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Electrode structure within PEFCs, including the Pt-ionomer interface, is created while making electrodes from catalyst inks based on ionomer dispersed in solvent. The relationship between final electrode structure and processing conditions is poorly understood. We have varied the solvent used in cathode catalyst inks, and then subjected the resulting MEAs to hydrogen-air performance and durability testing. Specifically, cathodes cast from inks based on inonomer dispersions in water-propanol-isopropanol (W/P cathode) initially perform better than cathodes cast from glycerol-based dispersions (Gly cathode), but are far less durable. After 10,000 potential cycles from 0.60 V to 1.0 V in N2, the performance on air of the W/P cathode falls significantly below that of the Gly cathode. NMR and neutron scattering measurements of ionomer dispersions, as well as AFM and TEM data from cast ionomer films, offer insight into how the effect of solvent choice on the ionomer structure may impact durability.

Partially fluorinated poly(arylene ether) copolymer having reactive functional group are used to fabricate the MEA to improve the interfacial adhesion between membrane and electrode. The optimum MEA processing procedure was studied using different hot pressing temperature and crosslinking. Good interfacial adhesion between hydrocarbon membrane and Nafion bonded electrode produced excellent fuel cell performance which was comparable to the MEA using Nafion 212.

Low temperature proton exchange membrane (PEM) fuel cells that use perfluorinated sulfonic acid are at present being commercialized in fuel cell vehicles, but these cells can operate only at relatively low temperatures, ca. < 100°C, and high hydration levels. High temperature PEM fuel cells that use phosphoric acid-doped polybenzimidazole can operate effectively up to 180°C; however, these are difficult to operate below 140°C without suffering loss of phosphoric acid when exposed to water.1 In this presentation, we discuss a new class of fuel cells based on ion pair-coordinated proton exchange membranes.2 In the ion pair-coordinated proton exchange membranes, quaternary ammonium functionalized membranes, also known as anion exchange membranes, are doped with phosphoric acid. Due to the high basicity of the quaternary ammonium hydroxide, the acidic proton of phosphoric acid is completely deprotonated to form a strong ionic interaction between quaternary ammonium and biphosphate. Our density functional theory calculation indicated that the ion-pair interaction is 8.5 times greater than the conventional acid base interaction in the phosphoric acid doped polybenzimidazole. The strong interaction between the ion pair enables fuel cell operation at lower temperatures with substantially higher water partial pressure than are possible for high-temperature phosphoric acid doped polybenimidazole fuel cells. In this presentation, the chemical structural difference between this new system and the conventional phosphoric acid-doped polybenzimidazole system will be compared. The benefits and challenges of the new system in fuel cell operations will be further discussed. Acknowledgment This work was supported by the US Department of energy, Energy Efficiency and Renewable Energy, Fuel Cell Technology Office (Program Manager: Dimitrios Papageorgopoulos). References G. Bendlamudi Systematic Characterization of HT PEMFCs Containing PBI/H3PO4 Systems: Thermodynamic analysis and Experimental Investigations 104 (Logos Verlag Berlin GmbH, 2011). Kwan-Soo Lee, Jacob S. Spendelow, Yoong-Kee Choe, Cy Fujimoto, and Yu Seung Kim Nature Energy, 1, 16120 (2016).

Anion exchange membrane fuel cells (AEMFCs) have been a topic of extensive research from academia and industry as an alternative to proton exchange membrane fuel cells (PEMFCs). The AEMFCs offer benefits over PEMFCs such as facile fuel oxidation and enhanced oxygen reduction reaction catalysis1. However, the chemical stability of anion exchange membrane needs to be improved as most commonly used benzyltrimethyl ammonium cationic group undergoes direct nucleophilic substitution reaction, which results in loss of conductivity and fuel cell performance. One of the approaches to enhance the chemical stability is introducing electron conjugation into cationic functional group. Previous study demonstrated that the conjugated guanidinium possess better stability than non-conjugated guanidinium2. Herein, we report the progress on resonance stabilization of the guanidinium functional group. The extended-resonance stabilized guanidinium functionalized poly(phenylene) (PP-TMG) AEM was synthesized from the Diels-Alder poly(phenylene) by acylation reaction followed by activated fluorophenyl-guanidine reaction3. The alkaline stability of PP-TMG was compared with benzyltrimethyl ammonium-poly(phenylene) (PP-BTMA) and hexamethylenetrimethyl ammonium-poly(phenylene) (PP-HTMA). Spectroscopic analysis with small molecules and cationic group tethered polymers will be also provided to discuss the resonance stabilization effect. Acknowledgement This work is supported by the US Department of Energy, Energy Efficiency and Renewable Energy, Fuel Cell Technology Office (Program Manager Dr. David Peterson). References: (1) Varcoe, J. R.; Atanassov, P.; Dekel, D. R.; Herring, A. M.; Hickner, M. A.; Kohl, P. A.; Kucernak, A. R.; Mustain, W. E.; Nijmeijer, K.; Scott, K.; Xu, T.; Zhuang, L. Energy Environ. Sci. 2014, 7 (10), 3135–3191. (2) Kim, D. S.; Fujimoto, C. H.; Hibbs, M. R.; Labouriau, A.; Choe, Y.-K.; Kim, Y. S. Macromolecules 2013, 46 (19), 7826–7833. (3) Kim, D. S.; Labouriau, A.; Guiver, M. D.; Kim, Y. S. Chem. Mater. 2011, 23 (17), 3795–3797.

Anion exchange polymer electrolyte is a key element for alkaline membrane fuel cell (AMFC) applications. In fuel cells, the polymer electrolytes require alkaline stable covalently tethered cationic group to conduct hydroxide ion. Benzyltrimethyl ammonium cationic group has been mostly often employed in anion exchange polymer electrolytes because it is reasonably basic, stable and easily synthesized. However, the demands on more stable and less catalyst poisoning cationic groups are growing. One promising stable cationic groups that potentially can be tethered in the polymer backbone is guanidinium. However, benzyl guanidinium tethered polymers prepared via chloromethylation and subsequent cationization of the halomethyl group showed a limited stability in high pH conditions due to the nucleophilic degradation of the benzylic carbon. In 2011, we had developed a new synthetic method to synthesize guanidinium tethered polymer via activated fluorophenyl-amine reaction.1 This new synthetic method allows to prepare phenyl guanidinium (instead of benzyl guanidinium via conventional method) tethered polymer. The direct connection between phenyl group and guanidinium can stabilize the cationic group by whole resonance structure. However, continuing study indicates that the poly(arylene ether) polymer that we employed undergoes ether-cleavage degradation under high pH conditions.2 In this study, we report the phenyl guanidinium tethered ether-free poly(phenylene)s. Activated fluorophenyl-amine reaction was used to synthesize the poly(phenylene)s. The alkaline stability of the polymer is exceptional: no chemical structural degradation was found during 1000 h in 0.5 M NaOH at 80°C. The tailored poly(phenylene) anion exchange ionomers is well suited for the ionomeric binders, particularly for hydrogen oxidation reaction in alkaline membrane fuel cells. References: 1 D. S. Kim, A. Labouriau, M. D. Guiver, and Y.S. Kim, Chem. Mater. 2011, 23, 3795-3797. 2 C. Fujimoto, D. S. Kim, M. Hibbs, D. Wrobleski, Y.S. Kim, J. Memb. Sci. 2012, 423, 438-449.

Current fuel cells for transportation and residential applications use polymer electrolyte membrane fuel cells (PEMFCs) which require platinum catalysts and operate below 80 °C due to water management issues. However, PEMFCs operating at 100 °C or higher temperatures in anhydrous conditions do not need a humidifier, and do not suffer from water management issues created by the presence of liquid water. Excessive amount of liquid water in the electrode can flood the backing and catalysts layers at lower temperatures leading to poorer fuel cell performance. Furthermore, such intermediate temperature PEMFCs can solve the problem of carbon monoxide (CO) poisoning of the anode electrocatalyst leading to relaxation of the hydrogen fuel quality standards, thus lowering infrastructure costs. Finally, higher operating temperatures allow for simpler cooling systems in transportation applications, which results in smaller and lighter radiators. These advantages mean that a paradigm shift in fuel cells for transportation and residential applications can be achieved with an intermediate temperature proton conducting solid-electrolyte that can operate above 150 °C. Unfortunately, electrolyte membranes and ionomers developed so far do not have satisfactory conductivity and performance in the above temperature ranges, at low-humidity, or in non-humidified conditions. The further advancement of higher temperature PEMFCs relies on the development of membranes that possess the desired electrochemical and mechanical properties in dry (< 30% RH) and hot (> 100 oC) conditions. In this study, we have developed an organic/inorganic composite membrane using a SnP2O7 (TPP) inorganic conductor and evaluated the fuel cell performance under various conditions. Membrane electrode assemblies (MEA) were prepared from these membranes and gas diffusion electrodes (GDE) were optimized using either LANL ionomer dispersion or various commercial gas diffusion layer (GDL). A maximum power density (> 600mW/cm2 ) has been obtained for fuel cell operation at ≈ 220 oC under less than 2 % humidification condition.

Current fuel cells for transportation and residential applications use polymer electrolyte membrane fuel cells (PEMFCs) which require platinum catalysts and operate below 80 °C due to water management issues. However, PEMFCs operating at 100 °C or higher temperatures in anhydrous conditions do not need a humidifier, and do not suffer from water management issues created by the presence of liquid water. Excessive amount of liquid water in the electrode can flood the backing and catalysts layers at lower temperatures leading to poorer fuel cell performance. Furthermore, such intermediate temperature PEMFCs can solve the problem of carbon monoxide (CO) poisoning of the anode electrocatalyst leading to relaxation of the hydrogen fuel quality standards, thus lowering infrastructure costs. Finally, higher operating temperatures allow for simpler cooling systems in transportation applications, which results in smaller and lighter radiators. These advantages mean that a paradigm shift in fuel cells for transportation and residential applications can be achieved with an intermediate temperature proton conducting solid-electrolyte that can operate above 150 °C. Unfortunately, electrolyte membranes and ionomers developed so far do not have satisfactory conductivity and performance in the above temperature ranges, at low-humidity, or in non-humidified conditions. The further advancement of higher temperature PEMFCs this relies on the development of membranes that process the desired electrochemical and mechanical properties in dry (< 30% RH) hot (> 100 oC) conditions. In this study, we have developed an organic/inorganic composite membrane using a SnP2O7 (TPP) inorganic conductor and evaluated the fuel cell performance under various condition. Figure 1 illustrates the conductivity of this membrane under anhydrous conditions at various temperatures. The conductivity is a strong function of the % of TPP in the composite and reach as high as 0.1 S/cm at T ≥ 250oC using ≈ 90wt % TPP. Membrane electrode assemblies (MEA) were prepared from these membranes using either standard PEMFC Gas diffusion electrodes or Pt/C/TPP based electrodes painted into to the membrane. The performance of one of these MEAs is shown in Figure 2. A maximum power density of 300mW/cm2 (not shown) has been obtained for fuel cell operation at ≈ 250 oC and < 5 % relative humidity. While these preliminary results are promising, there are still challenges with low open circuit voltage (OCV) due to membrane porosity and high kinetic losses due to insufficient electrode morphology optimization. In this talk we will address these issues and discuss the progress made towards better performing intermediate temperature fuel cells. [1] Nagao et al., J Electrochem Soc, 2006 [2] Nagao et al. Electrochem Solid State Lett, 2006. Figure 1

Los Alamos National Laboratory fuel cell team has discovered that Nafion dispersion morphology in dilute liquid media ca. solid content: 2.5 wt.% has distinctive characteristics, depending on dispersing fluid:[ref. 1] Small angle neutron scattering (SANS) and 19F NMR analysis indicated (i) a well-defined cylindrical dispersion in polyhydric alcohols, (ii) a gel particles that have as open network structure with sufficiently sparse physical network connections in some aprotic dispersing fluids, and (iii) a less-defined highly solvated large particle in water-monohydric alcohol mixtures. In this talk, we present the impact of dilute Nafion dispersion morphology on film/electrode formation, fuel cell performance and durability. Following subjects will be discussed with some details: 1. Change of particle morphology and gelation behavior of Nafion dispersion during evaporation process (Fig.1).[ref. 2] 2. Characterization of fuel cell electrode by microscopy and electrochemical methods. 3. Impact on fuel cell initial and long-term performance during potential cycles.[ref. 3] Other critical effects including mechanical toughness of dispersion-cast membranes and electrode reaction uniformity [ref. 4] will be also discussed at the meeting. This presentation will give some insights on recent progress of engineering production and processing of perfluorinated sulfonic acid ionomers and their application for fuel cell membrane and electrode processing. Acknowledgment U.S. Department of Energy Fuel Cell Technologies Program (Dr. Dimitrios Papageorgopoulos) References 1. Welch, C.; Labouriau, A.; Hjelm, R.; Orler, B.; Johnston, C.; Kim, Y. S. ACS Macro Letters, 2012, 1, 1403-1407. 2. Kim, Y. S. Welch, C. F. Hjelm, R. P. Mack, N. H. Labouriau, A. Orler, E. B. Macromolecules 2015, 48, 2161-2172. 3. Kim, Y. S. Welch, C. F. Mack, N. H. Hjelm, R. Orler, E. B. Hawley, M. Lee, K. S. Yim, S.-D. and Johnston, C. M. Phy. Chem. Chem. Phy. 2014, 16, (13) 5927-5932. 4. Choi, B., Langlois, D. A. Mack, N. Johnston, C. M. Kim, Y. S. J. Electrochem. Soc. 2014, 161 (12), F1154-F1162. Figure 1

Anion exchange membranes have received attention for solid-state alkaline membrane water electrolysis. However, the harsh operating condicitions of alkaline membrane water electrolysis require good chemical stability of the membrane. Chemical degradation of anion exchange membranes can occur in the cationic functional group, cationic functional group-polymer linkage, and polymer backbone. The alkaline stability of cation-functionalized polyaromatic membranes has mainly been discussed in the context of cation stability. Thus far, lifetime studies of cation-fucntinalized polyaromatics indicate that cation stability is of paramount importnace for stable operation of alkaline membrane water electrolysis. However, equally important is the stability of the polymer backbone which may impact the key membrane properties such as mechanical toughness, hydroxide conductivity and water uptake.[1] In this study, comparative studies on cationic group vs. polymer backbone stabilities of cationic group functionalized polyaromatic membranes were made by computational modeling and experimenatal method. The computational modeling study suggests that the facile backbone degradation of anion exchange membranes is not only due to the electron deficincy of the polymer backbone but also due to the low bond dissociation energy of the molecular stucture. The relatively lower bond dissociation energy of heteroatom substitutuents in the polymer backbone of anion exchange membranes caused facile backbone degradation before cationic functional group degradation. For example, benzyl trimethyl ammonium has very high electonegativity but the degradation occurs after aryl-ether degradation due to the high bond dissociation energy of carbon-carbon or carbon-nitrogen bonds. Experimental study on degradation of benzyl trimethyl ammonium functionalized fluoirnated poly(arylene ether) membranes suggests further insight regarding polymer backbone degradation. The C-N stretching peaks of the poly(arylene ether) membranes is shifted to the higher wave number (blue shift) due to the cationic group degradation of the cationic group attached to the phenolic structure occurs before that of the cationic group attached to the un-degraded polymer backbone. This inidcates accessibility of water molecules also play a critical role in polymer backbone degradation. We will provide some other evidences on facile backbone degradation of polyaromatic polymers and their impact on membrane properties at the meeting. This presentation emphasizes on the importance of polymer backbone stability. [1] Fujimoto, C.; Kim, D. S.; Hibbs, M.; Wrobleski, D.; Kim, Y. S. J. Membr. Sci. 2012, 423, 438−449.

Perfluorinated ionomers have significant advantages over hydrocarbon-based ionomers due to the higher oxygen permeability, hydrophobicity, less catalyst poisoning, ideal three-phase interface and ability to create a porous electrode structure. There have been a few attempts to prepare perfluorinated polymers for the use of alkaline applications mostly in the late 1980s; however, none have been stable and all rapidly hydrolyzed under high pH conditions.2 We have synthesized stable hydroxide conducting perfluorinated ionomers through resonance structure formation upon functionalization of perfluorinated polymer.3 The synthesis of phenyl pentamethyl guanidinium functionalized perfluorinated ionomer was accomplished with a three-step procedure, i) attachment of a 4-fluoroaniline spacer to carboxylic acid Nafion precursor ii) functionalization of tetramethyl gunanidinium4 and iii) methylation with dimethyl sulfate. The alkaline membrane fuel cells (AMFCs) using the perfluorinated copolymer in the catalyst layers exhibited the peak power density of 577 mW/cm2, which was more than 2x greater than a state-of-the-art polyaromatic polymer electrolyte5 (335 mW/cm2). The performance decay rate of the perfluorinated polymer cell was 225 mV/dec/h at 80°C, comparable to the state-of-the-art polyaromatic alkaline polymer cell (183 mV/dec/h at 60°C). The interfacial dynamics of the perfluorinated ionomers using Pt disk microelectrodes indicate that the perfluorinated ionomers have two major benefits over the conventional hydrocarbon-based alkaline ionomers: i) cation desorption capability at an intermediate electrode potential range, ca. 0.2 to 0.6 V and ii) much faster oxygen permeability.6 The oxygen reduction reaction (ORR) of the platinum microelectrodes between liquid and polymer electrolytes are compared using 0.1 M guanidinium aqueous solution and the guanidinium functionalized perfluorinated ionomer. The ORR behavior of platinum micro-electrodes with the guanidinium solution exhibited an “electrostatic-defying” adsorption which limited the access of O2reactants into the Pt surface while the ORR behavior of platinum with guanidinium functionalized ionomer did not show the cation adsorption probably due to the conformation change of the cation by the polymer-cation linkage. Due to the absence of guanidinium adsorption at high potential, the ORR activity of platinum at the ionomer interface substantially improved. Acknowledgment U.S. Department of Energy Fuel Cell Technologies Program (Technology Development Manager: Dr. Nancy Garland) funded this research. We thank the Korea Institute of Energy Research for supporting the Visiting Scholar Program. References Golling, F. E.; Schuster, T.; Geidel, C.; Mamen, L.; Vollmer, D.; Mullen, K.; Klapper, M. ACS Symposium Series, Vol. 1106, Chapter 8, pp 111-126, 2012. Matsui, K.; Tobita, E.; Sugimoto, K.; Kondo, K.; Seita, T.; Akimoto A.; J. Appl. Polym. Sci. 1986, 32, 4137-4143. Kim, D.S.; Fujimoto, C.Y.; Hibbs, M.R.; Labouriau, A.; Choe, Y.-K.; Kim, Y.S. Macromolecules 2013, 46, 7826-7833. Kim, D.S.; Labouriau, A.; Guiver, M.D.; Kim, Y. S. Chem. Mater. 2011, 23, 3795-3797. Fujimoto, C.; Kim, D. S.; Hibbs, M. Wrobleski, D.; Kim, Y. S. J. Memb. Sci. 2012, 423, 438-449 Yim, S.D.; Chlistunoff, J.; Chung, H.; Choe, Y.-K.; Yang, T.-H.; Kim, Y.S. Manuscript in preparation (2014).

Particulate contamination is one of the critical problems that decrease product yield in semiconductor manufacturing. It is therefore important to quickly and correctly predict the particle deposition velocity for controlling the level of particulate contamination. Gaussian diffusion sphere model (GDSM) was employed to predict the mean mass transfer coefficient over a flat plate in a laminar parallel flow. The GDSM was validated for the one-dimensional flat plate by comparing with the laminar boundary layer theory in wide ranges of Schmidt number and fluid temperature. The GDSM was then used to predict the mean mass transfer coefficient over finite flat plates of common areal shapes, i.e., square, rectangle, circle, ellipse, and rhombus, with various aspect ratios. From the GDSM results, the mean Sherwood number correlation was suggested in the form of Sh w = B Re 1/2 w Sc 1/3 . The correlation constant was determined as B = 0.691 for square/rectangular flat plates, B = 0.769 for circular/elliptical flat plates, and B = 0.921 for rhombic flat plates. The applicable Reynolds number range of the correlation was proposed by comparing with the simulation data. Finally, the equation to predict the particle deposition velocity onto a wafer or a photomask surface exposed to a parallel flow was suggested.

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