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Henkensmeier, Dirk,Dang, Quoc Khanh,Nambi Krishnan, N.,Jang, Jong Hyun,Kim, Hyoung-Juhn,Nam, Suk-Woo,Lim, Tae-Hoon The Royal Society of Chemistry 2012 Journal of materials chemistry Vol.22 No.29
<P><I>ortho</I>-Dichlorobenzene (ODB) was investigated as a pore modifier for both Nafion membranes and proton exchange membrane fuel cell (PEMFC) catalyst layers. When ODB containing Nafion dispersions are cast into a film, evaporation leads to dense membranes with one highly porous surface layer occupying 20–30% of the overall thickness. Dense Nafion membranes with a porous top layer are interesting for use in membrane humidifiers, for increasing the electrode–membrane interface areas in electrochemical devices like fuel cells or electrolysers, and other applications. Fuel cell membrane electrode assemblies were obtained by spray coating commercial Nafion 212 membranes with ODB containing catalyst inks. ODB does not poison the catalyst, and 54–120% higher potentials in comparison to the 217 mV obtained with an ODB free ink were achieved at 1.5 stoic air flow, 100% rh and a current density of 1 A cm<SUP>−2</SUP>. This shows that the porous catalyst electrode structure is changed, resulting in a reduced contribution of mass transport limited overpotentials. Furthermore, MEAs prepared with ODB in the catalyst ink are less sensitive towards changes in the air flow rate and the cathode relative humidity (between 50% rh and 100% rh: 217–292 mV at 1 A cm<SUP>−2</SUP> without ODB and 439–478 mV with ODB).</P> <P>Graphic Abstract</P><P>Dense Nafion membranes with one porous surface layer were produced by simple solution casting. The performance of membrane electrode assemblies in a polymer electrolyte fuel cell was improved. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c2jm32146g'> </P>
Anion conducting polymers based on ether linked polybenzimidazole (PBI-OO)
Henkensmeier, D.,Cho, H.,Brela, M.,Michalak, A.,Dyck, A.,Germer, W.,Duong, N.M.H.,Jang, J.H.,Kim, H.J.,Woo, N.S.,Lim, T.H. Pergamon Press ; Elsevier Science Ltd 2014 International journal of hydrogen energy Vol.39 No.6
Anion conducting polymers are potentially interesting for fuel cells, electrochemical pumps, and dye sensitized solar cells. Ether-containing polybenzimidazoles (PBI-OO and PBI-OPO) were synthesized and turned into anion conducting polymers by methylation. The thermal stability was shown to depend on the polymer structure and degree of methylation (dom). Tensile strength and modulus decrease between 50% and 75% dom, but stay constant or slightly increase over 75% dom again. At 65 <SUP>o</SUP>C, hydroxide, iodide, chloride, carbonate and bicarbonate conductivities of 0.1, 0.6, 19, 20, 31 mS/cm were obtained, respectively. The low hydroxide conductivity is due to the formation of a C-O bond in position 2 of the imidazolium, which reduces the number of free ions and is known to lead to imidazolium ring opening and further degradation steps. The effect of introduction of phenoxy groups into the main chain on the charge distribution, especially on position 2 and the methyl groups (positive charge on the methyl groups decreases the thermal stability), as well as on the ion bonding was thoroughly investigated by DFT calculations and correlated with experimental data.
Tetrazole substituted polymers for high temperature polymer electrolyte fuel cells
Henkensmeier, Dirk,Duong, Ngoc My Hanh,Brela, Mateusz,Dyduch, Karol,Michalak, Artur,Jankova, Katja,Cho, Hyeongrae,Jang, Jong Hyun,Kim, Hyoung-Juhn,Cleemann, Lars N.,Li, Qingfeng,Jensen, Jens Oluf The Royal Society of Chemistry 2015 Journal of Materials Chemistry A Vol.3 No.27
<▼1><P>Tetrazole (TZ) has lower basicity than imidazole and may not be fully protonated by phosphoric acid. DFT calculations suggest that the basicity of TZ groups can be increased by introducing a 2,6-dioxy-phenyl-group in position 5.</P></▼1><▼2><P>While tetrazole (TZ) has much lower basicity than imidazole and may not be fully protonated in the presence of phosphoric acid (PA), DFT calculations suggest that the basicity of TZ groups can be increased by the introduction of a 2,6-dioxy-phenyl-group in position 5 of TZ. This structure allows hydrogen bonds between TZ protons and ether oxygen atoms, and thereby establishes a resonance stabilised, co-planar structure for tetrazolium ions. Molecular electrostatic potential (MEP) calculations also indicate that tetrazolium ions possess two sites for proton hopping. This makes such materials interesting for use in a high temperature fuel cell (HT PEMFC). Based on these findings, two polymers incorporating the proposed TZ groups were synthesised, formed into membranes, doped with PA and tested for fuel cell relevant properties. At room temperature, TZ-PEEN and commercial <I>meta</I>-PBI showed an equilibrium uptake of 0.5 and 4.7 mol PA per mol heterocycle, respectively, indicating that PBI has higher affinity for PA than TZ-PEEN. The highest achieved PA uptake was <I>ca.</I> 110 wt%, resulting in a proton conductivity of 25 mS cm<SUP>−1</SUP> at 160 °C with a low activation energy of about 35 kJ mol<SUP>−1</SUP>. In a first HT PEMFC test at 160 °C, a peak power density of 287 mW cm<SUP>−2</SUP> was achieved.</P></▼2>
Chang, Zhenjun,Henkensmeier, Dirk,Chen, Ruiyong Wiley (John WileySons) 2017 ChemSusChem Vol.10 No.16
<P>By using a one-step epoxide ring-opening reaction between 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl (4-hydroxy-TEMPO) and glycidyltrimethylammonium cation (GTMA(+)), we synthesized a cation-grafted TEMPO (g(+)-TEMPO) and studied its electrochemical performance against a Zn2+/Zn anode in a hybrid redox flow battery. To conduct Cl- counter anions, a crosslinked methylated polybenzimidazole (PBI) membrane was prepared and placed between the catholyte and anolyte. Compared to 4-hydroxy-TEMPO, the positively charged g(+)-TEMPO exhibits enhanced reaction kinetics. Moreover, flow battery tests with g(+)-TEMPO show improved Coulombic, voltage, and energy efficiencies and cycling stability over 140 cycles. Crossover of active species through the membrane was not detected.</P>
Sulfonation of PIM-1 - Towards Highly Oxygen Permeable Binders for Fuel Cell Application
김병각,Dirk Henkensmeier,김형준,장종현,남석우,임태훈 한국고분자학회 2014 Macromolecular Research Vol.22 No.1
The development of alternative, non-fluorinated membranes for polymer electrolyte membrane fuel cellsnecessitates the co-development of a non-fluorinated electrode catalyst binder to ensure compatibility betweenmembrane and electrode. However, most hydrocarbon based polymers have lower gas permeability than perfluorinatedNafion. In this work we tried to obtain a sulfonated, non-fluorinated binder based on PIM-1 (polymer of intrinsicmicroporosity 1) which has up to 2000 times higher permeability than Nafion. However, sulfonation was notstraightforward and often led to degradative side reactions. Sulfonated polymers were too brittle to give stable membranesand the highest experimental IEC was 1.03 meq/g, significantly lower than the theoretical IEC of 3.2 meq/g(2 sulfonic acid groups per repeat unit).
Alkyl chain modified sulfonated poly(ether sulfone) for fuel cell applications
Krishnan, N.N.,Henkensmeier, D.,Jang, J.H.,Kim, H.J.,Ha, H.Y.,Nam, S.W. Pergamon Press ; Elsevier Science Ltd 2013 INTERNATIONAL JOURNAL OF HYDROGEN ENERGY - Vol.38 No.6
A new alkyl chain modified sulfonated poly(ether sulfone) (mPES) was synthesized and formed into membranes. The MEAs were tested in the PEMFC and evaluated systematically in the DMFC by varying the methanol concentration from 0.5 to 5.0 M at 60 <SUP>o</SUP>C and 70 <SUP>o</SUP>C. The synthesized mPES copolymer has been characterized by nuclear magnetic resonance spectroscopy, fourier transform infrared spectroscopy, thermogravimetric analysis, and gel permeation chromatography. The proton conductivity of the resulting membrane is higher than the threshold value of 10<SUP>-2</SUP> S cm<SUP>-1</SUP> at room temperature for practical PEM fuel cells. The membrane is insoluble in boiling water, thermally stable until 250 <SUP>o</SUP>C and shows low methanol permeability. In the H<SUB>2</SUB>/air PEMFC at 70 <SUP>o</SUP>C, a current density of 600 mA cm<SUP>-2</SUP> leads to a potential of 637 mV and 658 mV for 50 μm thick mPES 60 and Nafion NRE 212, respectively. In the DMFC, mPES 60's methanol crossover current density is 4 times lower than that for Nafion NRE 212, leading to higher OCV values and peak power densities. Among all investigated conditions and materials, the highest peak power density of 120 mW cm<SUP>-2</SUP> was obtained with an mPES 60 based MEA at 70 <SUP>o</SUP>C and a methanol feed of 2 M.
Krishnan, N.N.,Henkensmeier, D.,Jang, J.H.,Kim, H.J.,Rebbin, V.,Oh, I.H.,Hong, S.A.,Nam, S.W.,Lim, T.H. Pergamon Press ; Elsevier Science Ltd 2011 INTERNATIONAL JOURNAL OF HYDROGEN ENERGY - Vol.36 No.12
Fuel Cell operation at high temperature (e.g. 120 <SUP>o</SUP>C) and low relative humidity (e.g. 50%) remains challenging due to creep (in the case of Nafion<SUP>(</SUP>R)) and membrane dehydration. We approached this problem by filling PES 70, a sulfonated poly(ether sulfone) with a T<SUB>g</SUB> of 235 +/- 5 <SUP>o</SUP>C and a theoretical IEC of 1.68 mmol g<SUP>-1</SUP>, with 5-20% silica nano particles of 7 nm diameter and 390 +/- 40 m<SUP>2</SUP> g<SUP>-1</SUP> surface area. While simple stirring of particles and polymer solutions led to hazy, strongly anisotropic (air/glass side) and sometimes irregular shaped membranes, good membranes were obtained by ball milling. SEM analysis showed reduced anisotropy and TEM analysis proved that the nanoparticles are well embedded in the polymer matrix. The separation length between the ion-rich domains was determined by SAXS to be 2.8, 2.9 and 3.0 nm for PES 70, PES 70-S05 and Nafion<SUP>(</SUP>R) NRE 212, respectively. Tensile strength and Young's modulus increase with the amount of silica. Ex-situ in-plane proton conductivity showed a maximum for PES 70-S05 (2 mS cm<SUP>-1</SUP>). In the fuel cell (H<SUB>2</SUB>/air, 120 <SUP>o</SUP>C, <50%), it showed a current density of 173 mA cm<SUP>-2</SUP> at 0.7 V, which is 3.4 times higher than for PES 70.
임아연,김형준,Dirk Henkensmeier,유성종,김진영,이소영,성영은,장종현,박현서 한국공업화학회 2019 Journal of Industrial and Engineering Chemistry Vol.76 No.-
Polymer electrolyte membrane water electrolysis has been proposed to address production of high purityhydrogen for storage of excess renewable energy. Among them, alkaline electrolyte membrane based waterelectrolysis (AEMWE) has an advantage in the aspect of material costs, e.g. from non-noble catalysts andmembrane, but suffers from lower performance compared to proton exchange membrane based waterelectrolysis (PEMWE). However, there are fewer researches on single cell MEA and operation studycompared to material research to enhance AEMWE performance. Here, we analyze the effect of the cellconstruction and operation factors, i.e MEA pressing, torque of cell assembly, electrolyte pre-feed methods,and operation temperature, to obtain high performance in AEMWE single cell operation. 97.5 % currentimproves at 1.8 V by applying optimized torque. 94 % decrease of ohmic resistance are achieved fromelectrolyte pre-feeding. 50 mA cm 2 of current density is enhanced at 0.591 V of overvoltage per 10 Ctemperature increasedue to higherionic conductivityandreaction kinetics.Thesefactorssignificantlyaffectinternal factors such as not only material property during operation but also, catalysts structure and contactin MEA, leading 4.3 times progress of current density from 0.242 to 1.045 A cm 2 at 1.8 Vcell.