Published papers

Among many types of fuel cells, urea/H2O2 fuel cells have garnered attention from the scientific community due to the advantages of urea. In connection to this, a nickel-cobalt-modified boron-doped diamond (NiCo-BDD) electrode was prepared via chronoamperometry. A Ni/Co ratio of 4:1 in solution was determined as the optimum ratio for the urea oxidation reaction. Results showed that the Ni and Co particles were homogeneously deposited on the BDD surface and deposited without any interaction between the particles. The prepared NiCo-BDD electrode for a urea fuel cell showed optimum performance with a 0.1M KOH and 0.50M urea solution as the anode electrolyte and a 2.0M H2O2 and 2.0M H2SO4 solution as the cathode electrolyte. An opencircuit voltage of 0.817 V with a power density of approximately 0.632 mW/sq cm at room temperature and excellent stability after 6 hr of application were achieved. NiCo-BDD significantly enhanced the catalytic activity of urea oxidation reaction compared with the Ni plate, unmodified BDD, Ni-BDD, and Co-BDD.

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.

O3 and free chlorine play significant roles in disinfection and organic degradation. There are numerous reports about their mixed-use, yet detection of the residual concentrations is not easily accomplished, whilst the interactions between them remain unclear. Herein, we develop a detection method using a boron-doped diamond (BDD) electrode to achieve the simultaneous determination of O3 and free chlorine, which benefits from the unique property of the wide potential window of BDD electrodes. It is indicated that O3 can always be accurately determined at 0.35 V vs. Ag/AgCl in an acidic solution (pH = 4-5), whether or not free chlorine is present in the solution, whereas free chlorine can be precisely monitored at −0.78 V vs. Ag/AgCl only after the O3 is completely depleted. Furthermore, in a basic solution (pH = 9-10), the reduction peak of O3 at 0.57 V vs. Ag/AgCl promptly disappears accompanied by a decrease in the peak current of free chlorine at 1.41 V. All the phenomena observed in the acidic and basic solutions are concurrently confirmed in a quasi-neutral solution. Based on these complementary measurements, a mechanism is proposed, in which the O3 reduction results in partial oxidation of the BDD surface, hindering the reduction of free chlorine in the acidic mixture; whereas O3 reacts quickly with free chlorine in the basic solution, which causes the co-consumption of both of them. It is hoped these results will give us a guide as to how better utilize mixtures and more precisely simultaneously determine O3 and free chlorine in the mixture.

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.

© 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.

© 2018 American Chemical Society. Electrochemical surface oxidation in acidic solutions was investigated on a boron-doped diamond film electrode, fabricated on a silicon prism, using attenuated total reflection infrared spectroscopy. At positive potentials above +1.3 V (reversible hydrogen electrode, RHE), the bands of surface oxygen species appear at 1745 and 1250 cm-1. Since these bands exhibit no isotope shift in deuterium solution, they are assigned to the C=O and C-O stretching modes, respectively. These bands have the maximum intensity at +3.3 V (RHE) and reversibly disappear around +0.9 V (RHE) in the potential step to the negative direction. The potentials at which the bands appear and disappear are identical to those of the anodic and cathodic peaks of the cyclic voltammogram, respectively.

© 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.

© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Electrochemical reduction of CO2 to useful compounds have been actively investigated. The faradaic efficiency and selectivity for products of CO2 reduction depend on some factors, such as electrode materials and electrolytes. Recently, boron-doped diamond (BDD) was found to be a promising electrode material for production of formic acid by CO2 reduction, but the influence of electrolytes has not been sufficiently elucidated. Here, we studied the impact of various cations and anions on CO2 reduction using BDD electrodes. The faradaic efficiency for producing formic acid became higher by using larger alkali metal cations, because these hydrated cations would keep the pH near the cathode suitable for CO2 reduction by their buffer effect. Moreover, formic acid was efficiently obtained by using specifically-adsorbed anions such as halides and sulfate. Finally, we achieved the maximum faradaic efficiency for producing formic acid as high as 95% in RbBr aqueous solution.

© 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.

© Copyright 2018 American Chemical Society. The long-term durability of boron-doped diamond electrodes (BDD) used continuously in the electrochemical conversion of CO2 to formic acid was investigated. Although the Faradaic efficiency (FE) for the production of formic acid decreased with increasing electrolysis time, the FE was easily recovered by electrochemical oxidation of the BDD electrodes in H2SO4, Na2SO4 or K2SO4 solutions. For practical application, the long-term production of formic acid using BDD electrodes can be successfully accomplished just by successive polarity reversal of plus and minus terminals. Furthermore, at a current density of -20 mA cm-2, the rate of production reached 328 μmol h-1 cm-2, which is the highest value ever obtained using plate electrodes. Consequently, we found that BDD electrodes are ideal for industrial application of CO2 reduction.

© 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.

© 2019 the Owner Societies. In recent years, boron-doped diamond (BDD) has been utilized as an electrode for the electrochemical reduction of CO2, and several reports have been published on this. The wide potential window of BDD enables the hydrogen evolution reaction, which competes with CO2 reduction, to be suppressed. On the other hand, the high overpotential is still a problem. We attempted to overcome this problem by depositing metal on the BDD electrode. Pd metal was chosen to modify the surface of the BDD electrode (PdBDD). Employing this electrode at a lower potential of-1.6 V vs. Ag/AgCl, we increased the production of CO (53.3% faradaic efficiency) from the reduction of CO2. We present various attempts made to improve the CO production.

© 2020 Elsevier Ltd This study is among the first to systematically study the electrochemical reduction of nitrate on boron-doped diamond (BDD) films with different surface terminations and boron-doping levels. The highest nitrate reduction efficiency was 48% and the highest selectivity in the production of nitrogen gas was 44.5%, which were achieved using a BDD electrode with a hydrogen-terminated surface and a B/C ratio of 1.0%. C–H bonds served as the anchor points for attracting NO3− anions close to the electrode surface, and thus accelerating the formation of NO3−(ads). Compared to oxygen termination, hydrogen-terminated BDD exhibited higher electrochemical reactivity for reducing nitrate, resulting from the formation of shallow acceptor states and small interfacial band bending. The hydrophobicity of the hydrogen-terminated BDD inhibited water electrolysis and the subsequent adsorption of atomic hydrogen, leading to increased selectivity in the production of nitrogen gas. A BDD electrode with a boron-doping level of 1.0% increased the density of acceptor states, thereby enhancing the conductivity and promoting the formation of C–H bonds after the cathodic reduction pretreatment leading to the direct reduction of nitrate.

© 2019 American Chemical Society. An electrogenerated chemiluminescence (ECL) system by in situ coreactant production, where Ru(bpy)32+ emission is generated at a boron-doped diamond (BDD) electrode, is presented. The system takes advantage of the unique properties of BDD to promote oxidation of carbonate (CO32-) into peroxydicarbonate (C2O62-), which further reacts with water to form hydrogen peroxide (H2O2), which acts as a coreactant for Ru(bpy)32+ ECL. Investigation of the mechanism reveals that ECL emission is triggered by the reduction of H2O2 to hydroxyl radicals (OH•), which later react with the reduced Ru(bpy)3+ molecules to form excited states, followed by light emission. The ECL signal was found to increase with the concentration of CO32- therefore, with the concentration of electrogenerated H2O2, although at the same time, higher concentrations of H2O2 can quench the ECL emission, resulting in a decrease in intensity. The carbonate concentration, pH, and oxidation parameters, such as potential and time, were optimized to find the best emission conditions.

© The Royal Society of Chemistry . The coercivity of magnetic nanoparticles is enhanced by the exchange coupling effect at the interface of ferrimagnetic and antiferromagnetic self-assembled monolayers. Antiferromagnetic Co3O4 nanocubes were regularly stacked on an ordered monolayer of ferrimagnetic Fe3O4 nanocubes by layer-by-layer manipulation using evaporation-driven self-assembly. The ordered arrangements of the ferrimagnetic and antiferromagnetic nanocubes are effective for the enhancement of the ferromagnetic character.

© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim. The study of CO2 electrochemical reduction to useful compounds using bare or modified BDD electrode attracts numerous attentions. Meanwhile, the efficiency of products obtained from CO2 electrochemical reduction is known to be determined by the electrode material and the electrolyte. Formic acid as main product and CO as a minor product, have also been known on the CO2 reduction using BDD electrode. Recently, we reported the successful improvement of CO production from the reduction of CO2 by decorating the surface of BDD electrode with palladium particles. Following this, herein, we present further inves-tigation on electrolyte dependence, including cation and anion dependence and also concentration effect in order to understand deeply the CO2 reduction on surface of palladium modified BDD electrode. The results suggest the use of NaCl and KCl as a catholyte for optimum performance, in addition to the improvement of CO2 reduction product in higher electrolyte concentration.

© 2020 Elsevier B.V. Modification of iridium on the surface of boron-doped diamond (BDD) electrode has been performed to decrease the overpotential reduction of carbon dioxide (CO2) and produce value-added carbon compounds. The modification was performed using the cyclic voltammetry (CV) technique that successfully deposited iridium oxide on the surface of the BDD electrode with an Ir-to-C ratio of approximately 1:100. When the modified BDD electrode was utilized for CV of a dissolved-CO2-saturated solution, hydrogen evolution occurred at a potential of approximately −1.2 V (vs. Ag/AgCl), which was lower than that when an unmodified BDD was used. Furthermore, when this electrode was utilized for amperometry of the same solution at −1.7 V for 1 h, formic acid (HCOOH) was produced with a Faradaic efficiency of approximately 50%. Results indicated that the modified electrode has considerable potential for application to CO2 electrochemical reduction.

The electrochemical oxidation reaction of nitrogen dioxide (NO2) using boron doped diamond (BDD) electrodes is presented. Cyclic voltammetry of NO2 in a 0.1 M KClO4 solution exhibits oxidation peaks at +1.1 V and +1.5 V (vs. Ag/AgCl) which are attributable to oxidation of HONO and NO2−, respectively. Moreover, the pH and scan rate dependences were investigated to study the oxidation mechanism. A linear calibration curve was observed in the concentration range of ∼1 to 5 mM (R2=0.99) with a detection limit of 11.1 ppb (S/B=3) for HONO and 58.6 ppb (S/B=3) for NO2−. In addition, the analytical performance was compared with those using glassy carbon, platinum and stainless steel as the working electrode.

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.

The electrochemical reduction of CO2 has been attracted researcher attention around the world. There are many researches on how to improve the value of CO2 gas by converting it to useful chemicals or feedstock. In this report, we studied electrochemical behavior of Ti3C2Tx modified on the surface of boron-doped diamond (BDD) electrode for CO2 reduction. It is shown that the presence of Ti3C2Tx could improve the catalytic effect for CO2 reduction, as the CO2 reduction peak was shifted to positive potentials. This work is expected to provide an information of potential catalyst to be applied for real CO2 reduction application.