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Ikeshoji T.,Tohoku University | Ikeshoji T.,Fuel Cell Cutting Edge Center Technology Research Association Cubic | Ikeshoji T.,Japan National Institute of Advanced Industrial Science and Technology | Otani M.,Japan National Institute of Advanced Industrial Science and Technology | And 2 more authors.
Physical Chemistry Chemical Physics | Year: 2011

The water dissociation reaction and water molecule configuration on a positively charged platinum (111) surface were investigated by means of first principles molecular dynamics under periodic boundary conditions. Water molecules on the Pt surface were mostly in the O-down orientation but some H-down structures were also found. OH - ion, generated by removing H from H 2O in the bulk region, moved to the Pt surface, on which a positive charge is induced, by a Grotthuss-like proton-relay mechanism and adsorbed on it as OH(Pt). Hydrogen atom exchange between OH(Pt) and a near-by water molecule frequently occurred on the Pt surface and had a low activation energy of the same order as room temperature energy. When a positive charge (7 μC cm -2) was added to the Pt surface, H 3O + and OH(Pt) were generated from 2H 2O on the Pt. This may be coupled with an electron transfer to the Pt electrode [2H 2O → H 3O + + OH(Pt) + e -]. The opposite reaction was also observed on the same charged surface during a simulation of duration about 10 ps; it is a reversible redox reaction. When further positive charge (14 μC cm -2) was added, the reaction shifted to the right hand side completely. Thus, this one-electron transfer reaction, which is a part of the oxygen electrode reaction in fuel cells and water electrolysis, was confirmed to be a low activation energy process. © 2011 the Owner Societies.


Ikeshoji T.,Fuel Cell Cutting Edge Center Technology Research Association Cubic | Ikeshoji T.,Tohoku University | Ikeshoji T.,Japan National Institute of Advanced Industrial Science and Technology | Otani M.,Japan National Institute of Advanced Industrial Science and Technology | And 7 more authors.
AIP Advances | Year: 2012

The charged interface between a platinum electrode and an aqueous solution is investigated by first-principles molecular dynamics simulations in which charges in the system are controlled by the effective screening medium method under periodic boundary conditions. H3O+ and OH are located above or on the Pt surface. Water molecules rotate to screen the electric field induced by the charge accumulated on the Pt surface. The time-averaged electrostatic potential near the Pt surface is structured with a flattened "bulk" region. The potential difference between the Pt Fermi level and the bulk potential is proportional to the charge and is used to estimate the Pt electrode potential via the PZC (potential of the zero charge). The surface charge significantly polarizes the water molecules near the Pt surface. The OH stretching frequency of molecules on the negatively charged (7 ∼ 14 μC/cm2) Pt electrode shift to lower values (red shift) by 100 ∼ 200 cm-1. For the positively charged Pt lattice, a complex feature results from a charge transfer reaction that takes place there. The electrode structure is also influenced by accumulated charge as the distance between the top surface Pt layer and the next layer underneath increases for both the negatively and positively charged surfaces. Copyright 2012 Author(s).


Yagi I.,Fuel Cell Cutting Edge Center Technology Research Association Cubic | Yagi I.,Hokkaido University | Nomura K.,Fuel Cell Cutting Edge Center Technology Research Association Cubic | Notsu H.,Fuel Cell Cutting Edge Center Technology Research Association Cubic | And 2 more authors.
ECS Transactions | Year: 2011

The role of ionomer inside catalyst layers of polymer electrolyte fuel cell (PEFC) are much interested to understand the reaction mechanism and to optimize the structure of catalyst layer in the molecular scale. Electrochemical and spectroscopic investigations are performed in perfluoroalkylsulfonic acid electrolyte as models for side-chain of Nafion ionomers. Specific adsorption of Nafion side chain model anion is observed both at Pt(111) and Au(111)-like electrodes. The effect of perfluoroalkyl chain length seems clearer at Au(111)-like electrode than at Pt(111) and monitored by in situ SEIRA spectroscopy. © 2011 ECS - The Electrochemical Society.


Yagi I.,Fuel Cell Cutting Edge Center Technology Research Association Cubic | Yagi I.,Ochanomizu University | Inokuma K.,Fuel Cell Cutting Edge Center Technology Research Association Cubic | Ohta N.,Fuel Cell Cutting Edge Center Technology Research Association Cubic
ECS Transactions | Year: 2013

Focusing the void plasmon toward the rim part of the sphere segment void (SSV) type plasmonic crystalline structures are further developed by retaining the polystyrene nanospheres inside the voids. Plasmonic whispering gallery modes (WGMs) are proved to appear in such the hybrid structures by the measurements of reflectance spectroscopy and cause the improvement of signal/background ratio in the SERS spectra. From the detailed experimental analyses, a possibility of the plasmonic WGMs to enhance the molecular signal at the Pt electrode surfaces is shown. © The Electrochemical Society.


Yagi I.,Hokkaido University | Yagi I.,Fuel Cell Cutting Edge Center Technology Research Association Cubic | Inokuma K.,Fuel Cell Cutting Edge Center Technology Research Association Cubic | Kimijima K.,Fuel Cell Cutting Edge Center Technology Research Association Cubic | Notsu H.,Fuel Cell Cutting Edge Center Technology Research Association Cubic
Journal of Physical Chemistry C | Year: 2014

Perfluorosulfonated ionomer (PFSI), such as Nafion, in polymer electrolyte fuel cells (PEFCs) has been recognized as an important component to shuttle protons during the electrocatalytic reactions, especially the oxygen reduction reaction (ORR) at the cathode. However, a molecular structure of PFSIs inside catalyst layers in PEFCs has been unclear, since the polymers surrounding the gas-diffusion electrode with meso-to-macroporous structures have been considered to be much more complicated to resolve. Recent progress in the environmental electron microscopic technology clarified the real thickness of PFSI films to be only several nanometers, which can be analyzed by spectroscopic techniques and simulation modelings with molecular insights. Infrared and Raman spectroscopies were promptly applied to obtain the molecular arrangement of Nafion on the surface of Pt catalysts, but the thicknesses of the Nafion films seemed to be much thicker than the real thicknesses of PFSI in catalyst layers. In the present study, the preparation method of an ultrathin film of Nafion on Pt surface with <1 nm thickness was established and the vibrational sum frequency generation (VSFG) spectroscopy, which is an inherently surface-selective method, was applied to extract the interfacial molecular structure even at relatively thick Nafion films on Pt surfaces. By comparing thickness dependencies of IR and VSFG spectra, the molecular arrangement of Nafion at buried Nafion/Pt interface was confirmed to adsorb via sulfonate terminals of side-chains. © 2014 American Chemical Society.

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