Youngdon Lim

Synthesis and characterization of polycarbonates containing terminal and chain interior siloxane

Silicone polycarbonates having polydimethyl siloxane (PDMS) and heptamethyl trisiloxane (HMTS) were synthesized by the interfacial polymerization. Instead of common chain terminator p-tert-butyl phenol (PTBP), eugenol capped HMTS, and PDMS were used. PDMS was also attached into the chain interior of the polymer in different molar ratios. PDMS and HMTS were capped with eugenol through the hydrosilylation reaction using Karstedt’s catalyst. Both monohydroxy and dihydroxy terminated eugenosiloxanes were synthesized in order to use as chain terminator and interior subunit of polymer, respectively. Structural characterization and the study of the properties, such as thermal behavior, thermooxidative stability, surface morphology, wettability of the synthesized polymers were investigated. Flexibility and wettability of the synthesized polymers increases with increasing of silicone content. Polymers showed satisfactory thermo oxidative stability and transparency as good as bisphenol-A-polycarbonate.

Anion conductive aromatic ionomers containing a 1,2-dibenzoylbenzene moiety for alkaline fuel cell applications

Novel anion-exchange membranes with high conductivities have been prepared for application to alkaline fuel cells. A quaternary ammonium poly(dibenzoylbenzene ether sulfone) membrane was synthesized by chloromethylation, followed by substitution with trimethylamine with an ion-exchange reaction. The quaternary ammonium groups were selectively substituted in the para-position of the pendant phenyl groups of the dibenzoylbenzene unit. The di-quaternary ammonium hydroxide polymers showed an elevated molecular weight and exhibited excellent solubility in polar aprotic solvents. Quaternization and the subsequent ion-exchange reactions were quantitative such that the obtained ionomer membranes had a high ion-exchange capacity (IEC) of up to 1.69 mmolg−1. The resultant polymer membranes were studied by 1H NMR, FT-IR, thermogravimetric analysis (TGA), IEC, water uptake analysis, and ion conductivity analysis.

The Sulfonated poly(ether sulfone ketone) ionomers containing partial graphene of mesonaphthobifluorene for PEMFC

Novel sulfonated poly(ether sulfone ketone)s containing mesonaphthobifluorene (MNF) moiety were synthesized and their properties characterized. The prepared polymers had a partial graphene structure due to the MNF group. Poly(ether sulfone ketone)s bearing tetraphenylethylene (TPE) on the polymer backbone were synthesized by polycondensation, after which MNF was formed by the intra-cyclization of TPE by Friedel-Crafts reaction with Lewis acid (FeCl3). The sulfonation was performed selectively on MNF units with concentrated sulfuric acid. The synthesized polymer electrolyte membranes showed better thermal and dimensional stabilities owing to the MNF-induced graphene structure in the polymer backbone. The water uptake of the synthesized membranes ranged from 30%–55%, compared with 32.13% for Nafion 211® at 80°C. The proton conductivity (80°C, RH 90%) ranged from 74.6–101.2 mS/cm, compared with 102.7 mS/cm for Nafion 211®.

Preparation and characterization of sulfonated poly (ether sulfone)s containing hexabenzocoronene graphene moiety for PEMF

The novel sulfonated poly(ether sulfone)s containing hexabenzocoronene moiety that is partial graphene structure (SPGHPs) for polymer electrolyte membrane were synthesized and characterized their properties. Graphene is an allotrope of carbon and one-atom-thick planar sheets of sp2-bonded carbon atoms that are densely packed in a honeycomb crystal lattice. Poly(ether sulfone)s containing hexaphenylbenzenes on polymer backbone were synthesized by poly condensation and followed intra-cyclization by friedel-craft reaction with lewis acid (FeCl3) to form partial graphene structure. The sulfonation was taken selectively on hexabenzocoronen units with concentrated sulfuric acid. The structure properties of the sulfonated polymers were investigated by 1H-NMR spectroscopy. The resulted ion exchange capacities (IEC) were 1.09~1.61 meq./g. The water uptakes were 8.84~15.27% at 30 °C and 18.27%~42.38% at 80 °C with changing the ion exchange capacities. The SPGHP membranes exhibit proton conductivities (80 °C, RH 90) of 78.3~105.7 mS/cm compared with 106.2 mS/cm of Nafion 211®.

Anion conductive imidazolium-based Parmax alkaline membrane for fuel cell applications

The anion exchange polyphenylene membrane containing imidazolium hydroxide ionic functional group was synthesized by sequential chloromethylation, substitution with 1-methylimidazole and ion exchange. The imidazolium hydroxide Parmax 1200 membrane has all carbon-carbon bonds without ether linkages, which would be chemically strong. The polyphenylene structure of Parmax provides a stiff and resistant backbone, whereas the pendant benzoyl group provides sites for chemical modifications. The resulting ionomer membrane showed ion exchange capacity (IEC) of 2.14 mmol g-1 with maximum chloromethylation yield. The imidazolium-functionalized copolymer membrane showed lower water affinity and high durability in alkaline condition. It exhibited hydroxide ion conductivity above 10-2 S cm-1 at room temperature and good chemical stability for up to seven days without significant losses of ion conductivity. The structural properties of the synthesized polymer membrane were investigated by 1H NMR spectroscopy and FT-IR. The membranes were studied by IEC, water uptake, and conductivity assessment.

Synthesis and properties of sulfonated poly(N-methylisatin-biphenylene) proton exchange membrane by superacid-catalyzed polymerization

A series of poly(phenylene)-based polyelectrolytes were synthesized from trifluoroacetophenone and N-methylisatin by superacid catalyzed polyhydroxyalkylation reaction. Postsulfonation of this high molecular weight and thermochemically stable poly(phenylene) with concentrated sulfuric acid resulted in homogeneous polyelectrolytes with controllable ion content (IEC: 1.40–2.39 meq./g). All these membranes were casted from dimethylsulfoxide (DMSO). The structural properties of the synthesized polymers were investigated by 1H NMR spectroscopy. The membranes were studied by ion exchange capacity (IEC), water uptake, dimensional stability and proton conductivity assessment by comparing with Nation. The polymers containing fluoro group without ether linkage on polymer backbone were chemically stable towards nucleophiles (H 2 O, hydrogen peroxide, hydroxide anion and radical).

Graphene structured sulfonated poly(ether sulfone)s containing hexabenzocoronene for PEMFC

The novel sulfonated poly(ether sulfone)s containing hexabenzocoronene moiety that is partial graphene structure were synthesized and characterized their properties. Graphene is an allotrope of carbon and one-atom-thick planar sheets of sp2-bonded carbon atoms that are densely packed in a honeycomb crystal lattice. Poly(arylene ether sulfone)s containing hexaphenyls on polymer backbone were synthesized by polycondensation and followed intra-cyclization by Friedel-Craft reaction with Lewis acid (FeCl3) to form partial graphene structure. The sulfonation was taken selectively on hexabenzocoronen units with concentrated sulfuric acid. The structure properties of the sulfonated polymers were investigated by 1H-NMR spectroscopy. The resulted ion exchange capacities (IEC) were 1.09~1.61 meq./g. The water uptakes were 8.84~15.27% at 30°C and 18.27%~42.38% at 80°C with changing the ion exchange capacities. The S-PDHTPE membranes exhibit proton conductivities (80 °C, RH 90) of 78.3~ 105.7 mS/cm compared with 106.2 mS/cm of Nafion 211®.

Preparation and properties of hydroxide conducting membrane of poly(tetra phenyl ether sulfone) containing pendant quaternary ammonium hydroxide group for alkaline fuel cell application

Poly(tetra phenyl ether sulfone)s (PTPES) were functionalized with quaternary ammonium salt groups in order to investigate their properties as novel polymeric hydroxide exchange membrane materials. The PTPES-QAH (quaternary ammonium hydroxide)s were synthesized via chloromethylation of PTPESs, followed by reactions with chloromethylmethylether and ZnCl2, SOCl2 as Lewis acid catalyst, and then quaternized ammonium hydroxide with immersion of trimethylamine solution. The presence of CH2Cl groups in chloromethylated PTPES and PTPES-QAH were confirmed by 1H-NMR. Different contents of ammonium unit of PTPES-QAH (15, 20, 25 mol% of BHPTPB) were studied by FT-IR, 1H NMR spectroscopy, and thermo gravimetric analysis (TGA). Sorption experiments were conducted to observe the interaction of PTPES-QAH with water. The ion exchange capacity (IEC) and proton conductivity of PTPES-QAH were evaluated with different degree of quaternization.

Develop of advanced bipolar plate using carbon fiber prepreg and graphite/polymer composite materials

In this study, we introduce an advanced composite bipolar plate (BP) to improve mechanical behaviors of BPs as compared to conventional composite BPs. The new BPs are fabricated by compression molding process in which the mixture of natural graphite particles as a major filler, synthetic graphite and carbon blacks (CBs) as the additive are compacted and integrated with epoxy-carbon fiber prepreg. The new BPs are evaluated and the test results clearly demonstrate that the proposed BP is superior to typical carbon composite BPs in terms of key BP properties including electrical conductivity with emphasis on its outstanding flexural strength. The unique feature of this new BP enables to further reduce the thickness of BPs, which directly contributes the reduction in fuel cell stack weight and volume.

Fabrication and evaluation of composite bipolar plate to develop a compact and lightweight direct methanol fuel cell stack

A bipolar plate is a major component of a fuel cell stack, occupying a considerable portion of the overall stack cost and weight. In this study, a composite bipolar plate is designed and fabricated to develop a compact and lightweight direct methanol fuel cell (DMFC) stack for small-scale Unmanned Aerial Vehicle (UAV) applications. The composite bipolar plates for DMFCs are prepared with two different natural graphite particles, phenol resin and carbon black (CB) and fabricated by compression molding method. Then, the bipolar plates are tested in terms of electrical conductivity, mechanical strength and hydrogen permeability. The flexural strength of 63 MPa and the in-plane electrical conductivities of 191 S/cm are achieved under the optimum composition of bipolar plate materials with 18 wt.% phenol resin, 82 wt.% natural graphite, and 3 wt.% CB, which demonstrates that the composite bipolar plates exhibit sufficient mechanical strength, electrical conductivity and gas impermeability to be applied in a DMFC stack. A DMFC with the composite bipolar plate is tested and shows a superior cell performance as compared with a DMFC with a typical pure graphite-based bipolar plate.