl alcohol into acetophenone was suppressed by the electrochemical flow reactor.

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Photo-assisted electrochemical CO<inf>2</inf> reduction at a boron-doped diamond cathode

Iwai G., Fiorani A., Du J., Einaga Y.

Energy Advances (Energy Advances) 2023

We report on the coupling of photoelectrochemical water oxidation and electrochemical CO2 reduction to formic acid for a photoelectrochemical system capable of light and electrochemical energy conversion to chemical energy. Titanium oxide nanotubes (TiO2 NT) and boron-doped diamond (BDD) electrodes were used as a photoanode and a cathode, respectively. From CO2 electrochemical reduction at BDD, formic acid was obtained with a faradaic efficiency of about 86% and the system provided an overall energy conversion efficiency of 5.5%. From previous CO2 reduction at a dark electrolyzer based on a BDD cathode, the cell voltage was reduced from 2.7 V to 1.4 V with 52% saving of the electrical energy input. This resulted in an increase from 50% to nearly 80% of electrical-to-chemical energy conversion efficiency.

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The Dependence of Boron Concentration in Diamond Electrode for Ciprofloxacin Electrochemical Sensor Application

Savitri I.N.I., Jiwanti P.K., Putri I.Z.D., Irkham I., Einaga Y., Supriyanto G., Wong Y.H., Srivastava S.K., Abdullah C.A.C.

Indonesian Journal of Chemistry (Indonesian Journal of Chemistry) 23 ( 3 ) 809 - 822 2023

ISSN 14119420

This study investigates the effects of boron concentration on boron-doped diamond (BDD) electrodes for electrochemical sensors of ciprofloxacin. The effects of boron concentration, scan rate, and pH of BDD electrodes with boron concentrations of 0.1, 0.5, and 1% were examined to determine the optimal conditions. Furthermore, square wave voltammetry (SWV) in phosphate buffer pH 7 was used to analyze the electrochemical behavior of ciprofloxacin. The results revealed a linear calibration curve in the concentration range of 30–100 μM with a recovery of 85–110%. Meanwhile, BDD electrode with the highest boron concentration in this experiment (1%) showed a very low limit of detection of 0.17 μM, meaning that 1% BDD gave a highly sensitive and significant measurement result for the electrochemical sensor of ciprofloxacin. With the results given, this study provides new insights for controlling boron concentrations in diamond electrodes for the electrochemical sensors of quinolone antibiotics.

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Modification of Screen-printed Carbon Electrodes with Gold Particles to Enhance Luminol Electrochemiluminescence for Hydrogen Peroxide Detection

Syukur J.M., Rahmawati I., Sanjaya A.R., Ridwan M., Fiorani A., Einaga Y., Ivandini T.A.

Sensors and Materials (Sensors and Materials) 35 ( 5 ) 1785 - 1799 2023

ISSN 09144935

Screen-printed carbon electrodes (SPCEs) were modified with gold particles to improve luminol electrochemiluminescence (ECL) in the presence of H2O2 as the co-reactant. Gold particles with sizes ranging from 10 to 50 nm were successfully deposited by the electrochemical technique with around 3.4% (w/w) gold on the carbon surface. The gold-modified SPCE (Au-SPCE) increases the ECL intensity of luminol around 2.5 times more than that using the unmodified SPCE. These signals were also found to be linearly correlated to H2O2 concentration. At an optimum pH of 9, the ECL signals of 1 mM luminol in 0.1 M phosphate buffer solution using the Au-SPCE are linear in the H2O2 concentration range from 0.5 to 200 µM (R2 = 0.99) with an estimated detection limit of 4.78 µM. The developed sensor also showed the excellent repeatability and reproducibility of the ECL signals. Moreover, H2O2 detection in milk and tap water samples was also successfully demonstrated, indicating that the developed sensor is promising for H2O2 detection applications.

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Boron-Doped Diamond Electrodes: Fundamentals for Electrochemical Applications

Einaga Y.

Accounts of Chemical Research (Accounts of Chemical Research) 55 ( 24 ) 3605 - 3615 2022.12

ISSN 00014842

ConspectusBoron-doped diamond (BDD) electrodes have emerged as next-generation electrode materials for various applications in electrochemistry such as electrochemical sensors, electrochemical organic synthesis, CO2 reduction, ozone water generation, electrochemiluminescence, etc. An optimal BDD electrode design is necessary to realize these applications. The electrochemical properties of BDD electrodes are determined by important parameters such as (1) surface termination, (2) surface orientation, and (3) boron doping level.In this Account, we discuss how these parameters contribute to the function of BDD electrodes. First, control of the surface termination (hydrogen/oxygen) is described. The electrochemical conditions such as the solution pH and the application potential were studied precisely. It was confirmed that an acidic solution and the application of negative potential accelerate hydrogenation, and the mechanism behind this is discussed. For oxygenation, we directly observed changes in surface functional groups by in situ attenuated total reflection infrared spectroscopy and electrochemical X-ray photoelectron spectroscopy measurements.Next, the difference in surface orientation was examined. We prepared homoepitaxial single-crystal diamond electrodes comprising (100) and (111) facets with similar boron concentrations and resistivities and evaluated their electrochemical properties. Experimental results and theoretical calculations revealed that (100)-oriented single-crystal BDD has a wider space charge layer than (111)-oriented BDD, resulting in a slower response. Furthermore, isolated single-crystal microparticles of BDD with exposed (100) and (111) crystal facets were grown, and we studied the electrochemical properties of the respective facets by combination with hopping-mode scanning electrochemical cell microscopy.We also systematically investigated how the boron concentration and sp2 species affect the electrochemical properties. The results showed that the appropriate composition (boron and sp2 species level) is dependent on the application. The transmission electron microscopy images and electron energy loss spectra of highly boron-doped BDD are shown, and the relationship between the composition and electrochemical properties is discussed. Finally, we investigated in detail the effect of the sp2 component on low-doped BDD. Surprisingly, although the sp2 component is usually expected to induce a narrowing of the potential window and an increase in the charging current, low-doped BDD showed the opposite trend depending on the degree of sp2 carbon.The results and discussion presented in this Account will hopefully promote a better understanding of the fundamentals of BDD electrodes and be useful for the optimal development of electrodes for future applications.

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Boron-Doped Diamond as a Quasi-Reference Electrode

Peng Z., Fiorani A., Akai K., Murata M., Otake A., Einaga Y.

Analytical Chemistry (Analytical Chemistry) 94 ( 48 ) 16831 - 16837 2022.12

ISSN 00032700

As a working electrode, boron-doped diamond (BDD) has been studied in detail in electrochemical processes because of its superior electrochemical properties. However, these characteristics have rarely been mentioned when BDD is used as a quasi-reference electrode (QRE). Herein, we conducted a systematic investigation on BDD electrodes, with different boron-doping levels (1 and 0.1%) and different surface terminations (hydrogen and oxygen) for their application as a QRE. A BDD electrode with 1% boron and a hydrogen-terminated surface achieved the best stability. Its open-circuit potential (OCP) exhibited less than 100 mV of potential drift over 6000 s and showed a minuscule half-wave potential difference (E1/2) of 0.0037 V in 0.1 mM K3[Fe(CN)6]/1 M KCl solution before and after the OCP measurement. Based on these observations, anions are found to contribute to the potential, which we preliminarily speculate as related to the capacitance caused by electrostatic adsorption on the positively charged hydrogen-terminated surface. The repeatability of measurement was verified through continuous cyclic voltammetry tests in 0.1 mM K3[Fe(CN)6]/1 M KCl, showing a maximum E1/2 difference of 0.042 V. The contribution of the redox couples was excluded, and the repeatability was considered to originate from its surface stability. Finally, a linear response of the optimized BDD as a QRE was validated (R2 > 0.99) by determination of free chlorine and dopamine concentrations, respectively. These results consolidate the existing fundamental research on BDD electrodes and promote the possibility of its application as a QRE in harsh environments or in vivo biological monitoring.

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Electrochemical detection of triamterene in human urine using boron-doped diamond electrodes

Ishii K., Ogata G., Einaga Y.

Biosensors and Bioelectronics (Biosensors and Bioelectronics) 217 2022.12

ISSN 09565663

Urine is one of the most used biological fluids for screening drug delivery and the resultant metabolites. In sports, the use of diuretics such as triamterene is considered a violation of anti-doping rules and is stipulated to be present at less than 79 nM in urine by the World Anti-Doping Agency (WADA). It is therefore important to develop effective rapid and low-cost tests for this diuretic. Here we apply electrochemical analysis using boron-doped diamond (BDD) electrodes, which have superior properties such as low background current, a wide potential window, and high resistance to deactivation. Since real urine samples show clear oxidation current peaks in the potential range more positive than 0.5 V (vs. Ag/AgCl) due to the presence of bio-components such as protein, uric acid, and ascorbic acid, to detect triamterene effectively, the electrochemical protocol was optimized towards a potential range where the other components have limited effect. Our results show that reduced triamterene exhibits an oxidation peak at 0.1 V (vs. Ag/AgCl) in 0.1 M phosphate buffer (PB) and at 0.2 V (vs. Ag/AgCl) in pooled human urine. The peak current value increased according to the triamterene concentration. The limit of detection (LOD) was 3.15 nM in the PB and 7.80 nM in pooled human urine. Finally, triamterene detection was attempted in individual urine samples. Triamterene was electrochemically detectable in individual urine samples, excluding urine samples containing an excess amount of ascorbic acid. The limit of detection (LOD) in individual urine samples was determined to be 20.8 nM.

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Application of boron doped diamond electrodes to electrochemical gas sensor

Triana Y., Ogata G., Einaga Y.

Current Opinion in Electrochemistry (Current Opinion in Electrochemistry) 36 2022.12

ISSN 24519103

Boron-doped diamond (BDD) electrodes have been attracting attention as superior electrode materials for electrochemical sensing applications. Here, we focused on applications of the BDD electrodes to electrochemical gas sensing especially dissolved gas in aqueous solution. This article discusses arsine, hydrogen sulfide, nitrogen dioxide gas for environmental sensing, and oxygen in the blood for biomedical sensing. The analytical performances suggest that BDD electrodes are more than adequate for determining the concentration of these gas species.

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Amine-Functionalized Diamond Electrode for Boosting CO<inf>2</inf>Reduction to CO

Mikami T., Yamamoto T., Tomisaki M., Einaga Y.

ACS Sustainable Chemistry and Engineering (ACS Sustainable Chemistry and Engineering) 10 ( 45 ) 14685 - 14692 2022.11

Carbon capture, utilization, and storage (CCUS) have been attracting much attention as an initiative to achieve carbon neutrality. In the capture and storage strategy, amines are widely used for highly efficient separation and capturing of CO2since amines react with CO2to form carbamates. In the utilization strategy, CO2electroreduction is a promising method to convert CO2into value-added compounds because reaction conditions are relatively mild and easily controlled. In this work, toward combining CO2capture and storage technologies and CO2electroreduction, we focused on amine modification of the electrode surface, in which boron-doped diamond (BDD) was chosen as a sustainable electrode material. CO2electroreduction using the amine-modified BDD was performed, and an applied potential dependence of the product selectivity was examined. In situ attenuated total reflectance-infrared measurements showed that the peak intensity of the stretching vibration of the carbonyl group at around 1640 cm-1decreased as applied potentials became more negative. The effect of amine modification of the BDD surface lies in the formation of a C-N bond during CO2electroreduction, resulting in the enhancement of the selectivity of CO production up to 8 times compared to the unmodified BDD.

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Activation of Boron-Doped Diamond Electrodes for Electrochemical CO<inf>2</inf>Reduction in a Halogen-free Electrolyte

Otake A., Du J., Einaga Y.

ACS Sustainable Chemistry and Engineering (ACS Sustainable Chemistry and Engineering) 10 ( 44 ) 14445 - 14450 2022.11

The electrochemical reduction of carbon dioxide (CO2) has been attracting great interest in these days. In particular, the electrochemical production of formic acid from carbon dioxide in a halogen-free electrolyte is practically important for recently developed applications such as hydrogen carriers and fuel cells. In the present work, we have demonstrated highly selective electrochemical CO2 reduction in a halogen-free electrolyte by an "activation"process which involves an initial electrochemical CO2 reduction reaction at a boron-doped diamond (BDD) electrode. The BDD activation increased the Faradaic efficiency of formic acid from 10 to 90%. A mechanistic study on the BDD activation is presented, which can explain the drastic change of reaction selectivity from the perspective of reducing the energy of electron transfer from the BDD electrode and the mass transport of CO2 molecules to the electrode surface.

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