Oxygen Reduction Current Research Articles

Polymeric Benzothiadiazole, Benzooxadiazole, and Benzoselenadiazole Photocathodes for Photocatalytic Oxygen Reduction to Hydrogen Peroxide

AbstractVisible‐light‐driven semiconductor photoelectrodes are promising new devices for on‐demand photocathodic generation of hydrogen peroxide. Herein, the fabrication of organic polymeric photocathodes employing poly(4,7‐di(thiophen‐2‐yl)benzo[c][1,2,5]thiadiazole) (pThBTD), and comparatively seven other related derivatives is reported. The monomer dithienobenzodithiazole can be directly polymerized on an electrode via two methods: electropolymerization or iodine‐vapor‐assisted polymerization. Both give polymers with wide visible light absorption and suitable stability for photoelectrodes. These methods yield different active layer morphologies, with electropolymerization yielding photocathodes with better performance. Critical issues affecting oxygen reduction photocurrents are evaluated, namely thickness, wettability, and pH. Photocathodic oxygen reduction currents, as well as photovoltages, are among the highest reported for an organic photoelectrocatalyst, and pThBTD films can stably produce H2O2 with high faradaic yield over at least 8 h. This study shows that single‐component organic semiconductor devices can be highly competitive versus more complex heterostructures and that such low‐bandgap organic polymers can afford remarkable stability.

Manganese oxide nanocrystals embedded porous Graphene-like network for electrosynthesis of H2O2 and construction of Self-powered aptasensor

To improve the selectivity and production rate of the H2O2 electrosynthesis, an electrocatalyst was established based on ultrathin graphene-like mesoporous carbon nanosheets embedded with ultra-small manganese oxide (MnOx) nanocrystals (denoted as MnOx@C). A polymer-manganese-metal–organic framework (polyMn-MOF) was used as the precursor for the preparation of the series of MnOx@C hybrid by calcining at different temperature (600, 700, and 800 °C) under nitrogen atomsphere. Density functional theory simulation revealed that MnOx@C-700 obtained by pyrolyzing polyMn-MOF at 700 °C exhibited the optimization adsorption energy of *OOH, thus showing a high H2O2 selectivity of 96.5 % and large limited oxygen reduction current of 2.3 mA cm−2. Meanwhile a high mass activity of 35.56 A g−1 (at 0.4 V vs the reversible hydrogen electrode) and high durability over 10 h were attained for the MnOx@C-700 catalyst. Moreover, the MnOx@C-700-assembled Zn-air battery (ZAB) showed a large open-circuit voltage of 1.34 V and a remarkable peak power density of 2.22 mW cm−2. The constructed ZAB-driven self-powered aptasensor demonstrated a wide linear range of 0.1 pg mL−1–100 ng mL−1 and an ultralow detection limit of 0.08 pg mL−1 toward diethylstilbestrol. This work provided new insights onto the H2O2 electrosynthesis and detection of hazards using the self-powered biosensing strategy.

Kinetics of Oxygen Reduction Reaction of Polymer-Coated MWCNT-Supported Pt-Based Electrocatalysts for High-Temperature PEM Fuel Cell

Sluggish oxygen reduction reaction (ORR) of electrodes is one of the main challenges in fuel cell systems. This study explored the kinetics of the ORR reaction mechanism, which enables us to understand clearly the electrochemical activity of the electrode. In this research, electrocatalysts were synthesized from platinum (Pt) catalyst with multi-walled carbon nanotubes (MWCNTs) coated by three polymers (polybenzimidazole (PBI), sulfonated tetrafluoroethylene (Nafion), and polytetrafluoroethylene (PTFE)) as the supporting materials by the polyol method while hexachloroplatinic acid (H2PtCl6) was used as a catalyst precursor. The oxygen reduction current of the synthesized electrocatalysts increased that endorsed by linear sweep voltammetry (LSV) curves while increasing the rotation rates of the disk electrode. Additionally, MWCNT-PBI-Pt was attributed to the maximum oxygen reduction current densities at −1.45 mA/cm2 while the minimum oxygen reduction current densities of MWCNT-Pt were obtained at −0.96 mAcm2. However, the ring current densities increased steadily from potential 0.6 V to 0.0 V due to their encounter with the hydrogen peroxide species generated by the oxygen reduction reactions. The kinetic limiting current densities (JK) increased gradually with the applied potential from 1.0 V to 0.0 V. It recommends that the ORR consists of a single step that refers to the first-order reaction. In addition, modified MWCNT-supported Pt electrocatalysts exhibited high electrochemically active surface areas (ECSA) at 24.31 m2/g of MWCNT-PBI-Pt, 22.48 m2/g of MWCNT-Nafion-Pt, and 20.85 m2/g of MWCNT-PTFE-Pt, compared to pristine MWCNT-Pt (17.66 m2/g). Therefore, it can be concluded that the additional ionomer phase conducting the ionic species to oxygen reduction in the catalyst layer could be favorable for the ORR reaction.

Chemical Conversion Treatment of AA5083 Aluminum Alloy and AISI 1045 Carbon Steel under Galvanically Coupled Condition in Na<sub>2</sub>MoO<sub>4</sub>: Effect of pH on Corrosion Resistance

To ascertain the effect of solution pH of Na2MoO4 chemical conversion treatment for aluminum/steel joints on corrosion resistance, AA5083 aluminum alloy and AISI 1045 carbon steel were immersed in 50 mM Na2MoO4 at pH ranges of 8–12 under galvanically coupled condition. Subsequently, in diluted synthetic seawater, the galvanic corrosion resistance of the AA5083 alloy connected to the AISI 1045 carbon steel was assessed. The number of localized corrosion damages was counted, and AA5083 treated at pH 11 was found to be the better corrosion resistance. The oxygen reduction current on bulk Al6(Fe, Mn) decreased with increasing solution pH of the conversion treatment. The Al6(Fe, Mn) particles on AA5083 were not preferential cathodes, and alkalization through oxygen reduction would not occur when the treatment was performed above pH 9. Auger electron spectroscopy analysis showed that Mo-accumulation, Fe-removal, and film thickening occurred on the particles of AA5083 treated at pH 11. These factors contributed to the suppression of the cathodic activity of the Al6(Fe, Mn) particles, resulting in the improved galvanic corrosion resistance of AA5083.

Scanning Electrochemical Microscopy-Somatic Cell Count as a Method for Diagnosis of Bovine Mastitis.

Simple SummaryMastitis is inflammation/swelling in the breast, which is generally caused by an infection. In this study, we present scanning electrochemical microscopy-somatic cell count (SECM-SCC) as a novel method for diagnosis of mastitis in bovines. We developed a biosensor in this study that can serve as a highly promising portable electrochemical device for mastitis diagnosis in bovines.The method to diagnose mastitis is generally the somatic cell count (SCC) by flow cytometry measurement. When the number of somatic cells in raw milk is 2.0 × 105 cells/mL or more, the condition is referred to as mastitis. In the current study, we created a milk cell chip that serves as an electrochemical method that can be easily produced and used utilizing scanning electrochemical microscopy (SECM). The microelectrode present in the cell chip scans, and the difference between the oxygen concentration near the milk cell chip and in bulk is measured as the oxygen (O2) reduction current. We estimated the relationship between respiratory activity and the number of somatic cells in raw milk as a calibration curve, using scanning electrochemical microscopy-somatic cell count (SECM-SCC). As a result, a clear correlation was shown in the range of 104 cells/mL to 106 cells/mL. The respiration rate (F) was estimated to be about 10–16 mol/s per somatic cell. We also followed the increase in oxygen consumption during the respiratory burst using differentiation inducer phorbol 12-myristate 13-acetate (PMA) as an early stage of mastitis, accompanied with an increase in immune cells, which showed similar results. In addition, we were able to discriminate between cattle with mastitis and without mastitis.

Systematic Study of Effective Hydrothermal Synthesis to Fabricate Nb-Incorporated TiO2 for Oxygen Reduction Reaction.

Fuel cells are expected to serve as next-generation energy conversion devices owing to their high energy density, high power, and long life performance. The oxygen reduction reaction (ORR) is important for determining the performance of fuel cells; therefore, using catalysts to promote the ORR is essential for realizing the practical applications of fuel cells. Herein, we propose Nb-incorporated TiO2 as a suitable alternative to conventional Pt-based catalysts, because Nb doping has been reported to improve the conductivity and electron transfer number of TiO2. In addition, Nb-incorporated TiO2 can induce the electrocatalytic activity for the ORR. In this paper, we report the synthesis method for Nb-incorporated TiO2 through a hydrothermal process with and without additional load pressures. The electrocatalytic activity of the synthesized samples for the ORR was also demonstrated. In this process, the samples obtained under various load pressures exceeding the saturated vapor pressure featured a high content of Nb and crystalline TiNb2O7, resulting in an ellipsoidal morphology. X-ray diffraction results also revealed that, on increasing the Nb doping amounts, the diffraction peak of the anatase TiO2 shifted to a lower angle and the full width at half maximum decreased. This implies that the Ti atom is exchanged with the Nb atom during this process, resulting in a decrease in TiO2 crystallinity. At a doping level of 10%, Nb-incorporated TiO2 exhibited the best electrocatalytic activity in terms of the oxygen reduction current (iORR) and onset potential for the ORR (EORR); this suggests that 10% Nb-doped samples have the potential for enhancing electrocatalytic activity.

Agricultural by-product extracts as scale inhibitors of mild steel in tap water

Three industry by-products, namely rapeseed pomace from the wastes of edible oil production, sugar beet pulp from the wastes of sugar production and fodder radish cake, have been tested as scale inhibitors of mild steel in tap water. Ethanol extracts were prepared by maceration and the electrochemical approach to study the scale formation was utilized, based on the measurement of oxygen reduction current during nucleation and formation of calcium carbonate in the presence of extracts. Scaling time, porosity and area density of the scale was determined and used to characterize the inhibition efficiency. Chemical compositions of extracts were analysed by GC–MS analysis (gas chromatography with mass selective detector by mass selective integration). The rapeseed pomace extract and fodder radish cake extract at the concentration of 10 mL/L appeared to be efficient scaling inhibitors. Sugar beet pulp extract increases the crystallization time, however the amount of deposited scale appeared to be the same as in the tap water. The scale inhibition is caused mainly by the formation of adsorbed film on the scale nucleus that blocks the surface and prevent further crystal growth.

A Novel Bi-Functional Catalyst, Na-Bi-Ru-O, for Oxygen Reactions at Two or Three Phase Boundaries with Alkaline Media

Low carbon technology requires highly efficient energy conversion materials and systems which include the catalyst, the electrode, the separator, and etc. for uses in electrolytic hydrogen production (EHP) and air rechargeable batteries (ARB) linked to solar and wind power generation. One of the important materials is the oxygen catalyst working for OER and/or ORR at the anode of EHP and the positive electrode of ARB, and it has been reported a variety of materials including metals, alloys, oxides, sulfides, doped and un-doped carbon, and others [1-3]. We have been also developing pyrochlore oxides, general formula A2B2O7, containing bismuth at the A-site and ruthenium at the B-site especially for aqueous ARBs, e.g., metal hydride/air and zinc/air batteries, and recently have found that a novel oxide catalyst similar to bismuth ruthenium oxide (BRO) except that sodium is also the component and is highly active for OER and ORR with low Tafel slopes. This paper introduces the pyrochlore-like oxide containing sodium, bismuth, and ruthenium with the preparation process and the results on characterization and electrochemical properties for oxygen reactions of the obtained NBRO catalyst.NBRO was prepared by co-precipitation method, in which the calcination of the precipitates obtained by adding excess NaOH solutions into the metal salt solution containing bismuth and ruthenium. The preparation with LiOH solutions replacing NaOH solutions was also carried out for comparison. The obtained oxides were characterized by XRD, RBS, EXAFS, AES, AAS, and SEM, and electrochemical measurements were performed using a three-electrode cell. The working electrode was the titanium disk covered with the oxides, which was mounted in a rotating-disk electrode equipment (Titanium disk method, TDM), and the electrolyte was 0.1 mol/L KOH solutions. Linear sweep voltammetry was performed for anodic and cathodic polarization, and oxygen reduction current was obtained with the difference in current measured in the solutions under N2 or O2 bubbling. Tafel plots of polarization curves gave Tafel slope and exchange current density, i 0. The air electrode, 23mm x 23mm x 0.2 mm, comprising the oxide catalyst, graphite, and PTFE was also prepared and tested with a half-open cell using 6 mol/L KOH solutions, in which the air electrode contacted the solution at one side and faced to air at the other side.The XRD pattern of NBRO was close to that of BRO prepared by solid mixing of Bi2O3 and RuO2 [4], while the EXAFS results indicated that sodium occupied near the A-site of pyrochlore structure as well as bismuth, and the elemental analysis revealed that sodium was about 4 to 6 at%. SEM observation also showed that the primary particle size of NBRO ranged from 20 nm to 40 nm and the secondary one was under 500 nm. Polarization curves by TDM gave that the overpotentials for OER and ORR were 200 mV and 300 mV, respectively, and Tafel slopes for both the reactions were about 40 mV/dec, which are much lower than the other materials such as platinum, cobalt, and other types of oxides. The air electrode using NBRO further demonstrated a high catalytic activity at two phase or three phase boundaries with 6 mol/L KOH solutions, which are, for example, a very high current density, 800 mA/cm2, for both OER and ORR, and a good cyclability up to 3000 cycles. Therefore, NBRO is expected to reduce the polarization of ARB and alkaline water electrolysis for EHP.

Voltammetric Method for Determination of Glutathione on a Gold-Carbon-Containing Electrode

Glutathione (GSH) is one of the most important thiol-containing antioxidants involved in various biochemical processes in the human body. Glutathione determination in biological fluids (saliva, urine, serum) and pharmaceutical preparations is rather important for clinical practice. Various analytical methods such as spectrophotometry, fluorimetry, high-performance liquid chromatography, NMR spectroscopy, capillary electrophoresis, and electrochemical methods are widely used for this purpose. Electrochemical methods are characterized by easy implementation, low cost, and possibility of miniaturization. The electrochemical behavior of reduced (GSH) and oxidized (GSSG) glutathione on a gold-carbon-containing electrode (AuCE) was studied using cathodic voltammetry with different methods of removing oxygen from an electrochemical cell: nitrogen sparging and addition of sodium sulfite (4 mol/dm3). It has been shown that traces of H2O2 that remain in the near-electrode layer on the AuCE even after oxygen removal influence the electrochemical properties of GSH at a cathode sweep of the potential from 0 to –1.8 V: GSH is oxidized by H2O2 to GSSG; the most important product of this reaction is O2. An indirect determination of GSH by the current of oxygen reduction in the Na2SO3 medium in the concentration range from 0.5 × 10–8 to 4.2 × 10–8 mol/dmm3 with a detection limit of 2.5 × 10–9 mol/dm3 is proposed. The developed voltammetric method is approved for the determination of GSH in certain pharmaceutical preparations.

Measurement of Dissolved Oxygen Concentrations of Chloroaluminate Ionic Liquids in Dry Air

The electrodeposition of Al has been studied in various ionic liquids represented by the 1-ethyl-3-methylimidazolium chloride-AlCl3 system. However, AlCl3-based (chloroaluminate) ionic liquids are generally handled in an inert atmosphere of nitrogen or argon because they are highly hygroscopic and susceptible to hydrolysis through the reaction with moisture in the air. To maintain an inert atmosphere, a closed system that typically uses a glove box is required, but operation in a closed system leads to low productivity and high cost. Therefore, electrodeposition in an inert atmosphere is unsuitable for mass production on an industrial scale. To alleviate this problem, we have previously studied the feasibility of Al electrodeposition in dry air using chloroaluminate ionic liquids. Because the electrodeposition process in dry air does not require a glove box, it is considered to be more productive than the electrodeposition process under an inert atmosphere.In our previous study, four different chloroaluminate ionic liquids consisting of different organic cations ([cation]Cl-AlCl3) with a molar ratio of [cation]Cl : AlCl3 = 1 : 2 were used as Al electrodeposition baths to study Al electrodeposition behavior in dry air. The cations used were 1-ethyl-3-methylimidazolium (EMI+), 1-butylpyridinium (BP+), 1-butyl-1-methylpyrrolidinium (BMP+), and trimethylphenylammonium (TMPA+). We found that electrodeposition in dry air using the bath composed of EMI+ or BP+ could not produce an Al film covering the entire surface of the substrate, whereas electrodeposition using the bath composed of BMP+ or TMPA+ could produce an Al film covering the entire surface of the substrate in dry air as well as in an inert atmosphere.The reason for the difference in the results of Al electrodeposition in dry air according to cationic species has not yet been ascertained, but it is speculated that dissolved oxygen has some influence on the Al electrodeposition. In the present study, we measured the concentration of oxygen dissolved in four types of ionic liquids in dry air.For measuring the dissolved oxygen concentration, ionic liquids with a composition of [cation] Cl: AlCl3 = 1: 0.9 were used. This composition was chosen because only AlCl4 −, which is an ionic species that is difficult to be reduced to Al metal, is present in the bath when the AlCl3 mole fraction is less than 50 mol% (Lewis base)in chloroaluminate ionic liquids. Consequently, Al electrodeposition does not occur, and low extent of electrochemical reaction other than Al electrodeposition at a potential of 0 V vs. Al / Al (III) or less can be investigated. The concentration of dissolved oxygen was measured by chronoamperometry using two types of electrodes, a macroelectrode and a microelectrode, both of which have a circular active area with a diameter in the order of millimeter and micrometer, respectively. In the case of chronoamperometric measurement with a macroelectrode, the reduction current of oxygen follows the equation in the upper row in Table 1, assuming that the reaction rate is controlled by the planar diffusion of oxygen from the bulk electrolyte to the surface of the electrode. Upon measuring the current–time response, two unknowns remain, namely, the concentration and the diffusion coefficient of dissolved oxygen; and it is not possible to determine the dissolved oxygen concentration through the chronoamperometric measurement using the macroelectrode alone. In the case of chronoamperometric measurement with a microelectrode, the geometry of the diffusion of the reactant to the electrode surface changes to semi-spherical, and the reduction current of oxygen thus follows the equation in the lower row in Table 1. The concentration and diffusion coefficient of dissolved oxygen can thus be determined through the two chronoamperometric measurements.The chronoamperometric measurements revealed that there was no significant difference in the oxygen concentrations of the ionic liquids with different cationic species. The results that we have obtained so far are as follows: 1) In an inert atmosphere, an Al film covering the entire surface of the substrate can be electrodeposited from a bath containing any cation species. 2) In dry air, an Al film covering the entire surface of the substrate can only be electrodeposited from some baths composed of specific cation species. 3) There is no significant difference in the dissolved oxygen concentrations of the baths in dry air, even though the cation species in the baths are different. In consideration of these results, the reason for the different results of Al electrodeposition in dry air according to the cationic species is neither dissolved oxygen alone nor cationic species alone but the combined action of both dissolved oxygen and the cation. Figure 1

Effect of Semiconducting Properties of Oxide-Based Compounds on Oxygen Reduction Activity in Acidic Media

Polymer electrolyte fuel cells (PEFCs) are attractive as energy conversion systems with high conversion efficiency. Although theoretical energy conversion efficiency is high, 83% at 295 K, the actual efficiency is very low because of a large overpotential of oxygen reduction reaction (ORR). In addition, the durability of the catalysts becomes important for commercialization of PEFCs. Pt supported carbon cathode is easy to degrade at high potential region and potential fluctuation. Therefore, we have focused on group 4 and 5 oxide-based compounds as oxides with active sites and electro-conductive supports. We successfully demonstrated that the surface of the oxides had high quality active sites [1] and superior durability against start/stop and load cycle tests [2].Recently, DFT calculation by Sugino’s group revealed that Pd or Rh doped TiO2 had possibility that these surfaces reached equilibrium potential for the ORR [3]. However, the DFT calculation was only based on the adsorption Gibbs energies of reaction intermediates. Considering the actual active sites, sufficient electron supply is necessary to proceed ORR fluently. Group 4 and 5 oxide-based compounds are essentially semi-conductors. Therefore, the semi-conducting physico-chemical properties such as carrier density and Flat-band potential affect the supply of electrons to the active sites. However, the effect of the semi-conducting properties of the oxide-based compounds on the oxygen reduction activity in acidic media has not been investigated yet. In this study, we attempted to reveal the effect of Flat-band potential and capacitance of space charge layer on the ORR activity. Thus, we focused on titanium oxides and prepared Nb, Ta, and Zr added titanium oxide to investigate the effect of foreign element doping.The oxide-coating film was prepared on a Ti plate (10 mm× 10 mm× 1 mm) substrate by the conventional dip-coating method using a 0.5 M butanolic solution of metal salt: titanium tetrabutoxide, zirconium tetrabutoxide, niobium pentaethoxide or tantalum pentaethoxide. The titanium substrate was etched with 10wt% oxalic acid at 80 °C for 1 h and then rinsed with deionized water before the dipping procedure. Calcination of the dip-coated salts was con-ducted in air at 350 °C. The dip-drying/calcination (alternating 10 min each) procedure was typically repeated 15 times.Electrochemical measurements were carried out using a three-electrode cell at 30 ± 1 °C in 0.1 M H2SO4. Cyclic voltammetry was performed with 5 mV sec-1 in the potential range from 0.2 to 1.2 V in an oxygen and nitrogen atmosphere to obtain oxygen reduction current. The oxygen reduction current density, i ORR, was normalized by the geometric area of the electrode. The ORR activity was evaluated by onset potential for the ORR, E onset, defined as the electrode potential at i ORR = 0.02 mA/cm2 and i ORR at 0.2 V, |i ORR@0.2V|.Electrochemical impedance measurements were performed with amplitude of 0.01 V and frequency of 1000 Hz to obtain capacitance of space charge layer, C scl, every 0.1 V below 1.1 V. In addition, the values of the (1/C scl)2 were plotted against the electrode potential, that is, Mott-Schottky plot, to obtain the flat-band potential, E fb.Figure 1 shows the relationship between E fb and E onset of Nb, Ta, or Zr doped TiO2 electrodes. The relation of E onset－E fb≒0.3 V was obtained and it was independent of the doped elements. The difference between the electrode potential and E fb corresponded to the barrier height of space charge layer. When the electrode potential is higher than the E onset, the electrons cannot pass through the barrier of the space charge layer, resulting that the ORR cannot proceed because the supply of electrons from bulk of semi-conductor to the active sites at the interface between oxide-electrolyte. When the electrode potential reaches at Eonset, the ORR starts to proceed due to the continuous supply of the electrons because the electrons can pass through the barrier. According to the relation of E onset－E fb≒0.3 V, the barrier height of the space charge layer, which the electrons can pass through, was estimated to be 0.3 V.AcknowledgementThe authors wish to thank the support of the New Energy and Industrial Technology Development Organization (NEDO).

Effects of B-Site Modification of Bi-Ru Based Oxide on Catalytic Activity for Oxygen Reactions

An aqueous air secondary battery uses oxygen in air as the active mass of the air electrode, at which the reactions are oxygen reduction during discharge and oxygen evolution during charge. The polarization of the air electrode is known to be large and a highly active bi-functional oxygen catalyst is needed to reduce the polarization. We have been developing a metal hydride/air secondary battery using KOH solutions and have found that bismuth and ruthenium based oxide (BRO) can suppress the polarization of oxygen reactions [1]. Although BRO has a good bi-functionality, there is still an issue that the polarization of oxygen reduction is ca. 100 mV larger than that of oxygen evolution. In this work, we aimed to improve the catalytic activity of BRO with modification of B-site element by substituting ruthenium with manganese. Then, the modified BRO (MBRO) was examined by titanium disk method (TDM) developed by our group [2], which is very useful to know the activity of oxygen catalyst, because no oxygen reactions on titanium occur in the examined potential range so that no oxygen current from the substrate is excluded. The electrochemical polarization data was analyzed to obtain some kinetic parameters such as Tafel slope and exchange current density.MBRO was prepared by co-precipitation method, in which the calcination of the precipitates obtained by adding excess NaOH solutions into the metal salt solution containing bismuth, ruthenium, and manganese. BRO was also synthesized for comparison. The obtained oxides were characterized by XRD, SEM, and EDX, and electrochemical measurements were carried out using a three-electrode cell. The working electrode was the titanium disk covered with MBRO or BRO, which was mounted in a rotating-disk electrode equipment, and the electrolyte was 0.1 mol/L KOH solutions. Linear sweep voltammetry was performed for anodic and cathodic polarization, and oxygen reduction current was obtained with the difference in current measured in the solutions under N2 or O2 bubbling. The specific activity was evaluated with the normalized current by the catalyst’s weight, i w, or by the double layer charge, i c, and Tafel plots of polarization curves gave Tafel slope and exchange current density, i 0, for MBRO and BRO.The XRD patterns of MBRO were close to that of BRO except that some peaks of MBRO in the high 2θ region showed the peak sift to a higher angle with increasing manganese. EDX measurements of MBRO indicated that the metal ratio of the obtained oxide was almost the same as that of the precursor solution. SEM observation also revealed that the particle size of MBRO ranged from 20 nm to 60 nm with no clear dependence with the metal ratio. The polarization of MBRO for oxygen reduction was smaller than that of BRO and was more reduced with increasing manganese up to 30 at%, while a little difference in polarization for oxygen evolution was seen between MBRO and BRO. The analysis of Tafel slope and exchange current density from LSV data gave some interesting relationship between these parameters and the polarization for ORR and OER that the exchange current density of MBRO was 6 to 8 times larger than that of BRO at high manganese ratios, which is the main reason why MBRO showed a reduction in ORR polarization, while Tafel slope of MBRO for ORR was almost the same as or slightly higher than that of BRO, and Tafel slope for OER was hardly changed between MBRO and BRO. From the results, we found that the B-site modification of BRO with manganese can enhance the kinetics of electron transfer for the oxygen reactions.

(Invited) Cell Analysis Using Integrated Electrochemical Devices

For the fields of tissue engineering and organs-on-a-chip, three-dimensional (3D) cultured cells are widely used. These applications require a method that can easily measure cell activities of 3D cultured cells without any cell damages. For the purpose, electrochemical approaches have been proposed [1-3]. By using these electrochemical approaches, several kinds of cell activities such as respiratory activities can be measured.My group has developed several kinds of integrated electrochemical devices including chip and probe devices. The chip devices contained many electrodes based on complementary metal oxide semiconductor (CMOS)-based devices [3-9]. The detection system is useful for real-time imaging, because it rapidly obtains 2D electrochemical images consisting redox current signals at target positions. By using the CMOS-based electrochemical devices, respiration activity and cell differentiation status were clearly visualized. Also, the device provided electrochemical images of released molecules such as dopamine from 3D cultured cells.In addition to CMOS-based devices, bipolar electrode (BPE)-based electrode arrays was developed [10]. In BPE system, anodic and cathodic reactions are induced at both ends of the BPE with only a pair of driving electrodes. Therefore, many sensing elements can be incorporated into a small chip without complex wiring. In my BPE device, oxygen reduction currents at the sensor near 3D cultured cells converted electrochemiluminescence (ECL) to detect respiratory activity of 3D cultured cells.In addition to chip devices, scanning electrochemical microscopy was applied for electrochemical measurement of respiration activity of fibroblast spheroids containing endothelial cell networks [11]. This study reported the effects of endothelial cell networks on cell activity of 3D cultured cells.Thus, these integrated electrochemical devices were applied for cell analysis. They will be utilized for tissue engineering and organs on a chip. In this presentation, I will summarize these devices.

Factors Affecting ORR Activity of Nb-Added TiOx Catalyst Using Carbon Support for PEFC

1. IntroductionCarbon-supported platinum catalysts used for the cathode of present polymer electrolyte fuel cells (PEFCs) have some problems such as a large amount of platinum use and low durability under operation condition. Therefore, we have attempted to develop substitute of platinum based on group 4 and 5 transition metal oxides. We found that stable oxygen vacancies on the surface and lattice distortion of these metal oxides could act as active sites of oxygen reduction reaction (ORR)1). On the other hand, cup-stacked carbon nanotubes (CSCNTs) coated with TiO2 have been investigated as durable supports for a platinum-based catalysts2). We already revealed that Nb-added titanium oxide with lattice distortion showed some ORR activity1). Then, we thought that CSCNTs coated with Nb-added titanium oxide might show definite ORR activity. In this study, we prepared CSCNTs coated with Nb-added TiOx and evaluated their behavior to investigate the factors which affect the ORR activity.2. ExperimentalThe CSCNTs (GSI Creos) without amorphous carbon on the surface was added to 2-propanol and dispersed ultrasonically, then a desired amount of Ti isopropoxide and Nb ethoxide were added with stirring. A sufficient amount of water mixed with 2-propanol were added to proceed hydrolysis and stirred overnight. Suction filtration was performed to obtain a precursor. In this experiment, Nb was added into TiO2 with an atomic% of 10 against Ti, and a loading of oxide was adjusted to 30 wt% of total catalyst. The precursor was heat-treated under an Ar gas containing 4% hydrogen at desired temperature and time to obtain Nb-added TiOx catalysts, designated as Nb-added TiOx/CSCNTs.The Nb-added TiOx/CSCNT was supported on a glassy carbon rod to make a working electrode. Electrochemical measurements were carried out using a three-electrode cell at 30 ± 1 °C in 0.1 M H2SO4. Cyclic voltammetry was performed with 5 mV sec-1 in the potential range from 0.2 to 1.2 V in an oxygen and nitrogen atmosphere to obtain oxygen reduction current. ORR current based on oxides was obtained by subtracting the reduction current of carbon from the reduction current of the entire catalyst. The oxygen reduction current density, iORR, was normalized by the mass of the oxides.3. Results and discussionFigure 1 shows the dependence of iORR at 0.6 V of Nb-added TiOX/CSCNTs on heat treatment temperature. The results of Nb-added TiOx powders prepared without carbon were also plotted. Because the electro-conductivities of the Nb-added TiOx powders were very low, Ketjenblack was mixed as an electro-conductive material to evaluate the ORR activity. The current value of Nb-added TiOx/CSCNT is significantly improved compared to oxide powder. This is because the electron supply increased due to the deposition of oxides on the CSCNT. The highest ORR current density was observed at 800 oC.Figure 2 shows the SEM images of Nb-added TiOX/CSCNTs. Amorphous TiO2 covers with the surface of CSCNTs in the unheated catalyst. At 700 ° C and 800 ° C, the oxide particles of around 10 nanometers were supported with high dispersion. However, at 900 ° C, the particles aggregated to become larger.Figure 3 shows the Ti 2p XPS spectra of Nb-added TiOx/CSCNTs heat-treated at 600-1000 °C. Ti2p peak shifted to the lower binding energy from 600 ° C to 800 ° C and to the higher energy from 800 ° C to 1000 ° C. The proportion of low-valence state Ti3+ increased as the temperature increased from 600 to 800 ° C. The reason why the shift to the higher binding energy occurred above 800 ° C was that the oxide surface prepared at higher heat-treatment temperature was oxidized by exposure of the air.Figure 4 shows the relationship between ratio of Ti3+ / (Ti3+ + Ti4+) and ORR current density at 0.6 V. The ratio of Ti3+ was calculated from the Ti 2p XPS spectra. The iORR at 0.6 V increases as ratio of Ti3+ increases. The ratio of Ti3+ indicates the presence of oxygen vacancies on the surface of the oxide. Therefore, it is considered that the increase of oxygen vacancies on the oxide surface strongly affected the ORR activity.AcknowledgementThe authors wish to thank the supply of the CSCNT from GSI Creos and the support of the New Energy and Industrial Technology Development Organization (NEDO), JSPS grants-in-aid for scientific research, Suzuki Foundation, and Tonen General Sekiyu Research / Development Encouragement & Scholarship FoundationReferences1) A. Ishihara, et. al., Electrochim. Acta, 283,1779 (2018).2) F. Ando, et. al., Electrochim. Acta, 404, 232 (2010) Figure 1

Respiratory Burst Evaluation Using SECM in Milk from Mastitis Bovine and Healthy Bovine

1. Introduction A large number of somatic cells are found in milk from mastitis bovine than one from healthy bovine. About 70% of the somatic cells are neutrophils and monocytes1). We monitored respiratory burst and respiration activity of human immune cells using scanning electrochemical microscopy (SECM) 2). In this study, we have described the results on the respiratory burst of neutrophils and monocytes in bovine milk using SECM. 2. Methods 2.1 Sample and cell chip preparation We centrifuged the milk sample from mastitis bovine to remove fat. The cell number of the cell suspension obtained by centrifugation was 4.2×106 cells/mL. We then mixed the cell suspension and collagen in a 9:1 ratio. We transferred 1.5 μL aliquots of the aggregated cells to collagen-embedded and pyramidal wells that had been anisotropically etched with silicon.Collagen embedded cells in pyramid well are called the cell chip. For measurement of normal cellular respiration, somatic cells in bovine milk were added just prior to measurement. During measurement of respiratory burst, PMA was added under the same experimental conditions to the somatic cells at a final concentration of 100 nM. We prepared the cell chip of the milk sample from healthy bovine by the same method. The cell number of the cell suspension obtained from the milk of health bovine was 2.1×105 cells/mL. 2.2 SECM evaluation of respiratory burst using cell chip The respiration activity was measured by scanning using a Pt microelectrode in the Z direction between 30 μm (the cell suspension surface) and 530 μm (the bulk) from the cell suspension. The measurement solution was PBS buffer containing 11.4 mM glucose. The scanning distance, scanning speed and sampling time are 500 μm, 50 μm/s and 100 msec, respectively. In this study, we conducted experiments on two milk samples, one of which was diagnosed with mastitis and the other of which was control (non-mastitis), and we compared the results. 3. Results and discussion Fig. 1 (A) shows the result of mastitis sample, and (B) shows the result from a healthy sample. The working electrode was located 30 μm above the well top (N) at t = 0, 20, 40, and 60 s. The electrode was located 530 μm above the well top (Bulk) at t = 10, 30, and 50 s. From Fig. 1, in all measurement results, the reduction current value is lower at Point N than at Bulk. This indicates that the dissolved oxygen concentration in the vicinity is decreased due to the respiration of somatic cells. We calculated the average ΔI as the electrode moved up and down during N-bulk each of the three scans. The change in the oxygen concentration (ΔC) at 25 °C was calculated assuming a dissolved oxygen content of 248 μM and an oxygen reduction current of -1.7 nA (summarized in Table.1). From the PMA (-) experimental results, the magnitude relationship between the number of somatic cells and the oxygen consumption rate agree. Moreover, the values at PMA (+) are higher in both samples than PMA (-). This result suggests that PMA induced respiratory burst and increased respiratory volume of neutrophils and monocytes. The value of F in the mastitis sample is about 5 times that during normal respiration and about the value of F in the health sample is about 3 times during normal respiration. This suggests that the mastitis bovine has a higher proportion of neutrophils and monocytes in the somatic cells than healthy bovine. This result is consistent with the literature1). This result suggests that SECM respiratory burst assessment can distinguish mastitis bovine from healthy bovine. In addition, we suggest we can discover early stage of mastitis by measuring the increase in neutrophils. Reference M. Damm, C. Holm, M. Blaabjerg, M. N. Bro,D. Schwarz: J.Dairy Sci.100, 4926-4940 (2017).H. Kikuchi, A. Prasad, R. Matsuoka, S. Aoyagi, T. Matsue, S. Kasai, Frontiers in Physiology 7, 25, 1-6 (2016) Figure 1

Electrode material containing carbon nanotubes and its kinetic characteristics of oxygen electroreduction

In this article, we report on the study of the electrochemical characteristics of the electrode material of a proton exchange membrane (PEM) fuel cell containing carbon nanotubes (CNTs) as a functional additive in the oxygen reduction reaction. The data of appraisal by the methods of scanning and transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), differential thermal analysis, cyclic and direct voltammetry on a stationary and rotating disk electrode are given. The results showed that the material has a higher electrode activity in the presence of oxygen-modified carbon nanotubes, a higher half-wave potential of oxygen electroreduction (610 and 500 mV in the presence and absence of CNTs, respectively), showed a threefold higher density of the kinetic current of oxygen reduction, has a 2.5-fold higher density of exchange current in the oxygen reaction. This can be explained by the effect of oxygen-modified CNTs on the content of surface oxide (PtO); in the presence of CNTs, the PtO content is lower.

Pyrenyl Carbon Nanotubes for Covalent Bilirubin Oxidase Biocathode Design: Should the Nanotubes be Carboxylated?

Understanding the characteristics of nanomaterials in the context of electrode designs for bio-electrocatalysis is an emerging research direction. Applications for fuel cells, batteries, and biosensors are directly benefited. The objective of this study is to understand the influence of unfunctionalized multiwalled carbon nanotubes (MWNT) in comparison to carboxylated nanotubes (MWNT–COOH) for pi-pi stacking with 1-pyrenebutyric acid (Py) and covalent immobilization of bilirubin oxidase (BOD) enzyme toward the resulting oxygen reduction currents. We designed pyrolytic graphite-edge electrodes modified with MWNT/Py, MWNT–COOH/Py, or only MWNT–COOH for carbodiimide activation and BOD immobilization. The relative increase in surface –COOH groups as we move from MWNT to MWNT/Py to MWNT–COOH/Py modification is voltammetrically estimated. Although the MWNT–COOH/Py displayed the highest relative amount of surface −COOH groups, the oxygen reduction current was the largest for the BOD-immobilized MWNT/Py electrode than others. Results indicate that unfunctionalized MWNT is the optimal choice for pi-pi stacking with pyrene linkers and covalent BOD immobilization as biocathode for direct electrocatalysis with high current densities. Favorable hydrophobic MWNT surface to interact more closely with the electron-receiving T1 Cu site of BOD, as opposed to the relatively polar and more defective MWNT–COOH material due to functionalization, is suggested to be one of the underlying factors for the observed electrocatalytic trend.

Bipolar Method of Plasma Electrochemical Synthesis of Carbon Nanostructures Decorated with MnOx

A new one-step method for the synthesis of an oxygen reduction electrocatalyst based on a nanocomposite of few-layer graphene structures and manganese oxides is proposed. It has been shown that by using the bipolar method of graphite exfoliation in the plasma electrolysis mode in solutions containing manganese salts, it is possible to obtain graphene nanostructures decorated with manganese oxides exhibiting high catalytic activity in the oxygen reduction reaction, which consists in a significant reduction in overpotential and an increase in the oxygen reduction current.

Prussian Blue modified boron-doped diamond interfaces for advanced H2O2 electrochemical sensors

We report on the boron-doped diamond (BDD) electrodes modified with Prussian Blue (PB) through electrochemical synthesis, open-circuit deposition, and immobilization of Prussian Blue based nanozymes. The later allowed attaining the utmost sensitivity of the H2O2 sensor (≈0.14 A M−1 cm−2). Compared to conventional graphite electrodes modified with Prussian Blue, the use of BDD provided twenty times decreased oxygen reduction currents resulting in up to ten times increased signal-to-background ratio of the corresponding modified electrodes. The successful combination of exceptional diamond properties (including wide potential window for BDD electrodes) with advantageous performance characteristics of Prussian Blue sensing layers would open new horizons for H2O2 detection as well as biosensors elaboration.

ОСОБЕННОСТИ КАТОДНЫХ И АНОДНЫХ РЕАКЦИЙ НА УГЛЕРОДИСТОЙ СТАЛИ В ЗАВИСИМОСТИ ОТ ГЛУБИНЫ ПОГРУЖЕНИЯ В НЕЙТРАЛЬНЫЙ РАСТВОР

The investigation of the depth immersion of the specimens on corrosion rate of steel St3 in 3 % NaCl solution. Simulation of atmospheric corrosion (humid and wet) was performed by immersing of a steel sample by the size of (50×10×2) mm in a neutral solution of 3% NaCl at different depths. By leading the lower boundary of the working surface of the sample to the level of the solution (about 0 mm), humid corrosion was simulated, submerged to a depth of 2 mm (up to the upper boundary), wet corrosion, and 10 mm from the upper boundary - the electrolyte volume. The developed method allowed to carry out electrochemical researches by the method of polarization curves. The polarization curves were measured in the potentiodynamic mode with the potential scanning rate of 5∙10-4 V/s .The working electrode was a sample of steel St3 by the size (10×50×2) mm. A work surface (10×2) mm was separated on the sample, the rest of the surface was isolated with a non-conductive varnish. The results of the investigation of the effect of depth immersion of samples into electrolyte solution on corrosion rate of St3 steel are presented. The conditions of “humid” and “wet” atmospheric corrosion of the metal were simulated by the immersion of samples on a depth from 0 to 10 mm into 3% sodium chloride solution. It was found, that on the base on determination of the rate of particular electrode reactions occurring on the electrode at various depths of its immersion into the solution, the corrosion rate of steel St3 was determined by the value of the limiting diffusion current.It was shown that the value of limiting current increases from 0.51 to 2 A/m2 with decreasing of the film thickness. It has been established that the cathodic process rate depends both on the concentration of oxygen in the layers of the solution, which are at different distances from the solution/air boundary, and on the speed of its diffusion to the metal surface. Because the method of polarization resistance allows to measure the currents smaller than the currents of oxygen reduction in thin films of the solution, it can be used to estimate the rate of atmospheric corrosion of steel. Based on simulation of humid and wet atmospheric corrosion the effect of immersion depth of the specimens on the cathodic reaction rate of steel St3 in 3 % NaCl solution was established. The cathodic current density (limit diffusion current) is raised from 0,51 to 2 A/m2 under decreasing of immersion depth. The suggested method of simulation of atmospheric corrosion may be used for electrochemical investigations in thin films of moisture of different thickness which are form on the metals and sensors surfaces. The possibility of application of polarization resistance method for atmospheric conditions was presented.