• Journal of Electrochemical Science and Technology
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• v.14 no.3
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• pp.283-292
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• 2023

Currently, spray coating has attracted interest in the mass production of anode catalyst layers for proton exchange membrane water electrolysis (PEMWE). The solvent in the spray ink is a critical factor for the catalyst dispersion in ink, the microstructure of the catalyst layer, and the PEMWE performance. Herein, various pure organic solvents were examined as a substitute for conventional isopropanol-deionized water (IPA-DIW) mixture for ink solvent. Among the polar solvents that exhibited better IrO₂ dispersion over nonpolar solvents, 2-butanol (2-BuOH) was selected as a suitable candidate. The PEMWE single cells were fabricated using 2-BuOH at various ionomer contents, spray nozzle types, and drying temperatures, and their performance was compared to the cells fabricated using a conventional IPA-DIW mixture. The PEMWE single cells with 2-BuOH solvent showed good performances comparable to the conventional IPA-DIW mixture case and highly durable performances under accelerated degradation tests.

• Investigative Magnetic Resonance Imaging
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• v.2 no.1
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• pp.73-82
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• 1998

Purpose : A precise NMR technique for measuring the rate of water exchange and cell membrane permeability across the hepatocyte membrane using liver-specific MR contrast agent is described. Materials and Methods : The rat hepatocytes isolated by perfusion of the livers were used for the NMR measurements. All experiments were performed on an IBM field cycling relaxometer operating from 0.02MHz to 60 MHz proton Larmor frequency. spin-echo pulse sequence was empolyed to measure spin-lattice relaxation time, T1. The continuous distribution analysis of water proton T1 data from rat hepatocytes containing low concentrations of the liver specific contrast agent, Gd-EOB-DTPA, modeled by a general two compartment exchange model. Results : The mean residence time of water molecule inside the hepatocyte was approximately 250 msec. The lower limit for the permeability of the hepatocyte membrane was $(1.3{\pm}0.1){\;}{\times}{\;}10^{-3}cm/sec$. The CONTIN analysis, which seeks the natural distribution of relaxation times, reveals direct evidence of the effect of diffusive exchange. the diffusive water exchange is not small in the intracellular space in the case of hepatocytes. Conclusions : Gd-EOB-DTPA, when combined with continuous distribution analysis, provides a robust method to study water exchange and membrane permeability in hepatocytes. Water exchange in hepatocyte is much slower thatn that in red blood cells. Therefore, tissue-specific contrast agent may be used as a functional agent to give physiological information such as cell membrane permeability.

• Polymer(Korea)
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• v.36 no.6
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• pp.816-821
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• 2012

In this study, silane-crosslinked proton exchange membranes were prepared by step-wise radiation grafting of styrene and 3-(trimethoxysilyl)propyl methacrylate (TMSPM) onto an poly(ethylene-co-tetrafluoroethylene) (ETFE) film and followed by sol-gel processing and sulfonation. The sequentially grafted films with styrene to provide the proton conductivity and TMSPM to form the crosslinked structure were prepared by different grafting order. The structural changes and thermal properties of the prepared films were investigated by FTIR and TGA, respectively. After the introduction of sulfonic acid functional groups, the distributions of sulfonic acid group and silicon atoms at the inside of the sulfonated membranes were analyzed by SEM-EDX.

• Bulletin of the Korean Chemical Society
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• v.34 no.6
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• pp.1763-1770
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• 2013

A series of the block copolymers were successfully synthesized from post-sulfonated hydrophilic and hydrophobic macromers via three-step copolymerization. The degrees of sulfonation (DS) of the copolymers (10%, 30%, or 50%) were controlled by changing the molar ratio of the hydrophilic and hydrophobic parts. The resulting block copolymers were characterized by $^1H$ NMR and other technologies. The membranes were successfully cast using dimethyl sulfoxide (DMSO) solution at $100^{\circ}C$. The copolymers were characterized to confirm chemical structure by $^1H$ NMR and FT-IR. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) demonstrated that all sulfonated block copolymers exhibited good thermal stability with an initial weight loss at temperatures above $240^{\circ}C$. The membranes showed acceptable ion exchange capacity (IEC) and water uptake values in accordance with DS. The maximum proton conductivity was 184 mS $cm^{-1}$ in block copolymer-50 at $60^{\circ}C$ and 100% relative humidity, while the conductivity of Nifion-115 was 160 mS $cm^{-1}$ under the same measurement conditions. AFM images of the block copolymer membranes showed well separated the hydrophilic and hydrophobic domains. From the observed results it is that the prepared block membranes can be considered as suitable polymer electrolyte membranes for the application of polymer electrolyte membrane fuel cells (PEMFC).

• Membrane Journal
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• v.27 no.2
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• pp.182-188
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• 2017

Sulfonated poly(arylene ether sulfone) (SPAES)-3-mercaptopropyl silica gel (3MPTSG) composite membranes with improved oxidative stability were prepared for polymer electrolyte fuel cell application. It has been reported that ether part of main chain of aromatic hydrocarbon based membranes were weak to radical attack to decrease membrane durability. In this study, the hydrophilic inorganic particles were introduced by minimizing a decrease in ion conductivity and increasing an oxidative stability. The composite membranes were investigated in terms of ionic conductivity, ion exchange capacity (IEC), FT-IR, TGA and contact angle, etc. As a result, increasing amount of the 3MPTSG resulted in decrease in proton conductivities and water uptakes at 100% R.H. but enhanced thermal and oxidative stabilities.

• Journal of Hydrogen and New Energy
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• v.22 no.1
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• pp.42-50
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• 2011

The Montmorillonite (MMT) in the polymer matrix is expected to reduce methanol permeability due to the tortous path formed by dispersed silicate layers. However, the polymer composite membranes containing non-proton conducting inorganic particle tend to show low proton conductivity. To solve this problem, we used an ion exchange method to prepare functionalized MMT with various silane coupling agents. The modified MMT was randomly dispersed in sulfonated poly (arylene ether sulfone) (SPAES) matrix to prepare SPAES/modified MMT composite membranes. The performances of hybrid membranes for DMFCs application were investigated. The SPAES/modified composite membrane showed increased proton conductivity compared with the non-modified MMT composite membrane. However, the methanol permeability of the SPAES/modified membrane was higher than that of the non-modified MMT.

• Journal of the Korean Electrochemical Society
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• v.14 no.1
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• pp.9-15
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• 2011

The composite membranes comprising of sulfonated polymers as matrix and ionic liquids as ion-conducting medium in replacement of water are studied to investigate the effect of annealing of the sulfonated polymers. The polymeric membranes are prepared on recast Nafion containing the ionic liquid, 1-ethyl-3-methylimidazolium tetrafluoroborate ($EMIBF_4$). The composite membranes are characterized by thermogravitational analyses, ion conductivity and small-angle X-ray scattering. The composite membranes annealed at $190^{\circ}C$ for 2 h after the fixed drying step showed better ionic conductivity, but no significant increase in thermal stability. The mean Bragg distance between the ionic clusters, which is reflected in the position of the ionomer peak (small-angle scattering maximum), is larger in the annealed composite membranes containing $EMIBF_4$ than the non-annealed ones. It might have been explained to be due to the different level of ion-clustering ability of the hydrophilic parts (i.e., sulfonic acid groups) in the non- and annealed polymer matrix. In addition, the ionic conductivity of the membranes shows higher for the annealed composite membranes containing $EMIBF_4$. It can be concluded that the annealing of the composite membranes containing ionic liquids due to an increase in ion-clustering ability is able to bring about the enhancement of ionic conductivity suitable for potential use in proton exchange membrane fuel cells (PEMFCs) at medium temperatures ($150-200^{\circ}C$) in the absence of external humidification.

• Membrane Journal
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• v.24 no.4
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• pp.301-310
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• 2014

In this study, the silica nanoparticles were considerably chosen to improve a dimensional stability, proton transport and electrochemical performance of the resulting inorganic-organic nanocomposite membranes. For this purpose, hydrophobic silica (Aerosil$^{(R)}$ 812, Degussa) and hydrophilic silica (Aerosil$^{(R)}$ 380, Degussa) nanoparticles were, respectively, introduced into a Sulfonated poly(arylene ether sulfone) (SPAES) polymer matrix. The $SiO_2$ particles are evenly dispersed in a SPAES matrix by the aid of a non-ionic surfactant (Pluronics$^{(R)}$ L64). A $SiO_2$ content plays an important role in membrane microstructures and membrane properties such as proton conductivity and water uptake. Therefore, to study nanocomposite membranes with excessive amount of silica, the content of silica nanoparticles were increased up to 5 wt%. Interestingly, a hydrophobic $SiO_2$ containing nanocomposite membrane showed better electrochemical performance (29% higher than pristine SPAES) despite of low proton conductivity due to its adhesive properties with a catalyst layer in a single cell test. All the silica-SPAES membranes exhibited better performance than a pristine SPAES membrane.

• Applied Chemistry for Engineering
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• v.30 no.1
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• pp.74-80
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• 2019

$Nafion/TiO_2$ composite membranes were prepared via an in-situ sol-gel process with different immersing periods from 1 day to 7 days for the low humidifying proton exchange membrane fuel cell. As the immersing time increased, the $TiO_2$ content within the Nafion membrane increased. The contact angle decreased with the increased $TiO_2$ content in the composite membrane due to the increased hydrophilicity. The water uptake and proton conductivity reached to the highest level for 4 day immersing period, then decreased as the immersing period increased. A 7 days of immersing time was shown to be too long because too much $TiO_2$ aggregates were formed on the membrane surface as well as interior of the membrane, interfering the proton transfer from anode to cathode. Cell performance results were in good agreement with those of the water uptake and proton conductivity; current densities under a relative humidity (RH) of 40% were 0.54, 0.6, $0.63A/cm^2$ and $0.49A/cm^2$ for the immersing time of 1, 3, 4 and 7 days, respectively at a 0.6 V. The composite membrane prepared via the in-situ sol-gel process exhibited the enhancement in the cell performance under of RH 40% by a maximum of about 66% compared to those of using the recasting composite membrane and Nafion 115.

• Bulletin of the Korean Chemical Society
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• v.30 no.10
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• pp.2197-2198
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• 2009