The main challenges for commercialization of fuel cells are cost and durability. Using off-the-shelf materials for system components in Proton Exchange Membrane Fuel Cells (PEMFCs) may lower the cost provided they do not compromise function, fuel cell performance, or life. The purpose of this paper is to increase the understanding of contamination effects of these materials and the contaminants that leach from them. This paper in-situ screening data for six families of materials (i.e., urethane, silicone, epoxy, acrylic, methacrylate, and perfluoroalkylether) broadly classified as assembly aids that may be used as adhesive and lubricants in PEMFC systems.

Lower cost materials for stack hardware and system components help reduce the overall cost of the automotive and stationary fuel cell systems and make these competitive in the market. However, low-cost system component materials need to provide similar function, performance and durability. Intelligently selecting low cost materials for application in polymer electrolyte membrane fuel cell (PEMFC) systems requires understanding the potential adverse effects that system contaminants may have on the fuel cell performance and durability. There are many prospective balance of plant (BOP) materials that can be used in fuel cell systems. Families of material, based on input from OEMs, fuel cell system manufacturers and other attributes like cost, physical properties, were chosen for this study include structural materials, elastomers for seals and (sub)gaskets, and assembly aids (adhesives, lubricants). Two types of low cost structural plastic materials – a polythlalamide and a polyamide – have been studied. The contaminants from the BOP structural material were leached out via an accelerated aging procedure. The leachates obtained from these plastics were a mixture of organics, inorganics, and ions. Organics that were identified in the leachate solutions via gas chromatography mass spectrometry (GCMS) include 1,8 Diazacyclotetradecane-2,7-dione (DCTDD), aniline, and caprolactam. These plastic materials also released anions: chloride, phosphate, nitrates, and sulfates. Of the organics, inorganics, and ions found in the leachate solution, caprolactam and sulfate were chosen for further study. These model compounds were introduced individually and as mixtures to a working fuel cell to determine their effect on fuel cells performance. Several in-situ diagnostics such as infusion, cyclic voltammetry, electrochemical impedance spectroscopy, and I-V curves were carried out to better characterize the contaminant effects of each model compound and mixtures of compounds. The preliminary in-situ results indicated that the organic compound caprolactam had a large negative effect on fuel cell performance and that the effect was not recoverable. On the other hand, infusion of sulfate into the fuel cell seemed to have no effect. The results also suggested that there is an interaction between caprolactam and sulfate. Ex-situ electrochemical measurements were also carried out to understand the impact of these individual and mixtures of compounds on the catalyst electrochemical surface area and the oxygen reduction reaction. The goal is to better understand the contamination mechanisms of specific species and their interaction with one another, leading to mitigation strategies. The authors would like to acknowledge funding from the U.S. Department of Energy EERE Fuel Cell Technologies Office, under Contract No. AC36-08GO28308 with the National Renewable Energy Laboratory and collaborations with colleagues at GM. Structural plastic materials and leachates were provided by GM for this study.

Anion exchange membranes (AEMs) are of interest as hydroxide conducting polymer electrolytes in electrochemical devices like fuel cells and electrolyzers. AEMs require hydroxide stable covalently tetherable cations to ensure required conductivity. Benzyltrimethylammonium (BTMA) has been the covalently tetherable cation that has been most often employed in anion exchange membranes because it is reasonably basic, compact (limited number of atoms per charge), and easily/cheaply synthesized. Several reports exist that have investigated hydroxide stability of BTMA under specific conditions, but consistency within these reports and comparisons between them have not yet been made. While the hydroxide stability of BTMA has been believed to be a limitation for AEMs, this stability has not been thoroughly reported. We have found that several methods reported have inherent flaws in their findings due to the difficulty of performing degradation experiments at high temperature and high pH. In order to address these shortcomings, we have developed a reliable, standardized method of determining cation degradation under conditions similar/relevant to those expected in electrochemical devices. The experimental method has been employed to determine BTMA stabilities at varying cation concentrations and elevated temperatures, and has resulted in improved experimental accuracy and reproducibility. Most notably, these results have shown that BTMA is quite stable at 80 degrees C (half-life of similar to 4 years), a significant increase in stability over what had been reported previously. (C) The Author(s) 2015. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. All rights reserved.

Extensive research on fuel cell stack materials has led to advances in lower cost, high performing materials. With the decrease in the cost of stack materials, lowering the cost of the balance of plant (BOP) components has increased in importance. In order to decrease the overall cost of the automotive and stationary fuel cell systems and make them as competitive as possible, low-cost system component materials that provide similar function, performance and durability are needed. However, intelligently selecting low cost materials for application in polymer electrolyte membrane fuel cell (PEMFC) systems requires understanding the potential adverse effects that system contaminants may have on the fuel cell performance and durability. Limited work in this area has been conducted to-date. There are many prospective BOP materials that can be used in fuel cell systems. Our material selection was based on the material’s physical properties (i.e., whether it will be stable in fuel cell operating conditions), commercial availability, cost and input from OEMs and fuel cell system manufacturer. Families of material chosen for the study include structural materials, elastomers for seals and (sub)gaskets, and assembly aids (adhesives, lubricants). Two types of low cost structural plastic materials – a polythlalamide and a polyamide – were studied. Leachates obtained from these plastics were a mixture of organics, inorganics, and ions and were introduced to a working fuel cell to determine their effect on the fuel cells performance. Organics that were identified in the leachate solutions via gas chromatography mass spectrometry (GCMS) include 1,8 Diazacyclotetradecane-2,7-dione (DCTDD), aniline, and caprolactam. These plastic materials also released anions: chloride, phosphate, nitrates, and sulfates. In-situmeasurements such as infusion, cyclic voltammetry, impedance spectroscopy, and I-V curves were carried out to better characterize the contaminants effects of the mixtures of compounds in the extracts. The effect of the individual organic model compound (caprolactam), anion (sulfate) and mixtures of the two species were also studied to better understand the contamination mechanisms of specific species and their interaction with one another. This presentation will also briefly describe the ex-situ electrochemical quartz crystal microbalance (EQCMB) technique used to study the adsorption effect of organic compounds, derived from system contaminants, on Pt surface. EQCMB was used to measure the change in mass of the electrode as a function of potential. The authors would like to acknowledge funding from the U.S. Department of Energy EERE Fuel Cell Technologies Office, under Contract No. AC36-08GO28308 with the National Renewable Energy Laboratory and collaborations with colleagues at GM and 3M. Structural plastic materials were provided by GM and membrane degradation products for this study were provided by 3M.

Using cyclic voltammetry as a quick ex situ screening tool, the impact of the extracted solution and the individual leachable constituents from prospective balance of plant component materials on the performance and recoverability of the platinum catalyst were evaluated. Taking an extract from Zytel HTN51G35HSLR (polyphthalamide) as an example, the major leachable organic components are caprolactam and 1,6-hexanediol. While these organic compounds by themselves do poison the Pt catalyst to some extent, such influence is mostly recoverable by means of potential holding and potential cycling. The extracted solution, however, shows a more drastic poisoning effect and it was not recoverable. Therefore, the non-recoverable poisoning effect observed for the extracted solution is not from the two organic species studied. This demonstrates the complexity of such a contaminant study. Inorganic compounds that are known poisons (like sulfur) even in very low concentration may have a more dominant effect on the Pt catalyst and the recoverability.

Anion-exchange membrane fuel cells (AMFCs) are of increasingly popular interest as they enable the use of non-Pt fuel cell catalysts, the primary cost limitation of proton exchange membrane fuel cells. Benzyltrimethyl ammonium (BTMA) is the standard cation that has historically been used in anion exchange membranes (AEMs)/AMFCs. BTMA degradation has been a topic of past studies; however, methodologies of degradation were not standardized or fully validated. In fact, in our efforts on the topic we had become perplexed by the variability of results between tests. In order to advance the state of the art technology in AMFC and the cations used therein, a standardized degradation method is necessary and would be of great value to the community. BTMA is a logical choice for developing a standardized method for cationic degradation in AMFCs. The method that will be presented in this presentation focuses on BTMA degradation studies in 2M KOH utilizing Teflon Parr reactors at varying temperatures and concentrations. NMR analysis was used to find the concentration of remaining BTMA at specific time points with GCMS analysis verifying product distribution. Our earlier studies involved the use of glass or quartz vessels and the use of internal NMR standards that were not isolated from the basic solution. High temperature, high hydroxide concentration studies have the potential of resulting in unintended reactions that can impact data interpretation regarding rates (e.g., our initial studies in glass vessels resulted in the appearance of precipitates/etched glass within the reaction vessels). Our current system contains only BTMA, additional base, and water, which are in contact with a sealed Teflon vessel. This experimental setup resulted in slower, more reproducible rates being observed for the degradation of BTMA, suggesting that the BTMA cation may be more robust than previously believed. Because BTMA is a relatively compact, easily synthesized, and potentially low cost cation, any other cations being pursued for use in AEMs should offer substantial advantages over BTMA for consideration for use in AEMs. Also appropriate baseline performance needs to be established. Although a caveat to this is that the stability of the free cation in solution may be different than that of the tethered cation in the AEM. The main pathway of BTMA decomposition leads to trimethyl amine and benzyl alcohol. Our findings conclude that, under these alkaline conditions, BTMA at 80 °C has negligible degradation over 2000 hours. Elevated temperatures (e.g., 120 and 160 °C) were utilized to accelerate the cation degradation process (Figure 1). BTMA was found to have a half-life of 600 hours (120 °C) and 9 hours (160 °C) at concentrations of 0.01 and 0.1M BTMA. These results show higher stability than previously reported.1,2The degradation rate appears to be identical at concentrations of 0.01 and 0.1M BTMA; however, at a concentration of 1.0 M, degradation rates were observed to be much higher. Additionally at 1.0 M, a second phase was observed and appeared to coincide with an increase in degradation rate. Employing a standardized degradation method, with BTMA stability as a baseline, will allow for a more accurate assessment of the relative stability of the next generation cations for use in AEMs. In addition, a more relevant and straightforward comparison between different cations and experimental conditions will be possible. References: (1) Bauer, B.; Strathmann, H.; Effenberger, F. Desalination 1990, 79, 125. (2) Enisla, B.; Chempath, S.; Pratt, L., Boncella, J.; Rau, J.; Macomber, C.; Pivovar, B. ECS TransactionsI 2007, 11, 1173.

The cost of the balance of plant (BOP) fuel cell system has increased in importance with recent decreases in fuel cell stack cost. In order to lower the cost of the BOP system, low cost but relatively clean components must be used. Selection of these materials requires an understanding of potential materials and the contaminants that evolve from them, which have been shown to affect the performance and durability of fuel cells. The present work evaluates the influence of leachable constituents from prospective materials and model compounds on the electrochemical performance of a platinum catalyst.

The mechanism of the thermal decomposition of a series of alkyl trimethyl ammonium hydroxides ([RMe{sub 3}N][OH], R = Et, n-Pr, i-Bu, PhCH{sub 2}, Me{sub 3}CCH{sub 2}) was studied using TGA, evolved gas analysis and NMR spectroscopy due to the importance of these and related ions in anion exchange fuel cell membranes. Isotopic labeling with deuterium showed that deprotonation of the methyl groups of the ammonium ions by deuteroxide establishes a rapid equilibrium between the tetraalkyl ammonium ions and the nitrogen ylide species and water that scrambles the deuterium with the proton on the methyl groups. The products of the thermal decomposition when R = Et, n-Pr, i-Bu are predominately olefins arising from Hoffmann elimination, while the neopentyl substituted ammonium ion gives only neopentyl trimethyl amine and methanol, the products of S{sub N}2 attack of hydroxide on the methyl groups. DFT studies of these reactions confirm the relative activation barriers that are observed in the experimental decomposition studies.

A systematic study that altered the number of β-hydrogen atoms susceptible to Hofmann elimination and introduced increased steric hindrance of substituted (ethyl, n-propyl, isobutyl, and neopentyl) alkyltrimethylammonium cations was performed. The mechanism of the thermal decomposition of these four ammonium cations in deuteroxide form was studied using evolved gas analysis (EGA) because of their potential importance in alkaline membrane fuel cells or electrolyzers. The products of the decomposition reactions are in many cases the expected Hofmann elimination products (trimethylamine and olefins), however, as the number of β-hydrogen atoms decrease or they become more sterically encumbered (from the addition of adjacent methyl groups), nucleophilic attack of hydroxide on the methyl groups increases in relative importance. The use of deuterated water and deuteroxide in our study shows that deprotonation of the tetraalkylammonium ions establishes a rapid equilibrium between the nitrogen ylide species that is formed by methyl group deprotonation and water that scrambles deuterium into the methyl groups of the amine. The results of this work show that at high temperature and low water content tetraalkylammonium hydroxide salts are relatively unstable in membranes.

The role of system contaminants in the performance degradation of Proton Exchange Membrane (PEM) fuel cells has been underappreciated to date. This work seeks to identify potential contaminants derived from balance of plant (BOP) system components with the ultimate goal of tying contaminant exposure to changes in PEMFC performance and durability. After accelerated aging of select assembly aid materials in DI water at 90{degree sign}C, the resulting leachant solutions were qualitatively and quantitatively characterized through a suite of analytical methods for organic and inorganic components. By design, the materials studied fall into a wide range of 'clean' and 'dirty' solutions. Potential routes of entry for species were examined for plausibility of identification, and determination of model compounds. Systematic identification and selection of model compounds provide the basis for in-situ and ex-situ testing to determine the potential degradation mechanisms and effects of these system contaminants on catalysis and membrane performance.

Transparent nanocomposites have been developed which consist of nanocrystals embedded in an organic matrix. The materials are comprised of up to 60% by volume of 7–13 nm crystals of the phosphor CexLa1−xF3, and are greater than 70% transparent in the visible region at a thickness of 1 cm. Consistencies of the nanocomposites range from a solid polymer to a wax to a liquid, depending on the workup conditions of the nanoparticle synthesis. These transparent nanophosphor composite materials have potential applications in radiation detection as scintillators, as well as in other areas such as imaging and lighting, and can be produced on large scales up to near-kilogram quantities at near ambient conditions, much lower in temperature than typical nanoparticle syntheses.

The cost and durability of polymer electrolyte membrane fuel cell (PEMFC) systems have limited their deployment. The relative cost of the balance of plant (BOP) has risen in importance with decreasing fuel cell stack cost. Lowering costs of PEMFC system components require the understanding of potential contaminants from these materials. System contaminants have received very limited attention publicly. We here present ex-situ leaching tests with materials that could be considered as gasket materials to quickly screen BOP component materials. Aliquots of the leachant solutions were collected periodically and analyzed (pH, conductivity, etc.) to identify and quantify contaminants. The influence of the leachant on the electrochemical performance of Pt was also investigated.

The role of system contaminants in the performance degradation of Proton Exchange Membrane (PEM) fuel cells has been underappreciated to date. This work seeks to identify potential contaminants of system components with the ultimate goal of tying contaminant exposure to performance and durability After aging of select polymers in solution, leachant samples were qualitatively identified via GCMS and FTIR-ATR. Total Organic Carbon (TOC) content quantitatively provided information relative to contaminant level extracted from polymeric samples. Results will be presented focusing on SBR rubber and neoprene. Qualitative concentration vs. time charts elucidate leachant evolution, showing among other things potential chemical degradation in solution.