The launch of the fuel cell vehicle (FCV) in December 2014 has moved our society into the era of hydrogen energy. Expectations for, and demands on, this technology will first increase steadily and then explosively. Owing to the scarcity of available natural resources and considering costs, the development of cathodes using non-platinum catalysts is an important issue to be addressed for the stable and secure provision of FCVs. We have been developing carbon alloy catalysts, such as nanoshell-containing carbon and boron nitrogen (BN)-doped carbon catalysts, where catalytic activities originate from the carbon surface and not from surface metal complexes. First, we discuss the discovery of carbon materials exhibiting electrocatalytic activity followed by their application to ORR. Second, we provide experimental evidence for ORR activity originating from warped graphitic layers. Next, we describe useful methods to obtain highly active carbon alloy catalysts. Finally, we report a notable single cell performance of 0.65 W/cm2 using air as the oxidant.
An amperometric determination based on flow injection analysis (FIA) of hydrogen peroxide was first developed using nitrogen-doped glassy carbon electrodes prepared by stepwise electrolysis as the working electrode. A glassy carbon electrode was covalently modified by electrochemical oxidation/reduction procedures. The electrocatalytic activity for the electrode oxidation of hydrogen peroxide has successfully been applied to the FIA of hydrogen peroxide. The typical current vs. time curve was obtained by the repetitive measurement of 20 µM hydrogen peroxide and when flow rate is 2.0 ml/min, the measurement of hydrogen peroxide was finished completely in a short time (10 sec.).
A porous carbon electrode with a branch structure composed of macropores and mesopores was prepared using MgO-templated carbon and MgO particles by screen-printing. The electrode characteristics were investigated using electrochemical impedance spectroscopy. Loci of the straight line with angles at 22.5° and 45° were observed in the high- and mid-frequency ranges, respectively. A partial semicircle appeared in the low-frequency range. The impedance analysis revealed that almost the entire charge-transfer reaction occurred only at the mesopore interface of the electrode. The current density of the bilirubin oxidase (BOD)-immobilized branch structure carbon electrode was 1.3 times higher than that of the BOD-immobilized non-branch structure carbon electrode.
We fabricated graphene modified glassy carbon (Gr/GC) electrodes to enhance the direct electron transfer (DET) of bilirubin oxidase (BOD) by casting graphene-dispersed solutions with different concentrations. With a concentration of 2 µg µL−1, a large increase was observed in the reduction current at the BOD-modified Gr/GC electrode, and the value was 74 times that of a BOD-modified GC electrode (unmodified with graphene). Moreover, with graphene modification the capacitance increase was much less than with other carbon materials including carbon black and graphite powder. These results demonstrate that a graphene nanostructure is suitable for achieving the efficient DET of BOD.
Impedance simulation was performed for analysis of a branch structure porous carbon electrode composed of macropores and mesopores. Theoretical equations were derived by introducing a new branch structure transmission line model, in which the charge-transfer reactions in the pores are considered. The loci of the straight line with angles at 22.5° and semicircle were observed in the high and low frequency ranges. It was found that the charge-transfer resistance in the mesopore interface had no influence on the loci of the straight line.
A new electrode catalyst prepared using methane gas by microwave-assisted catalytic decomposition has been developed. The prepared catalyst has a graphene-covered nickel particle (GCNP) structure. GCNPs were fabricated as a powder microelectrode. Oxygen reduction activity was evaluated using an electrochemical potential sweep method. This activity was evaluated by comparing the oxygen reduction reaction (ORR) at the GCNP and commercially available Pt/C. The ORR at the GCNP was found to be similar to that of Pt/C in neutral solution. In acidic solution, the GCNP exhibited higher corrosion resistance than a nickel particle. The result was due to the prepared graphene.
Boron-doped diamond (BDD) is promising as electrocatalyst for alternative material to platinum (Pt) because of its superior chemical stability. Electrochemically catalytic activity of BDD on the redox couple of I−/I0 was studied by using the electrochemical method. It showed the parabolic dependence on the doping level of boron in diamond and the maximum value was 0.94 µA/cm2 in terms of the exchanging current density. This value is slightly higher than graphite and smaller than Pt. Additional surface modification of BDD could improve the catalytic activity.
The structure of carbon obtained from the thermal reduction of graphite oxide at 900°C after electrochemical storage sodium ions was investigated. X-ray diffraction measurement of the carbon sample after charged to various potentials indicated that sodium ions are stored between the layers of carbon below 0.3 V vs. Na/Na+ though the interlayer spacing of it was similar to that of graphite. The lower LUMO energy as revealed from the broad π* peak in the region of CK observed in soft X-ray absorption measurement was responsible for the intercalation of a large amount of sodium ions into the present carbon material.
Polyacrylonitrile-derived carbon particles with uniform size and high porosity were synthesized and their capacitor properties were investigated. The carbon particles were simply prepared just by carbonizing and activating monodisperse polyacrylonitrile particles which were synthesized by polymerization of acrylonitrile in the mixture of methanol and N,N-dimethylformamide. The electrochemical measurements revealed that the carbon particles electrode maintained large specific capacitance even at high charge-discharge current densities.
Activated carbon was prepared from Amygdalus pedunculata shell by carbonization and KOH activation. A. pedunculata is a good candidate plant for desert greening in China. By choosing the activation conditions, the activated carbon with the microporous structure and the large surface area (2900 m2 g−1) was obtained. The resulting activated carbon exhibited the good electrochemical capacitive behavior. The present activated carbon from A. pedunculata is a promising electrode material for high-performance electric double-layer capacitor.
Iron/carbon nano-fiber composite electrodes on the basis of Fe3+ but containing Fe2+ or Ni2+ ions have been prepared via sol-gel precipitation. The influence of the Fe2+ doping on the nano-structure and the utility of iron in alkaline electrolyte has been confirmed. The mixing of Fe2+ in composite provides larger iron oxide particles with high crystallinity, and changes the specific capacity of composite electrode. The specific capacity of the composite electrode introducing Fe2+:Fe3+ at 4:1 increases about 1.4 times compared with analogue having only Fe3+. In contrast, the doping of Ni2+ in the composite reduces the iron utility.
This study emphasizes the electrochemical detection of Neuraminidase (NA) based on NA inhibition by Zanamivir. The detection method was developed based on the difference of electrochemical responses of Zanamivir in the presence and the absence of NA in phosphate buffer solution (pH 5.5). Gold and gold-modified boron-doped diamond was used as the working electrode and the measurement was conducted using cyclic voltammetry method. A linear calibration curve of Zanamivir was observed in the concentration range of 5 × 10−6–1 × 10−4 mol/L (R2 = 0.991), with the estimated limit of detection (LOD) of 1.49 × 10−6 mol/L. The presence of NA increases the peak current of gold oxidation and reduction with linear calibration curves were monitored in the concentration range of 0–15 mU (R2 = 0.996). An estimated LOD of 0.25 mU NA and an excellent reproducibility of the detection with an RSD of 1.18% can be achieved. Application of a real sample was successfully demonstrated for NA detection in the presence of mucin, suggested that the method is promising for pharmaceutical or medical application.
Voltammetric detection using a boron doped diamond (BDD) electrode coupled with capillary liquid chromatography (CLC) was developed for determining nobiletin, one of the polymethoxyflavones (PMFs), in plasma samples. CLC with electrochemical detection (CLC-ECD) was performed using a capillary octadecylsilica (ODS) column, water-acetonitrile-phosphoric acid (65:35:0.5, v/v/v), as a mobile phase, and an applied potential at +1.45 V vs. Ag/AgCl. Chromatographic peak heights were found linearly related to the amounts of nobiletin injected from 0.48 pg to 0.40 ng (r = 0.999). The detection limit (S/N = 3) was 0.13 pg. The concentrations of nobiletin in rat plasma after oral ingestion of 5.0 mL kg−1Citrus depressa juice, corresponding to 0.17 mg kg−1 nobiletin, were determined to obtain a concentration-time profile of nobiletin by the present CLC-ECD method, which required only 30 µL of plasma sample for each time point. Based on the concentration-time profile of nobiletin in the rat plasma, the pharmacokinetic parameters of maximum drug concentration (Cmax), maximum drug concentration time (tmax), and area under the concentration-time curve (AUC0-3 h) were obtained.
A carbon with Pt (C–Pt) catalyst was prepared by a co-sputtering technique. Pt4f peaks of the prepared sample were observed at higher binding energies than those of a Pt sputtered sample. These Pt4f peaks shifted to the low binding energies with an increase in a post-annealing temperature, whereas the C1s peak position was unchanged. For the C–Pt catalyst as sputter-deposited, the methanol oxidation performance was enhanced by the presence of O2. This O2-enhnaced methanol oxidation was suppressed by the post-annealing at 160°C, while the reaction selectivity of the methanol oxidation was retained.
MgO-templated porous carbon (MgOC) was developed for D-fructose dehydrogenase (FDH) electrodes. MgOCs with an average pore diameter ranging from 10 to 100 nm were used in this study. FDH adsorbed on a MgOC electrode exhibited significant catalytic currents for D-fructose-oxidation without a redox mediator. When the pore size of MgOC was much larger than the size of FDH, a sufficient amount of FDH was adsorbed in the mesopore on and even inside the MgOC structure. In contrast, when the pore size of MgOC was comparable to the size of FDH, the catalytic current depended only on the amount of enzyme adsorbed in mesopores formed at the surface of the carbon particles; however, an enhanced thermal stability of FDH was observed. Thus, FDH was stabilized through encaging in carbon mesopores with a size comparable to that of the enzyme.
The redox reaction of iron phthalocyanine (FePc) combined with electrochemically-reduced graphene oxide (ER-GO) was investigated as a function of FePc fraction. A FePc/ER-GO/GC electrode was fabricated and the redox response of Fe3+/2+ couple was analyzed by cyclic voltammetry. The formal potential was observed to change with the FePc fraction, and the most positive value was obtained at the full monolayer coverage. The onset potential of oxygen reduction reaction at the fabricated electrode shifted linearly with the formal potential of FePc. Such a coverage-dependent potential shift was explained in terms of the electronic interaction between FePc and substrate graphene surface based on the X-ray photoelectron spectroscopy as well as the theoretical DFT calculation of a model adsorption system.
The application of a microporous layer (MPL) between the gas diffusion layer and the catalyst layer (CL) plays a crucial role in the performance of the direct methanol fuel cell (DMFC). To this end, this study investigates the effects of carbon loading and the nature of the carbon material used in the anode MPL on the performance of DMFC using transmission and scanning electron microscopy, polarization technique, and electrochemical impedance spectroscopy (EIS). DMFC was indigenously fabricated using 30 wt% PtRu catalyst supported on carbon nanocoil and commercial Pt catalyst as the anode CL and the cathode CL, respectively. Carbon nanoballoon (CNB) and Vulcan XC-72R (Vulcan) were used as the anode MPL. According to polarization studies, a membrane electrode assembly (MEA) with CNB and Vulcan MPLs (loading of 1.5 mg cm−2) shows higher power density. This is 1.3 and 1.8 times higher than that without the anode MPL when methanol concentration was 0.5 M (M = mol dm−3), respectively. Electrochemical impedance spectra (EIS) results indicate that the MEAs with the anode MPLs have lower high-frequency resistance and charge transfer resistance when compared to those without the anode MPL. Thus, it can be realized that the anode MPL plays a significant role in the effective utilization of CNC-supported PtRu anode catalyst, thereby improving DMFC performance.
In this study the formula for expressing contact resistance Rc between the aluminum (Al) current collector and positive electrode composite in lithium secondary batteries is derived as follows: (1) Rc is proportional to the thickness of the Al oxide film and apparent electric susceptibility of the composite χe. (2) Rc decreases when the active material is coated with Carbon Nanotubes (CNT) due to the reduction of χe. (3) χe can be formulated by the contribution ratio Ci of the component i of the composite, with Ci determined by the dispersed condition of the composite.
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