| POLYMERS Vol.66 No.2 |
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COVER STORY
Presence of Walls |
| COVER STORY: Highlight Reviews |
| Ionomer Thin-Film Network in PEFC: The Impact of Interface on Mass Transport | Seiichi KURODA, Akihiro OHIRA |
| <Abstract> An ionomer is a binder of a catalyst layer (CL), that covers the carbon (C) supported platinum (Pt) catalyst nanoparticles (NP) with a nanometer thin-film. High proton conductivity and high oxygen permeability are required for an ionomer in a cathode CL that also is one of the keys for high-performance and high-durability of polymer electrolyte fuel cells (PEFC). Studies using a model ionomer thin film on Pt and/or carbon electrodes have reported that proton conductivity and gas permeability differ from the bulk membrane. Here, interfaces inside CL are reproduced by coating ionomer thin films (2-10 nm) on a surface consisting of various surface areas of Pt-NPs (2-3 nm) embedded in amorphous C (40 nm) films. A remarkable reduction of the proton conductivity in a thin film thinner than 5 nm confirmed the difference with the bulk. We also found that the changes of morphology and proton conduction significantly depend on the ratio of the Pt/C surface area. These results suggest that the hydrous behavior in the ionomer thin film is altered, which could be affecting the amount of protons transported inside the thin film. Keywords: Polymer Electrolyte Fuel Cell / Ionomer / Catalyst Layer / Dispersion / Thin Film / Morphology / Proton Conductivity / Gas Permeability |
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| Design of Fuel Cell Membranes for Improving Interface with Catalyst Layers | Kenji MIYATAKE |
| <Abstract> Proton conducting ionomer membrane is one of the key materials in polymer electrolyte fuel cells. An ionomer membrane has to have high proton conductivity, durability, and compatibility with electrocatalyst layer. While a number of researches on ionomer membranes have been carried out including state-of-the-art perfluorosulfonic ionomers and sulfonated hydrocarbon polymers, studies on the interface between the ionomer membrane and the catalyst layer are insufficient. In this article, a novel copolymer (SPAF) as a combination of perfluoroalkylene and sulfonated phenylene groups is described. Since this copolymer membrane contains the characteristic properties both as fluorinated and hydrocarbon ionomer membranes, it functions well in an operating fuel cell with good compatibility with the catalyst layer. Easy synthesis and molecular design flexibility are advantages of this emerging polymer. Keywords: Fuel Cells / Ionomers / Membranes / Interface |
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| Proton Conductive Nano-Thin Films | Yuki NAGAO |
| <Abstract> Improving fuel cell performance is one of the issues toward a hydrogen society. Proton conductive nano-thin films play an important role as a proton transport material (Ionomer) on the electrochemical catalysts. Nafion is a well known material as a high proton conductor. Recently, a Nafion nano-thin film attracts much attention because the Nafion thin film exhibits unique structural and physical properties: molecular orientation, organized structure, water uptake, proton conductivity etc. An organized structure is one of the attractive concepts for designing novel proton conductive materials. Sulfonated polyimide thin films exhibit high proton conductivity over 10－1 S cm－1. These materials show lamellar structure with water nano-channels, which enhances proton conductivity in the direction parallel to the substrate surface. The proton conductivity depends on the degree of the molecular ordering confirmed by the grazing incidence small-angle X-ray scattering. In this perspective, the studies from the viewpoint of the development of proton conductive nano-thin films in the last 10 years will be introduced. Keywords: Organized Structure / Interfacial Structure and Property / Fuel Cells |
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| COVER STORY: Topics and Products |
| Local Conformation at Ionomer/Metal Interfaces | Ichizo YAGI |
| <Abstract> Molecular conformation at Nafion/Pt interfaces was investigated with vibrational spectroscopies. Attenuated total reflection infrared (ATR-IR) and vibrational sum frequency generation (VSFG) spectroscopies were applied to monitor the thickness dependencies of Nafion. By the inherent surface- or interfacial- selectivity of VSFG, sulfonate terminal groups in the Nafion sidechains were confirmed to be oriented toward Pt surfaces. To correlate the sulfonate orientation with the pseudo-capacitive current responses on Nafion-modified Pt(111) single crystalline electrodes, in situ dynamic VSFG measurements are desired. Keywords: VSFG / Ionomer / Nafion / Pt / ATR-IR / Ultrathin Film / PEFC |
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| Polymer Synthesis in Li-ion Battery Technology | Masashi HARADA |
| <Abstract> At the interface of the negative electrode and the electrolyte solution of lithium-ion batteries, a coating layer including polymers is formed on the eletrode as a side reaction of the intercalation of the lithium ions into carbon particles. The coating layer, which is called solid electrolyte interphase or SEI, was observed during the charging process by neutron reflectivity measurements. The change of the thickness and the scatterig length density in the SEI was evaluated while the potential is decreased. Understanding of electrochemistry at liquid/solid interfaces should be accelerated by application of neutron reflectometry. Keywords: Lithium-Ion Battery / Interface of Electrode and Electrolyte / Solid Electrolyte Interphase / Neutron Reflectometry |
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| Proton Conductivity in the Interlayer of Polymer Nanosheet Assembly | Jun MATSUI |
| <Abstract> We have reported that the hydrophilic interlayer in the polymer nanosheet assembly can be applied as a two-dimensional proton conduction nanochannel. Proton conductivity of polymer nanosheets using acrylic acid as a proton source shows a high conductivity through the two-dimensional nanochannel and the value is comparable to state-of-the-art Nafion membranes. We propose that the formation of a uniform two dimensional hydrogen bonding network among water and carboxylic acid molecules is the reason for the high proton conductivity. In general, it is believed that a strong acid must be used to obtain a proton conductivity of ～0.1 Scm－1. Our results suggest that the high conductivity can be achieved by constructing two dimensional proton conductive nanochannels, even with just using a weak acid as a proton source. Keywords: Langmuir-Blogett Film / Nanoconfinement / Hydrogen Bonding / Fuel Cell |
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| Polymer Science and I: A Personal Account |
| Can We Feel Molecules by Hand ? | Koichi MAYUMI |
| <Abstract> My research interest is to bridge a huge gap between the macroscopic mechanical properties of polymeric materials and their molecular structure/dynamic. Can we feel the molecular behavior by touching the material with hands ? |
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| Front-Line Polymer Science |
| Recent Progress in Bio-Based Plastics | Tadahisa IWATA |
| <Abstract> Plastics are the most important materials considering their widespread usage in various fields. Currently, used plastics are mostly produced from petrochemical products. However, there is a growing demand for “Bio-based Plastics” produced from renewable resources to establish the sustainable society and to solve the global environmental. Bio-based plastics have been eagerly researched worldwide with the aim of achieving a balance between human activities and the natural environment. In future, bio-based plastics with superior properties should be produced from non-edible resources such as wood components, agricultural waste, etc. In this Front-Line Polymer Science, I will introduce the recent progresses in Bio-based Plastics in Japan. Keywords: Bio-Based Plastics / Non-Edible Resources / Polyesters / Polysaccharide Derivatives / Aromatic Polymers / High-Performance Materials / Physical Properties / Bio-Based Content |
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