Proton-conducting Polymer Electrolyte Membranes Research Articles

Sulfonated poly(ether ether ketone)-Protic ionic Liquid-Based anhydrous Proton-Conducting composite polymer electrolyte membranes for High-Temperature fuel cell applications

A high-temperature polymer electrolyte membrane fuel cell (PEMFC) has enormous potential to produce clean energy with minimal environmental pollution along with high energy density and conversion efficiency. In the present work, anhydrous proton-conducting polymer electrolyte membranes for prospective high-temperature fuel cell application were successfully prepared using different protic ionic liquids (PILs) and sulfonated poly(ether ether ketone) (SPEEK). The protic ionic liquids (PILs), 2-hydroxyethylammonium formate, diethylmethyl ammonium triflate, 1-ethylimidazolium bis(trifluoromethylsulfonyl)imide, 1,2-dimethyl imidazolium bis(trifluoro methylsulfonyl)imide, and diethylmethylammonium methanesulfonate were selected based on their favorable physicochemical properties. The effect of the incorporation of the PIL on the structural, thermal, and electrical transport properties of the composite SPEEK polymer electrolyte membranes was studied. The prepared polymer electrolyte membranes (PEMs) were characterized using Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), X-ray diffractometry (XRD), and electrochemical impedance spectroscopy (EIS) techniques. FTIR results indicated an interaction between the PIL and the SPEEK, which resulted in homogeneous and flexible membranes. The DSC results confirmed good miscibility and elucidated plasticizing effect of the incorporated PIL on the SPEEK polymer matrix. All the PEMs showed good thermal stability and high-temperature anhydrous proton conductivity, achieving best proton conductivity, ≈8 × 10–3 S cm−1 at 120 °C and low activation energy ≈0.26 eV, making it suitable for prospective high-temperature PEMFC applications.

Effect of Plasma pretreatment and Graphene oxide ratios on the transport properties of PVA/PVP membranes for fuel cells

In this study, a novel proton-conducting polymer electrolyte membrane based on a mixture of polyvinyl alcohol (PVA)/polyvinyl pyrrolidone (PVP) (1:1) mixed with different ratios of graphene oxide (GO) and plasma-treated was successfully synthesized. Dielectric barrier dielectric (DBD) plasma was used to treat the prepared samples at various dose rates (2, 4, 6, 7, 8, and 9 min) and at fixed power input (2 kV, 50 kHz). The treated samples (PVA/PVP:GO wt%) were soaked in a solution of styrene and tetrahydrofuran (70:30 wt%) with 5 × 10−3 g of benzoyl peroxide as an initiator in an oven at 60 °C for 12 h and then sulfonated to create protonic membranes (PVA/PVP-g-PSSA:GO). The impacts of graphene oxide (GO) on the physical, chemical, and electrochemical properties of plasma-treated PVA/PVP-g-PSSA:x wt% GO membranes (x = 0, 0.1, 0.2, and 0.3) were investigated using different techniques. SEM results showed a better dispersion of nanocomposite-prepared membranes; whereas the AFM results showed an increase in total roughness with increasing the content of GO. FTIR spectra provide more information about the structural variation arising from the grafting and sulfonation processes to confirm their occurrence. The X-ray diffraction pattern showed that the PVA/PVP-g-PSSA:x wt% GO composite is semi-crystalline. As the level of GO mixing rises, the crystallinity of the mixes decreases. According to the TGA curve, the PVA/PVP-g-PSSA:x wt% GO membranes are chemically stable up to 180 °C which is suitable for proton exchange membrane fuel cells. Water uptake (WU) was also measured and found to decrease from 87.6 to 63.3% at equilibrium with increasing GO content. Ion exchange capacity (IEC) was calculated, and the maximum IEC value was 1.91 meq/g for the PVA/PVP-g-PSSA: 0.3 wt% GO composite membrane. At room temperature, the maximum proton conductivity was 98.9 mS/cm for PVA/PVP-g-PSSA: 0.3 wt% GO membrane. In addition, the same sample recorded a methanol permeability of 1.03 × 10−7 cm2/s, which is much less than that of Nafion NR-212 (1.63 × 10−6 cm2/s). These results imply potential applications for modified polyelectrolytic membranes in fuel cell technology.

Studies on Polybenzimidazole and Methanesulfonate Protic-Ionic-Liquids-Based Composite Polymer Electrolyte Membranes.

In the present work, different methanesulfonate-based protic ionic liquids (PILs) were synthesized and their structural characterization was performed using FTIR, 1H, and 13C NMR spectroscopy. Their thermal behavior and stability were studied using DSC and TGA, respectively, and EIS was used to study the ionic conductivity of these PILs. The PIL, which was diethanolammonium-methanesulfonate-based due to its compatibility with polybenzimidazole (PBI) to form composite membranes, was used to prepare proton-conducting polymer electrolyte membranes (PEMs) for prospective high-temperature fuel cell application. The prepared PEMs were further characterized using FTIR, DSC, TGA, SEM, and EIS. The FTIR results indicated good interaction among the PEM components and the DSC results suggested good miscibility and a plasticizing effect of the incorporated PIL in the PBI polymer matrix. All the PEMs showed good thermal stability and good proton conductivity for prospective high-temperature fuel cell application.

Synthesis and Studies on Polymer Electrolyte Membrane using Polyvinyl Alcohol, Polyvinylidene Fluoride and Ammonium Bromide as Dopants for Proton-conducting Electrolyte

Different compositions of Polyvinyl alcohol (PVA), Polyvinylidene fluoride (PVDF) and Ammonium bromide (NH4Br) were employed to synthesize the proton-conducting polymer electrolyte membranes by Solution casting method, which have potential applications in proton (H+) ion batteries and fuel cells. Structural, vibrational and electrical properties of the synthesized polymer electrolyte membrane were characterized by X-Ray Diffraction (XRD), Fourier Transform Infrared (FTIR) spectroscopy and Electrical Impedance Spectroscopy (EIS) analysis and results were reported. The semi-crystalline nature of the prepared polymer was confirmed by XRD analysis. FTIR spectroscopy revealed the vibrational spectra of the prepared polymer membrane. The Nyquist plot drawn from the AC Impedance analysis was a straight line, confirming the dielectric nature of the prepared membrane.

(Energy Technology Division Research Award) The Emerging Research Needs of Polymer Electrolyte Membrane Electrolysis Cells

Proton conducting polymer electrolyte membrane (PEM) electrolysis has emerged as the currently favored research area to enable a global transformation of the energy system with hydrogen from renewable sources as a critical central feature. The hydrogen council has suggested that hydrogen impacts by 2050 could be $2.5T annually and 18% of total global energy demand.[1] While other electrolysis routes including traditional alkaline (based on aqueous KOH), alkaline membrane (emerging) and solid oxide electrolysis are all also being explored, and other possible hydrogen production pathways exist. The ability of PEM electrolysis to fit the needs of the emerging energy system as a dispatchable resource meeting cost, performance and durability requirements most effectively has led to a greater focus on PEM electrolysis than other electrolysis approaches within the global R&D community. The extent PEM electrolysis will establish itself commercially will depend largely on the advances made in the next several years.Much of the focus on PEM electrolysis has been centered around the advances made in PEM fuel cells, and the belief that these advances can be translated to PEM electrolysis systems. In particular, PEM fuel cells have largely been designed for transportation applications where they operate at low duty cycles (mostly off), and experience significant start-stop cycling (multiple times per day) while still achieving requisite performance and durability (several years).[2] Renewable energy sources are dramatically impacting the cost and availability of electricity and the ability to translate these resources into other energy sectors – most notably transportation and industry. While it is hoped that PEM electrolyzers can achieve cost, performance and durability targets, the research needs and challenges are not identical to PEM fuel cells.A new Department of Energy Consortium (H2NEW – Hydrogen from Next-generation Electrolyzers of Water) funded out of the Hydrogen and Fuel Cell Technologies Office is focused on enabling the cell-level fundamental understanding and advances required to address achieving $2/kg hydrogen through electrolysis. The primary focus of this effort is PEM electrolysis, the focus of the talk.A challenge in meeting the cost, performance and durability of PEM electrolysis systems is that current systems have had a strong emphasis on efficiency and durability. This means that cost has not been a primary concern such that systems could be “over-engineered” using extra or more expensive components and processing techniques. This approach has meant that little is understood about fundamental degradation rates relevant to systems that have not been over-engineered. Additionally, the markets that these devices have been sold into have typically operated under continuous conditions rather than the variable, intermittent load profiles that could couple to renewable or low-cost electricity inputs expected in the future. A clear understanding of the optimum system and operating conditions is not well understood at this time, nor is the impact of such operating conditions on performance and durability.Research needs place a high priority on durability under variable operating conditions. Specific components have susceptibility to different performance and durability impacts. In this talk, the impact of operating conditions and a discussion of projected operating conditions will be discussed. The concerns for both performance and durability will be discussed at the cell level with consideration of various cell components including catalyst, polymer, electrode, and porous transport layers. Accelerated stress tests for components in cells is a critical need and will also be presented. Finally, system and techno-economic considerations will also be included.References Hydrogen Council. “Hydrogen Scaling Up.” November 2017. http://hydrogencouncil.com/hydrogen-scaling-up/ B Pivovar, N Rustagi, S Satyapal, Electrochemical Society Interface 27 (1), 47.

Electrocatalysis for the Oxygen Evolution Reaction in Acidic Media: Progress and Challenges

The oxygen evolution reaction (OER) is the efficiency-determining half-reaction process of high-demand, electricity-driven water splitting due to its sluggish four-electron transfer reaction. Tremendous effects on developing OER catalysts with high activity and strong acid-tolerance at high oxidation potentials have been made for proton-conducting polymer electrolyte membrane water electrolysis (PEMWE), which is one of the most promising future hydrogen-fuel-generating technologies. This review presents recent progress in understanding OER mechanisms in PEMWE, including the adsorbate evolution mechanism (AEM) and the lattice-oxygen-mediated mechanism (LOM). We further summarize the latest strategies to improve catalytic performance, such as surface/interface modification, catalytic site coordination construction, and electronic structure regulation of catalytic centers. Finally, challenges and prospective solutions for improving OER performance are proposed.

Effect of ZnO Nanoparticle Content on the Structural and Ionic Transport Parameters of Polyvinyl Alcohol Based Proton-Conducting Polymer Electrolyte Membranes.

Proton conducting nanocomposite solid polymer electrolytes (NSPEs) based on polyvinyl alcohol/ammonium nitrate (PVA/NH4NO3) and different contents of zinc oxide nanoparticles (ZnO-NPs) have been prepared using the casting solution method. The XRD analysis revealed that the sample with 2 wt.% ZnO-NPs has a high amorphous content. The ionic conductivity analysis for the prepared membranes has been carried out over a wide range of frequencies at varying temperatures. Impedance analysis shows that sample with 2 wt.% ZnO-NPs has a smaller bulk resistance compared to that of undoped polymer electrolyte. A small amount of ZnO-NPs was found to enhance the proton-conduction significantly; the highest obtainable room-temperature ionic conductivity was 4.71 × 10−4 S/cm. The effect of ZnO-NP content on the transport parameters of the prepared proton-conducting NSPEs was investigated using the Rice–Roth model; the results reveal that the increase in ionic conductivity is due to an increment in the number of proton ions and their mobility.

Development of proton-exchange polymer nanocomposite membranes for fuel cell applications

The design and development of proton conducting polymer electrolyte membranes from a linear constituent, sulfonated poly (ether ether ketone) (SPEEK), and inorganic additive, niobium oxide (NBO), have been achieved. The degree of sulfonation of SPEEK was measured by back titration method and found to be 57%. The physicochemical properties such as water uptake ability, ion-exchange capacity, swelling ratio, proton conductivity, and thermal stability of the prepared polymer nanocomposite membranes were studied in detail. The distribution of NBO throughout the polymer matrix has been examined by scanning electron microscopic and X-ray diffraction analyses and found to be uniform. The SP-NBO-10 composite membrane shows 38.4% of water uptake, whereas the pristine membrane limits to 27.1%. The prepared electrolyte membranes exhibit good proton conductivity at temperature varying from 30°C to 90°C and possess less activation energy for the transportation of proton by the incorporation of NBO filler. The thermal studies demonstrated that the stability of the composite membranes was significantly enhanced by the impregnation of NBO. The filler NBO shows excellent improvements on the polymer nanocomposite, making it a very promising additive for other polymers and offers new roads for energy applications.

Durability and degradation analysis of hydrocarbon ionomer membranes in polymer electrolyte fuel cells accelerated stress evaluation

The chemical durabilities of two proton-conducting hydrocarbon polymer electrolyte membranes, sulfonated benzophenone poly(arylene ether ketone) (SPK) semiblock copolymer and sulfonated phenylene poly(arylene ether ketone) (SPP) semiblock copolymer are evaluated under accelerated open circuit voltage (OCV) conditions in a polymer electrolyte fuel cell (PEFC). Post-test characterization of the membrane electrodes assemblies (MEAs) is carried out via gel permeation chromatography (GPC) and nuclear magnetic resonance (NMR) spectroscopy. These results are compared with those of the initial MEAs. The SPP cell shows the highest OCV at 1000 h, and, in the post-test analysis, the SPP membrane retains up to 80% of the original molecular weight, based on the GPC results, and 90% of the hydrophilic structure, based on the NMR results. The hydrophilic structure of the SPP membrane is more stable after the durability evaluation than that of the SPK. From these results, the SPP membrane, with its simple hydrophilic structure, which does not include ketone groups, is seen to be significantly more resistant to radical attack. This structure leads to high chemical durability and thus impedes the chemical decomposition of the membrane.

Proton-conducting polymers derived from radiation grafting and sulphonation of poly(tetraflouroethylene-perflourovinyl ether) film with three rare-earth elements

Progress in the area of proton conducting polymer electrolyte membranes is closely with the enhancing of polymer electrolyte membrane fuel cells. Fluorinated polymers, e.g. poly(tetraflouroethylene-perflourovinyl ether) (PFA) film is largely driven by their thermal properties. In this article PFA film was developments to be suitable as proton conducting polymer electrolyte membranes. The grafting of acrylic acid (80%) onto the PFA film achieved by irradiation techniques and PFA-COOH was obtained. In addition, to synthesis of completely a new protonconducting sulfonated polymer ionomers this could be acheived by sequences of chemical modification steps. PFA-COOH has been anilination and sulfonated to a sufficient ionomers formation and complexion with the three rare-earth elements (Li, Cs, and Sr). After that the obtained PFA-CO-NH-ph-SO3M contains a sufficient equilibrium concentration of protons in a wet atmosphere to show useful proton conduction at ambient temperatures. The sulfonated polymers containing 63 mol% sulfonic acid, and characterized by FTIR-ATR and SEM The results show that PFACO-NH-ph-SO3M wet film showed a high proton-conductivity in water (10-3 Scm-1) rather than methanol (10-6 Scm-1) in order Li+> Sr++>Cs+. This approach has interesting potential for smart thin film materials and offers also the possibility to be used in sensors and fuel cells provided that the electrolyte film thickness is in the micrometre range.

The Effect of Membrane Casting Irregularities on Initial Fuel Cell Performance

The polymer electrolyte membrane fuel cell (PEMFC) is a clean alternative to petroleum-based technologies such as the internal combustion engine (ICE). In order to be competitive with the ICE in transportation applications, fuel cell systems must have less than a 10% performance loss after 5,000 hours of operation while reaching cost targets of $40/kW [1,2]. The membrane electrode assembly (MEA), a proton conducting polymer electrolyte membrane (PEM) with attached platinum-containing catalyst layers and gas diffusion layers (GDLs), may possess non-uniformities in any of its constituent components, which could lead to performance losses [3,4]. This work studies a subset of casting irregularities located within the PEM to understand their potential impacts on PEMFC initial performance. If the MEA experiences statistically significant lower initial performance as a result of a casting irregularity, then this irregularity should be classified as a defect. Classification of irregularities as defects will ultimately assist the industry by developing threshold detection limits for in-line quality control diagnostics. Membrane material was cast on a web-line operating within and at the boundaries of the process window by controlling process parameters such as slot and coating gap, flow rate, and substrate speed. The resulting membrane material was either pristine or contained air bubbles, cracks, and contamination, ranging from 0.6 to 3 mm. Gas-diffusion electrodes (GDEs) were fabricated using an ultrasonic spray system. The active area and nominal loading of these GDEs were 50 cm2 and 0.2/0.2 mg Pt/cm2, respectively. MEAs were assembled in the cell by placing a sheet of fabricated membrane material in between two pristine GDEs. Operating conditions for all samples were Tcell: 80°C, anode/cathode relative humidity (RH) at 32/32 and 100/50%, 1.5/2 stoichiometric flow rates of H2/Air, and 150/150 kPa backpressure. Voltage controlled polarization (VI) curves were conducted using a 121 channel segmented fuel cell system. To quantify performance impacts the VI performance of the MEAs containing casting irregularities was subtracted from that of pristine reference MEAs. Thermal imaging was performed subsequent to the performance experiments to map hydrogen crossover to spatial performance [5]. Figure A shows initial VI curves performed at 32/32% RH for four pristine reference samples as well as two samples with casting irregularities. The VI curve data indicate that the samples with irregularities have statistically lower OCV values than the pristine samples. Figure B illustrates the experimental method using GT118 as a representative sample. Prior to the experiment the morphology and size of the casting irregularities were determined using optical microscopy. Sample GT118 contained two air bubbles with sizes of approximately 660 and 1416 µm as shown on the left of Figure B. Then spatial current density distributions were measured with the segmented cell to determine to what extent the casting irregularities caused localized performance losses. The red regions in the spatial current density distribution, shown in the center of Figure B, indicated the lowest local performances in the cell. Subsequent to the performance experiment, a spatial thermal imaging diagnostic was applied to determine regions of increased hydrogen crossover. In the thermal imaging map for GT118 as shown on the right of Figure B, the red boxes indicate air bubble locations and the white regions denote areas of increased hydrogen crossover. These data show the correlation between casting irregularity location, local performance decrease, and increased local hydrogen crossover. In this presentation, we will discuss the impacts of the various casting irregularities in the membrane, and how certain experimental methodologies can be potentially used as defect classification tools. References Marcinkoski, Jason et al. “Fuel Cell System Cost – 2015”. September 30, 2015.James, Brian et al. “Mass Production Cost Estimation of Direct H2 PEM Fuel Cell Systems for Transportation Applications: 2015 Update”. December 2015.Kundu, S., et al. Journal of Power Sources 157.2 (2006): 650-656.Benchmarking and Best Practices Center of Excellence. Manufacturing Fuel Cell Manhattan Project, November 2011 Bender, Guido, et al. Journal of Power Sources 253 (2014): 224-229. Figure 1

A novel proton conducting polymer electrolyte membrane for fuel cell applications

A series of phenolphthalein-based sulfonated poly(ether ether sulfone) (SPEES) membranes were synthesized by aromatic nucleophilic polymerization reaction. The degree of sulfonation was controlled by direct synthesis of sulfonated polymer, which leads to high thermal stability. The physicochemical properties of the SPEES membranes were studied in order to evaluate the suitability of these membranes in fuel cell applications. The ion-exchange capacity of the synthesized SPEES membranes was found in the range between 2.19 mequiv. g−1 and 2.35 mequiv. g−1. The morphology of the membranes was investigated with high-resolution scanning electron microscopy and confirmed the presence of hydrophilic domains that impart good proton conductivity. The membrane electrode assembly of SPEES-30 and SPEES-50 membranes has been successfully fabricated, where SPEES-50 produced a maximum peak power density of 643 mW cm−2 while applying in hydrogen–oxygen fuel cell.

Anhydrous Proton Conducting Polymer Electrolyte Membranes via Polymerization-Induced Microphase Separation.

Solid-state polymer electrolyte membranes (PEMs) exhibiting high ionic conductivity coupled with mechanical robustness and high thermal stability are vital for the design of next-generation lithium-ion batteries and high-temperature fuel cells. We present the in situ preparation of nanostructured PEMs incorporating a protic ionic liquid (IL) into one of the domains of a microphase-separated block copolymer created via polymerization-induced microphase separation. This facile, one-pot synthetic strategy transforms a homogeneous liquid precursor consisting of a poly(ethylene oxide) (PEO) macro-chain-transfer agent, styrene and divinylbenzene monomers, and protic IL into a robust and transparent monolith. The resulting PEMs exhibit a bicontinuous morphology comprising PEO/protic IL conducting pathways and highly cross-linked polystyrene (PS) domains. The cross-linked PS mechanical scaffold imparts thermal and mechanical stability to the PEMs, with an elastic modulus approaching 10 MPa at 180 °C, without sacrificing the ionic conductivity of the system. Crucially, the long-range continuity of the PEO/protic IL conducting nanochannels results in an outstanding ionic conductivity of 14 mS/cm at 180 °C. We posit that proton conduction in the protic IL occurs via the vehicular mechanism and the PEMs exhibit an average proton transference number of 0.7. This approach is very promising for the development of high-temperature, robust PEMs with excellent proton conductivities.

Influence of TiO2 as Filler on the Discharge Characteristics of a Proton Battery

Different concentrations of TiO2 dispersed nano-composite proton conducting polymer electrolyte membranes were prepared using solution casting technique. Fourier Transform Infrared Spectroscopic analysis was carried out to determine the vibrational investigations about the prepared membranes. Variation of conductivity due to the incorporation of TiO2 in polymer blend electrolyte was analyzed using Electrochemical Impedance Spectroscopy and the value of maximum conductivity is 2.8×10-5 Scm-1 for 1mol% of TiO2 dispersed in polymer electrolytes. Wagner polarization technique has been used to determine the value of charge transport number of the composite polymer electrolytes. The electrochemical stability window of the nano-composite polymer electrolyte was analyzed using Linear Sweep Voltammetry. Fabrication of Proton battery is carried out with configuration of Zn+ZnSO4.7H2O+AC ǁ Polymer electrolyte ǁ MnO2+AC. Discharge characteristics were investigated for polymer blend electrolytes and 1mol% TiO2 dispersed nano-composite polymer electrolytes at constant current drain of 10μA. There is evidence of enhanced performance for proton battery which was constructed using 1mol% TiO2 dispersed nano-composite polymer electrolytes compared to the blend polymer electrolytes.

Functionalized Al2O3 particles as additives in proton-conducting polymer electrolyte membranes for fuel cell applications

This study reports on the synthesis and characterization of sulfated Al2O3 and of composite membranes, prepared by dispersing the functionalized oxide in Nafion, acting as electrolytes in proton-exchange membrane fuel cells.Different synthetic routes were explored to obtain nanometric alumina particles with sulfate groups. Structural and morphological characteristics of the inorganic compounds and the nature of the bond of the sulfates with the oxide were investigated by x-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, N2 adsorption and thermal gravimetric analysis. Key properties of the hybrid membranes were elucidated in terms of thermal characteristics, water uptake and ionic exchange capacity. Functionality of the nanocomposite membranes, compared with plain Nafion, was tested in hydrogen-fed fuel cells. Polarization and power density curves and in-situ electrochemical impedance spectroscopy were accomplished to evaluate the effect of temperature on the cell performance.It is shown that well-addressed variations in the synthetic routes are able to determine different morphologies and dimensions of the particles and different degrees of functionalization. The incorporation of alumina in Nafion changes the characteristics of the membrane, with special regard towards hydration. In-situ fuel cell electrochemical tests reveal improved electrode-composite membrane interface properties as the working temperature of the cell increases.

Poly(vinyl)alcohol/1-butyl-3-methylimidazolium hydrogen sulfate solid polymer electrolyte: Structural and electrical studies

Proton conducting polymer electrolyte membranes consisting of poly(vinyl)alcohol and 1-butyl-3-methylimidazolium hydrogen sulfate ionic liquid are prepared by solution cast technique. The membranes are found to be free-standing and mechanically stable for the 40, 60 and 80wt.% concentration of ionic liquid. The membranes have been characterized by X-ray diffraction, differential scanning calorimetry, thermogravimetric analysis, complex impedance spectroscopy and cyclic voltammetry. The crystallinity and melting point of the membranes are found to decrease with increasing concentration of ionic liquid. The membrane with 80wt.% ionic liquid has been found to be completely amorphous. The highest ionic conductivity has been found to be ~10−3Scm−1 at room temperature for the membrane with 80wt.% ionic liquid. The variation of ionic conductivity with temperature follows Arrhenius type behavior in the temperature range of 40–130°C. The membranes show protonic conduction as established by cyclic voltammetry and complex impedance spectroscopic studies. The electrochemical window of the membranes has been found to be ~3.4V.

Comparison of proton conducting polymer electrolyte membranes prepared from multi-block and random copolymers based on poly(arylene ether ketone)

Multi-block and random copolymers based on poly(arylene ether ketone) with the similar IEC values are synthesized. The chemical structure of the hydrophobic and hydrophilic oligomers and the copolymers synthesized from them is identified using 1H - and 19F- nuclear magnetic resonance (NMR) spectroscopy, attenuated total reflection fourier transform infrared (ATR-FTIR) spectroscopy, and gel permeation chromatography (GPC). The development of distinguished hydrophobic-hydrophilic phase separation is confirmed by small-angle X-ray scattering (SAXS) spectroscopy. The proton conductivity and water uptake along with the thermal, mechanical, oxidative stabilities are measured to investigate the effect of the copolymer structure on the membrane properties. While water uptake is similar with respect to each other, the proton conductivity of the multi-block copolymer membrane is higher than that of random one at the same levels of IEC. It results from much more distinct hydrophobic-hydrophilic phase separation formed in the multi-block copolymer membrane than the random one. The ion cluster dimension of the multi-block copolymer membranes is larger than that of the random copolymer membranes from the SAXS analysis. Also, the ion cluster dimension distribution of the block copolymer membranes is much narrower than that of random ones. The multi-block copolymer membranes illustrate superior oxidation stability to the random copolymer membrane due to the same phase separation difference.

Invited: Developing Alkaline Anion Exchanging Membrane Fuel Cells

To achieve sustainable development with limited natural resources and environmental concerns, fuel cells are expected to play an important role in providing clean power at high efficiency. After past decades of intensive development, the proton conducting polymer electrolyte membrane fuel cells (PEMFCs) have made substantial advancement in cost, performance and stability. As the results, some real commercial applications have been demonstrated around the world, such as in the combined heat and power generations, vehicle powers, stationary backup powers, and portable powers. Still, the high cost, scarceness and performance stability of the highly dispersed platinum catalysts in the strong acid environment under dynamic fuel cell operation conditions remain as the major challenges for the PEMFCs to reach widespread mass applications. To address these difficulties, alternative approach in developing alkaline anion exchanging membrane fuel cells (AEMFCs) has recently gained momentum. In this presentation, we report our efforts in developing AEMFCs at Army Research Laboratory. It covers our non-precious metal catalysts development, alkaline polymer electrolyte membrane characterization, fuel cell electrode optimization, and fuel cell tests. The results of this study illustrate some of the key factors affecting the current AEMFCs performance, and the remaining challenges.Non-precious metal development was focused on producing high performance catalysts for oxygen reduction reaction (ORR) at low cost. Catalysts prepared with high temperature heat treatment of the transition metals embedded in nitrogen containing polymer matrix supported on carbon have demonstrated comparable mass activity to that of Pt-based catalysts, in addition to their superior performance stability and contamination tolerance under the alkaline conditions. Some key properties of an anion exchanging polymer electrolyte membrane (AEPEM) measured include ion-exchanging capacity, water uptake, anion conductivity, electro-osmotic drag coefficient, methanol permeation rate, and CO2 permeation rate. These properties are compared to the proton exchanging membrane to illustrate the limitations of current AEPEM.With current available AEPEM and ionomer materials, fuel cell electrode optimization was conducted by varying the ionomer content in the catalyst layer. Compared to Nafion ionomer used for PEMFCs, the current ionomer for the AEMFCs was made from hydrocarbon polymer, which has a lower ionic conductivity, a higher water uptake and a lower polymer density. All these properties limit the fuel cell electrode performance in term of catalyst layer ionic conductivity, catalyst utilization, and reactant gas mass transport. The optimized fuel cell performance has demonstrated to achieve a power density at 300 mW/cm2, which is still much lower than that achieved by PEMFCs. The performance in AEMFCs limitation could be overcome by developing a new generation ionomers with improved properties.

Proton conducting electrolyte membranes based on the pendant-sulfonated poly(arylene ether ketone)/polyorganosiloxane interpenetrating polymer networks

An organosiloxane polymer network (OSPN) was pre-synthesized from 3-glycidyloxypropyltrimethoxysilane and 1-hydroxyethane-1,1-diphosphonic acid, and a pendant-sulfonated poly(arylene ether ketone) (PSPAEK) from the intermediate containing carboxylic acid. Proton-conducting polymer electrolyte membranes were prepared in semi-interpenetrating polymer network (semi-IPN) form from PSPAEK and OSPN. The prepared membranes exhibited superior proton conductivity but similar methanol permeability to the pristine PSPAEK. The water uptake increased only to 64% as the OSPN content was increased to 50%, even at 80°C. The single direct methanol fuel cell (DMFC) performance based on the semi-IPN membrane possessing 50wt% OSPN showed an excellent power density of 70mWcm−2. The chemical and morphological structures of the synthesized membranes were characterized using Fourier transform infrared (FTIR) spectroscopy and small angle X-ray scattering (SAXS) and their results were correlated with the essential membrane properties such as water uptake, proton conductivity, and methanol permeability. The thermal and mechanical stabilities were also investigated using thermogravimetric analysis (TGA) and a universal tensile machine (UTM).

Durability of an aromatic block copolymer membrane in practical PEFC operation

The durability of a novel proton-conducting polymer electrolyte membrane, sulfonated polybenzophenone/poly (arylene ether) (SPK) block copolymer, was evaluated at middle temperature (80°C), low humidity (53% RH), and a low current density, 0.02Acm−2, in a polymer electrolyte fuel cell for 980h. The electrochemical properties and drain water collected from the anode and cathode were monitored during the test, followed by post-test analyses of the membrane. The nuclear magnetic resonance (NMR) spectra and ion exchange capacity (IEC) value of the post-test membrane showed very minor changes compared to those of the pristine one. The post-test membrane retained 94% of its original weight-averaged molecular weight (Mw)org. There was no remarkable change in Qoxide (oxide formation charge of the cathode catalyst) after the test, which indicates that the specific adsorption of decomposition products of the SPK membrane on the cathode catalyst was not significant.