量子ビームを利用したグラフト型フッ素系高分子電解質膜の構造/機能相関に関する研究

学位の種別:課程博士University of Tokyo(東京大学

Internal and interfacial structure analysis of graft-type fluorinated polymer electrolyte membrane by smallangle X-ray scattering in the high-q range

The hierarchical structures of poly(styrenesulfonic acid)-grafted poly(ethylene-co-tetrafluoroethylene)　polymer electrolyte membrane (ETFE-PEM) with different scale ranges including lamellar spacing, interfacial　thickness, and intra-structure of conducting layers consisting of graft-polymers and water were evaluated by　SAXS in terms of background scattering (IB(q)). First, IB(q) was roughly estimated by modifying Ruland’s　method and then optimized to avoid overestimation using a “contribution factor”, which is defined as the　contribution of IB(q) to the observed scattering intensities over the entire q range. Then, IB(q) was optimized　again by using Ruland’s equation to select proper q-range for interfacial thickness evaluation. The lamellar　spacing, which is observed in the low-q range, was not altered by background correction. In contrast, in the　high-q range, the interfacial thickness and the internal structures of the conducting layers can be estimated only　after correction for the background scattering data. These results clearly show that the hierarchical structures　of graft-type PEMs were strongly affected by the background correction in the high-q range. Moreover, the　proposed procedure for IB(q) is crucial for the determination of accurate interfacial thickness but not intrastructure　of conducting layers. Note that the modified Ruland’s method can be used as an altermative method　for determination of background intensity

Investigation of ortho-positronium annihilation for porous materials with different geometries and topologies

Abstract In this work, we present the results of the ortho-positronium (o-Ps) annihilation lifetimes and nitrogen adsorption measurements for different porous materials and an approach for describing the annihilation of o-Ps in a pore, which results in a surface-volume formula (SVF) for calculating the pore-related o-Ps lifetime. This proposed formula gives the relationship between the o-Ps annihilation rate and the effective pore radius, bulk composition, and pore structure, including pore geometry and topology. The pore-related o-Ps lifetimes of different materials calculated by the SVF are consistent with experimental results for both micro- and mesopores (and macropores) with different geometries and topologies. The SVF is convenient for calculations of pore dimensions for many cases of metal organic frameworks and zeolites. This approach enables us to fully explain the temperature dependence of the o-Ps annihilation lifetime over a wide temperature range, 20–700 K

SAXS Investigation on Morphological Change in Lamellar Structures During Propagation Steps of Graft‐Type Polymer Electrolyte Membranes for Fuel Cell Applications

The changes of the lamellar periods (L1D), thickness of lamellar crystals (Lc), and amorphous layers (La) within the stacked lamellae of poly(styrenesulfonic acid)‐grafted poly(ethylene‐co‐tetrafluoroethylene) polymer electrolyte membranes (ETFE‐PEMs), induced by the preparation and water‐absorbing steps are investigated using the small‐angle X‐ray scattering method. The L1D values of all the samples quickly increase at a grafting degree (GD) range of less than 19% and then level off. The solvent‐induced recrystallization is observed at the early stage of grafting (GD 34%), leading to the conclusion that most water molecules in the PEMs with higher GDs exist at the outside of the lamellar stacks. Accordingly, for the PEMs with low GD (<19%), all the hydrophilic graft‐polymers (ion‐channels) locate in the lamellar stacks and are strongly restricted by lamellar crystalline layers, which suppress the swelling of the PEMs. The unique lamellar structures of ETFE‐PEMs characterized by La and Lc are well connected with the high conductance and mechanical properties of the membranes, and are suitable for fuel cell applications

Determination of Cobalt in Seawater Using Neutron Activation Analysis after Preconcentration by Adsorption onto γ-MnO2 Nanomaterial

The γ-MnO2 nanomaterial has been used to adsorb cobalt in the seawater at Phan Thiet City, Binh Thuan Province, Vietnam. Its concentration is determined by using the neutron activation analysis (NAA) method at the Dalat nuclear research reactor. Factors affecting the uptake of cobalt on the γ-MnO2 material such as the pH, adsorption time, and initial cobalt(II) concentration are investigated. The irradiated experiment data are calculated using the K0-Dalat program. The results obtained show that the trace dissolved cobalt in Phan Thiet seawater is found equal to 0.25 ± 0.04 μg/L (n=5, P=95%) with the adsorption efficiency being higher than 95% (n=4, P=95%)

Humidity and temperature effects on mechanical properties and conductivity of graft-type polymer electrolyte membrane

我々は放射線グラフト法を活用し、高温・低湿度下で作動する燃料電池用の高分子電解質膜の開発を行っている。電解質膜の作製は、エチレン・テトラフルオロエチレン共重合体(ETFE)基材膜へのガンマ線照射、スチレンのグラフト重合、スチレンユニットのスルホン化、という手順で行った。イオン交換容量を2.03 mmol/gに制御したグラフト電解質膜は、従来膜Nafionと比べて、高温・低湿度下で高い引張弾性率とプロトン伝導度を示した。この結果から、グラフト電解質膜は燃料電池への適用に好ましいと言える。またX線回折法によって膜構造を調べたところ、優れた機械的特性およびプロトン伝導特性は基材ETFE膜の結晶構造に起因することが示唆された

Morphological characterization of grafted polymer electrolyte membranes at a surface layer for fuel cell application

The morphology and elemental compositions at the surface of poly(styrene sulfonic acid) (PSSA) grafted poly(ethylene-co-tetrafluoroethylene) polymer electrolyte membranes (ETFE-PEMs) in a grafting degree (GD) range of 0%–127% are investigated by using FE-SEM and XPS analyses. The concentrations of elemental components at the surface are not a linear function of GDs, resulting from different grafting speeds at the surface and bulk. In addition, low accumulation of PSSA grafts on the surface of ETFE-PEMs in the low GDs of 0%–19%, as well as their homogeneous distribution through the membranes at least at a GD of 19% are observed. At higher GDs of 19%–127%, the PSSA accumulation on the surface is relatively limited, indicating the presence of more PSSA grafts inside the bulk than on the surface. The surface signatures of ETFE-PEMs over the entire GD range can be determined based on the grafting process. These interesting observations suggest the significant advantages of interfacial properties of ETFE-PEMs for fuel cell applications

Hierarchical Structure–Property Relationships in Graft-Type Fluorinated Polymer Electrolyte Membranes Using Small- and Ultrasmall-Angle X‑ray Scattering Analysis

The hierarchical structures of graft-type poly­(ethylene-<i>co</i>-tetrafluoroethylene) (ETFE)-based polymer electrolyte membranes (ETFE-PEMs) were investigated using small- and ultrasmall-angle X-ray scattering experiments. The ETFE-PEMs with ion exchange capacities (IECs) <2.4 mmol/g possessed conducting graft domains around lamellar crystals, with a <i>d</i>-spacing of 21.8–29.1 nm, and oriented crystallites (lamellar grains) with short and long correlation distances of 218–320 and 903–1124 nm, respectively. The membranes with IECs > 2.7 mmol/g showed a new phase of crystallite network domains with a <i>d</i>-range of 225–256 nm, indicating a phase transition from oriented crystallite to crystallite network structures in the IEC range of 2.4–2.7 mmol/g. Noted that for the ETFE-PEMs with high IECs higher conductivity at 30% RH and compatible tensile strengths at 100% RH and 80 °C, compared with Nafion, originated from the well-interconnected ion channels around the crystallites and the remaining lamellar crystals and crystallites, respectively