Polymer/layered silicate nanocomposites: a review from preparation to processing

Equivalent weight (EW) is the number of grams of dry Nafion per mole of sulfonic acid groups when the material is in the acid form. This is an average EW in the sense that the comonomer sequence distribution (that is usually unknown to the investigator and largely unreported) gives a distribution in m in this formula. EW can be ascertained by acid-base titration, by analysis of atomic sulfur, and by FT-IR spectroscopy. The relationship between EW and m is EW ) 100m + 446 so that, for example, the side chains are separated by around 14 CF2 units in a membrane of 1100 EW. Common at the time of this writing are Nafion 117 films. The designation “117” refers to a film having 1100 EW and a nominal thickness of 0.007 in., although 115 and 112 films have also been available. Early-reported studies involved 1200 EW samples as well as special experimental varieties, some being rather thin. The equivalent weight is related to the property more often seen in the field of conventional ion exchange resins, namely the ion exchange capacity (IEC), by the equation IEC ) 1000/EW. The mention of the molecular weight of high equivalent weight (EW > 1000 g‚mol-1) Nafion is almost absent in the literature, although the range 105-106 Da has been mentioned. As this polymer does not form true solutions, the common methods of light scattering and gel permeation chromatography cannot be used to determine molecular weight as well as the size and shape of isolated, truly dissolved molecules. Studies of the structure of this polymer in solvent (albeit not a true solution) will be mentioned in the scattering section of this review. It should be noted that Curtin et al. performed size exclusion chromatography determinations of the molecular weight distribution in Nafion aqueous dispersions after they were heated to high temperatures (230, 250, and 270 °C).1 Before heating, there was a high molecular weight shoulder on a bimodal distribution, due to molecular aggregates, but this shoulder disappeared upon heating, which indicated that the aggregates were disrupted. The peaks for the monomodal distribution for the heated samples were all located at molecular weights slightly higher than 105 g‚mol-1. Also, light scattering experiments revealed that the radius of gyration had a linear dependence on the molar mass of the aggregates, which suggests that the particles are in the form of rods or ribbons, or at least some elongated structure. Nafion ionomers are usually derived from the thermoplastic -SO2F precursor form that can be extruded into sheets of required thickness. Strong interactions between the ionic groups are an obstacle to melt processing. This precursor does not possess the clustered morphology that will be of great concern in this article but does possess Teflon-like crystallinity which persists when the sulfonyl fluoride form is converted to, for example, the K+ form by reacting it with KOH in water and DMSO. Thereafter, the -SO3H form is achieved by soaking the film in a sufficiently concentrated aqueous acid solution. Extrusion of the sulfonyl fluoride precursor can cause microstructural orientation in the machine direction, * Address correspondence to either author. Phone: 601-266-5595/ 4480. Fax: 601-266-5635. E-mail: Kenneth.Mauritz@usm.edu; RBMoore@usm.edu. 4535 Chem. Rev. 2004, 104, 4535−4585

State of Understanding of Nafion

Rod Borup is a Team Leader in the fuel cell program at Los Alamos National Lab in Los Alamos, New Mexico. He received his B.S.E. in Chemical Engineering from the University of Iowa in 1988 and his Ph.D. from the University of Washington in 1993. He has worked on fuel cell technology since 1994, working in the areas of hydrogen production and PEM fuel cell stack components. He has been awarded 12 U.S. patents, authored over 40 papers related to fuel cell technology, and presented over 50 oral papers at national meetings. His current main research area is related to water transport in PEM fuel cells and PEM fuel cell durability. Recently, he was awarded the 2005 DOE Hydrogen Program R&D Award for the most significant R&D contribution of the year for his team's work in fuel cell durability and was the Principal Investigator for the 2004 Fuel Cell Seminar (San Antonio, TX, USA) Best Poster Award. Jeremy Meyers is an Assistant Professor of materials science and engineering and mechanical engineering at the University of Texas at Austin, where his research focuses on the development of electrochemical energy systems and materials. Prior to joining the faculty at Texas, Jeremy workedmore » as manager of the advanced transportation technology group at UTC Power, where he was responsible for developing new system designs and components for automotive PEM fuel cell power plants. While at UTC Power, Jeremy led several customer development projects and a DOE-sponsored investigation into novel catalysts and membranes for PEM fuel cells. Jeremy has coauthored several papers on key mechanisms of fuel cell degradation and is a co-inventor of several patents. In 2006, Jeremy and several colleagues received the George Mead Medal, UTC's highest award for engineering achievement, and he served as the co-chair of the Gordon Research Conference on fuel cells. Jeremy received his Ph.D. in Chemical Engineering from the University of California at Berkeley and holds a Bachelor's Degree in Chemical Engineering from Stanford University. Bryan Pivovar received his B.S. in Chemical Engineering from the University of Wisconsin in 1994. He completed his Ph.D. in Chemical Engineering at the University of Minnesota in 2000 under the direction of Profs. Ed Cussler and Bill Smyrl, studying transport properties in fuel cell electrolytes. He continued working in the area of polymer electrolyte fuel cells at Los Alamos National Laboratory as a post-doc (2000-2001), as a technical staff member (2001-2005), and in his current position as a team leader (2005-present). In this time, Bryan's research has expanded to include further aspects of fuel cell operation, including electrodes, subfreezing effects, alternative polymers, hydroxide conductors, fuel cell interfaces, impurities, water transport, and high-temperature membranes. Bryan has served at various levels in national and international conferences and workshops, including organizing a DOE sponsored workshop on freezing effects in fuel cells and an ARO sponsored workshop on alkaline membrane fuel cells, and he was co-chair of the 2007 Gordon Research Conference on Fuel Cells. Minoru Inaba is a Professor at the Department of Molecular Science and Technology, Faculty of Engineering, Doshisha University, Japan. He received his B.Sc. from the Faculty of Engineering, Kyoto University, in 1984 and his M.Sc. in 1986 and his Dr. Eng. in 1995 from the Graduate School of Engineering, Kyoto University. He has worked on electrochemical energy conversion systems including fuel cells and lithium-ion batteries at Kyoto University (1992-2002) and at Doshisha University (2002-present). His primary research interest is the durability of polymer electrolyte fuel cells (PEFCs), in particular, membrane degradation, and he has been involved in NEDO R&D research projects on PEFC durability since 2001. He has authored over 140 technical papers and 30 review articles. Kenichiro Ota is a Professor of the Chemical Energy Laboratory at the Graduate School of Engineering, Yokohama National University, Japan. He received his B.S.E. in Applied Chemistry from the University of Tokyo in 1968 and his Ph.D. from the University of Tokyo in 1973. He has worked on hydrogen energy and fuel cells since 1974, working on materials science for fuel cells and water electrolysis. He has published more than 150 original papers, 70 review papers, and 50 scientific books. He is now the president of the Hydrogen Energy Systems Society of Japan, the chairman of the Fuel Cell Research Group of the Electrochemical Society of Japan, and the chairman of the National Committee for the Standardization of the Stationary Fuel Cells. ABSTRACT TRUNCATED« less

Scientific aspects of polymer electrolyte fuel cell durability and degradation.

Organic–inorganic hybrid materials do not represent only a creative alternative to design new materials and compounds for academic research, but their improved or unusual features allow the development of innovative industrial applications. Nowadays, most of the hybrid materials that have already entered the market are synthesised and processed by using conventional soft chemistry based routes developed in the eighties. These processes are based on: a) the copolymerisation of functional organosilanes, macromonomers, and metal alkoxides, b) the encapsulation of organic components within sol–gel derived silica or metallic oxides, c) the organic functionalisation of nanofillers, nanoclays or other compounds with lamellar structures, etc. The chemical strategies (self-assembly, nanobuilding block approaches, hybrid MOF (Metal Organic Frameworks), integrative synthesis, coupled processes, bio-inspired strategies, etc.) offered nowadays by academic research allow, through an intelligent tuned coding, the development of a new vectorial chemistry, able to direct the assembling of a large variety of structurally well defined nano-objects into complex hybrid architectures hierarchically organised in terms of structure and functions. Looking to the future, there is no doubt that these new generations of hybrid materials, born from the very fruitful activities in this research field, will open a land of promising applications in many areas: optics, electronics, ionics, mechanics, energy, environment, biology, medicine for example as membranes and separation devices, functional smart coatings, fuel and solar cells, catalysts, sensors, etc.

Applications of hybrid organic–inorganic nanocomposites

This article reviews the progress made in CO2 separation and capture research and engineering. Various technologies, such as absorption, adsorption, and membrane separation, are thoroughly discussed. New concepts such as chemical-looping combustion and hydrate-based separation are also introduced briefly. Future directions are suggested. Sequestration methods, such as forestation, ocean fertilization and mineral carbonation techniques are also covered. Underground injection and direct ocean dump are not covered.

Progress in carbon dioxide separation and capture: a review.

Nafion®/SiO2, Nafion®/[ORganically MOdified SILicate (ORMOSIL)] and Nafion®/dimethylsiloxane hybrids were created via in situ sol–gel reactions for tetraethoxysilane, diethoxydimethylsilane, and their mixtures. Differential scanning calorimetry studies showed a broad endotherm for unfilled Nafion®-H+ at Tα ≈ 215°C that shifts upward for the Q : D = 1 : 0 (mol : mol) [Q = Si(O1/2)4, D = (O1/2)2Si(CH3)2] hybrid, then shifts downward with decreasing Q : D. This endotherm likely arises from release of H2O molecules bound to ≡Si—OH groups and condensation reactions among silanol groups. The decrease in Tα is rationalized in terms of an increasing fraction of flexible D units that disrupt hydrophilic Q structures. Tm shifts to lower temperatures with decreasing Q : D, and it is suggested that main chains are restricted by side chains embedded in silicon oxide nanoparticles, but D unit insertion causes side chains to be anchored less strongly. Thermal gravimetric analysis indicates that the first mass loss step for Nafion®-H+ shifts to higher temperatures as D : Q increases; an increase in D unit fraction inhibits Q unit degradation by evolved HF. A dynamic mechanical transition at Tα may arise from side chain motions, and the increase in Tα in passing from unfilled Nafio®-H+ to the 1 : 0 hybrid is due to side chain immobilization by their entrapment in silicon oxide domains. The progression 0 : 1 1 : 2 1 : 1 2 : 1 generates increasing mechanical tensile strength and decreasing ductility; strength enhancement might be due to entanglements between ORMOSIL and pure silicon oxide phases and side chains. Liquid sorption experiments quantified the affinity of these hybrids for solvents of varying polarity. A dielectric relaxation for the 0 : 1 hybrid at about 1.5 kHz might be related to side chain mobility. A weaker relaxation in the range 104–105 Hz exists for the 0 : 1 and 1 : 1 hybrids and Nafion®-H+, but not for the 1 : 0 hybrid that exhibits the behavior e′ ∼ f−n over a broad frequency (f) range, suggestive of intercluster proton hopping. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68:747–763, 1998

Nafion®/(SiO2, ORMOSIL, and dimethylsiloxane) hybrids via in situ sol–gel reactions: Characterization of fundamental properties

https://epublications.marquette.edu/cgi/viewcontent.cgi?article=1760&context=chem_fac

TGA–FTi.r. investigation of the thermal degradation of Nafion® and Nafion®/[silicon oxide]-based nanocomposites

Discussion de la loi de puissance decrivant la perte dielectrique de membranes Nafion contenant des electrolytes aqueux obtenue par Mauritz a l'aide de la theorie du transport dispersif des porteurs de charge dans les materiaux amorphes et de la theorie du phenomene de dispersion dielectrique anormal a basse frequence. Les resultats montrent que l'indice de puissance n pourrait etre utilise comme indice qualitatif de la regularite morphologique ou un indice quantitatif de la tortuosite du reseau conducteur

Dielectric relaxation studies of ion motions in electrolyte-containing perfluorosulfonate ionomers. 4. Long-range ion transport

[Perfluorosulfonate ionomer]/silicate hybrid membranes via base-catalyzed in situ sol–gel processes for tetraethylorthosilicate

Microcomposite membranes were produced via the in situ diffusion-controlled, acid-catalyzed sol-gel reaction for tetraethoxysilane in prehydrated and methanol-swollen Nafion perfluorosulfonic acid films. The thermal behavior of these microcomposites was investigated using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). It was found by TGA that significant

Kenneth A. Mauritz

Papers

Nafion®/(SiO2, ORMOSIL, and dimethylsiloxane) hybrids via in situ sol–gel reactions: Characterization of fundamental properties

TGA–FTi.r. investigation of the thermal degradation of Nafion® and Nafion®/[silicon oxide]-based nanocomposites

Dielectric relaxation studies of ion motions in electrolyte-containing perfluorosulfonate ionomers. 4. Long-range ion transport

[Perfluorosulfonate ionomer]/silicate hybrid membranes via base-catalyzed in situ sol–gel processes for tetraethylorthosilicate

Microstructural evolution of a silicon oxide phase in a perfluorosulfonic acid ionomer by an in situ sol-gel reaction. 3. Thermal analysis studies