Hidenori Kuroki

Connected nanoparticle catalysts possessing a porous, hollow capsule structure as carbon-free electrocatalysts for oxygen reduction in polymer electrolyte fuel cells

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.

Biomolecule-recognition gating membrane using biomolecular cross-linking and polymer phase transition.

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.

Nanoscale Morphological Control of Anode Electrodes by Grafting of Methylsulfonic Acid Groups onto Platinum–Ruthenium-Supported Carbon Blacks

An increase in catalyst utilization in direct methanol fuel cells (DMFCs) is necessary to improve performance and reduce costs. We propose an electrode fabrication method, based on the process of grafting a proton-conducting agent onto catalyst-supported carbons before the conventional electrode fabrication process where catalyst-supported carbons are simply mixed with the perfluorosulfonic ionomer. In this study, methylsulfonic acid groups (-CH 2 SO 3 H) as proton-conducting agents have been successfully introduced to the pores of catalyst-supported carbons. We found that the chemical connections between the grafted methylsulfonic acid groups and the surface of catalyst-supported carbons were stable up to around 380°C. Furthermore, by morphological analysis, we found that the grafted methylsulfonic acid groups were homogeneously introduced into both the primary and the secondary pores, and produced no significant structural change in the secondary pore that could affect the mass transfer process. The DMFC performance of the membrane electrode assembly (MEA) made using our grafting method was superior to that of an MEA made using the conventional method. A maximum power density of 87 mW cm -2 was obtained by using grafted catalyst-supported carbons at an anode electrode in the DMFC in the low Pt-Ru loading amount of ca. 0.7 mg cm -2 (Pt loading amount: ca. 0.5 mg cm -2 ) at 50°C under atmospheric pressure.