Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：MYU K.K.  

The durability of enzymatic electrochemical devices depends on the durability of enzymes and on that of mediators that shuttle electrons between enzymes and electrodes. The degradation of 2,2’-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) in the presence of laccase was evaluated in this study. The evaluation of the ABTS-adsorbed electrode in the presence and absence of laccase showed that the redox peak area of ABTS decreased to approximately 40% of the initial value with laccase, whereas the retention of the peak area was approximately 90% without laccase. The characterization of the degradation products in a mixed solution of ABTS and laccase was then performed using Fourier transform (FT)-IR, 1H-NMR, 13C-NMR, and electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS). The comparison of the spectra of the products of the mixed solution of ABTS and laccase with those of the solution containing only ABTS or laccase showed the formation of nitrosamine from FT-IR spectra and newly appeared sp2 and sp3 carbon from 13C-NMR spectra. By also considering the peaks observed in ESI-TOF-MS spectra, a possible degradation mechanism was proposed to be initiated by the adduct formation of the ABTS radical with water.

DOI： 10.18494/sam3905

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society  

Enzymatic biofuel cells with the possible use of nontoxic fuels under moderate operating conditions have the potential to power portable devices and medical assistance devices used near the body. Moving toward the rational design of an enzyme electrode with a high current density, the present study clarified the factor that limits the current density of enzymatic biofuel cells. Comparison of the experimental results of a thin-film electrode with a physically adsorbed mediator and enzyme with the model calculation using parameters obtained from the enzyme adsorption and electrochemical experiments showed that the ratio between the Michaelis constants for the mediator and the effective concentration of the mediator was the important parameter. The model calculation was then used to design the electrode of biofuel cells with a high current density, which revealed the importance of the immobilization method of the mediator.

DOI： 10.1021/acs.iecr.1c04210

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.ijhydene.2022.03.008

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society  

The design of advanced catalysts for newer-generation fuel cells such as direct formate fuel cells (DFFCs) is an important milestone for energy generation and environmental sustainability. Formate as an alternative for alcohols in direct liquid fuel cells is gaining momentum since they can be regenerated from CO2, providing dual benefits of energy generation and carbon footprint reduction under the framework of the circular economy. Anticipating advantages from the oxyphilicity and lower electronegativity in tin (Sn)-alloyed palladium (Pd) crystals than to pure palladium catalysts (Pd/C), we developed effective nano-PdSn alloy crystals over carbon support (PdxSny/C) through a colloidal crystal growth scheme. The alloyed nanocrystals were characterized for the alkaline formate oxidation reaction (FOR) intended for their suitability as DFFC anode catalysts, and several-fold enhancement was observed with higher current density, lower onset potential, and enhanced stability compared to Pd/C. Density functional theory (DFT) calculations provided proper insights into the promotional effects upon appropriate alloying of Sn with Pd, with structural changes and the consequent modifications of the density of states, enhanced OHads in alkaline conditions, reduced intermediate poisoning (Hads and COads), and lowering of work function being identified as factors leading to excellent formate oxidation kinetics. The results obtained and detailed here could be used to design and process Pd nanocatalysts for better-performing DFFCs.

DOI： 10.1021/acsaem.1c02817

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry (RSC)  

As phosphonic acid groups are more concentrated in the synthesized samples, their proton conductivities exhibit lower dependence on the relative humidity.

DOI： 10.1039/D2QM00428C

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing  

Further increases in the current density of biofuel cells are partly limited by the deactivation of enzymes upon adsorption on hydrophobic carbon materials. A hyperthermophilic enzyme, hyperthermophilic laccase, was employed in the present study and the change in the activities and secondary structures upon adsorption on carbon black (CB) were evaluated by the oxidation rate of 2,2 '-azinobis(3-ethylbenzothiazoline-6-sulfonate) and by Fourier transform infrared spectroscopy, respectively, in comparison with the mesophilic enzymes, laccase from Trametes versicolor (denoted as mesophilic laccase), and glucose oxidase (GOx). Hyperthermophilic laccase retained its specific activities and secondary structures upon adsorption on CB compared with the other two enzymes mesophilic laccase and GOx.

DOI： 10.1088/2515-7655/abe2f6

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society  

Rapid, simple, and sensitive point-of-care testing (POCT) has attracted attention in recent years due to its excellent potential for early disease diagnosis and health monitoring. The flow-through biosensor design is a candidate for POCT that utilizes the small-sized pores of a porous membrane as a recognition space where it emits a signal comparable to that of a conventional enzyme-linked immunosorbent assay within 35 min of detection time. In this paper, we present a numerical model for this immunosensing technology to systematically design an improved recognition system. The model considers mass transfer into the pore (convection and diffusion), the kinetics between the immobilized receptor and the target molecule, and the flow conditions, successfully leading to a bottleneck step (capture of secondary antibody) in sandwich-type detection. Our simulation results also show that this problem can be solved by adopting both appropriate receptors and analytical conditions. Eventually, the requirements to achieve the sensitivity required for POCT were fulfilled, which will allow for further development of immunosensing devices for disease detection.

DOI： 10.1021/acs.analchem.1c00250

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry  

DOI： 10.1039/D0CY01437K

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry  

Proton conducting materials suffer from low proton conductivity under low-relative humidity (RH) conditions. Previously, it was reported that acid-acid interactions, where acids interact with each other at close distances, can facilitate proton conduction without water movement and are promising for overcoming this drawback [T. Ogawa, H. Ohashi, T. Tamaki and T. Yamaguchi, Chem. Phys. Lett., 2019, 731, 136627]. However, acid groups have not been compared to find a suitable acid group and density for the interaction, which is important to experimentally synthesize the material. Here, we performed ab initio calculations to identify acid groups and acid densities as a polymer design that effectively causes acid-acid interactions. The evaluation method employed parameters based on several different optimized coordination interactions of acids and water molecules. The results show that the order of the abilities of polymer electrolytes to readily induce acid-acid interactions is hydrocarbon-based phosphonated polymers > phosphonated aromatic hydrocarbon polymers > perfluorosulfonic acid polymers ≈ perfluorophosphonic acid polymers > sulfonated aromatic hydrocarbon polymers. The acid-acid interaction becomes stronger as the distance between acids decreases. The preferable distance between phosphonate moieties is within 13 Å.

DOI： 10.1039/D1CP00718A

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society  

DOI： 10.1021/acsanm.0c01962

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society  

DOI： 10.1021/acsaem.9b01996

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry  

DOI： 10.1039/C9NA00568D

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley  

Formate is the one legitimate carbon-neutral fuel that has the capability of being considered an alternative to alcohol fuels amidst the growing demand for efficient fuel-cell systems. In this manuscript, we demonstrate, for the first time, a class of binary Pd−Ni alloy nanoparticles over two different carbon supports showing exceptional enhancement of the formate oxidation reaction (FOR) performance in alkaline medium, compared to Pd/C. The synergistic effects of Pd and oxophilic Ni along with the electronic structure alteration of Pd induced through alloying resulted in an effective change in its catalytic ability, leading to a 5-time enhancement in the overall current density along with a lower overpotential during formate oxidation compared to Pd/C. The more active Pd catalytic sites of the nanoalloy helped to yield mass activities as high as 4.5 A mg−1Pd and 7.8 A mg−1Pd during FOR. The structural and electrochemical analysis justifies the synergistic effects and alterations in the Pd lattice ensuing a superior enhancement of electrochemically active Pd sites.

DOI： 10.1002/cctc.201900960

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Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1002/cctc.201900960

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

The packed-acid mechanism has been recently proposed as a proton conduction mechanism in environments with a high concentration of proton donors, whereby protons are conducted via acid-acid interaction. The acid-acid interaction was originally stated to occur only when a hydrogen bond (H-bond) is formed directly between proton donors. This study clarifies that proton donors can indirectly interact with each other through several H-bonds, even when the donors are separated distantly (indirect acid-acid interactions). Ab initio calculations confirmed that indirect interaction make a non-negligible contribution to proton diffusivity.

DOI： 10.1016/j.cplett.2019.136627

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry  

DOI： 10.1039/C8CY02232A

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/acsaem.8b00790

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer  

We evaluated the performance and durability of platinum-iron-copper with an L1(0) ordered face-centered tetragonal structure (fct-PtFeCu) as cathode catalysts of membrane-electrode assemblies (MEAs) in polymer electrolyte fuel cells. The exchange current density per unit active surface area of Pt in fct-PtFeCu/C, measured in the MEA, was sufficiently higher than that of commercial Pt/C. The durability of the MEAs was evaluated by three accelerated degradation tests: (1) a load cycle durability test, which mainly accelerates the degradation of catalysts; (2) an open-circuit voltage (OCV) hold test, which mainly degrades membranes; and (3) a hybrid of the load cycle test and OCV hold test. Despite the possible negative effects of dissolved transition metals on the durability of MEAs, fct-PtFeCu/C showed higher durability than commercial Pt/C and at least comparable durability with in-house Pt/C in the OCV hold test, and showed high durability in the hybrid test up to 200 h. These results suggest that the presence of Fe and Cu did not negatively affect the durability of the MEA with fct-PtFeCu/C, and rather the other factor, carbon support, affected more in retaining the durability.[GRAPHICS].

DOI： 10.1007/s10800-018-1193-3

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier Ltd  

The tolerance to corrosion of cathode catalyst supports comprising carbon nanofibers with differing alignments of graphene layers was evaluated, and its correlation with structural parameters obtained from Raman spectra was discussed. The carbon nanofibers employed in this study were platelet-type carbon nanofibers (PCNF) and tubular carbon nanofibers (TCNF). The tolerance to carbon corrosion was evaluated in a membrane electrode assembly using a start-stop durability testing protocol. While the ratio of the D band peak intensity to that of the G band (ID/IG) does not show any correlation with tolerance to carbon corrosion, full width at half maximum of the G band (FWHM(G)) correlates well with tolerance to carbon corrosion. The results suggest that carbon materials with low FWHM(G) values are promising as cathode catalyst supports in PEFCs.

DOI： 10.1016/j.ijhydene.2018.01.205

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society  

© 2018 American Chemical Society. Carbon-free connected Pt-Fe nanoparticle catalysts exhibit excellent oxygen reduction reaction (ORR) activity. Unlike conventional ORR catalysts, connected Pt-Fe catalysts comprise a beaded network structure formed by the connection of Pt-Fe nanoparticles. The refined structural analyses reveal that the connected Pt-Fe network comprises a polycrystalline structure, whereas the commercial Pt nanoparticle on carbon is formed by a single crystal. In addition, a Pt-rich thin layer made of three-to-four platinum atomic layers with high-index stepped facets was observed on the catalyst surface in the connected Pt-Fe catalyst after electrochemical treatment in an acid electrolyte. Lattice spacing analysis showed that the Pt-Pt bond distance in the Pt-rich surface layer is longer than that inside the network of Pt-Fe alloys. Such surface structures play a beneficial role in enhancing ORR activities. The obtained results provide guidelines for catalyst structural designs that can improve ORR activity.

DOI： 10.1021/acsaem.7b00295

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry (RSC)  

<p>The carbon nanotube interpenetrated porous doped carbon alloy derived from trimetallic ZIF displays excellent oxygen reduction activity in alkaline media.</p>

DOI： 10.1039/c7se00249a

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Chemical Society of Japan  

In this study, as a proton-conducting material for polymer electrolyte fuel cell applications, the properties of an organic-inorganic electrolyte comprising zirconium sulfophenylphosphonate (ZrSPP) and sulfonated poly(arylene ether sulfone) (SPES) are investigated by changing the ZrSPP/SPES ratio. An increase in this ratio enhances proton conductivity and shifts the O-S-O wavenumber to a high value.

DOI： 10.1246/cl.160935

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Electrochemical Society  

We investigate the performance of platinum (Pt)-nickel (Ni) alloy catalysts with very low amounts of Pt, namely PtNi3, PtNi7, and PtNi15. Pre-treatment of the alloys was performed in bulk acid solution, and activities for the oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) were measured in alkaline solution. Structural analysis suggests the removal of Ni only near the surface of the alloys. Pre-treated PtNi3 and PtNi7 are shown to be promising catalysts for both ORR and MOR in alkaline media. (C) 2017 The Electrochemical Society. All rights reserved.

DOI： 10.1149/2.1611707jes

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society  

We develop platinum-iron-nickel (PtFeNi) trimetallic alloy catalysts having a chemically ordered L1(0)-type superlattice structure. The PtFeNi catalyst annealed at 800 degrees C possesses a superlattice structure and exhibits oxygen reduction reaction (ORR) activity that is much higher than that of the disordered PtFeNi catalysts and a commercial Pt catalyst supported on carbon black. Moreover, the ORR specific activities in the PtFeNi trimetallic systems are enhanced more than those in the PtFe and PtNi bimetallic systems. Analyses of in situ X-ray absorption spectroscopy reveals Pt-Pt bond distances in the PtFeNi annealed at 800 degrees C (2.70-2.72 angstrom) are shorter than those in a commercial Pt (2.77 angstrom), leading to a suitable balance of oxygen species chemisorption energies on the Pt atoms. In addition, high durability of the PtFeNi catalyst with a superlattice structure is demonstrated. Therefore, tuning the atomic structures of Pt-alloy catalysts by the formation of a superlattice structure and trimetallic system effectively enhances both ORR activity and durability.

DOI： 10.1021/acs.iecr.6b02298

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Society of Chemical Engineers, Japan  

Knowledge of the relationship between the activity and structural features of enzymes is critical for designing conjugation materials. Nonetheless, few studies have addressed the decrease in enzyme activity after modifications of the corresponding enzymes. In cytochrome P450cam, the structural changes around the heme active center can be easily evaluated by spectrophotometric analysis. Thus, with the use of P450cam, we evaluated the relationship between enzyme activity and structural changes after its modification. Our study revealed the existence of a new mode for P450 activity downregulation, which was distinct from a well-known inactivation mode for the conversion of P450 to the inactive P420 form. In this new mode, the activity decreased due to a reduction in binding or accessibility of a substrate to the heme pocket of P450cam, while the enzymatic tertiary structure was retained after conjugations.

DOI： 10.1252/jcej.15we136

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Electrochemical Society  

In this study, the nanostructures of the carbon-free cathode catalyst layers using connected platinum-iron nanoparticle catalysts with porous hollow capsule structures are controlled by the ionomer morphologies (aggregated or not) formed by different treatments (ultrasonication or autoclaving) to the catalyst inks, and the relationship between the catalyst-layer nanostructures and the fuel-cell performances is investigated. Structural and electrochemical analyses of the capsule catalyst layers reveal that the nanosized ionomer morphologies on the capsules strongly influence the oxygen mass-transport resistance; the fully-swollen and thick ionomer layer would cause blocking of the interspaces between the capsules and slow oxygen-diffusion to the capsule surfaces. Thus, the uniform and thin ionomer coating formed by autoclaving produces a higher cell performance due to lower oxygen mass-transport resistance, compared with the nonuniform and partially thick coating formed by ultrasonication. Moreover, the thinner ionomer layer with a very small ionomer/capsule ratio reduces cell performance at high current densities when the humidity at the capsule catalyst layer increases, probably due to the increased oxygen mass-transport resistance through liquid water inside the catalyst layer. Therefore, in addition to the ionomer morphologies, water management in the capsule catalyst layers is important for further improving cell performance. (C) 2016 The Electrochemical Society. All rights reserved.

DOI： 10.1149/2.0971608jes

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society  

Design of Pt alloy catalysts with enhanced activity and durability is a key challenge for polymer electrolyte membrane fuel cells. In the present work, we compare the durability of the ordered intermetallic face-centered tetragonal (fct) PtFeCu catalyst for the oxygen reduction reaction (ORR) relative to its counterpart bimetallic catalysts, i.e., the ordered intermetallic fct-PtFe catalyst and the commercial catalyst from Tanaka Kikinzoku Kogyo, TICK-PtC. Although both fct catalysts initially exhibited an ordered structure and mass activity approximately 2.5 times higher than that of TKK-Pt/C, the presence of Cu at the ordered intermetallic fct-PtFeCu catalyst led to a significant enhancement in durability compared to that of the ordered intermetallic fct-PtFe catalyst. The ordered intermetallic fct-PtFeCu catalyst retained more than 70% of its mass activity and electrochemically active surface area (ECSA) over 10 000 durability cycles carried out at 60 degrees C. In contrast, the ordered intermetallic fct-PtFe catalyst maintained only about 40% of its activity. The temperature of the durability experiment is also shown to be important: the catalyst was more severely degraded at 60 degrees C than at room temperature. To obtain insight into the observed enhancement in durability of fct-PtFeCu catalyst, a postmortem analysis of the ordered intermetallic fct-PtFeCu catalyst was carried out using scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDX) line scan. The STEM-EDX line scans of the ordered intermetallic fct-PtFeCu catalyst over 10 000 durability cycles showed a smaller degree of Fe and Cu dissolution from the catalyst. Conversely, large dissolution of Fe was identified in the ordered intermetallic fct-PtFe catalyst, indicating a lesser retention of Fe that causes the destruction of ordered structure and gives rise to poor durability. The enhancement in the durability of the ordered intermetallic fct-PtFeCu catalyst is ascribed to the synergistic effects of Cu presence and the ordered structure of catalyst.

DOI： 10.1021/acsami.5b03137

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

We developed a molecular recognition gating membrane by grafting a conjugate polymer comprising of aptamer and poly(N-isopropylacrylamide) (PNIPAM) in porous substrate pores. Thrombin-binding aptamer forms double-stranded DNA (dsDNA) with anchor DNA conjugated to PNIPAM. dsDNA is dissociated to single-stranded DNA by the thrombin recognition of the aptamer, and this transformation varies charge state around PNIPAM and induces PNIPAM aggregation. Grafting of the DNA-conjugated PNIPAM to membrane pores can enable the membrane pores to open by PNIPAM aggregation; thus, the pores are controlled by thrombin recognition. In this study, we examined PNIPAM aggregation due to thrombin recognition in a linear polymer system. Next, we characterized the opening and closing behavior of the membrane and proved the concept of gating membrane. (C) 2015 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.polymer.2015.02.027

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Electrochemical Society  

In solid-state alkaline fuel cells, anion exchange membrane fuel cells without free alkali, Mg-Al type layered double hydroxide (LDH) and fractionally delaminated LDH (dLDH) were introduced in the catalyst layer to explore the use of an inorganic anionic clay as a non-swelling durable electrolyte. An improved current-voltage performance was obtained by the LDH introduction due to the formation of ionic conduction pathways, whereas the dLDH introduction resulted in the disruption of the electron conduction pathway and the contact between dLDH and the catalyst, leading to a deteriorated performance. The results provide guidelines for utilizing inorganic clays as solid electrolytes. (c) 2015 The Electrochemical Society. All rights reserved.

DOI： 10.1149/2.0111507eel

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry  

We employ connected nanoparticle catalysts with a porous, hollow capsule structure as carbon-free electrocatalysts for the cathode in polymer electrolyte fuel cells (PEFCs) or proton exchange membrane fuel cells (PEMFCs). The catalysts consist of fused ordered alloy platinum-iron (Pt-Fe) nanoparticles. This unique beaded network structure enables surprisingly high activity for the oxygen reduction reaction, 9 times that of the state-of-the-art commercial catalyst. Because the connected nanoparticle catalysts are formed without sacrificing the high surface area of the nanoparticles and can conduct electrons, the catalysts show good performance in an actual PEMFC without a carbon support. Moreover, the elimination of carbon intrinsically solves the problem of carbon corrosion. Thus, the connected nanoparticle catalysts with a unique structure are a significant advancement over conventional electrode catalysts and will lead to an ultimate solution for PEMFC cathodes.

DOI： 10.1039/c5ee02450a

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

A cathode catalyst with enhanced activity for the oxygen reduction reaction and high durability is greatly required in polymer electrolyte fuel cells (PEFCs). We report that chemically ordered intermetallics, Pt2FeCo/C with L1(0) ordered structure and Pt6FeCo/C with L1(2) ordered structure, achieve both higher activity in solution and higher durability as the cathode catalyst of a membrane electrode assembly (MEA) under actual PEFC operating conditions, compared with a commercial Pt/C. The mass activity of Pt2FeCo/C is about twice as high as that of a commercial Pt/C, and Pt6FeCo/C has a slightly higher mass activity than a commercial Pt/C in solution. These intermetallics were evaluated for durability as the cathodes of MEAs. During the load cycle durability test, the electrochemical surface area (ECSA) of Pt2FeCo/C is retained, while that of Pt6FeCo/C decreases, although less than a commercial Pt/C. The retention of ECSA is consistent with smaller changes in the particle size, observed with transmission electron microscopy, of the intermetallics than of a commercial Pt/C. X-ray diffraction patterns after the durability test show that while some part of ordered intermetallics is transformed into pure Pt, the chemically ordered structure of Pt2FeCo/C is largely retained. Highly active and durable ordered intermetallics are promising as cathode catalysts of PEFCs. (C) 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jpowsour.2014.08.005

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society  

Available methods to analyze proton conduction mechanisms cannot distinguish between two proton conduction processes derived from the Grotthuss mechanism. The two mechanistic variations involve structural diffusion, for which water movement is indispensable, and the recently proposed "packed acid mechanism," which involves the conduction of protons whithout the mvoement of water and is typically, observed in materials consisting of highly concentrated (packed) acids. The latter mechanism could improve proton conductivity under low humidity conditions, which is desirable for polymer electrolyte fuel cells. We proposed a method with which to confirm quantitatively the packed-acid mechanism by combining H-2 and O-17 solid-state magic-angle-spinning nuclear magnetic resonance (MAS-NMR) measurement and H-1 pulsed-field gradient (PFG)-NMR analysis. In particular, the measurements were performed below the water-freezing temperature to prevent water movement, as confirmed by the O-17-MAS-NMR spectra. Even without water movement, the high mobility of protons through short- and long-range proton conduction was observed by using H-2-MAS-NMR and H-1-PFG-NMR techniques, respecively, in the composite of zirconium sulfophenylphosphonate and sulfonated poly(arylene ether slufone) (Zr-SPP-SPES) which is a material composed of highly concentrated acids. Such behavior contrasts with that of a material conducting protons through structural diffusion or vehicle mechanisms (SPES), in which the peaks in both H-2 and O-17 NMR spectra diminished below water-freezing temperature. The activation energies of short-range proton movement are calculated to be 2.1 and 5.1 kJ/mol for ZrSPP-SPES and SPES, respecively, which indicate that proton conduction in ZrSPP- SPES is facilitated by the packed-acid mechanism. Furthermore, on the basis of the mean-swquare displacement using the diffusivity coefficient below water-freezing temperature, it was demonstrated that long-range proton movement, of the order of 1.3 mu m, can take place in the packed-acid mechanism in ZrSPP-SPES.

DOI： 10.1021/ac5021485

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

The restacking of graphene or reduced graphite oxide (r-GO) is commonly regarded as a severe obstacle for potential applications. We propose the application of exfoliated carbon nanotube (e-CNT) as an effective carbon spacer for fabricating a sandwich-like three-dimensional (3D) carbon composite with GO. The 3D carbon combination of GO + e-CNT is successfully prepared via homogenously mixing of GO and e-CNT in an aqueous dispersion in which carbon spacers are homogenously intercalated with graphene layers. With the addition of a carbon spacer, the BET surface area of 3D carbon (51.6 m(2) g(-1)) is enhanced by a factor of three compared with r-GO (17.2 m(2) g(-1)) after thermal reduction. In addition, the 3D GO + e-CNT supported PtPd catalyst (PtPd-GO + e-CNT) shows homogenous distribution of PtPd nanoparticles of 3.9 +/- 0.6 nm in size, with an enlarged electrochemical active surface area (ECSA) value of 164 m(2) g(-1) and a mass activity of 690 mA mg(-1) toward the methanol oxidation reaction (MOR), which is the typical anode reaction for direct methanol fuel cells (DMFC). (C) 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jpowsour.2014.03.014

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry  

Binding of intercalators to dsDNA switches the aggregation phenomena of DNA-PNIPAM because the binding decreases the dsDNA conformational entropy and/or the shielding of dsDNA charges. Thus, dsDNA-PNIPAM was dramatically aggregated in response to molecular recognition of the DNA-intercalator.

DOI： 10.1039/c4py00600c

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Society of Chemical Engineers, Japan  

We immobilized 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonate) through a spacer to polymer grafted onto carbon black to fabricate a three-dimensional biocathode with high surface area that reduces oxygen in the presence of laccase. Cyclic voltammetry using a rotating disk electrode shows that an oxygen reduction reaction (ORR) current density greater than 1 mA cm(-2) at 200 rpm was obtained using the grafted redox polymer in the presence of 1.0 mg mL(-1) of laccase in solution. The onset potential of the ORR current suggests that the electron transfer from carbon through grafted redox polymer to laccase was more effective than that through cast linear redox polymer.

DOI： 10.1252/jcej.13we319

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry  

Proton conduction due to acid-acid interactions is an important topic in a variety of fields, from materials science to biochemistry. We observed a distinctive proton conduction phenomenon for a material consisting of packed acids at the interface of zirconium sulphophenylphosphonate (ZrSPP) and sulphonated poly(arylene ether sulphone) (SPES). The proton in the composite was found to be active, while water, a general proton carrier, remained immobile. Moreover, the conductivity of the composite material was higher than the sum of the individual conductivities of ZrSPP and SPES, which can be attributed to the packed acids present at the interface. We propose a "packed-acid mechanism" based on the results of ab initio calculations in order to explain such a significant and interesting behaviour of protons. During common proton conduction, pseudo-shuttling of a proton between a proton donor and acceptor is a general event that disrupts the reorientation phenomenon, which is an important process associated with common proton conduction. Based on our results, it could be inferred that in packed acid materials, the acid-acid interaction eliminates the pseudo-shuttling (interception) and facilitates reorientation, resulting in successive proton conduction.

DOI： 10.1039/c4sc00952e

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry  

We have designed a chemically ordered face-centred tetragonal intermetallic PtFeCo (trimetallic) (fct-TM) alloy catalyst using a simple solid-state impregnation method for the oxygen-reduction reaction (ORR) in polymer electrolyte membrane fuel cells (PEMFCs). The fct-TM catalyst has demonstrated both enhanced activity and durability, unlike many Pt alloys. The chemical ordering of the fct-TM was verified by high-angle annular dark-field scanning transmission electron microscopy. The ORR activity of fct-TM was examined using the rotating-disk electrode (RDE) technique and the results are compared with those for a chemically disordered face-centred cubic (fcc), fcc-TM catalyst, and a commercial catalyst from Tanaka Kikinzoku Kogyo, TKK-PtC. The fct-TM displayed superior catalytic (mass) activity relative to disordered fcc-TM and TKK-PtC. The mass activity of fct-TM (0.505 A mgPt(-1)) is 2.5 times higher than that of TKK-PtC (0.23 A mgPt(-1)). The durability of these catalysts was evaluated over 5000 (5k) potential cycles in the lifetime regime. The fct-TM retained 80% of its initial mass activity and electrochemically active surface area (ECSA); however, fcc-TM and TKK-PtC maintained about 50% and 70% activity, respectively. The fct-TM also retained the chemically ordered structure after 5k durability cycles. This was confirmed using selected-area electron-diffraction (SAED) patterns. Furthermore, scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDX) line scans of the fct-TM catalysts after 5k durability cycles revealed that Fe and Co were found similar to as before cycling, which signifies that the dissolution of Fe and Co was impeded by the fct-TM catalysts. The observed enhancement in durability might be due to the ordered arrangement of Pt and Fe/Co within the alloy.

DOI： 10.1039/c4ra04744c

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Electrochemical Society  

Reducing the physical adsorption of enzymes on carbon black and their resultant deactivation are the key factors to increasing the current density of enzymatic biofuel cells, and thus enabling their use in a wide range of applications. The effect of the surface treatment of carbon black on the physical adsorption of glucose oxidase (GOx) was investigated. GOx was then immobilized on a high-surface-area three-dimensional carbon electrode using a method other than physical adsorption. Acid treatment followed by graft polymerization of an anionic polymer and the mixing of carbon black with polyethylene glycol ( PEG) were both effective in reducing the physical adsorption of GOx. The combination of the surface modification using PEG and the immobilization of GOx via ammonium sulfate precipitation with crosslinking increased the glucose-oxidation current density obtained in an electrode fabricated using poly(vinylferrocene-co-acrylamide)-grafted carbon black. (C) 2014 The Electrochemical Society. All rights reserved.

DOI： 10.1149/2.0181413jes

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Chemical Society of Japan  

It is possible to switch between the different aggregation phenomena of deoxyribonucleic acid (DNA)-conjugated poly(N-isopropylacrylamide) (PNIPAM) by controlling the balance of DNA charges and flexibility. The shift in the balance between DNA charges and flexibility occurs by changing the salt concentration in polymer solutions and the DNA fraction in polymer chains. Single-stranded DNA (ssDNA)-conjugated PNIPAM was more aggregated than double-stranded (dsDNA) when DNA charges are predominant. In contrast, dsDNA-conjugated PNIPAM was more aggregated than ssDNA when flexibility was predominant.

DOI： 10.1246/cl.130794

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

A mathematical model to explain the mechanism of molecular recognition by an ion gating membrane oscillator has been proposed, in which the hydrostatic pressure-driven flow (pore-open state) and osmotic flow (pore-closed state) are switched alternatively in response to a specific ion signal. The model was based on transport equations derived from nonequilibrium thermodynamics, where the dependency of the reflection coefficient and the solvent hydrostatic permeability On the signal ion concentration were assumed to follow the Hill equation, based on experimental data. A time-delay effect was also introduced into the permeation parameters by first derivation. As a result, the model reproduced the characteristic parameters of the oscillator, such as the period and amplitude It also clarified that an autocatalytic process, the key for nonlinear oscillation, was generated for an osmotic period by a slow response of the reflection coefficient and a fast response of the solvent hydrostatic permeability, i.e., the osmotic flow removes the signal ions out of the membrane to the ion-fed side, which increases the osmotic flow, and then more ions are removed from the membrane on opening the pores from the solvent side of the membrane. (C) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.memsci.2013.08.001

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Society for Biotechnology, Japan  

We site-specifically conjugated biotin-PEG derivatives with spacer arms of different lengths to mutant P450cam (3mD) and evaluated the activity of and structural changes in the conjugates as a first step toward clarifying the mechanism whereby the activity of the 3mD conjugate is inhibited. 3mD was prepared by site-specific mutation to inhibit its enzymatic activity artificially, after which the derivative compounds were conjugated to the enzyme. 3mD has one cysteine on its surface with a reactive thiol group that can react with compounds near the active site, where a conformational change will be induced after conjugation. The activity of 3mD was retained in the biotin-PEG(2)-3mD conjugate, but was dramatically reduced in the biotin-PEG(11)-3mD conjugate. To investigate the effect of poly(ethylene glycol) (PEG) length on the enzymatic activity after conjugation, PEGs of different lengths, exceeding that in biofin-PEG(11), and whose termini were not biotin, were conjugated to 3mD. The activity of 3mD decreased in all these conjugates. This indicates that the activity of 3mD in these conjugates decreased after its conjugation with PEG molecules that exceeded a certain length. The biotin-PEG(2)-3mD, which retains enzymatic activity after conjugation, showed avidin responsiveness; the enzymatic activity decreased after avidin binding. (C) 2013, The Society for Biotechnology, Japan. All rights reserved.

DOI： 10.1016/j.jbiosc.2013.04.003

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society  

In contrast with proton-exchange membrane fuel cells (PEMFCs), in a solid-state alkaline fuel cell (SAFC) water reacts at the cathode and is generated at the anode. This systematic difference leads to the new challenge of water management for SAFCs. To explore the relationship between water movement in the cell and cell performance we used 3-methacryloylamino propyl trimethylammonium chloride and styrene as the electrolyte monomers to synthesize different hydrophilic/hydrophobic anion-exchange membranes (AEMs) using a pore-filling technique. We discovered that the cell performance changed remarkably by changing the AEM properties. The cell performance was affected significantly by the water movement in the cell, which also depends on the AEM properties. In a highly hydrophilic membrane, the water movement direction is from the anode to the cathode, which can increase the cathode relative humidity (RH) to improve the ion conductivity and suppress flooding at the anode. In contrast, the result is the opposite in a hydrophobic membrane. On the basis of experimental and calculation approaches, we show that the cell performance of SAFCs can be improved by promoting water movement from the anode to the cathode with a high water permeability AEM and adjustment of the anode RH.

DOI： 10.1021/jp405088s

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Society for Biotechnology, Japan  

We conjugated a molecular recognition moiety, biotin, with an enzyme site-specifically near to its active site and succeeded in inactivating the enzyme by binding the specific target biomolecule avidin to biotin. Bacterial P450 was used as a model enzyme, which has attracted much attention in several fields. Site-directed mutagenesis was conducted to produce a mutant P450 that could attach biotin site-specifically. The activity of the conjugate decreased markedly to one tenth of that of biotinylated P450 after binding to avidin. Ultraviolet-visible spectroscopy of the carbon monoxide-bound P450, circular dichroism data, and the ratio of the active form to the sum of the active form and the inactive form indicated that this decrease in activity was because of a conformational change in the tertiary structure surrounding the active center after avidin binding, while the secondary structure of P450 remained unchanged. (C) 2013, The Society for Biotechnology, Japan. All rights reserved.

DOI： 10.1016/j.jbiosc.2012.12.019

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Chemical Society of Japan  

In this study, hydroxide ion mobility is reduced by controlling water movement in the membrane to improve its stability. The water movement was decreased by structuring the water with pore-filling membranes synthesized by confining an anionexchange polymer in nanopores of a porous substrate. Compared with bare films of the same polymer, the pore-filling membranes showed higher stability subsequent to immersion in water at 100 °C. © 2013 The Chemical Society of Japan.

DOI： 10.1246/cl.2013.14

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Other Link： http://orcid.org/0000-0002-7728-9397

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry  

Proton conduction in zirconium sulphate (ZrSO4) composed of a Lewis acid-base pair was studied. ZrSO4 exhibits non-humidified proton conductivity, comparable to other proton conductors under similar conditions. Ab initio calculation shows that a proton transfers in ZrSO 4 from a Lewis acid to a Lewis base without a proton carrier. © 2013 The Owner Societies.

DOI： 10.1039/c3cp51697k

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Other Link： http://orcid.org/0000-0002-7728-9397

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry  

Excellent oxygen reduction reaction (ORR) activity of Pt-based bimetallic alloys like CoPt and PdPt has been studied in detail. A simple solution-phase synthetic procedure for the bimetallic alloys of CoPt and PdPt is described here. This method, involving a single-step reaction, is believed to be suitable for large-scale synthesis of both monometallic and multimetallic nanocrystals with required size and shape. Among various catalyst compositions, Pd 22Pt78 and Co15Pt85 catalysts have shown excellent ORR activity compared with Pt/C and commercial PtCo/C (PtCo/C(comm)) samples. At 0.9 V, Co15Pt85/C and Pd 22Pt78/C exhibit mass activities with values ∼3.8 times and ∼2.1 times higher than that of Pt/C, and Co15Pt 85/C exhibits 1.8 times higher activity than that of PtCo/C(comm). Quantification and the effect of surface-oxygenated species generated at higher potentials were studied by stripping voltammetry, in the form of total charge. © The Royal Society of Chemistry 2013.

DOI： 10.1039/c3ra40920a

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Other Link： http://orcid.org/0000-0002-7728-9397

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry  

We have demonstrated that the aggregation of DNA-conjugated thermoresponsive polymer was inhibited by the formation of double strand DNA (dsDNA) from single strand DNA (ssDNA) by the change in the number of electric charges and hydrophilic states of DNA. The polymer was prepared by conjugation of short ssDNA with poly(N-isopropylacrylamide) (PNIPAM) and subsequent hybridization of the conjugated DNA with complementary DNA to form dsDNA. The ssDNA-conjugated PNIPAM highly aggregated with an increase in temperature, while the dsDNA-conjugated PNIPAM was inhibited from aggregation by the hybridization with fully matched complementary DNA and further prevented by hybridization with longer complementary DNA with a protruding sequence. Further characterizations suggest that the difference in the degree of aggregation between the ssDNA- and dsDNA-conjugated PNIPAM was mainly driven by the change in the number of electric charges associated with the conjugated DNA.

DOI： 10.1039/c3sm27230c

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Electrochemical Society  

Decreasing the size of an electrolyte used as a catalyst layer increased the platinum (Pt) utilization ratio by introducing the electrolyte into the primary pores, which are the spaces inside the agglomerated Pt-supported carbon black. An organic-inorganic hybrid material, a capping electrolyte, composed of autoclave-treated Nafion and surface-modified zirconium oxide with acetylacetone and aminosilane coupling agent, has a smaller Stokes diameter in solution than Nafion. Electrochemical measurements of a membrane electrode assembly (MEA) show that the Pt utilization ratio was improved when the capping electrolyte was used. Furthermore, a combination of the introduction of capping electrolyte into the primary pores and formation of the proton-transport pathway around the agglomerated particles improved the performance of the MEA in the low current density region, where the reaction area affects the performance, compared with the MEA made with a Nafion electrode. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.065302jes] All rights reserved.

DOI： 10.1149/2.065302jes

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society  

In living bodies, specific molecular recognition triggers various kinds of autonomous behaviors. To artificially reconstruct one such distinct phenomenon, an autonomous shrinking and subsequent reswelling of poly(N-isopropylacrylamide) (pNIPAM) having a beta-cyclodextrin (CD) pendant group was induced by a specific signal of a guest molecule for CD, 8-anilino-1-naphthalenesulfonic acid. The autonomous phenomenon is realized as a consequence of mutual influences between the pNIPAM main chain as actuator and the CD moiety as sensor. The mutual communications were found to have quite different dependence on the length of the spacer connecting pNIPAM and CD; a long spacer hinders the communication from CD to pNIPAM, whereas a short spacer does not. However, the reverse communication from pNIPAM to CD is maintained even with long spacers, possibly because of the pNIPAM main chain spatially close to the CD moiety. This knowledge is useful for the design of highly functional polymeric materials conjugating sensors and actuators.

DOI： 10.1021/ma3018603

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

The effect of the size and surface area on the ion conductivity of layered double hydroxide (LDH) containing Mg2+ and Al3+ intercalated with CO32- was investigated, with a focus on particles smaller than 100 nm. The size of LDH was controlled by changing the pH during coprecipitation and the hydrothermal treatment time. The ion conductivity increased with the decrease in the crystallite size and the increase in the specific surface area. We thus found that surface conduction greatly contributed to the total ion conduction for small-size LDH, in addition to the interlayer conduction previously proposed as the dominant conduction mechanism in LDH. (C) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.elecom.2012.09.003

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer  

Enzymatic biofuel cells can use a variety of fuels such as glucose and ethanol, and they have the potential to power portable devices. This article summarizes recent advances made in the use of three-dimensional conducting materials as electrode matrices of enzymatic biofuel cells from the point of view of the current density and the power density.

DOI： 10.1007/s11244-012-9895-y

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry  

We show conversion of a biomolecule signal into a visual color by nanoparticle permeation through a biomolecule-recognition gating membrane. The permeability of colored nanoparticles through the membrane changed due to the presence of a specific biomolecule and the membrane pores' opening/closing, and amplification of the biomolecule signal was induced.

DOI： 10.1039/c2ay25265a

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society  

In a solid-state alkaline fuel cell (SAFC), water reacts at the cathode and is generated at the anode, in contrast to proton-exchange membrane fuel cells (PEMFCs). Water behavior in the SAFC membrane electrode assembly is particularly important: without water movement, the relative humidity at the cathode, which affects the membrane resistance, cannot be enhanced, and flooding at the anode cannot be suppressed. Thus, optimization is required to establish design methodology for SAFCs. In this study, water movement in a SAFC system has been observed accurately using a water collection method. We confirm for the first time the movement of water from the anode to the cathode during an actual fuel cell performance test. Compared with a PEMFC, water movement occurs leading to difficult water management in the SAFC. With the knowledge obtained, water management SAFC by careful control of humidity. in the opposite direction has been achieved in the

DOI： 10.1021/jp211084b

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society  

A facile and one-pot method for the synthesis of Pt, Pd, and their alloy nanocrystals along with their exciting electrocatalytic activities toward methanol oxidation have been reported. Unique structures like truncated octahedrons of Pd, Pt, and their alloys like CoPt and PdPt have been synthesized in presence of a reducing solvent like N-methyl pyrrolidone (NMP) and stabilizer like polyvinyl pyrrolidone (PVP). Among these nanocrystals, Pd16Pt84 and Co5Pt95 show tremendous improvement in the electro-oxidation of methanol in acidic media with mass activities of 1790 and 1417 mA/mg(Pt), respectively (with lower onset potential compared to Pt alone), which is believed to be much higher compared to that of previous reports and state-of-art Pt/C and RuPt/C catalysts, indicating a better alloy formation and stable particle-support interactions.

DOI： 10.1021/jp300140s

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society  

When using a hydrocarbon polyelectrolyte, such as sulfonated poly(arylene ether sulfone) (SPES), in a catalyst layer of a polymer electrolyte fuel cell, significantly decreased performance was observed. We clarified the main reason for this decrease from a systematic investigation into the humidity dependence of the polymer properties, such as the swelling ratio and oxygen permeability, and by comparison with the performance of a membrane electrode assembly (MEA) with SPES electrodes. The swelling ratio of SPES increased markedly at &gt;90% relative humidity (RH), which led to blocking of the catalyst layer pores. This tendency semiquantitatively corresponds to the decreased performance of MEA at &gt;90% RH, considering the water generated by the reaction. Therefore, the main cause of the decrease is the blocking of oxygen diffusion in the pores from the swelling of SPES in the catalyst layer rather than oxygen permeation through the SPES layer, as previously suggested.

DOI： 10.1021/jp206552k

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Society of Photopolymer Science and Technology  

DOI： 10.2494/photopolymer.25.555

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society  

Molecular collisions, which are the microscopic origin of molecular diffusive motion, are affected by both the molecular surface area and the distance between molecules. Their product can be regarded as the free space around a penetrant molecule defined as the "shell-like free volume" and can be taken as a characteristic of molecular collisions. On the basis of this notion, a new diffusion theory has been developed. The model can predict molecular diffusivity in polymeric systems using only well-defined single-component parameters of molecular volume, molecular surface area, free volume, and pre-exponential factors. By consideration of the physical description of the model, the actual body moved and which neighbor molecules are collided with are the volume and the surface area of the penetrant molecular core. In the present study, a semiempirical quantum chemical calculation was used to calculate both of these parameters. The model and the newly developed parameters offer fairly good predictive ability.

DOI： 10.1021/jp2068717

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society  

We present for the first time a biomolecule-recognition gating system that responds to small signals of biomolecules by the cooperation of biorecognition cross-linking and polymer phase transition in nanosized pores. The biomolecule-recognition gating membrane immobilizes the stimuli-responsive polymer, including the biomolecule-recognition receptor, onto the pore surface of a porous membrane. The pore state (open/closed) of this gating membrane depends on the formation of specific biorecognition cross-linking in the pores: a specific biomolecule having multibinding sites can be recognized by several receptors and acts as the cross-linker of the grafted polymer, whereas a nonspecific molecule cannot. The pore state can be distinguished by a volume phase transition of the grafted polymer. In the present study, the principle of the proposed system is demonstrated using poly(N-isopropylacrylamide) as the stimuli-responsive polymer and avidin-biotin as a multibindable biomolecule-specific receptor. As a result of the selective response to the specific biomolecule, a clear permeability change of an order of magnitude was achieved. The principle is versatile and can be applied to many combinations of multibindable analyte-specific receptors, including antibody-antigen and lectin-sugar analogues. The new gating system can find wide application in the bioanalytical field and aid the design of novel biodevices.

DOI： 10.1021/ac202629h

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley  

The effects of methanol crossover on cathode overpotential of direct methanol fuel cells (DMFCs) were investigated by focusing on a mixed potential effect and surface poisoning of the catalyst. Experiments using different membranes and catalyst loadings were performed and compared with a semi-quantitative model to discuss the main cause of the cathode overpotential. When the measured methanol crossover increased, cathode overpotential increased at particular threshold values, which were 150 mA cm(-2) at 0.3 mg cm(-2) of cathode platinum (Pt) loading and above 200 mA cm(-2) at 1.1 mg cm(-2). The modelling results also supported this tendency, and showed that Pt surface was poisoned to a great extent above the threshold methanol crossover where the cathode overpotential increased sharply, while the cathode overpotential remained low and was explained solely by the mixed potential below the threshold value. The threshold methanol crossover can be regarded as the acceptable value, below which the cathode overpotential from methanol crossover remains low, and was related with the Pt loading in the cathode. The reduction of methanol crossover through membranes below the acceptable values will contribute greatly to a decrease in the cathode overpotential and to the reduction of catalyst loadings.

DOI： 10.1002/fuce.201000141

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

A novel anion exchange pore-filling membrane allowing low liquid fuel permeation while maintaining hydroxide ion conduction has been developed for use in solid-state alkaline fuel cells (SAFCs). Mechanical stability of the exterior porous substrate suppresses swelling of the interior polyelectrolyte and controls the inner water to be wholly bound water even under fully humidified conditions. Using this membrane, hydroxide ion conduction through bound water has been discovered for the first time. At the same time, we also have clarified that this bound water effectively reduces permeation of the high-energy-density liquid fuels, methanol and ammonia, which is beneficial in the design of efficient SAFCs. (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.memsci.2011.02.044

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Society of Photopolymer Science and Technology  

DOI： 10.2494/photopolymer.24.471

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society  

The current density of biofuel cell needs to be increased by 2 orders of magnitude to reach 10(-1) A cm(-2), which is the required density for portable energy devices. Model calculations have suggested that high-surface-area biofuel cell electrodes can achieve the required current density. However, experimental current density has amounted to only about 10(-3) A cm(-2) because of low enzyme surface coverage. In this study, we investigated the low surface coverage of glucose oxidase (GOD) in a high-surface-area biofuel cell electrode made of redox-polymer-grafted carbon black. Three possible explanations were considered: (i) low total amount of GOD, (ii) poor contact between GOD and mediator in the redox polymer, and (iii) deactivation of GOD. Among them, iii was found to be the main problem. Reducing this deactivation is the key for achieving a current density of approximately 10(-1) A cm(-2).

DOI： 10.1021/ie1001789

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

We have attained the thermal-responsive gating membrane with a drastic permeability change by several hundredfold; N-isopropylacrylamide (NIPAM) polymers were grafted on the pore surface by the plasma-induced graft polymerization. In this study, we fabricated the gating membrane using a polycarbonate (PC) substrate with straight cylindrical pores. This substrate can be degraded in a strong-alkaline solution, thus the grafted NIPAM polymer was isolated from the substrate and evaluated. Accordingly, we found the grafted polymer has a high molecular weight (from several hundred thousand to a few million) and the polymer chain density is low at ca. 0.01 chains nm(-2). These results indicate factors significant to drastic pore gating; the pores are fully open in a shrunken state at the low chain density, by the existence of enough space for shrinking grafted polymers. Further, the pores are sufficiently closed by swollen NIPAM polymers with a small number of high molecular weight polymers. From the above, we clarified the relationship between the property of the grafted polymer and the permeation behavior of the thermal-responsive gating membrane for the first time. Moreover, the knowledge obtained in this study can provide useful guideline for clarifying the gating function obtained by other grafting technique. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.memsci.2010.01.052

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

The response behavior of a molecular recognition ion gating membrane to an ion signal was investigated in an aqueous ethanol solution. The linear poly-N-isopropylacrylamide (NIPAM)-co-benzo[18]-crown-6-acrylamide (BCAm) copolymer showed phase separation in response to variation in ethanol mole fraction in the mixed solvent of water and ethanol, which is called a reentrant coil-to-globule-to-coil transition. The phase diagram of poly-NIPAM-co-BCAm changed in response to the concentration of a specific ion signal. Based on this reentrant phase transition behavior of the copolymer, the gating membrane, which was prepared by grafting the copolymer of NIPAM and BCAm onto the surface of a porous polyethylene film, opened and closed its pores by the swelling and shrinking of the grafted copolymer in an aqueous ethanol solution. In addition, the complex formation constant of BCAm increased with increasing ethanol mole fraction, which enhanced the response sensitivity and selectivity to ion species; thus, the sensitivity to BaCl2 was 10 times higher in 19.6 mol% aqueous ethanol solution than it was in pure water. (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.memsci.2009.11.028

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry  

Layered proton conductors of three different materials, zirconium phosphate (ZrP), zirconium sulfophenylphosphonate (ZrSPP), and zirconium sulfate (ZrS) were synthesized from the same surface-modified nano zirconium oxide precursor through novel, mild conversion routes. The conversions were performed at 80 degrees C under mild acidic conditions. The phase formation of ZrP, ZrSPP, and ZrS were confirmed by FT-IR and XRD techniques. Thermal stabilities of ZrSPP and ZrS were evaluated by thermogravimetric analysis and hydrothermal tests at 150 degrees C for 24 h. Proton conductivities of ZrP, ZrSPP, and ZrS were measured at 90 degrees C under various relative humidities. The mild conversion routes will enable in situ synthesis of these layered proton conductors inside a polymer matrix from the same nano zirconium oxide precursor, which has been reported to form a nanodispersed structure in polymer electrolytes such as perfluorosulfonated ionomers and aromatic hydrocarbon electrolytes.

DOI： 10.1039/c0jm00130a

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Society of Chemical Engineers, Japan  

We report achieving a very high voltage of 1.17V, corresponding to an energy-conversion efficiency greater than 90%, for the first time in a polymer electrolyte fuel cell (PEFC) below 10 nA/cm(2). We achieved this high efficiency by optimizing various parameters, such as humidity, catalyst and electrolyte membranes, so as to reduce the amount of adsorbed oxygen-containing species that originate from water on Pt.

DOI： 10.1252/jcej.43.623

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Society of Photopolymer Science and Technology  

DOI： 10.2494/photopolymer.23.571

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley  

A mathematical model considering reaction and diffusion processes in biofuel cells, such as enzyme reactions, apparent electron diffusion in the redox polymer, and diffusion of a substrate in a redox polymer film, verified the effectiveness of a high-surface-area biofuel cell electrode with a thin, grafted redox polymer layer. The model calculation shows that the rate-limiting step of apparent electron diffusion can be overcome by using the electrode with a thin redox polymer, even when the redox polymer used has a low apparent electron diffusion coefficient. In the electrode, increase in the second-order rate constant for the reaction between an enzyme and a mediator above a certain value does not increase the current density, and thus the mediator used in the electrode should have an adequate second-order rate constant and a more negative redox potential. In addition, increase in the turnover rate of the enzyme and the surface coverage of the enzyme allows an increase in the current density; the surface coverage of the enzyme has the most influence. Based on these calculations, it is important to realise high-surface-area electrodes with a thin redox polymer, and with high enzyme loading.

DOI： 10.1002/fuce.200800028

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society  

We immobilized hydroquinone through a spacer to polymer grafted on carbon black and achieved a high-surface-area biofuel cell electrode. Quinone compounds are well-known to transfer electrons in the respiratory chain and have been considered prospective mediators in biofuel cells because of their relatively negative redox potentials. Evaluation of three different spacer arms tethering hydroquinone to linear polymers revealed that only the hydrophilic and flexible di(ethylene oxide) spacer made it possible for immobilized hydroquinone to transfer electrons from glucose oxidase (GOD) to an electrode; direct immobilization and an alkyl spacer did not. The electrode comprising hydroquinone immobilized through di(ethylene oxide) spacer to polymer grafted on carbon black transferred electrons from GOD to the electrode. The potential at which an anodic current began to increase was more negative by about 0.2 V than that for a vinylferrocene-mediated electrode, while the increase in the anodic current density was of the same order.

DOI： 10.1021/jp074334n

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society  

A novel biofuel cell electrode has been developed using surface-modified carbon to obtain high current density. Until now, the amount of enzyme effectively used in electrode reactions has been restricted as a result of electron conduction via a redox polymer, which shuttles electrons from the enzyme to the electrode. In the novel electrode described herein, conduction of electrons was divided between a redox polymer and carbon, and thus, the electron conduction distance in the redox polymer was decreased. The redox polymer was chemically immobilized onto a carbon black surface using a graft polymerization method. Using this modified carbon black, a three-dimensional carbon electrode containing the enzymes was fabricated. The electrode was employed as a glucose-oxidizing anode, using glucose oxidase as the enzyme and a poly(vinylfeffocene-co-acrylamide) as the redox polymer. Cyclic voltammetry showed that the glucose was electro-oxidized at a rate of 3 mA/cm(2) at 0.6 V vs Ag/AgCl in a quiescent solution.

DOI： 10.1021/ie051142a

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer  

The proton conduction and superionic phase transition of cesium dihydrogen phosphate, CsH2PO4 (CDP), were investigated under various humid conditions to evaluate the applicability of a CsH2PO4 solid electrolyte to an intermediate temperature fuel cell operating between 230 degrees C and 300 degrees C. The phase stability, superionic phase transition, and reversibility of dehydration of CsH2PO4 were evaluated under different ambient water vapor concentrations, from 0 to 90 mol%, through the measurements of conductivity. The dependence of conductivity on the water vapor concentration and the demonstrated reversibility of dehydration clearly showed the range in which CsH2PO4 is applicable to the intermediate temperature fuel cell. Additionally, we evaluated the protonic transport number of CsH2PO4, which was almost unity, and demonstrated fuel cell operation at 250 degrees C using a single cell fabricated with the CsH2PO4 electrolyte.

DOI： 10.1007/s10800-005-4727-4

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Total pages：246   Responsible for pages：123-129   Language：Japanese Book type：Scholarly book

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Total pages：320   Responsible for pages：157-168   Language：Japanese Book type：Scholarly book

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Authorship：Lead author,　Last author,　Corresponding author   Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

CiNii Books

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Authorship：Lead author   Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

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Authorship：Lead author,　Last author,　Corresponding author   Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

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Language：Japanese  

CiNii Books

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Language：Japanese   Publisher：燃料電池開発情報センター  

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Event date： 2024.7

Language：Japanese   Presentation type：Poster presentation  

Country：Japan  

Event date： 2024.7

Language：Japanese   Presentation type：Poster presentation  

Country：Japan  

Event date： 2024.7

Language：Japanese   Presentation type：Poster presentation  

Country：Japan  

Event date： 2024.6

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Country：Japan  

Event date： 2024.6

Language：Japanese   Presentation type：Poster presentation  

Country：Japan  

Event date： 2024.6

Language：Japanese   Presentation type：Poster presentation  

Country：Japan  

Event date： 2024.3

Language：English   Presentation type：Oral presentation (invited, special)  

Country：Japan  

Event date： 2023.11

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Country：Japan  

Event date： 2023.11

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Country：Japan  

Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Country：Japan  

Event date： 2023.7

Language：Japanese   Presentation type：Poster presentation  

Country：Japan  

Event date： 2023.7

Language：Japanese   Presentation type：Poster presentation  

Country：Japan  

Event date： 2023.1

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Country：Japan  

Event date： 2022.12

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Country：Japan