Ohira A.,Japan National Institute of Advanced Industrial Science and Technology |
Ohira A.,Fuel Cell Cutting Edge Research Center Cubic |
Kuroda S.,Fuel Cell Cutting Edge Research Center Cubic |
Mohamed H.F.M.,Fuel Cell Cutting Edge Research Center Cubic |
And 2 more authors.
Physical Chemistry Chemical Physics | Year: 2013
To understand the relationship between surface morphology and proton conduction of polymer electrolyte thin films, perfluorinated ionomer Nafion® thin films were prepared on different substrates such as glassy carbon (GC), hydrophilic-GC (H-GC), and platinum (Pt) as models for the ionomer film within a catalyst layer. Atomic force microscopy coupled with an electrochemical (e-AFM) technique revealed that proton conduction decreased with film thickness; an abrupt decrease in proton conductance was observed when the film thickness was less than ca. 10 nm on GC substrates in addition to a significant change in surface morphology. Furthermore, thin films prepared on H-GC substrates with UV-ozone treatment exhibited higher proton conduction than those on untreated GC substrates. However, Pt substrates exhibited proton conduction comparable to that of GCs for films thicker than 20 nm; a decrease in proton conduction was observed at ∼5 nm thick film but was still much higher than for carbon substrates. These results indicate that the number of active proton-conductive pathways and/or the connectivity of the proton path network changed with film thickness. The surface morphology of thinner films was significantly affected by the film/substrate interface and was fundamentally different from that of the bulk thick membrane. © 2013 the Owner Societies.
Iden H.,Nissan Motor Co. |
Ohma A.,Nissan Motor Co. |
Tokunaga T.,Fuel Cell Cutting Edge Research Center Cubic |
Yokoyama K.,Fuel Cell Cutting Edge Research Center Cubic |
Shinohara K.,Fuel Cell Cutting Edge Research Center Cubic
Physical Chemistry Chemical Physics | Year: 2016
The optimization of the catalyst layers is necessary for obtaining a better fuel cell performance and reducing fuel cell cost. Although the ionomer coverage of the Pt catalyst is said to be a key parameter in this regard, the proportion of Pt either directly or indirectly covered by the ionomer is thought to be an important parameter with regard to gas transport (indirectly covered Pt: its gas transport paths are completely blocked by the ionomer even if it does not directly cover Pt). In this study, a new technique has been developed for evaluating the proportion of Pt covered indirectly or directly by the ionomer, which is defined as the "capped proportion", based on the carbon monoxide (CO) adsorption properties at different temperatures. The validity of the method was thoroughly examined by identifying the CO adsorption properties of the components of the catalyst layers. The capped proportion and oxygen transport resistance in the catalyst layers showed a good correlation, indicating that the capped proportion is a dominant factor of oxygen transport resistance. This technique thus enables the evaluation of the dominant factor of the gas transport properties of the catalyst layers. The method has another significant advantage in that it does not require a membrane electrode assembly, let alone electrochemical measurement, which should be helpful for catalyst layer optimization. © 2016 the Owner Societies.
Yamaguchi M.,Fuel Cell Cutting Edge Research Center Cubic |
Ohira A.,Japan National Institute of Advanced Industrial Science and Technology
Journal of Solution Chemistry | Year: 2016
Infrared absorption spectra of hydrated protons are very sensitive to their different structures that change with the number of water molecules as well as their hydrogen bonds with anions and/or solvent molecules. Hydronium ion (H3O+) in nonaqueous solutions of trifluoromethanesulfonic (triflic) acid monohydrate shows largely red-shifted and very broad OH stretching bands in their infrared absorption spectra. We found that four triflate anions and four hydronium ions form a hydrogen-bonded cluster in which sulfur and oxygen atoms of anions and cations have a cubic structure with red-shifted OH stretching bands; from its ab initio molecular dynamics simulation large widths of the OH stretching absorption bands were successfully reproduced. Based on the very similar infrared absorption bands of perfluorinated sulfonic acid ionomer membranes with low water content their acid sites are supposed to have very similar cluster configurations. © 2016 Springer Science+Business Media New York