Junhwa Shin

PVDF-HFP/PMMA-coated PE separator for lithium ion battery

Microporous poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP)/poly(methyl methacryate) (PMMA)-coated polyethylene (PE) separators were prepared by a simple dip-coating process with various compositions of PVDF-HFP/PMMA mixture under 40% relative humidity condition. The results indicate that the porosity, liquid electrolyte uptake, and ionic conductivity of the coated separators are largely affected by a ratio of PVDF-HFP/PMMA mixture and the highest porosity, electrolyte uptake, and ionic conductivity can be achieved at a composition of PVDF-HFP/PMMA (5/5). The results of the cell performance tests also reveal that the PE separator coated with PVDF-HFP/PMMA in a ratio of 5:5 provides better rate capability and cycle stability than other PE separators coated with different ratios.

Ionic aggregation characterization of sulfonated PEEK ionomers using by X-ray and DMA techniques

AbstractCommercial Victrex® poly(ether ether ketone) was dissolved and sulfonated using sulfonic acid at an elevated temperature of 55–70 °C. Various techniques such as thermogravimetric analysis, dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), and small-angle X-ray scattering (SAXS) were employed to investigate the mechanical properties and morphology of sulfonated poly(ether ether ketone) (SPEEK) film. Sulfonation temperatures were shown to have a direct effect on the degree of sulfonation. The DMA study showed that well-developed α-relaxation peaks related to chain relaxation in the ionic regions shifted to higher temperatures as sulfonation degree increased. However, the β- and γ-relaxation peaks showed that the peaks related to chain relaxation in the crystalline regions shifted to lower temperatures as sulfonation degree increased. These DMA results suggest that the sulfonic acid groups act as very effective plasticizers for the intercrystalline regions. DSC thermograms showed that the glass transition shifted systematically to higher temperatures as the sulfonation degree increased. In the SAXS study, an ionic domain peak was observed and the peak position shifted to a slightly higher angle as sulfonation degree increased, implying that the number of ionic aggregates increased.

Radiation Grafting of Binary Monomers for the Preparation of Organic/Inorganic Hybrid Membrane for Proton Exchange Membrane Fuel Cell Application

AbstractTo fabricate silane-crosslinked oraganic/inorganic hybrid proton exchange membranes (PEMs), poly(styrene sulfonic acid-co-(trimethoxysilyl)propyl methacrylate (TMSPM))-grafted ethylene-alt-tetrafluoroethylene (ETFE) membranes (ETFE-g-PSSA/PTMSPM) were prepared by a simultaneous irradiation grafting of various compositions of binary monomers (styrene and TMSPM) onto ETFE film and followed by hydrolysis-condensation and sulfonation to provide crosslinked structures and proton conducting ability, respectively. The effects of the individual degree of grafting of each graft polymer component on the chemical, physical, and morphological properties of the prepared PEMs, were also investigated. The results indicate that the silane-crosslinked PEM prepared with the monomers composition (Styrene (St)/TMSPM=5/5, v/v) has not only a lower water uptake but also a high proton conductivity, compared to those of ETFE-g-PSSA with similar ion exchange capacities (IEC). The silane-crosslinked PEM with 35% of the degree of grafting for PTMSPM were also found to have an improved chemical stability.

Characterization and Performance of MEA for Direct Methanol Fuel Cell Prepared with PFA Grafted Polystyrene Membranes via Radiation-Grafting Method

In order to develop a novel polymer electrolyte membrane for direct methanol fuel cell (DMFC), styrene monomer was graft-polymerized into poly(tetrafluoroethylene perfluoropropyl vinyl ether) (PFA) film followed by a sulfonation reaction. The graft polymerization was prepared by the -ray radiation-grafting method. Subsequently, sulfonation of the radiation-grafted film was carried out in a chlorosulfonic acid/1,2-dichloroethane (2 v/v%) solution. The chemical, physical, electrochemical and morphological properties of the radiation-grafted membranes (PFA-g-PSSA) were characterized by fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The water uptake, ionic conductivity, and methanol permeability of the PFA-g-PSSA membrane were also measured. The cell performances of MEA prepared with the PFA-g-PSSA membranes were evaluated and the cell resistances were measured by an impedance analyzer. The MEA using PFA-g-PSSA membranes showed superior performance for DMFCs in comparison with the commercial Nafion 112 membrane.

Preparation of stable polyethylene membranes filled with crosslinked sulfonated polystyrene for membrane capacitive deionization by γ-irradiation

Qian Qiu, Ji-Hoon Cha, Young-Woo Choi, Jae-Hwan Choi, Junhwa Shin, and Youn-Sik Lee* 1Division of Chemical Engineering, Nanomaterials Processing Research Center, Chonbuk National University, 567 BaekjeDaero, Deokjin-gu, Jeonju, Jeonbuk 54896, Korea 2Hydrogen & Fuel Cell Center for Industry, Academy, and Laboratories, New & Renewable Energy Research Division, Korea Institute of Energy Research, Buan, Jeonbuk 56332, Korea 3Department of Chemical Engineering, Kongju National University, 1223-24, Cheonan-daero, Seobuk-gu, Cheonan, Chungnam 31080, Korea 4Advanced Radiation Technology Institute, Korea Atomic Energy Research Institute, Jeongup-si, Jeonbuk 56212, Korea

Highly cross-linked poly(styrene sulfonic acid)-grafted poly(tetrafluoroethylene-co-perfluoropropyl vinyl ether) membranes with various thicknesses and their application to direct methanol fuel cell

Highly cross-linked poly(styrene sulfonic acid)-grafted poly(tetrafluoroethylene-co-perfluoropropyl vinyl ether) (PFA-g-PSSA) membranes with various thicknesses have been successfully prepared through the simultaneous irradiation grafting of styrene/divinylbenzene (DVB) onto PFA films with thicknesses of 25, 50, and 100 μm followed by sulfonation to introduce sulfonic acid moiety. It was observed that a concentrated chlorosulfonic acid solution and a high reaction temperature are needed to provide sufficient sulfonic acid as the thickness of the PFA films and the content of DVB both increase. The physicochemical properties of the prepared membranes such as water uptake, proton conductivity, methanol permeability, and chemical stability, were also investigated in this study.