Publications by authors named "Takeo Ohsaka"

42 Publications

High-Efficiency Electrolyte for Li-Rich Cathode Materials Achieving Enhanced Cycle Stability and Suppressed Voltage Fading Capable of Practical Applications on a Li-Ion Battery.

ACS Appl Mater Interfaces 2020 Nov 20;12(44):49666-49679. Epub 2020 Oct 20.

Qingdao Industrial Energy Storage Research Institute, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, No. 189 Songling Road, Qingdao 266101, China.

Li-rich cathodes have been in considerable attention for their high reversible capacity. However, they have serious problems like poor cycling with intense capacity decay and voltage fading, which restrict their access to practical applications. In this work, a facile and efficient strategy is proposed to alleviate these intrinsic issues with a high-efficiency electrolyte system. This special electrolyte enables Li-rich cathodes to deliver superior integrated performance with a high initial discharge capacity of 301 mAh·g, outstanding cycling stability with a capacity retention of 88% at 0.5 C over 500 cycles, and a remarkable rate capability of 136 mAh·g at 5 C, respectively. What is more, the voltage fading is largely suppressed. Physical and electrochemical characterizations demonstrate that the robust CEI film formed on the cathode surface contributes to the improved electrochemical performance. This work provides a new approach to surmount defects of Li-rich materials and will largely promote their practical applications on Li-ion batteries.
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http://dx.doi.org/10.1021/acsami.0c14995DOI Listing
November 2020

Self-assembled nitrogen-doped fullerenes and their catalysis for fuel cell and rechargeable metal-air battery applications.

Nanoscale 2017 Jun;9(22):7373-7379

Department of Chemical and Biomolecular Engineering, Yonsei University, Seoul, 03722, Republic of Korea.

In this study, we report self-assembled nitrogen-doped fullerenes (N-fullerene) as non-precious catalysts, which are active for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), and thus applicable for energy conversion and storage devices such as fuel cells and metal-air battery systems. We screen the best N-fullerene catalyst at the nitrogen doping level of 10 at%, not at the previously known doping level of 5 or 20 at% for graphene. We identify that the compressive surface strain induced by doped nitrogen plays a key role in the fine-tuning of catalytic activity.
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http://dx.doi.org/10.1039/c7nr00930eDOI Listing
June 2017

Enhancement in Kinetics of the Oxygen Reduction Reaction on a Nitrogen-Doped Carbon Catalyst by Introduction of Iron via Electrochemical Methods.

Langmuir 2015 May 4;31(19):5529-36. Epub 2015 May 4.

†Department of Electronic Chemistry, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, 4259 Nagatsuta, Yokohama, Kanagawa 226-8502, Japan.

The iron (Fe) electrodeposition-electrochemical dissolution has been employed on nitrogen-doped carbon material (P-PI) prepared via multi-step pyrolysis of a polyimide precursor to achieve the introduction of Fe species, and its influence on the oxygen reduction reaction (ORR) is investigated by cyclic and rotating ring-disk electrode voltammetry in 0.5 M H2SO4. After the electrochemical treatment, the overpotential and H2O2 production percentage of ORR on the P-PI are decreased and the number of electrons transferred is increased in the meanwhile. In combination with the results of X-ray absorption fine structure spectra, the presence of Fe-Nx sites (Fe ions coordinated by nitrogen) is believed to be responsible for the improved ORR performance. Further kinetic analysis indicates that a two-electron reduction of O2 is predominant on the untreated P-PI with coexistence of a direct four-electron transformation of O2 to H2O, while the introduction of Fe species leads to a larger increase in the rate constant for the four-electron reduction than that for the two-electron process, being in good agreement with the view that Fe-Nx sites are active for four-electron ORR.
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http://dx.doi.org/10.1021/acs.langmuir.5b00310DOI Listing
May 2015

A novel fabrication of a polymeric ionic liquid hybrid film modified electrode and its successful application to the electrogeneration of a superoxide anion in aqueous media.

Chem Commun (Camb) 2015 Feb;51(16):3343-6

Department of Electronic Chemistry, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, 4259-G1-5 Nagatsuta, Midori-Ku, Yokohama 226-8502, Japan.

A novel polymeric ionic liquid hybrid film-modified electrode, in which the electrode surface is coated with a hydrophobic hybrid material composed of an ionene polymer with quaternary ammonium sites in its polymeric backbone and ionic liquids, was fabricated by electropolymerization of N,N-dimethylaniline in a hydrophobic ionic liquid, which can be applied for the electrogeneration of a superoxide anion via one-electron reduction of O2 in aqueous media.
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http://dx.doi.org/10.1039/c4cc08410aDOI Listing
February 2015

Characterization by electrochemical and X-ray photoelectron spectroscopic measurements and quantum chemical calculations of N-containing functional groups introduced onto glassy carbon electrode surfaces by electrooxidation of a carbamate salt in aqueous solutions.

Langmuir 2014 May 1;30(18):5297-305. Epub 2014 May 1.

Department of Electronic Chemistry, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology , 4259-G1-5 Nagatsuta, Midori-ku, Yokohama 226-8502, Japan.

The present paper deals with characterization of an aminated glassy carbon electrode (GCE) surface obtained by electrooxidation of ammonium carbamate in its aqueous solution (amination reaction) using electrochemical and XPS methods. From the XPS analysis, it was found that not only the primary amine group (i.e., aniline-like aromatic amine moiety) but also other N-containing functional groups (i.e., the secondary amine-like moieties containing pyrrole-type nitrogen and quaternary amine-like moieties containing graphitic quaternary nitrogen) are introduced onto the GCE surface during the amination reaction. Moreover, the presence of the primary and secondary amine groups was ascertained based on the difference in the reactivity of a Michael reaction-type addition reaction of amine groups introduced onto the GCE surface with quinone compounds having a carbonyl group and a C═C double bond (i.e., in this case, 1,2-benzoquinone which is in situ prepared by the electrooxidation of catechol) and on the electrochemical redox response of the introduced benzoquinones. This electrochemical treatment of aminated GCE with catechol led to catechol-grafted aminated GCE which indicated two surface redox couples (i.e., the Ia/Ic and IIa/IIc couples with formal potentials of E(0)'(Ia/Ic) = ca. 0.17 V and E(0)'(IIa/IIc) = ca. 0.03 V vs Ag|AgCl|KCl(sat.) in phosphate buffer solution (pH 7)). From the electrochemical behavior of catechols grafted onto the maleimide-treated aminated GCE and on the methylamine-treated GCE, it was found that the catechol associated with the primary amine groups gave the IIa/IIc redox peaks, while the catechol bound to the secondary amine groups gave the Ia/Ic redox peaks. Further electrochemical measurements and quantum chemical calculations concluded that the IIa/IIc redox peaks are ascribed to the surface-redox reaction of the 1,2-dihydroxybenzene/1,2-benzoquinone couple, while those of the 1,2-dihydroxybenzene/1,2-benzoquinone and the N-(4'-hydroxyphenyl)-p-aminophenol/indophenol couples can be associated with the Ia/Ic redox peaks.
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http://dx.doi.org/10.1021/la4044667DOI Listing
May 2014

Continuous and simultaneous electrochemical measurements of glucose, lactate, and ascorbate in rat brain following brain ischemia.

Anal Chem 2014 Apr 24;86(8):3895-901. Epub 2014 Mar 24.

Beijing National Laboratory for Molecular Sciences, Key Laboratory of Analytical Chemistry for Living Biosystems, Institute of Chemistry, The Chinese Academy of Sciences , Beijing 100190, China.

Developing new tools and technologies to enable recording the dynamic changes of multiple neurochemicals is the essence of better understanding of the molecular basis of brain functions. This study demonstrates a microfluidic chip-based online electrochemical system (OECS) for in vivo continuous and simultaneous monitoring of glucose, lactate, and ascorbate in rat brain. To fabricate the microfluidic chip-based detecting system, a microfluidic chip with patterned channel is developed into an electrochemical flow cell by incorporating the chip with three surface-modified indium-tin oxide (ITO) electrodes as working electrodes, a Ag/AgCl wire as reference electrode, and a stainless steel tube as counter electrode. Selective detection of ascorbate is achieved by the use of single-walled carbon nanotubes (SWNTs) to largely facilitate the electrochemical oxidation of ascorbate, while a dehydrogenase-based biosensing mechanism with methylene green (MG) adsorbed onto SWNTs as an electrocatalyst for the oxidation of dihydronicotiamide adenine dinucleotide (NADH) is employed for biosensing of glucose and lactate. To avoid the crosstalk among three sensors, the sensor alignment is carefully designed with the SWNT-modified electrode in the upstream channel and paralleled glucose and lactate biosensors in the downstream channels. With the microfluidic chip-based electrochemical flow cell as the detector, an OECS is successfully established by directly integrating the microfluidic chip-based electrochemical flow cell with in vivo microdialysis. The OECS exhibits a good linear response toward glucose, lactate, and ascorbate with less crosstalk. This property, along with the high stability and selectivity, enables the OECS for continuously monitoring three species in rat brain following brain ischemia.
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http://dx.doi.org/10.1021/ac4042087DOI Listing
April 2014

Direct electrochemistry and intramolecular electron transfer of ascorbate oxidase confined on L-cysteine self-assembled gold electrode.

Bioelectrochemistry 2014 Feb 19;95:15-22. Epub 2013 Oct 19.

Department of Electronic Chemistry, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, 4259-G1-5 Nagatsuta, Midori-ku, Yokohama 226-8502, Japan; Interfacial Nanostructure Research Lab., The Institute of Physical and Chemical Research (RIKEN), 2-1 Hirosawa, Wako-shi, Saitama 351-0198, Japan.

A direct electrochemistry and intramolecular electron transfer of multicopper oxidases are of a great importance for the fabrication of these enzyme-based bioelectrochemical-devices. Ascorbate oxidase from Acremonium sp. (ASOM) has been successfully immobilized via a chemisorptive interaction on the l-cysteine self-assembled monolayer modified gold electrode (cys-SAM/AuE). Thermodynamics and kinetics of adsorption of ASOM on the cys-SAM/AuE were studied using cyclic voltammetry. A well-defined redox wave centered at 166±3mV (vs. Ag│AgCl│KCl(sat.)) was observed in 5.0mM phosphate buffer solution (pH7.0) at the fabricated ASOM electrode, abbreviated as ASOM/cys-SAM/AuE, confirming a direct electrochemistry, i.e., a direct electron transfer (DET) between ASOM and cys-SAM/AuE. The direct electrochemistry of ASOM was further confirmed by taking into account the chemical oxidation of ascorbic acid (AA) by O2 via an intramolecular electron transfer in the ASOM as well as the electrocatalytic oxidation of AA at the ASOM/cys-SAM/AuE. Thermodynamics and kinetics of the adsorption of ASOM on the cys-SAM/AuE have been elaborated along with its direct electron transfer at the modified electrodes on the basis of its intramolecular electron transfer and electrocatalytic activity towards ascorbic acid oxidation and O2 reduction. ASOM saturated surface area was obtained as 2.41×10(-11)molcm(-2) with the apparent adsorption coefficient of 1.63×10(6)Lmol(-1). The ASOM confined on the cys-SAM/AuE possesses its essential enzymatic function.
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http://dx.doi.org/10.1016/j.bioelechem.2013.10.005DOI Listing
February 2014

Online electrochemical monitoring of dynamic change of hippocampal ascorbate: toward a platform for in vivo evaluation of antioxidant neuroprotective efficiency against cerebral ischemia injury.

Anal Chem 2013 Oct 3;85(20):9947-54. Epub 2013 Oct 3.

Beijing National Laboratory for Molecular Sciences, Key Laboratory of Analytical Chemistry for Living Biosystems, Institute of Chemistry, The Chinese Academy of Sciences , Beijing 100190, P. R. China.

Effective monitoring of cerebral ascorbate following intravenous antioxidant treatment is of great importance in evaluating the antioxidant efficiency for neuroprotection because ascorbate is closely related to a series of ischemia-induced neuropathological processes. This study demonstrates the validity of an online electrochemical system (OECS) for ascorbate detection as a platform for in vivo evaluation of neuroprotective efficiency of antioxidants by studying the dynamic change of hippocampal ascorbate during the acute period of cerebral ischemia and its responses to intravenous administration of antioxidants including ascorbate and glutathione (GSH). The OECS consists of a selective electrochemical detector made of a thin-layer electrochemical flow cell integrated with in vivo microdialysis. With such a system, the basal level of hippocampal ascorbate is determined to be 5.18 ± 0.60 μM (n = 20). This level is increased by 10 min of two-vessel occlusion (2-VO) ischemia treatment and reaches 11.51 ± 3.43 μM (n = 5) at the time point of 60 min after the ischemia. The 2-VO ischemia-induced hippocampal ascorbate increase is obviously attenuated by immediate intravenous administration of ascorbate (2.94 g/kg) or glutathione (5.12 g/kg) within 10 min after ischemia and the ascorbate level remains to be 3.75 ± 1.66 μM (n = 4) and 5.30 ± 0.79 μM (n = 5), respectively, at the time point of 60 min after ischemia. To confirm if the attenuated hippocampal ascorbate increase is attributed to the antioxidant-induced oxidative stress alleviation, we further study the immunoreactivity of 8-hydroxy-2-deoxyguanosine (8-OHdG) in the ischemic hippocampus and find that the 8-OHdG immunoreactivity is decreased by the administration of ascorbate or GSH as compared to the ischemic brain without antioxidant treatment. These results substantially demonstrate that the OECS for ascorbate detection could be potentially used as a platform for evaluating the efficiency of antioxidant neuroprotection in cerebral ischemia treatment.
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http://dx.doi.org/10.1021/ac402620cDOI Listing
October 2013

Electroless deposition of platinum nanoparticles in room-temperature ionic liquids.

Langmuir 2013 Sep 13;29(38):11931-40. Epub 2013 Sep 13.

Department of Electronic Chemistry, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology , Nagatsuta 4259-G1-5, Midori-ku, Yokohama 226-8502, Japan.

The electroless deposition of Pt nanoparticles (Pt-NPs) could be carried out by dissolving potassium tetrachloroplatinate(II) (K2[PtCl4]) in 1-ethyl-3-methylimidazolium (EMI(+)) room-temperature ionic liquids (RTILs) containing bis(trifluoromethylsulfonyl) imide (NTf2(-)) or tetrafluoroborate (BF4(-)) anion and small cations, such as H(+), K(+), and Li(+). In this case, no deposition of Pt-NPs occurred in RTILs without such small cations. The formation of Pt-NPs was only observed in RTILs containing trifluoromethanesulfonimide (HNTf2) and protons at high temperature (≥80 °C) when potassium hexachloroplatinate(IV) (K2[PtCl6]) was dissolved in the RTILs. The obtained Pt-NPs gave a characteristic absorption spectrum of ultrasmall Pt-NPs. The ultrasmall and uniform Pt-NPs of ca. 1-4 nm in diameter were produced and the Pt-NPs/EMI(+)NTf2(-) dispersion was kept stably for several months without adding any additional stabilizers or capping molecules. The identified Fourier-transform patterns along the [0 1 1] zone axis were observed for the TEM images of Pt-NPs. On the basis of the results obtained, a probable mechanism of the electroless formation of Pt-NPs is discussed.
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http://dx.doi.org/10.1021/la402429vDOI Listing
September 2013

Microfluidic chip-based online electrochemical detecting system for continuous and simultaneous monitoring of ascorbate and Mg2+ in rat brain.

Anal Chem 2013 Aug 19;85(15):7599-605. Epub 2013 Jul 19.

College of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou 510640, China.

This study demonstrates a microfluidic chip-based online electrochemical detecting system for in vivo continuous and simultaneous monitoring of ascorbate and Mg(2+) in rat brain. In this system, a microfluidic chip is used as the detector for both species. To fabricate the detector, a single-channel microfluidic chip is developed into an electrochemical flow cell by incorporating the chip with an indium-tin oxide (ITO) electrode as working electrode, an Ag/AgCl wire as reference electrode, and a stainless steel tube as counter electrode. Selective detection of ascorbate and Mg(2+) is achieved by drop-coating single-walled carbon nanotubes (SWNTs) and polymerizing toluidine blue O (polyTBO) film onto the ITO electrode, respectively. Moreover, the alignment of SWNT-modified and polyTBO-modified electrodes and the solution introduction pattern are carefully designed to avoid any cross talk between two electrodes. With the microfluidic chip-based electrochemical flow cell as the detector, an online electrochemical detecting system is successfully established by directly integrating the microfluidic chip-based electrochemical flow cell with in vivo microdialysis. The microfluidic system exhibits sensing properties with a linear relationship from 5 to 100 μM for ascorbate and from 100 to 2000 μM for Mg(2+). Moreover, this system demonstrates a high selectivity and stability and good reproducibility for simultaneous measurements of ascorbate and Mg(2+) in a continuous-flow system. These excellent properties substantially render this system great potential for continuous and simultaneous online monitoring of ascorbate and Mg(2+) in rat brain.
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http://dx.doi.org/10.1021/ac401727dDOI Listing
August 2013

Biofuel cell-based self-powered biogenerators for online continuous monitoring of neurochemicals in rat brain.

Analyst 2013 Jan 2;138(1):179-85. Epub 2012 Nov 2.

Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, the Chinese Academy of Sciences, Beijing 100190, China.

This study demonstrates a new electrochemical method for continuous neurochemical sensing with a biofuel cell-based self-powered biogenerator as the detector for the analysis of microdialysate continuously sampled from rat brain, with glucose as an example analyte. To assemble a glucose/O(2) biofuel cell that can be used as a self-powered biogenerator for glucose sensing, glucose dehydrogenase (GDH) was used as the bioanodic catalyst for the oxidation of glucose with methylene green (MG) adsorbed onto single-walled carbon nanotubes (SWNTs) as the electrocatalyst for the oxidation of dihydronicotinamide adenine dinucleotide (NADH). Laccase crosslinked onto SWNTs was used as the biocathodic catalyst for the O(2) reduction. To enable the bioanode and biocathode to work efficiently in their individually favorable solutions and to eliminate the interference between the glucose bioanode and O(2) biocathode, the biofuel cell-based biogenerator was built in a co-laminar microfluidic chip so that the bioanodic and biocathodic streams could be independently optimized to provide conditions favorable for each of the bioelectrodes. By using a home-made portable voltmeter to output the voltage generated on an external resistor, the biogenerator was used for glucose sensing based on a galvanic cell mechanism. In vitro experiments demonstrate that, under the optimized conditions, the voltage generated on an external resistor shows a linear relationship with the logarithmic glucose concentration within a concentration range of 0.2 mM to 1.0 mM. Moreover, the biogenerator exhibits a high stability and a good selectivity for glucose sensing. The validity of the biofuel cell-based self-powered biogenerator for continuous neurochemical sensing was illustrated by online continuous monitoring of striatum glucose in rat brain through the combination of in vivo microdialysis. This study offers a new and technically simple platform for continuously monitoring physiologically important species in cerebral systems.
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http://dx.doi.org/10.1039/c2an36385bDOI Listing
January 2013

A promising dehydrogenase-based bioanode for a glucose biosensor and glucose/O2 biofuel cell.

Analyst 2012 May 14;137(9):2233-8. Epub 2012 Mar 14.

Department of Electronic Chemistry, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8502, Japan.

A new type of dehydrogenase-based amperometric glucose biosensor was constructed using glucose dehydrogenase (GDH) which was immobilized on the edge-plane pyrolytic graphite (EPPG) electrode modified with poly(phenosafranin)-functionalized single-walled carbon nanotubes (PPS-SWCNTs). The PPS-SWCNT-modified EPPG electrode was prepared by electropolymerization of phenosafranin on the EPPG electrode which had been previously coated with SWCNTs. The performance of the GDH/PPS-SWCNT/EPPG bioanode was evaluated using cyclic voltammetry and amperometry in the presence of glucose. The GDH/PPS-SWCNT/EPPG electrode possesses promising characteristics as a glucose sensor: a wide linear dynamic range of 50 to 700 μM, low detection limit of 0.3 μM, fast response time (1-2 s), high sensitivity (96.5 μA cm(-2) mM(-1)), and anti-interference and anti-fouling abilities. Moreover, the performance of the GDH/PPS-SWCNT/EPPG bioanode was tested in a glucose/O(2) biofuel cell. The maximum power density delivered by the assembled glucose/O(2) biofuel cell could reach 64.0 μW cm(-2) at a cell voltage of 0.3 V with 40 mM glucose.
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http://dx.doi.org/10.1039/c2an15971fDOI Listing
May 2012

Gd-DTPA-based MR-visible polymer for direct visualization of interventional devices.

Magn Reson Med Sci 2011 ;10(4):263-7

Department of Electronic Chemistry, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, Yokohama, Japan.

We developed a Gd-DTPA (gadolinium(III)-diethylenetriaminepentaacetic acid)-based coating copolymer of hydrophilic and hydrophobic subunits to obtain visibility, hydrophilicity, and durability for passive visualization of catheters used in MR-guided interventions. We then examined a metal-free catheter coated with the polymer in a phantom and in porcine brain tissue ex vivo. Successful visualization of the coated device demonstrated the applicability of the new coating technique for visualizing catheters used in MR-guided interventions.
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http://dx.doi.org/10.2463/mrms.10.263DOI Listing
April 2012

Electrodeposition of platinum nanoparticles in a room-temperature ionic liquid.

Langmuir 2011 Dec 8;27(23):14662-8. Epub 2011 Nov 8.

Department of Electronic Chemistry, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, Nagatsuta 4259-G1-5, Yokohama 226-8502, Japan.

The electrochemistry of the [PtCl(6)](2-)-[PtCl(4)](2-)-Pt redox system on a glassy carbon (GC) electrode in a room-temperature ionic liquid (RTIL) [i.e., N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium tetrafluoroborate (DEMEBF(4))] has been examined. The two-step four-electron reduction of [PtCl(6)](2-) to Pt, i.e., reduction of [PtCl(6)](2-) to [PtCl(4)](2-) and further reduction of [PtCl(4)](2-) to Pt, occurs separately in this RTIL in contrast to the one-step four-electron reduction of [PtCl(6)](2-) to Pt in aqueous media. The cathodic and anodic peaks corresponding to the [PtCl(6)](2-)/[PtCl(4)](2-) redox couple were observed at ca. -1.1 and 0.6 V vs a Pt wire quasi-reference electrode, respectively, while those observed at -2.8 and -0.5 V were found to correspond to the [PtCl(4)](2-)/Pt redox couple. The disproportionation reaction of the two-electron reduction product of [PtCl(6)](2-) (i.e., [PtCl(4)](2-)) to [PtCl(6)](2-) and Pt metal was also found to occur significantly. The electrodeposition of Pt nanoparticles could be carried out on a GC electrode in DEMEBF(4) containing [PtCl(6)](2-) by holding the potential at -3.5 or -2.0 V. At -3.5 V, the four-electron reduction of [PtCl(6)](2-) to Pt can take place, while at -2.0 V the two-electron reduction of [PtCl(6)](2-) to [PtCl(4)](2-) occurs. The results obtained demonstrate that the electrodeposition of Pt at -3.5 V may occur via a series of reductions of [PtCl(6)](2-) to [PtCl(4)](2-) and further [PtCl(4)](2-) to Pt and at -2.0 V via a disproportionation reaction of [PtCl(4)](2-) to [PtCl(6)](2-) and Pt. Furthermore, the deposition potential of Pt nanoparticles was found to largely influence their size and morphology as well as the relative ratio of Pt(110) and Pt(100) crystalline orientation domains. The sizes of the Pt nanoparticles prepared by holding the electrode potential at -2.0 and -3.5 V are almost the same, in the range of ca. 1-2 nm. These small nanoparticles are "grown" to form bigger particles with different morphologies: In the case of the deposition at -2.0 V, the GC electrode surface is totally, relatively compactly covered with Pt particles of relatively uniform size of ca. 10-50 nm. On the other hand, in the case of the electrodeposition at -3.5 V, small particles of ca. 50-100 nm and the grown-up particles of ca. 100-200 nm cover the GC surface irregularly and coarsely. Interestingly, the Pt nanoparticles prepared by holding the potential at -2.0 and -3.5 V are relatively enriched in Pt(100) and Pt(110) facets, respectively.
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http://dx.doi.org/10.1021/la202992mDOI Listing
December 2011

Generation of gaseous sulfur-containing compounds in tumour tissue and suppression of gas diffusion as an antitumour treatment.

Gut 2012 Apr 11;61(4):554-61. Epub 2011 Aug 11.

FAP Dental Institute, Tokyo, Japan.

Background And Aims: The mechanisms of cancer cell growth and metastasis are still not entirely understood, especially from the viewpoint of chemical reactions in tumours. Glycolytic metabolism is markedly accelerated in cancer cells, causing the accumulation of glucose (a reducing sugar) and methionine (an amino acid), which can non-enzymatically react and form carcinogenic substances. There is speculation that this reaction produces gaseous sulfur-containing compounds in tumour tissue. The aims of this study were to clarify the products in tumour and to investigate their effect on tumour proliferation.

Methods: Products formed in the reaction between glucose and methionine or its metabolites were analysed in vitro using gas chromatography. Flatus samples from patients with colon cancer and exhaled air samples from patients with lung cancer were analysed using near-edge x-ray fine adsorption structure spectroscopy and compared with those from healthy individuals. The tumour proliferation rates of mice into which HT29 human colon cancer cells had been implanted were compared with those of mice in which the cancer cells were surrounded by sodium hyaluronate gel to prevent diffusion of gaseous material into the healthy cells.

Results: Gaseous sulfur-containing compounds such as methanethiol and hydrogen sulfide were produced when glucose was allowed to react with methionine or its metabolites homocysteine or cysteine. Near-edge x-ray fine adsorption structure spectroscopy showed that the concentrations of sulfur-containing compounds in the samples of flatus from patients with colon cancer and in the samples of exhaled air from patients with lung cancer were significantly higher than in those from healthy individuals. Animal experiments showed that preventing the diffusion of sulfur-containing compounds had a pronounced antitumour effect.

Conclusions: Gaseous sulfur-containing compounds are the main products in tumours and preventing the diffusion of these compounds reduces the tumour proliferation rate, which suggests the possibility of a new approach to cancer treatment.
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http://dx.doi.org/10.1136/gutjnl-2011-300721DOI Listing
April 2012

pH Dependence of the size and crystallographic orientation of the gold nanoparticles prepared by seed-mediated growth.

Langmuir 2011 Apr 16;27(8):5126-35. Epub 2011 Mar 16.

Department of Electronic Chemistry, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, 4259-G1-5 Nagatsuta, Yokohama 226-8502, Japan.

The effect of the pH of the growth solution on the size and crystallographic orientation of gold nanoparticles (GNPs) was studied during the course of the preparation of surface-confined spherical GNPs following a two-step protocol (electrochemical and chemical). GNPs were first electrodeposited onto a clean glassy carbon (GC) electrode and these GNPs were used as seeds. Seed-mediated growth of the electrodeposited GNPs was performed in a solution of H[AuCl(4)] at various pHs (5.0 to 0.5) using NH(2)OH as a reducing agent. The thus-prepared GNPs were characterized by electrochemical, UV-visible absorption spectral, SEM, and TEM studies. The nucleation (i.e., formation of the new seeds) was found to dominate over growth (i.e., enlargement of the seed particles) process at higher pH during NH(2)OH seeding, whereas only growth was recognized at low pH (0.5). Nonspherical byproducts were noticed when the seed-mediated growth was performed at higher pHs, but at pH 0.5 only spherical GNPs were observed. The present method provides a way out for the preparation of GNPs with homogeneous shape resolving the problem of simultaneous formation of nonspherical byproducts during the seed-mediated growth as well as for the preparation of GNPs with a Au(111) facet ratio as high as 97%. On the basis of the obtained results, the mechanism of the growth process at low pH is also discussed. Interestingly, an enhanced electrochemical response was obtained for the oxidation of H(2)O(2) using the GNPs prepared at pH 0.5.
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http://dx.doi.org/10.1021/la200150hDOI Listing
April 2011

Selective detection of As(III) at the Au(111)-like polycrystalline gold electrode.

Anal Chem 2010 Nov 25;82(22):9169-76. Epub 2010 Oct 25.

Department of Electronic Chemistry, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, 4259-G1-5 Nagatsuta, Midori-ku, Yokohama 226-8502, Japan.

Selective electrochemical detection of As(III) using a highly sensitive platform based on a Au(111)-like surface is described. The Au(111)-like surface was achieved for the first time by the partial reductive desorption of n-butanethiol (n-BT) from polycrystalline gold (poly-Au), on which a self-assembled monolayer (SAM) of n-BT was formed previously, which allows the selective blockage of the Au(100) and Au(110) surface domains by n-BT while the Au(111) domain remains bare. Square wave anodic stripping voltammetry (SWASV) using the Au(111)-like poly-Au electrode confirms the successful detection of As(III) without any interference from Cu(II). The fabricated electrode is stable and highly sensitive even in the presence of Cu(II), and it shows a linear response for As(III) up to 15 μM. The detection limit (S/N = 3) toward As(III) is 0.28 ppb, which is far below the guideline value given by World Health Organization (WHO). The electrode was applicable for the analysis of spiked arsenic in tap water containing a significant amount of various other ion elements. The results indicate that the Au(111)-like poly-Au electrode could be promising for the electrochemical detection of trace level of As(III) in real samples without any interference from Cu(II).
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http://dx.doi.org/10.1021/ac101206jDOI Listing
November 2010

Determination of formal potential of NADH/NAD+ redox couple and catalytic oxidation of NADH using poly(phenosafranin)-modified carbon electrodes.

Bioelectrochemistry 2011 Feb 7;80(2):121-7. Epub 2010 Jul 7.

Department of Electronic Chemistry, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, 4259-G1-5 Nagatsuta, Midori-ku, Yokohama 226-8502, Japan.

The electrochemical regeneration of NADH/NAD(+) redox couple has been studied using poly(phenosafranin) (PPS)-modified carbon electrodes to evaluate the formal potential and catalytic rate constant for the oxidation of NADH. The PPS-modified electrodes were prepared by electropolymerization of phenosafranin onto different carbon substrates (glassy carbon (GC) and basal-plane pyrolytic graphite (BPPG)) in different electrolytic solutions. The formal potential was estimated to be -0.365±0.002V vs. SHE at pH 7.0. As for the bare carbon electrodes, the oxidation of NADH at the BPPG electrode was found to be enhanced compared with the GC electrode. For the PPS-modified electrodes, it was found that the electrocatalysis of PPS-modified electrodes for the oxidation of NADH largely depends on the carbon substrate and electrolyte solution employed for their preparation, i.e., the PPS-modified BPPG electrode prepared in 0.2M NaClO(4)/acetonitrile solution exhibits an excellent and persistent electrocatalytic property toward NADH oxidation in phosphate buffer solution (pH 7.0) with a diminution of the overpotential of about 740 and 670mV compared with those at the bare GC electrode and the PPS-modified GC electrode prepared in 0.2M H(2)SO(4) solution, respectively. A quantitative analysis of the electrocatalytic reaction based on rotating disk voltammetry gave the electrocatalytic reaction rate constants of the order of 10(3)-10(4)M(-)(1)s(-1) depending on the preparation conditions of the PPS-modified electrodes.
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http://dx.doi.org/10.1016/j.bioelechem.2010.07.001DOI Listing
February 2011

Fabrication of Au(111) nanoparticle-like electrode through a seed-mediated growth.

Chem Commun (Camb) 2010 Jul 11;46(28):5172-4. Epub 2010 Jun 11.

Department of Electronic Chemistry, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, 4259-G1-5 Nagatsuta, Midori-ku, Yokohama 226-8502, Japan.

We demonstrate a seed-mediated growth of electrodeposited gold-nanoparticles (GNPs) onto a glassy carbon (GC) electrode from a solution of H[AuCl(4)] containing NH(2)OH at pH 0.5, resulting in a Au(111) facet ratio as high as 97%.
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http://dx.doi.org/10.1039/c0cc00442aDOI Listing
July 2010

Sulfur-adlayer-coated gold electrode for the in vitro electrochemical detection of uric acid in urine.

Anal Chim Acta 2010 Jun 14;669(1-2):75-80. Epub 2010 May 14.

Department of Electronic Chemistry, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, Mail Box G1-5, 4259 Nagastuta, Midori-ku, Yokohama 226-8502, Japan.

The present article demonstrates the electrochemical oxidation of uric acid (UA) at sulfur-adlayer-coated gold (S-Au) electrode in alkaline media. At S-Au electrode, UA oxidized at a significantly lower overpotential with a higher current density as compared to the bare Au electrode. The oxidation of UA at the S-Au electrode is highly selective in the presence of the other commonly existing bio-molecules in urine. The proposed electrochemical sensor not only exhibited good reproducibility, but also showed a fast amperometric response to UA in the concentration range of 0.0025-5 mM with a low detection limit of 0.4 microM.
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http://dx.doi.org/10.1016/j.aca.2010.04.048DOI Listing
June 2010

EQCM study of the [Au(III)Cl4](-)-[Au(I)Cl2](-)-Au(0) redox system in 1-ethyl-3-methylimidazolium tetrafluoroborate room-temperature ionic liquid.

Langmuir 2010 Jun;26(11):9069-75

Department of Electronic Chemistry, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, 4259-G1-5 Nagatsuta, Midori-ku, Yokohama 226-8502, Japan.

The electrochemical behavior of the [Au(III)Cl(4)](-)-[Au(I)Cl(2)](-)-Au(0) redox system in room temperature ionic liquid (RTIL) of 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF(4)) has been investigated quantitatively using an in situ electrochemical quartz crystal microbalance (EQCM) technique based on a Pt film-coated quartz crystal electrode (Pt-QCE). A series of two-electron (2e) and one-electron (1e) reductions of the [Au(III)Cl(4)](-) to [Au(I)Cl(2)](-) and [Au(I)Cl(2)](-) to Au metal were recognized at the Pt surface. Besides, the disproportionation reaction of [Au(I)Cl(2)](-) (i.e., the 2e-reduction product of [Au(III)Cl(4)](-)) to [Au(III)Cl(4)](-) and Au metal was also observed. Electro-dissolution of the Au deposited on the Pt electrode through a 1e-oxidation reaction in the presence of chloride ions was also confirmed using the Pt-QCE based EQCM technique. A 2e-oxidation reaction of [Au(I)Cl(2)](-) (i.e., the dissolved product) to [Au(III)Cl(4)](-) along with the oxidation of Cl(-) ion on the Pt surface was also realized at high anodic potential. The results demonstrate that in situ EQCM technique is applicable and powerful in elucidating electrochemical surface phenomena accompanying a mass change in RTIL.
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http://dx.doi.org/10.1021/la904483yDOI Listing
June 2010

Enhanced catalytic reduction of oxygen at tantalum deposited platinum electrode.

Chem Commun (Camb) 2010 Feb 8;46(7):1165-7. Epub 2010 Jan 8.

Department of Electronic Chemistry, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, 4259-G1-5 Nagatsuta, Midori-ku, Yokohama 226-8502, Japan.

A tantalum deposited platinum electrode that offers an enhanced catalytic four-electron reduction of oxygen over the bare platinum electrode in acidic solution is explored.
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http://dx.doi.org/10.1039/b916826eDOI Listing
February 2010

Noncovalent attachment of NAD+ cofactor onto carbon nanotubes for preparation of integrated dehydrogenase-based electrochemical biosensors.

Langmuir 2010 Apr;26(8):6028-32

Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, the Chinese Academy of Sciences, Beijing 100190, China.

This study describes a facile approach to the preparation of integrated dehydrogenase-based electrochemical biosensors through noncovalent attachment of an oxidized form of beta-nicotinamide adenine dinucleotide (NAD(+)) onto carbon nanotubes with the interaction between the adenine subunit in NAD(+) molecules and multiwalled carbon nanotubes (MWCNTs). X-ray photoelectron spectroscopic and cyclic voltammetric results suggest that NAD(+) is noncovalently attached onto MWCNTs to form an NAD(+)/MWCNT composite that acts as the electronic transducer for the integrated dehydrogenase-based electrochemical biosensors. With glucose dehydrogenase (GDH) as a model dehydrogenase-based recognition unit, electrochemical studies reveal that glucose is readily oxidized at the GDH/NAD(+)/MWCNT-modified electrode without addition of NAD(+) in the phosphate buffer. The potential for the oxidation of glucose at the GDH/NAD(+)/MWCNT-modified electrode remains very close to that for NADH oxidation at the MWCNT-modified electrode, but it is more negative than those for the oxidation of glucose at the MWCNT-modified electrode and for NADH oxidation at a bare glassy carbon electrode. These results demonstrate that NAD(+) molecules stably attached onto MWCNTs efficiently act as the cofactor for the dehydrogenases. MWCNTs employed here not only serve as the electronic transducer and the support to confine NAD(+) cofactor onto the electrode surface, but also act as the electrocatalyst for NADH oxidation in the dehydrogenase-based electrochemical biosensors. At the GDH/NAD(+)/MWCNT-based glucose biosensor, the current is linear with the concentration of glucose being within a concentration range from 10 to 300 microM with a limit of detection down to 4.81 microM (S/N = 3). This study offers a facile and versatile approach to the development of integrated dehydrogenase-based electrochemical devices, such as electrochemical biosensors and biofuel cells.
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http://dx.doi.org/10.1021/la903799nDOI Listing
April 2010

Stability of superoxide ion in imidazolium cation-based room-temperature ionic liquids.

J Phys Chem A 2009 Feb;113(5):912-6

Department of Electronic Chemistry, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, Mail Box G1-5, 4259 Nagatsuta, Midori-ku, Yokohama 226-8502, Japan.

The stability of superoxide ion (O(2)(*-)) generated chemically by dissolving KO(2) in dried dimethyl sulfoxide solutions containing imidazolium cation [e.g., 1-ethyl-3-methylimidazolium (EMI(+)) and 1-n-butyl-2,3-dimethylimidazolium (BMMI(+))] based ionic liquids (ILs) was investigated with UV-visible spectroscopic, NMR, and voltammetric techniques and an ab initio molecular orbital calculation. UV-visible spectroscopic and cyclic voltammetric measurements reveal that the O(2)(*-) species reacts with BMMI(+) and EMI(+) cations of ILs to form hydrogen peroxide. The pseudo first order rate constant for the reaction of BMMI(+) and O(2)(*-) species was found to be about 2.5 x 10(-3) s(-1). With a molecular orbital calculation, the O(2)(*-) species is understood to attack the 2-position (C-2) of the imidazolium ring (i.e., BMMI(+)) to form an ion pair complex in which one oxygen atom is bounded to C-2 and the other to the hydrogen atom of -CH(3) group attached to C-2. Eventually, the ion pair complex of BMMI(+) cation and O(2)(*-) species undergoes a ring opening reaction as evidenced with (1)H NMR measurement.
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http://dx.doi.org/10.1021/jp807541zDOI Listing
February 2009

Water electrolysis: an excellent approach for the removal of water from ionic liquids.

Chem Commun (Camb) 2008 Nov 17(42):5330-2. Epub 2008 Sep 17.

Department of Electronic Chemistry, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, 4259-G1-5 Nagatsuta, Midori-ku, Yokohama, Japan.

An electrochemical system based on platinum cathode and glassy carbon anode was assembled for a successful removal of water from ionic liquids via the water electrolysis strategy.
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http://dx.doi.org/10.1039/b811174jDOI Listing
November 2008

In situ cationic ring-opening polymerization and quaternization reactions to confine ferricyanide onto carbon nanotubes: a general approach to development of integrative nanostructured electrochemical biosensors.

Anal Chem 2008 Sep 1;80(17):6587-93. Epub 2008 Aug 1.

Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, the Chinese Academy of Sciences (CAS), Beijing 100080, China.

This study demonstrates a new and relatively general route to the development of multiwalled carbon nanotube (MWNT)-based integrative electrochemical biosensors by confining ferricyanide redox mediator onto MWNTs. The ferricyanide-confined MWNTs are synthesized first through grafting of epoxy chloropropane onto MWNTs with in situ cationic ring-opening polymerization and then introducing the positively charged methylimidazolium moieties into the grafted polymer with a quaternization reaction. The grafted polymers with positively charged methylimidazolium moieties tethered onto MWNTs can essentially be used to confine redox-active ferricyanide onto MWNTs to form a redox mediator-confined nanocomposite with a good stability and excellent electrochemical property. The synthetic nanocomposite with surface-confined ferricyanide is demonstrated to be well-competent as the efficient electronic transducers for the general development of electrochemical biosensors upon combination with biorecognition units, which is illustrated by using glucose oxidase and laccase as two model biorecognition units. This study essentially paves a facile and general approach to the development of integrative nanostructured electrochemical biosensors.
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http://dx.doi.org/10.1021/ac800733tDOI Listing
September 2008

Electrochemical, HPLC and electrospray ionization mass spectroscopic analyses of peroxycitric acid coexisting with citric acid and hydrogen peroxide in aqueous solution.

Talanta 2008 Feb 16;74(5):1355-62. Epub 2007 Sep 16.

Department of Electronic Chemistry, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, Mail Box G1-5, 4259 Nagatsuta, Midori-ku, Yokohama 226-8502, Japan.

We successfully determined the molecular structure of peroxycitric acid (PCA) coexisting in the aqueous equilibrium mixture with citric acid (CA; 1,2,3-tricarboxylic-2-hydroxy propane) and hydrogen peroxide (H(2)O(2)) by a combined use of reversed-phase HPLC (RP-HPLC), potentiometric, hydrodynamic chronocoulometric (HCC) and electrospray ionization mass spectroscopic (ESI-MS) methods. Firstly, the RP-HPLC was employed to separate CA, PCA and H(2)O(2) coexisting in the equilibrium mixture and the concentration of CA consumed (DeltaC(CA)) in the formation of PCA that was evidenced to be fairly stable during the RP-HPLC measurement was quantitatively measured based on the standard calibration curve of CA. Secondly, the total oxidant concentration (C(Ox)) corresponding to peroxycarboxylic (-COOOH) group in PCA in the equilibrium mixture was determined using potentiometric measurement. The ratio of C(Ox)/DeltaC(CA) was found to be 1.07, which indicates that only one -COOH group in CA molecule is oxidized to the corresponding -COOOH group in PCA molecule. Thirdly, using the HCC technique the diffusion coefficient of PCA, which could be electroreduced at a more positive potential by 1.0 V than the coexisting H(2)O(2), was independently measured as 0.3 x 10(-5)cm(2)s(-1) and at the same time, by considering DeltaC(CA) as the concentration of PCA, the number of electrons (n) required for the reduction of PCA was determined to be 2. The result obtained from RP-HPLC and HCC, i.e., n=2 which is equivalent to one -COOOH group in PCA, is in agreement with that obtained from the combination of RP-HPLC and potentiometric measurements. Finally, the structure of PCA was proposed to contain one -COOOH group with a molecular mass of 208 confirmed by negative ion ESI-MS method. A probable molecular structure of PCA was discussed.
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http://dx.doi.org/10.1016/j.talanta.2007.09.006DOI Listing
February 2008

Nonlinear phenomena at mercury Hg electrode/room-temperature ionic liquid (RTIL) interfaces: polarographic streaming maxima and current oscillation.

J Phys Chem B 2007 Nov 18;111(44):12849-56. Epub 2007 Oct 18.

Department of Electronic Chemistry, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, Mail Box G1-5, 4259 Nagatsuta, Yokohama 226-8502, Japan.

The polarographic streaming maxima and cyclic voltammetric anodic current oscillation (CVACO) at a hanging mercury drop electrode (HMDE) in room-temperature ionic liquid (RTIL) have been studied for the first time using cyclic voltammetric, potential step chronoamperometric and pulse voltammetric techniques. The reversible redox reaction of the 2,1,3-benzothiadiazole (BTD)/BTD*- (an anion radical of BTD) couple with a formal potential (E0') of -1.36 V versus Ag/AgCl/NaCl(saturated) in 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF4) RTIL was typically employed for this purpose. A maximum was observed at the rising part of the normal pulse voltammogram for the reduction of BTD to BTD*- as well as of the reversed pulse voltammogram for the reoxidation of BTD*- to BTD at the HMDE. The conditions of the initiation and control of the CVACO at the HMDE in EMIBF4 were extensively investigated. Generally, the CVACO was enhanced by increasing the concentration of BTD at a given potential scan rate (upsilon) and was attenuated by increasing upsilon. An electrocapillary curve was measured using a dropping mercury electrode in EMIBF4, and the potential of zero charge was determined to be -0.23 V. On the basis of the modern theory of the polarographic streaming maxima of the first kind, the observed streaming maxima and CVACO phenomena are successfully explained to originate from the macroscopic instability at the electrode/solution interface wherein the oscillating mode creates the CVACO.
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http://dx.doi.org/10.1021/jp075749bDOI Listing
November 2007

Manganese oxide nanoparticles electrodeposited on platinum are superior to platinum for oxygen reduction.

Angew Chem Int Ed Engl 2006 Sep;45(36):5963-6

Department of Chemistry, Faculty of Science, Cairo University, Cairo, Egypt.

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http://dx.doi.org/10.1002/anie.200600692DOI Listing
September 2006

Eccentric phenomena at liquid mercury electrode/solution interfaces: upward, downward, and circular motions.

J Phys Chem B 2006 May;110(17):8619-25

Department of Electronic Chemistry, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, Mail Box G1-5, 4259 Nagatsuta, Midori-ku, Yokohama 226-8502, Japan.

The present paper describes a visualization of unidirectional and circular motions triggered by an electrochemical redox reaction at a charged, bent, and streamed liquid electrode/liquid solution interface. The novel circular motion that induces a conversion of electrochemical energy into mechanical energy could be visualized for the first time at a hanging mercury drop electrode (HMDE)/dimethyl sulfoxide (DMSO) solution interface via the electrochromic reaction of 2,1,3-benzothiadiazole (BTD) by using a CCD-color video camera. The observed motions are self-insisting in nature and are tunable into upward, downward, clockwise, and anticlockwise ones by an appropriate choice of the experimental conditions. This circular motion is visualized for the first time as the cause of the well-known cyclic voltammetric anodic current oscillation at the HMDE. Several small perturbations, for example, surface tension, surface motion, bulk motion, diffusional mass transport, and surface electrochemical potential are considered to be endlessly amplified by their coupling in a cyclic chain, resulting in such macroscopic motions at the electrode/solution interface. All of the phenomena can be explained on the basis of the modern theory proposed by Aogaki et al. for the polarographic streaming maxima of the first kind.
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http://dx.doi.org/10.1021/jp060558eDOI Listing
May 2006
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