Polybenzimidazole (PBI-OO) based composite membranes using sulfophenylated TiO₂ as both filler and crosslinker, and their use in the HT-PEM fuel cell

Krishnan, N. Nambi,Lee, Sangrae,Ghorpade, Ravindra V.,Konovalova, Anastasiia,Jang, Jong Hyun,Kim, Hyoung-Juhn,Han, Jonghee,Henkensmeier, Dirk,Han, Haksoo Elsevier 2018 Journal of membrane science Vol.560 No.-

<P><B>Abstract</B></P> <P>Crosslinked metal oxide containing nanocomposite membranes, in which the filler also acts as crosslinker, were prepared by blending polybenzimidazole (PBI-OO) and phenylsulfonated TiO<SUB>2</SUB> particles (s-TiO<SUB>2</SUB>). Thermal curing changes the ionically crosslinked system into a covalently crosslinked system. The synthesized s-TiO<SUB>2</SUB> nanoparticles were analyzed by thermal gravimetric analysis and scanning electron microscopy. The covalently crosslinked nanocomposite membranes (c-sTiO<SUB>2</SUB>-PBI-OO) were doped with phosphoric acid (PA) for high temperature proton exchange membrane fuel cell (HT-PEMFC) application. The membrane properties, such as PA uptake, dimensional change, gel content, proton conductivity, mechanical property, and single cell performance were evaluated and compared with the properties of acid-doped c-PBI-OO. PA doped 6-c-sTiO<SUB>2</SUB>-PBI-OO (6 wt% sTiO<SUB>2</SUB>) showed the highest uptake of 392 wt%, and a proton conductivity at 160 °C of 98 mS cm<SUP>−1</SUP>. In the fuel cell, a peak power density of 356 mW cm<SUP>−2</SUP> was obtained, which is 76% higher than that of a c-PBI-OO based system (202 mW cm<SUP>−2</SUP>). To evaluate the stability of the membrane performance over time, the best performing membrane was tested for over 700 h.</P> <P><B>Highlights</B></P> <P> <UL> <LI> PBI-OO is filled with sulfophenylated TiO<SUB>2</SUB> nanoparticles. </LI> <LI> the ionically crosslinked structure changes into a covalent network by thermal curing. </LI> <LI> conductivity at 160 °C is 98 mS cm<SUP>−1</SUP>. </LI> <LI> peak power density in the HT-PEMFC is 356 mW cm<SUP>−2</SUP>. </LI> <LI> at 600 mA cm<SUP>−2</SUP> the voltage degrades at 55.4 µV h<SUP>−1</SUP>, indicating a stable performance. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Sulfonated poly(ether sulfone)-based catalyst binder for a proton-exchange membrane fuel cell

Krishnan, N. Nambi,Kim, Hyoung-Juhn,Jang, Jong Hyun,Lee, Sang-Yeop,Cho, EunAe,Oh, In-Hwan,Hong, Seong-Ahn,Lim, Tae-Hoon Wiley Subscription Services, Inc., A Wiley Company 2009 Journal of applied polymer science Vol.113 No.4

<P>Sulfonated poly(ether sulfone) copolymer (PES 60) and its partially fluorinated analogue (F-PES 60) were synthesized via the nucleophilic aromatic polycondensation of commercially available monomers to make a polymer electrolyte membrane and a binding material in the electrodes of a membrane–electrode assembly (MEA). PES 60 and F-PES 60 showed proton conductivities of 0.091 and 0.094 S/cm, respectively, in water at room temperature. The copolymer was dissolved in the mixture of alcohol and water to get a 1 wt % binder solution. A catalyst slurry was prepared with the copolymer solution and sprayed on the copolymer (PES 60 or F-PES 60) membrane to obtain a MEA. Both PES 60 and F-PES 60 based MEAs were fabricated with different amounts of their binder in the electrodes to examine the effect of the copolymer binder in the catalyst layer on the fuel cell performance. The MEA with 2 wt % copolymer binder in the electrodes showed the best fuel cell performance. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009</P>

Organic Solvents Containing Zwitterion as Electrolyte for Li Ion Cells

Krishnan, Jegatha Nambi,Kim, Hyung-Sun,Lee, Jae-Kyun,Cho, Byung-Won,Roh, Eun-Joo,Lee, Sang-Gi Korean Chemical Society 2008 Bulletin of the Korean Chemical Society Vol.29 No.9

Imidazolium based zwitterions, 1,2-dimethylimidazolium-3-n-propanesulfonate (DMIm-3S) and 1-Butylimidazolium-3-n-butanesulphonate (BIm-4S), were synthesized, and utilized them as additive for Li ion cell comprising of graphite anode and $LiCoO_2$ cathode. The use of 10 wt% of DMIm-3S in 1 M $LiPF_6$, EC-EMCDMC (1:1:1 (v/v)) resulted in the increased high rate charge-discharge performance. The low temperature performance of the Li ion cells at about −20 ${^{\circ}C}$ was also enhanced by these zwitterion additives. The DMIm- 3S additive resulted in the better capacity retention by the Li-ion cells even after 120 cycles with 100% depth of discharge (DOD) at 1 C rate in room temperature. Surface morphology of both graphite and $LiCoO_2$ electrode before and after 300 cycles was studied by scanning electron microscopy. An analogous study was performed using liquid electrolyte without any additive.

Fuel cell performance of polymer electrolyte membrane based on hexafluorinated sulfonated poly(ether sulfone)

Krishnan, N. Nambi,Kim, Hyoung-Juhn,Jang, Jong Hyun,Cho, EunAe,Lee, Sang-Yeop,Lim, Tae-Hoon,Hong, Seong Ahn Springer-Verlag 2009 Polymer bulletin Vol.62 No.4

Rapid microfluidic separation of magnetic beads through dielectrophoresis and magnetophoresis

Krishnan, Jegatha Nambi,Kim, Choong,Park, Hyun Jik,Kang, Ji Yoon,Kim, Tae Song,Kim, Sang Kyung WILEY-VCH Verlag 2009 ELECTROPHORESIS Vol.30 No.9

<P>We present the design and fabrication of a new microfluidic device in which the dielectrophoresis and magnetophoresis phenomena were used for the separation of the superparamagnetic microbeads of different sizes. By exploiting the fact that two different particles can exhibit different dielectrophoretic force–frequency spectra, we utilize this device to perform multiplex detection from a single sample solution. We found the transition frequency range for 1, 2.8, and 4.5 μm magnetic beads using our device. Bead-based analysis revealed that a high separation efficiency (∼90%) could be obtained from a single sample solution containing both 4.5 and 2.8 μm beads. The average flow velocity of the beads was maintained at 9.8 mm/s, enabling fast analysis with a smaller amount of reagents. The magnetic field distribution on the beads and the bead flow at the channel cross section for different dielectrophoretic conditions was obtained using CFD-ACE<SUP>+</SUP> simulation. Issues relating to the fabrication and operation of the device are discussed in detail. Finally, we demonstrated the feasibility of parallel detection/trapping of different beads on the same chip. This separation approach offers the performance of multiplex analysis in lab-on-a-chip devices.</P>

Thermally crosslinked sulfonated polybenzimidazole membranes and their performance in high temperature polymer electrolyte fuel cells

Nambi Krishnan, N.,Konovalova, Anastasiia,Aili, David,Li, Qingfeng,Park, Hyun Seo,Jang, Jong Hyun,Kim, Hyoung-Juhn,Henkensmeier, Dirk Elsevier 2019 Journal of membrane science Vol.588 No.-

<P><B>Abstract</B></P> <P>The degradation pathway of phosphoric acid doped polybenzimidazole membranes in high temperature polymer electrolyte membrane fuel cells depends on the acid contents. If it is high, creep is discussed as the main reason. If it is low (membranes prepared by solvent evaporation and post-doping), the main cause may be loss of acid due to evaporation. The net transport of acid to the anode side at high current densities should also lead to local softening of the membrane, which could be mitigated by crosslinking the membrane.</P> <P>Here we show that sulfonated <I>para</I>-polybenzimidazole membranes can be stabilized by curing at 350 °C. In contrast to <I>meta</I>-polybenzimidazole and sulfonated <I>para</I>-polybenzimidazole, crosslinked sulfonated <I>para</I>-polybenzimidazole is insoluble in dimethylacetamide at room temperature and phosphoric acid at 160 °C. At 160 °C and 5% relative humidity the conductivity of crosslinked sulfonated <I>para</I>-polybenzimidazole and <I>meta</I>-polybenzimidazole is 214 mS cm<SUP>−1</SUP> and 147 mS cm<SUP>−1</SUP>, respectively. At 600 mA cm<SUP>−</SUP> <SUP>2</SUP>, the voltage decay rate is 16 μV h<SUP>−1</SUP>, much lower than published for commercial <I>meta</I>-polybenzimidazole (308 μV h<SUP>−1</SUP>). Furthermore, the average voltage at 600 mA cm<SUP>−</SUP> <SUP>2</SUP> is 523 mV, while a previously published cured <I>meta</I>-polybenzimidazole membrane only reaches 475 mV.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Sulfonated <I>para</I>-PBI is covalently crosslinked by heating. </LI> <LI> Membranes are stable in DMAc at 27 °C and in 85 wt% phosphoric acid at 160 °C. </LI> <LI> Non-crosslinked sulfonated <I>para</I>-PBI and <I>meta</I>-PBI dissolve under these conditions. </LI> <LI> Conductivity is 44% higher than for <I>meta</I>-PBI. </LI> <LI> Fuel cell performance is stable; test time was 2100 h, half of that at 600 mA/cm<SUP>2</SUP> </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Electroless deposition of SERS active Au-nanostructures on variety of metallic substrates

Jegatha Nambi Krishnan,김인태,안성현,김지환,조소혜,김상경 한국바이오칩학회 2013 BioChip Journal Vol.7 No.4

In this study, flower-like Au structures (three dimensional branched nanoparticles) were constructed by using a simple, template-free and cost effective electroless plating method. The key synthesis strategy was to perform controlled plating of Au on a variety of metals (Ag, Cu and Pt) deposited on the Si substrate. Herein, gold is deposited purely as a result of reaction of chemicals in bath to form Au nanoflowers/lawns. The size and shape of the Au nanoflowers could be tailored by controlling the immersion Au plating time on multitude of metallic substrates. Time course measurements by SEM and HRTEM were used to follow reaction progress and evolution of flower-like shape. The generation of unique and reproducible morphological Au nanostructures onto each substrate implies that the Au nanostructures are substrate dependent. Fast Fourier Transform measurements were conducted using HR-TEM on isolated samples that proved the presence of anisotropic growth of Au polycrystalline structures. The gold nanostructures have shown the surface-enhanced Raman scattering (SERS) by detecting the enhanced Raman spectra of 4-Aminobenzenethiol (4-ABT)molecules. The enhancement of Raman signal was stronger for Au structures built on Pt or Ag thin films. The Au nanoflowers produced by this simple method exhibited effective surface-enhancement for biosensing applications.

Microfluidic Superparamagnetic Bead based Manipulator

Jegatha Nambi Krishnan,김태송,김상경 한국바이오칩학회 2008 BioChip Journal Vol.2 No.3

This paper describes the design and fabrication of a new detection system in which the dielectrophoresis and magnetophoresis phenomena were used as a tool for the manipulation of superparamagnetic microbeads within the microchannel. By exploiting the two facts that each superparamagnetic particle exhibit different dielectrophoretic forces at different applied frequencies and do not exhibit permanent magnetic dipoles in the absence of external magnetic field, we utilized this device to perform detection of beads. We found the transition frequency range for 2.8 μm beads using our device. This device has higher trapping efficiency and less particle adsorption rate for beads. Bead based analysis revealed that high collection efficiency (~90%) could be obtained from small amount of sample solution. This high throughput detection system offers a fast analysis of magnetic beads with their velocity being maintained as 9.8 mm/s. The magnetic field distribution on the beads and the bead flow at the channel cross-section for different dielectrophoretic conditions was obtained using CFD-ACE⁺ simulation. Our novel platformwould be a useful tool in manipulating different sized superparamagnetic microbeads paving way for a multiplex detection system.

Long-term durability test for direct methanol fuel cell made of hydrocarbon membrane

Prabhuram, Joghee,Krishnan, N. Nambi,Choi, Baeck,Lim, Tae-Hoon,Ha, Heung Yong,Kim, Soo-Kil Elsevier 2010 International journal of hydrogen energy Vol.35 No.13

<P><B>Abstract</B></P><P>A long-term durability test has been conducted for a direct methanol fuel cell (DMFC) using the commercial hydrocarbon membrane and Nafion ionomer bonded electrodes for 500 h. Membrane electrode assembly (MEA) made by a decal method has experienced a performance degradation about 34% after 500 h operation. Cross-sectional analysis of the MEA shows that the poor interfacial contact between the catalyst layers and membrane in the MEA has further deteriorated after the durability test. Therefore, the internal resistance of a cell measured by electrochemical impedance spectroscopy (EIS) has considerably increased. The delamination at the interfaces is mainly attributed to incompatibility between polymeric materials used in the MEA. Furthermore, X-ray diffraction (XRD) analysis reveals that the catalyst particles have grown; thereby decreasing the electrochemical surface area. Electron probe micro analysis (EPMA) shows a small amount of Ru crossover from anode to cathode; and its effect on the performance degradation has been analyzed.</P>

Porous-Nafion/PBI composite membranes and Nafion/PBI blend membranes for vanadium redox flow batteries

Jung, Mina,Lee, Wonmi,Nambi Krishnan, N.,Kim, Sangwon,Gupta, Gaurav,Komsiyska, Lidiya,Harms, Corinna,Kwon, Yongchai,Henkensmeier, Dirk Elsevier 2018 APPLIED SURFACE SCIENCE - Vol.450 No.-

<P><B>Abstract</B></P> <P>Although Nafion membranes have a high chemical stability against VO<SUB>2</SUB> <SUP>+</SUP> and a low resistance, their low coulomb efficiency (CE), due to crossover of vanadium cations, should be addressed. PBI membranes are chemically stable and effectively block vanadium cations, but have a lower conductivity than Nafion. Here we describe the fabrication of layered membranes, which consist of a 40 µm thick porous Nafion layer and a 2–17 µm thin PBI blocking layer. To promote adhesion, a <2 µm thick layer of a 1:1 Nafion/PBI blend is introduced between the outer layers. While this bonding layer is necessary to promote adhesion, the strong ionic interactions between Nafion and PBI reduce the acid uptake. Immersed in 1 M sulfuric acid (SA), the weight of meta-PBI increases 17%, while that of NP1:3, NP1:1 and NP3:1 only increases 16%, 8% and 7%, respectively. This decreases the conductivity in 2 M SA from 2.8 mS cm<SUP>−1</SUP> for meta-PBI to 1.5, 0.4 and 0.04 mS cm<SUP>−1</SUP> for NP1:3, NP1:1 and NP3:1, respectively. The initial CE of a flow battery using p-Nafion-1:1-PBI20 was as good as one with Nafion 212 (93% at 80 mA cm<SUP>−2</SUP>), while one with p-Nafion-1:3-PBI3 showed exactly the same voltage efficiency as one with Nafion 212.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A trilayer membrane of porous Nafion, an adhesion promoting layer and PBI. </LI> <LI> The layers are applied on porous Nafion by spray coating. </LI> <LI> Polybenzimidazole (PBI) reduces crossover of vanadium ions in flow batteries. </LI> <LI> A blend of Nafion and PBI promotes adhesion but increases ionic resistance. </LI> <LI> The closed pores in Nafion are not easily filled with acid and increase resistance. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>