Fuel Cell MEA Research Articles

Do Melamine and Melamine-Formaldehyde Surface Modifiers Improve Fuel Cell Activity and Durability?

Precious group metal-based catalysts based on Pt- and Pt-alloys are currently used as catalysts for the kinetically sluggish Oxygen Reduction Reaction (ORR) on the cathode of fuel cells. The activity of Pt or Pt-alloy catalysts towards ORR is severely compromised by the adsorption of spectator-species such as sulfonate anions from perfluorosulfonic acid (PFSA) ionomer or Pt-O(H)ad via water activation. Considering recent evidence pointing to the improvement in ORR activity via the use of melamine organic molecule or melamine-formaldehyde copolymeric additives as surface blocking agents for the prevention of sulfonate or Pt-OHad adsorption, we evaluated these additives in fuel cells. The catalysts were modified with either of these additives and characterized using ex situ and in situ methods to verify successful adsorption and eventual performance in fuel cells. These surface modifying agents were found to suppress Pt-OHad formation as well as suppress ORR activity. There was no evidence to point out that these additives improved ORR activity and H2/air polarization performance in a fuel cell MEA on supported, polycrystalline Pt catalyst.

Fabrication and Scale-up of Highly Durable Heavy Duty Fuel Cell MEAs

Medium and heavy-duty PEM fuel cells operate under much harsher conditions than light duty fuel cells and are expected to last 25,000 hours in the field. These systems must therefore operate successfully in the presence of impurities, starting and stopping, freezing and thawing, humidity and load cycling. Therefore, materials, components, and interfaces used in such systems need to be highly resistant to severe mechanical and chemical stress.Novel, highly active stable Pt and ordered PtCo intermetallic nanoparticles with well-controlled particle size and composition have been synthesized on a highly efficient PGM-free single metal active site rich carbon, to maximize their synergistic effects for enhanced performance and durability. These catalysts were integrated with a variety of ionomers (Aquivion, Nafion, HOPI and high O2 permeability ionomer (HOPI)) to further improve fuel cell performance and to achieve >600 mA/mgPt at 0.9 VIR-free with a mass activity loss less than 30% after 150k square wave accelerated durability cycles; and > 600 mA/cm2 (~65% efficiency) at 0.8 V, with a performance loss < 40 mV after 150K cycles (0.6 to 0.95 V).In a PEM fuel cell, the catalyst ink formulation and mixing processes control catalyst layer coating quality, electrode morphology, and the resulting fuel cell performance and durability. Catalyst ink properties are a result of complex solvent-catalyst-ionomer interactions that depend on the mixing method employed. Here, we will compare the performance and durability of electrodes made from bath sonicated inks for ultrasonic spray coating vs. ball milled inks for Meyer rod coating. Ink rheology and catalyst particle size will be used to correlate ink properties to electrode morphology and structure and ensure consistency from batch to batch, and from small lab scale to subsequent scale-up. We will evaluate and discuss the challenges that arise when transitioning from spray coating catalyst ink on a small scale, directly on a membrane, to coating more viscous inks on gas diffusion layers (GDLs), and finally developing a roll-to-roll (R2R) fabrication process. The MEA performance and durability of the novel catalyst will be evaluated under heavy duty operating conditions. Finally, the electrode performance and durability of R2R fabricated GDEs will be tested, and compared to small scale GDEs made at Giner.This work provides a comprehensive understanding of interactions between Pt, PtCo, carbon, ionomer, membrane, and GDLs and their impact on electrode structure, fuel cell performance and durability, as well as considerations for scale up to a R2R fabrication process. The attained information will be used to improve fuel cell electrode design, fabrication and scale-up.Acknowledgement: The project is financially supported by the Department of Energy’s Fuel Cell Technology Office under the Grant DE-FOA-0002360.

Whole life cycle performance degradation test and RUL prediction research of fuel cell MEA

Understanding the degradation mechanism and accurate prediction of the remaining useful life (RUL) of proton exchange membrane fuel cells (FCs) can provide guidance for improving durability and reducing their operation and maintenance costs. In this paper, we measured the actual lifetime of an FC for more than 7000 h until the end of its life and developed an RUL model based on the degradation mechanism. The particle filter (PF) algorithm was used to eliminate the influence of random errors on the key model parameters and on the prediction of RUL. RUL prediction was carried out and the contributions of key factors to FC voltage degradation were calculated and analyzed. The results demonstrated that the RUL of the FC could be accurately predicted with the RUL model and the PF algorithm. Over the lifetime of the FC, catalyst degradation was responsible for the majority of FC voltage degradation, contributing as much as 84. 3% of the performance degradation. In the latter stage of the FC lifetime, the rapid increase in leakage current caused by membrane degradation and the increase in MEA mass transfer resistance became increasingly significant, with their voltage degradation contribution rates increasing from 0.12% to 35.19% and from −4.04% to 14.32%, respectively. The influence of evolutions to the internal resistance on FC performance degradation was determined to be negligible.

PGM-Free Oxygen Reduction Reaction Electrocatalyst: From the Design to Manufacturing

Recently, a significant interess to the development of PGM-free catalysts for both the anode [1] and cathode [2] catalysts for the low temperature fuel cells resulted in increasing of their activity, stability and durability [3]. The activity of transition metal/nitrogen/carbon (M-N-C) materials already achieved ~30% of Pt/C. In order to further advance the research, development and commercialization of these materials Pajarito Powder, LLC utilizes the manufacturing platform under a trade mark VariPore™ which allow to control morphology and hydrophobicity/hydrophilicity, level of graphitization and final activity [4-8]. In a close collaboration with world leaders in MEA manufacturing EWII Fuel Cells these materials were integrated in high performed fuel cell MEAs, which were comprehensively tested in segmented cell at Hawaii Natural Energy Institute, University of Hawaii. All three organization are part of US DOE ElectroCat consortium.The synthetic approach is based forming the M-N-C ORR electrocatalyst from organic molecules (ranged from low molecular weight ones up to polymeric materials), which are combined with precursors of transition metals: M=Fe, Ni, Co, Mn. The main parameter which allow to control mentioned above properties is an addition to hybrid Organic-Transition Metal (TM) mixture the particles and pore forming agents (PFs). In the present work these agents were selected from the family of so called “hard templates”: silica, magnesia and a number of high surface area oxides of transition metal. The fine mixture of Organic-TM-PF was heat treated in an inert atmosphere of nitrogen in order to create the matrix of the catalyst enriched with M-Nx active sites [3]. The catalytically inactive PFs were removed from the heat-treated material by the know-how leaching process developed at Pajarito Powder.The family of Fe-N-C materials prepared at Pajarito Powder by the VariPore™ method at the scale of 200 gram per batch were provided to the EWII Fuel Cell MEA manufacturing Team, where a series of MEAs were fabricated with a variation of catalyst:ionomer ratio, deposition method and other. The electrochemical evaluation of these MEAs at low potentials (OCV-0.85V) were performed at Hawaii Natural Energy Institute using a segmented cell. The main focus of these experiments was the understanding the PGM-free ORR behavior during the MEA activation and revealing the highest intrinsic ORR activity of these catalysts. It should be mentioned that all fuel cell experiments were performed at recommended by DOE ElectroCat consortium conditions and can be compared around the ElectroCat community as well as around research groups adopted these protocols. The details on the materials synthesis and evaluation will be presented.Acknowledgments:We would like to acknowledge the financial support from US DOE EERE under the grant DE-EE0008419 “Active and Durable PGM-free Cathodic Electrocatalysts for Fuel Cell Application” (PI: Alexey Serov).

Determination of Ce3+ and Co2+ Diffusion Coefficients in NR211 Membrane

The proton exchange membrane fuel cell (PEMFC) is a promising clean energy propulsion system for automobiles and other vehicles. A critical component of the PEMFC is the polymeric ionomer membrane which enables proton conduction and provides a crucial barrier to both reactant gas crossover and electrical shorting. Many fuel cell systems employ thin (12-25 µm) perfluorosulfonic acid (PFSA) based membranes due to their superior mechanical and chemical stability properties. The primary product of a PEMFC is water, generated via the four-electron oxygen reduction reaction. However, smaller amounts of highly oxidizing species such as hydroxyl radical (•OH), and hydrogen peroxide (H2O2) are generated either chemically or electrochemically. These, and other, oxidizing species can react with non-fluorocarbon end groups or with acid side chain functional groups to degrade and weaken the polymeric membrane until causing a physical breach. In the absence of effective chemical mitigation, proton exchange membranes will survive no more than a few hundred hours of operation under typical automotive duty cycles involving large humidity and potential variations. Fortunately, PFSA lifetimes can be extended up to and beyond 10,000 hours of operation using •OH redox quenchers such as Ce3+ and Mn2+ that efficiently reduce •OH to H2O. The remarkable effectiveness of these redox quenchers is due to their high competitive activity toward •OH reduction and the rapid and benign reduction of the oxidized metal to the reduced form via reaction with ubiquitous H2O2. Within an ionomer, cations, including Ce3+, associate (ion pair) with the negatively charged sulfonate groups to varying degrees and have been observed to diffuse in-plane on the centimeter length scale during ten to100 hours of fuel cell operation. More rapid migration of cations into the electrode layers has been observed over the µm length scale of MEA thickness. The movement of cations within the MEA is governed by local water content (λ = n H2O/-SO3 -), water content gradients (Δλ) and electrical potential gradients. The observed in-plane movement of Ce3+ and other cations such as Co2+ can lead to large cation concentration gradients within a fuel cell MEA. This redistribution of cations can have a significant impact on cell performance and mitigation of chemical degradation processes. Accordingly, there is great interest in understanding and quantifying the factors that govern cation movement to optimize fuel cell efficiency and durability. We will report the in-plane isotropic diffusion coefficients of Ce3+ and Co2+ within NRE211 membrane over a wide range of uniform temperature and relative humidity values. The cation concentrations have been monitored using a variety of analytical techniques including FTIR, x-ray fluorescence and UV spectroscopy (Figure 1). The derived diffusion coefficients show a strong dependence on both temperature and relative humidity value (water content) and are consistent with the macroscale redistribution of cations seen in operating fuel cells. Quantitative structure activity relationships and cation movement under RH gradients will also be discussed. Figure 1

Comparing Novel PGM-Free, Platinum, and Alloyed Platinum Catalysts for HT-PEM Fuel Cells

The Nyquist plot of impedance spectra of high-temperature polymer electrolyte fuel cells (HT-PEMFCs) is recorded to characterize the polarization losses. However, without further analysis, it only gives qualitative information about the overpotential of the inspected fuel cell, as the overlapping arcs in the Nyquist plot cannot be distinguished by mere eye. The Distribution of Relaxation Times (DRT) analysis is a powerful tool used to resolve the individual contributions to the impedance spectrum and to allocate them to their respective frequencies [1]. The peaks in the DRT spectrum can be sectioned into frequency ranges related to mass transport, the oxygen reduction reaction (ORR) and high frequency impedance related to anode processes and proton transport [2], as seen in Figure 1 a). In this work, we evaluate the performance of three catalysts by analyzing their impedance at different frequencies using DRT and explaining the catalytic behaviour. The three catalysts are a standard platinum catalyst (Pt on Vulcan X-72, Heraeus), a platinum alloy catalyst (Pt0.7Co0.3, Tanaka), and a novel Fe-C-N catalyst, a highly active and durable catalyst of the platinum-free, transition metal-nitrogen-carbon family, derived from Nicarbazin and possessing an open frame structure which is controlled by a silica sacrificial support method [3]. For each material, we assembled a HT-PEM fuel cell MEA and recorded polarization curves and EIS spectra at 100 mAcm-2. This data is shown in Figure 1 b) and c). The EIS spectra were processed using the DRT method (Figure 1 a) and yielded the frequency resolved impedance, giving insight into the processes causing the performance differences. Quantitative results were obtained by DRT analysis for the operation of the cells at 100 mAcm-2. We found the platinum/cobalt alloy catalyst to be outperforming platinum with an increased ORR activity, explained by the facilitated adsorption and reduction of oxygen resulting from the lower interatomic distance in the alloyed catalytic system [4]. The Fe-N-C system exhibits a lower performance compared to the noble metal catalysts, showing a significantly increased mass transport region and a higher ORR resistance. Contrary to our expectation, the mass transport resistance is dominating the ORR resistance. This can be explained by the narrow spaces in between the nitrogen-doped graphenic layers in which the reactive sites are present [3]. The reactivity of the non-PGM active sites is not the primarily inhibiting factor of the performance. DRT proves to be a powerful tool to inspect the impedance of a fuel cell in great detail and to learn about the inner mechanisms, highlighting positive and negative aspects of different catalysts. This tool allows us to systematically investigate the performance of catalysts and to elucidate the influence of single parameters, making the optimization straight forward and focused instead of depending on trial and error experiments. 1. F. Ciucci, C. Chen, Electrochim. Acta, 167, 439 (2015). 2. A. Weiß, S. Schindler, S. Galbiati, M.A. Danzer, R. Zeis, Electrochim. Acta, 230, 391 (2017). 3. A. Serov, K. Artyushkova, P. Atanassov, Adv. Energy Mat., 4, 7 (2014). 4. C.V. Rao, J. Parrondo, S.L. Ghatty, B. Rambabu, J. Pow. Sources, 195, 3425 (2010). Figure 1

New Approach to Improve the DMFC Performance By Nafion-Functionalized Graphene Oxide Matrix Membranes Using the Electrochemical Exfoliation of Graphite As a Source of the Graphene Oxide

Direct Methanol Fuel Cell (DMFC) is one of the most attractive and effective source of energy for portable applications. Methanol, which is used as fuel, is a manageable liquid with excellent energy storage densities. Beside the advantages of the DMFC, some main issues are still present in the performance of this fuel cell. One of the major disadvantages is the methanol crossover, which is attributed to the transport along with water molecules. Nafion is the most common materials used as electrolyte membrane in fuel cells. It is a perfluorosulfonic acid polyetectrolyte polymer which has an excellent chemical stability and high proton conductivity. However, Nafion allows the methanol permeation from anode to cathode leading to a mixed potential and the reduction of methanol concentration at the anode side with the consequent decreasing of the fuel cell performance. Therefore, finding a membrane able to hinder the methanol permeation while maintaining the proton conductivity has been heavily researched [1, 2]. To minimize the methanol crossover problems in Nafion membranes, many researches focused on fillers to modify the Nafion membrane and create a barrier for the methanol or improve the water/methanol selectivity. Zeolites, zirconium, SiO2 or polypyrrole are some of the materials which were tested. Another approach to modify the Nafion membrane is developing mixed matrix membranes where the filler materials are incorporated in situ in the membrane along with the polymer[2]. Graphene oxide (GO) has unique properties for membranes applications because of its 2D structure and interesting mechanical and thermal stability. Moreover, abundant oxygen-containing functional groups provide amphiphilic nature and allow convenient chemical functionalization, which makes this material and its derivatives promising inorganic filler for composite membranes. Different studies have been carried out for The University of Manchester to prove that incorporating CVD Graphene and GO into the different layers of the PEM fuel cell MEAs, improves the overall performance of the fuel cell [3,4]. This work presents a new functionalized GO-Nafion mixed matrix membrane in order to enhance the DMFC performance by decreasing the methanol crossover. The GO is produced by Electrochemical Exfoliation of Graphite (EGO) as an alternative to the traditional Hummer’s method. EGO has been presented as a green and cost-effective approach for producing high quality of graphene in high yield using simple equipment [5-7]. Further functionalization of GO will improve the compatibility of the graphene-based material with the Nafion and allowing less methanol crossover and higher proton conductivity.

Membrane-Electrode-Assemblies with Electrospun Fiber Mat Electrodes for Hydrogen/Air Fuel Cells

When MEAs are made by a decal, catalyst-coated-membrane, or catalyst-coated GDL method, there is little or no control over the macro-scale organization of the catalyst and binder. Thus, the high ORR catalytic activity of Pt-based catalysts seen in rotating disk experiments is rarely observed in an operating fuel cell MEA. Features such as particle and binder interconnectivity, macroporosity, and microporosity become more critical when high-performance nanomaterial catalysts are employed in fuel cell electrodes. Consequently, new electrode fabrication techniques are needed for next-generation MEAs. Nanofiber electrospinning is just such a method, which can address fuel cell electrode manufacturing and structure/performance issues. As a fabrication method, electrospinning is scalable, robust, and cost-effective, especially for the creation of non-woven mats of sub-micron diameter polymer fibers. Although not as well studied, the method can also be used to prepare particle/polymer fiber networks with high particle loading and high intra- and inter-fiber porosity. Mats from such fibrous materials can be used as electrodes in fuel cells [1-4], batteries [5,6], and capacitors [7], where high interfacial electrode area is of prime importance. In this talk, recent experimental work on nanofiber mat cathodes for hydrogen/air fuel cells will be described. Procedures for fabricating high particle-loaded nanofibers containing various Platinum and platinum-alloy catalysts with different polymer binders will be presented. The effects of catalyst type/loading and binder type on cathode mass activity and electrochemical surface area, cathode durability, and fuel cell power output at high and low relative humidity conditions will be discussed. Acknowledgments This work was funded by the Fuel Cell Consortium for Performance and Durability, DOE-EERE FC-PAD Project DE-EE0007653. References Zhang and P. N. Pintauro, ChemSusChem, 4, 1753-1757 (2011).Brodt, R. Wycisk, and P. N. Pintauro, J. Electrochem. Soc., 160, F744-F749 (2013).Brodt, T. Han, N. Dale, E. Niangar, R. Wycisk, and P. Pintauro, J. Electrochem. Soc., 162, F84-F91 (2015).Brodt, R. Wycisk, N. Dale, and P. Pintauro, J. Electrochem. Soc., 163, F401-F410 (2016).C. Self, R. Wycisk, and P. N. Pintauro, J. Power Sources, 282, 187-193 (2015).Self, E. McRen, P. N. Pintauro, ChemSusChem, 9, 208-215 (2016).Gao, Z. Shao, J. Li, X. Wang, X. Peng, W. Wang and F. Wang, J. Mater. Chem. A, 1, 63-67 (2013).

(Invited) MEA Studies of Transition Metal Nitride Core-Pt Shell Materials for Fuel Cell Applications

Since the first report of Pt monolayer core-shell catalysts by Adzic’s group(1), attractive owing to both their high Pt utilization and ECSAs, numerous efforts have been devoted to the development of these electrocatalysts for fuel cell applications(2-6). Although many varieties of core-shell catalysts have demonstrated improved activity and durability under RDE conditions, reports on the MEA-level tests are still limited(4). Moreover, since a majority of the reported core materials include significant precious metals (e.g. Pd, Au, etc.), the overall cost of the catalysts remains an ongoing concern. Further, the stability of non-precious metal components (Ni, Co, etc.) in the core still presents severe challenges precluding widespread adoption. To address these concerns, various efforts has been devoted to develop durable electrocatalysts with low or non-PGM cores. Nitridation of the core materials is one promising approach to realizing low cost, durable catalysts. Transition metal nitride cores have exhibited enhanced durability for the oxygen reduction reaction at the RDE level(6, 7). Here we report the development of metal nitrides as catalyst cores or support materials and their performance in fuel cell MEAs. Initial results show durability improvements coupled with higher retentions of Pt mass activities and electrochemical surface areas. These results indicate that Pt monolayer catalysts with metal nitride cores or supports are potential candidates for next-generation fuel cell electrocatalysts. Reference R. Adzic, J. Zhang, K. Sasaki, M. Vukmirovic, M. Shao, J. Wang, A. Nilekar, M. Mavrikakis, J. Valerio and F. Uribe, Top. Catal., 46, 249 (2007).H. Yang, Angew. Chem., Int. Ed., 50, (2011).C. Koenigsmann, A. C. Santulli, K. Gong, M. B. Vukmirovic, W.-p. Zhou, E. Sutter, S. S. Wong and R. R. Adzic, J. Am. Chem. Soc., 133, (2011).K. Sasaki, H. Naohara, Y. Choi, Y. Cai, W.-F. Chen, P. Liu and R. R. Adzic, Nat Commun, 3, (2012).K. A. Kuttiyiel, K. Sasaki, Y. Choi, D. Su, P. Liu and R. R. Adzic, Nano Lett., 12, (2012).X. Tian, J. Luo, H. Nan, H. Zou, R. Chen, T. Shu, X. Li, Y. Li, H. Song, S. Liao and R. R. Adzic, J. Am. Chem. Soc., 138, (2016).K. A. Kuttiyiel, Y. Choi, S.-M. Hwang, G.-G. Park, T.-H. Yang, D. Su, K. Sasaki, P. Liu and R. R. Adzic, Nano Energy, 13, (2015).

Novel Fuel Cell MEA Based on Pt-C Deposited by Magnetron Sputtering

Based on the concept of single atom catalysis for the development of low-cost catalytic materials and supported metal nanostructures (most widely used type of heterogeneous catalyst in industrial processes) a novel Pt-C composite catalysts was developed for the proton exchange membrane fuel cell (PEMFC) application. Nanostructured Pt-C thin films catalysts with thickness range 25-150 nm were deposited on carbon paper gas diffusion layer substrates covered with standard microporous layer (MPL) by magnetron sputtering method. Total Pt loading in the thin films varied in the range 5.5-60 µg/cm2 as determined by XPS. These thin film catalysts were examined for their activity at both sides of proton exchange membrane fuel cell. Thin film catalyst with total Pt loading of 19.9 µg/cm2 giving maximum power of 0.93 W/cm2 was checked during 450-h accelerated durability test. The average cell voltage decay of only 15.6 µV/h showed very high catalyst stability despite very low loading of noble metal.

Mitigating Membrane Degradation: Investigation of Lifetime and Fluoride Emission Rate from Modified Short-Side-Chain and Long-Side-Chain PFSA Membrane Electrode Assemblies during High Temperature Open Circuit Voltage Hold

The incorporation of radical traps in the membrane or electrode of a fuel cell MEA based on perfluorosulfonic acid (PFSA)type ionomers has emerged as an important development enabling much increased fuel cell lifetime. Effective radical scavengers include transition metal ions and their oxides, in particular of cerium. We have developed novel nanofibre-networks comprising inorganic and organic polymer radical trap materials for incorporation either within the membrane or at the membrane electrode interface of MEAs comprising long-side-chain (LSC) and short-side-chain (SSC) PFSA membranes. MEAs were submitted to open circuit voltage hold testing at 50% relative humidity and 90 °C and the voltage decay and fluoride and sulfur emission rates were monitored with time. MEAs were investigated post-mortem for evidence of Pt migration (SEM-EDX), cerium migration where relevant, and PFSA backbone modification (19F NMR, Raman and XPS spectroscopies). The results show that non-protected SSC PFSA MEAs have a significantly lower (factor >20) fluoride emission rate on OCV hold than non-protected LSC PFSA MEAs, and the interpretations of this finding will be discussed. Implementing a nanofibre PFSA network enriched with cerium oxide nanoparticles at the membrane electrode interface at the anode side further reduces the FER of SSC PFSA MEAs, such that fluoride emission rate of anode-protected Aquivion® E79-03S MEAs is 300 times lower than that of non-protected Nafion®-212. These results will be compared in this presentation with those obtained on embedding a polymer nanofibre radical scavenger within PFSA membranes such as to establish a ranking of the effectiveness of CeOx type and alternative polymer type radical scavengers in reducing fluoride loss and membrane thinning, and extending MEA lifetime.

Combinatorial discovery of Ni-based binary and ternary catalysts for hydrazine electrooxidation for use in anion exchange membrane fuel cells

Ni-based catalysts, binary Ni–M (with M = Mn, Fe, Zn, La) and ternary Ni–Mn–Fe and Ni–Zn–La were investigated for hydrazine oxidation in direct hydrazine hydrate fuel cell anodes by a temperature controlled 16-channel electrochemical combinatorial array. The binary Ni0.8Zn0.2 and Ni0.9La0.1 catalysts are significantly more active than the Ni reference catalyst for hydrazine oxidation. While the best Ni0.8Zn0.1La0.1 ternary catalyst is close to the high active binary catalysts in composition. Additionally, Ni0.6Fe0.2Mn0.2 catalysts also showed high catalytic activity for hydrazine oxidation in alkaline media over standard Ni catalyst. The X-ray diffraction (XRD) analysis indicated that the alloying effect between Ni and added elements improves the catalytic activity for hydrazine oxidation. As a result of the screening tests and our previous research, unsupported binary Ni0.87Zn0.13 and Ni0.9La0.1 catalysts were synthesized by spray pyrolysis and tested in a direct hydrazine hydrate fuel cell MEA (DHFC) producing 486 mW cm−2 and 459 mW cm−2, respectively.

Position dependent analysis of membrane electrode assembly degradation of a direct methanol fuel cell via electrochemical impedance spectroscopy

The performance of a direct methanol fuel cell MEA degraded during an operational period of more than 3000 h in a stack is locally examined using electrochemical impedance spectroscopy. Therefore, after disassembling the MEA is cut into small pieces and analyzed in a 1 cm2 test cell. Using a reference electrode, we were capable of measuring the anode and cathode spectra separately. The spectra of the segments at different positions do not follow a specified trend from methanol inlet to outlet of the stack flow field. The anode spectra were analyzed with an equivalent circuit simulation. The conductance of the charge transfer was found to increase with current density up to a point where a raising limitation process of the complex methanol oxidation dominates, which is not a bottleneck at low current density. Further, an increase of the double layer capacitance with current density was observed. The diffusion resistance was calculated as an effective diffusion coefficient in the order of 10−10 m2 s−1; implying that the diffusion limitation is not the bulk diffusion in the backing layer. Finally, the degree of poisoning of the catalysts by carbon monoxide was measured as a pseudo inductive arc and decreases with increasing current.

Electrooxidation of hydrazine hydrate using Ni–La catalyst for anion exchange membrane fuel cells

Carbon supported Ni, La, and Ni1−xLax (0.1 ≤ x ≤ 0.9) catalysts were synthesized by an impregnation/freeze-drying procedure followed by thermal annealing. The catalytic activity for electro-oxidation of hydrazine hydrate on anionic ionomer-coated catalysts was evaluated using a (4 × 4) 16-channel electrochemical electrode array in 1.0 M KOH + 1.0 M hydrazine hydrate solution at 60 °C. The Ni0.9La0.1/C catalyst oxidized hydrazine hydrate at a lower potential and exhibited higher mass activity in comparison with a similarly made Ni/C catalyst. Chemical insight suggests that the cause of improved performance for the Ni0.9La0.1/C catalyst is likely multifunctional synergism of the components. However, X-ray absorption fine structure (XAFS) and high voltage electron microscopy (HVEM) unexpectedly show some hcp−LaNi5 shells coating the fcc−Ni catalyst particles. As a result of the screening tests, an unsupported Ni0.9La0.1 catalyst was synthesized by spray pyrolysis and tested in a direct hydrazine hydrate fuel cell MEA (DHFC) producing 453 mW cm−2.

Investigation of the local catalyst distribution in an aged direct methanol fuel cell MEA by means of differential synchrotron X-ray absorption edge imaging with high energy resolution

Synchrotron X-ray absorption edge imaging with high energy resolution was applied to study aging of fuel cell catalyst materials. The combination of an imaging and a high X-ray energy resolution set-up allows acquiring spatially resolved XAS (XANES and EXAFS) spectra. We analyzed the two-dimensional distribution of Pt and Ru in fresh and aged fuel cell catalysts. Spatially resolved XAS images were taken at the RuK edge and at the PtL3 edge. Taking radiographs above and below the absorption edges provides quantitative information about the thickness of the catalytic materials and additional chemical information. A strong influence of the flow field channels and the structure of the gas diffusion layers on the thicknesses of the catalytic elements were found: a thinner catalyst layer was found below the ribs of the flow field geometries as well as under crossing points of fiber bundles of the woven gas diffusion layers.

Effect of Gas Diffusion Layer Design on PEM Fuel Cell MEA Water Removal in an Under Humidified Environment

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Ionomers for Alkaline Fuel Cell Electrodes and MEAs

not Available.

Oxygen activation over engineered surface grains on YDC/YSZ interlayered composite electrolyte for LT-SOFC

This paper reports the role of surface grain boundaries in enhancing oxygen incorporation kinetics on oxide ion conducting yttria-doped ceria (YDC) ceramic electrolyte. Thin YDC interlayered (∼400 nm) YSZ composite electrolyte was successfully fabricated by pulsed laser deposition (PLD) on the cathode side of 100 μm-thick polycrystalline substrate. Oxygen isotope exchange experiment was conducted employing secondary ion mass spectrometry (SIMS) with high spatial resolution (50 nm). Surface mapping result of 18O/ 16O shows that high activity at surface grain boundary regions indicating that the grain boundary regions are electrochemically active for oxygen incorporation reaction. In addition, fuel cell current–voltage measurements and electrochemical impedance spectroscopy study were performed in the temperature range of 350–450 °C on surface-engineered electrode-membrane assemblies (MEA) having different YDC surface grain sizes. Results from both dc and ac measurements confirm again that fuel cell MEAs having smaller surface grain size show better performance than large grain surfaces. Up to 4-fold increase was observed in power density and correspondingly lower electrode interface resistance. The collective results of SIMS and electrochemical measurements indicate that the YDC grain boundary regions at the cathode side are electrochemically active for oxygen surface kinetics. The results of this study provide an opportunity and incentive for designing high performing LT-SOFCs by surface engineering of YSZ electrolyte with nano-granular, catalytically superior thin YDC cathodic interlayers.

Nano to Micro Scale Characterization of Water Uptake in PEM Fuel Cell MEAs Measured by Scanning Transmission Soft X-ray Microscopy

not Available.

Ex Situ Potentiostatic and Potentiodynamic Durability of Low Pt Loading Fuel Cell MEAs

not Available.