Fuel Cell Operating Conditions Research Articles

Fracture Properties of Catalyst Coated Membranes

Recent studies have shown that a suitable approach for analyzing the mechanical durability of fuel cell stacks is to study the mechanical behavior of catalyst coated membranes (CCMs) under hygrothermal loading conditions [1–4]. Previous studies have also indicated that under cyclic mechanical and hygrothermal loadings, cracks are initiated and propagated inside the membrane [5,6] eventually leading to the cell/stack failure. The crack propagation rate of pure membranes is found to be a strong function of applied stress, temperature, and humidity [7]. Given the significant difference in mechanical properties of pure membrane and CCM [1], their crack propagation characteristics can also be expected to differ. In an operating fuel cell, this implies that a crack could potentially propagate differently when it has penetrated through the entire CCM compared to when it is confined within the membrane. To investigate this, a series of experiments were conducted to characterize the rate of crack propagation in the CCM. Rectangular specimens with a width of 10 mm and artificially created double edge cracks were used. The initial crack length on each side was approximately 0.7 mm. Under pre specified levels of environmental conditions (temperature and relative humidity), the specimens were subjected to cyclic mechanical loading [3–6] which led to crack propagation as shown in Fig. 1. The rate of crack propagation as a function of loading and environmental conditions was measured and analyzed. It is found that at elevated levels of relative humidity and temperature, the sensitivity of propagation rate to the applied mechanical loading increases.In a parallel study, a fracture mechanics model based on Paris Law theory and capable of simulating the ex situ crack propagation in the CCM during typical fuel cell operating conditions is developed. The model incorporates the characteristic time, temperature, and humidity dependent elastic-viscoplastic mechanical behaviour of CCMs [1] through a sub model developed using the finite element method (FEM) in COMSOL Multiphysics® . The stress-strain relationship of CCM simulated by the FEM sub model is validated at all combinations of 23 ºC and 70ºC temperature, 50% and 90% relative humidity; and 0.0001 s-1 and 0.001 s-1 strain rates. Fundamental fracture mechanics parameters, viz. J-integral, stress intensity factor (K), and configuration correction factor (ccf) are obtained iteratively for incremental changes in the crack length. These parameters together with the experimental crack propagation data enable the construction of Paris Curves at various temperature and humidity conditions. Information from the Paris Curves is used to predict the time taken by a CCM crack to increase from initial crack length ai to final crack length af under typical fuel cell conditions. The CCM crack propagation data collected and simulation capability developed during this work are considered to be important contributions towards developing a holistic understanding of mechanical fatigue and fracture phenomenon which are active during fuel cell operation and which ultimately lead to its failure. Acknowledgements: This research is supported by Ballard Power Systems and the Natural Sciences and Engineering Research Council of Canada through an Automotive Partnership Canada (APC) grant.

Non-PGM membrane electrode assemblies: Optimization for performance

The performance of non-platinum group metals (non-PGM) iron–nitrogen–carbon (Fe–N–C) based cathode in fuel cell operation conditions was studied. The effect of Nafion to catalyst ratio as well as carbon additives on the activity was studied. It was found that ionomer plays a key role in proton and water transport within the MEA. To compensate intrinsic low electronic conductivity of Fe–N–C materials additional carbons such as Vulcan XC72R, Ketjen Black 600 EC, and carbon nanotubes (CNTs) were added to MEA inks. X-ray Phototelectron Spectroscopy studied the effect of these carbon additives on chemical composition of catalysts. It was determined that inks with 35 wt% of Nafion ionomer resulted in the optimal performance of the Fe–N–C cathode catalyst in the air.

Electrocatalytic activity and operational stability of electrodeposited Pd–Co films towards ethanol oxidation in alkaline electrolytes

Direct alkaline ethanol fuel cells (DEFCs) are usually run with Pd anodic catalysts, but their performance can be improved by utilizing alloys of Pd and Co. The oxyphilic Co serves to supply ample –OH to the ethanol oxidation reaction, accelerating the rate limiting step at low overpotential under alkaline conditions. Pd–Co films with compositions between 20 and 80 at% Co can be prepared by electrodeposition from a NH3 complexing electrolyte. Cyclic voltammetry studies show that the ethanol oxidation peak exhibits increasing current density with increasing Co content, reaching a maximum at 77% Co. In contrast, potentiostatic measurements under conditions closer to fuel cell operating conditions show that a 50 at% Co alloy has the highest performance. Importantly, the Co–Pd film is also found to undergo phase and morphological transformations during ethanol oxidation, resulting in a change from a compact film to high surface area flake-like structures containing Co3O4 and CoOOH; such a transformation instead is not observed when operating at a constant potential of 0.7 VRHE.

Water uptake and swelling hysteresis in a nafion thin film measured with neutron reflectometry.

Water uptake and swelling in a thin (∼15 nm) Nafion film on SiO2 native oxide on a Si wafer is studied as a function of relative humidity (8-97%) at room temperature and as a function of temperature (25-60 °C) at 97% relative humidity by neutron reflectometry. This is the first report on the behavior of thin Nafion films at elevated temperatures and high humidity. Large hysteresis is observed during the temperature cycle. The observed swelling strain in the film at 60 °C is 48% as compared to the as-deposited state, which is far above any previously observed trend at room temperature. A small decrease in the average SLD suggests that part of the additional swelling is due to thermal expansion, but the estimated D2O/SO3 ratio also increases by 70%. Half of the "excess" absorption and 73% of the additional swelling are retained during cooling back to room temperature. The results provide new insights into the dynamics of Nafion on nanometer scales under fuel cell operating conditions.

Multiple Advance Diagnostics to Probe the Effect of Balance of Plant Materials on Fuel Cell Performance

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.

An Innovative Carbonate Fuel Cell Matrix

Introduction The electrolyte matrix is a microporous ceramic structure sandwiched between the electrodes to isolate the fuel from the oxidant, store electrolyte and facilitate ionic transport. The electrolyte distribution and fill levels in carbonate fuel cell are controlled by the balance in capillary forces of the porous cell components. The matrix needs to remain completely filled; therefore, pores are required to be fine and significantly smaller than the electrodes to exert sufficient capillary force to prevent electrolyte from moving to the electrodes at all times during endurance operation. A balanced pore structure between matrix and electrodes is necessary to avoid electrodes flooding and gas cross-over and to maintain stable cell resistance (1). FCE has advanced direct fuel cell (DFC) electrolyte matrix over the years and demonstrated that the matrix meets the requirements for greater than 5 year life based on accelerated tests and field stack operations. However, development of advanced designs and materials that can further increase the performance and extend cell life will enable accelerated MCFC deployment. This paper will report the progress on the development of an unique and innovative matrix design that offers numerous benefits to the carbonate fuel cell performance and durability. In addition, this paper will also review parameters that affect matrix material stability and approaches to extend cell life. Experimental Experiments were performed with button and single cells (3 cm2 and 250 cm2, respectively). Each cell consisted of a porous Ni-alloyed anode, a porous in-situ lithiated NiO cathode and a porous matrix (LiAlO2) filled with the carbonate electrolyte. Tests were performed at different temperatures under standard fuel (72.8%H2-18.2%CO2-9%H2O) and oxidant (18%CO2-12%CO2-67%N2-3%H2O) conditions. Other specially designed out of cell tests (OCT) were also performed at different temperatures and gas atmospheres to investigate parameters and processes affecting matrix material stability. Different techniques such as XRD, SEM, Mercury porosimetry, AC-impedance and steady-state polarization were carried out to evaluate and characterize matrix stability under fuel cell operating conditions. Results and Discussion The carbonate fuel cell matrix stability holds an important key to maintain higher electrolyte capacity and longer service life. The matrix particles (LiAlO2) stability is mainly controlled by the material purity, particles uniformity, temperature and electrolyte composition. Literature studies and accelerated tests showed localized matrix particles coarsening during long-term use. Such coarsening may lower capillary force, leading to an increase in cell ohmic resistance and gas crossover. FCE has made a substantial improvement in the matrix structure and the mechanical strength to enhance electrolyte storage capacity and extend cell life. Figure 1 shows a comparison of the snap strength of the advanced and the conventional matrix designs. Results showed that the advanced matrix offers >40% improvement in mechanical strength and more than 20% reduction of large pores at (0.2µm). These improvements are projected to enable low electrolyte loss from the fuel cell matrix and extend cell life. This paper reports the requirements, approaches and progress in achieving a higher performance and longer life carbonate fuel cell matrix. Acknowledgement The advanced matrix research is funded by the Office of Energy Efficiency and Renewable Energy (EERE), U.S. Department of Energy, under Award Number DE-EE0006606 1. C. Yuh, A. Franco, L. Chen, A. Hilmi, R. Venkataraman and M. Farooque., “Liquid-Electrolyte Fuel Cells Electrolyte Management Progress,” 192, Fuel Cell Seminar and Energy Exposition, November 10-13, 2014, Los Angeles, CA. Figure 1

(Energy Technology Division Research Award) PEM Fuel Cell Electrode Layer Degradation

PEM fuel cells (PEMFCs) show great promise to increase the fuel efficiency for transportation applications; however, for this increase in efficiency to be implemented in a wide-spread manner, these systems need to be competitive with current technologies. As PEMFCs have evolved for transportation applications from prior applications (space and stationary), materials changes have been made to increase the power density and decrease the cost (including thinner, higher conductivity membranes and higher surface area/lower Pt loadings) that have negatively affected the durability. In addition, as these systems were developed for transportation, the operating conditions changed, including frequent start-up/shut-downs, power cycling, and higher temperature/lower relative humidity operation. While there has been significant progress in improving durability with lower cost materials, further improvements are needed to meet the commercialization targets. Past improvements have largely been made possible because of the fundamental understanding of the underlying degradation mechanisms. By investigating component and cell degradation modes and defining the fundamental degradation mechanisms of individual components and component interactions, new materials can be designed to improve durability. The primary degradation modes involve materials in the the electrode layer. The high cost of the noble metal(s) used as the catalyst makes this a crucial area requiring durability improvement. Other degradation modes include decreases in electrode kinetics and increases in resistance of both transport and conductivity. Although the electrode structure and durability thereof has been studied extensively, perfect solutions for commercialization do not yet exist. The primary degradation mechanisms within the cathode catalyst layer include catalyst nanoparticle stability, catalyst support degradation, porosity losses, and ionomer degradation. Catalyst support carbon corrosion occurs under normal fuel cell operating conditions and is exacerbated by the voltage cycling inherent in transportation drive cycles. An example of how the drive cycle potential cycling affects carbon corrosion, as measured by CO2 evolution, is shown in Figure 1. The peak in CO2 evolution occurs when the cell potential increases from high power operation to low power near open circuit. This correlates with when CO2 evolution is observed during cyclic voltammograms, which occurs during the positive sweep at ~ 0.55 to 0.60 V. The evolution of this CO2 peak suggests that oxygen is adsorbed onto the carbon and/or CO is formed on the Pt surface. Many materials and operating variables affect the amount of carbon corrosion, including the type of carbon support used, the Pt loading and dispersion, and operating conditions, such as relative humidity (RH) and temperature. Not surprisingly, high surface area carbons with a low extent of graphitization, exhibit the greatest amount of corrosion, followed by Vulcan carbon, which has some meso-graphitic structure, and the least amount of carbon corrosion occurs with graphitized, low surface area carbon (LSAC). Higher Pt loadings and poor Pt dispersions lead to higher rates of carbon corrosion, which in turn leads to loss of Pt surface area, thinning of the electrode layer, and increases in mass transport losses. However, as Figure 2 demonstrates, carbon corrosion is only a portion of the issues in play. Figure 3 shows the initial and final Pt particle sizes for the same carbon support materials. In this case, the Pt size (measured by XRD) is inversely correlated to the amount of carbon corrosion, with the greatest Pt size observed after shut-down/start-up ageing for graphitized LSAC carbon. Together with the other degradation mechanisms, a reduction in catalyst layer thickness is observed during drive cycle operation, which can be due to the loss of carbon through carbon corrosion or due to compaction; both effects likely lead to a loss of void volume. This reduction in thickness includes a sharp decrease in catalyst layer thickness within the first 100 hours of operation (30%), eventually reaching ~50% of its thickness after 1000 hours. Most of this reduction in electrode thickness does not appear to be directly due to carbon corrosion as there is little evidence for carbon corrosion from microscopic analysis, especially during the early stages of operation, where the thickness reduction is substantially more than what should be due to carbon corrosion. Acknowledgments Funding for this work is from DOE EERE FCTO, Technology Development Manager Nancy Garland I gratefully acknowledge all of my collaborators from Los Alamos, Ion Power, University of Nancy, Commissariat à l'énergie atomique et aux énergies alternatives, Argonne National Lab and Oak Ridge National Lab. Figure 1

N-Hexadecane Fuel for a Phosphoric Acid Direct Hydrocarbon Fuel Cell

The objective of this work was to examine fuel cells as a possible alternative to the diesel fuel engines currently used in railway locomotives, thereby decreasing air emissions from the railway transportation sector. We have investigated the performance of a phosphoric acid fuel cell (PAFC) reactor, with n-hexadecane, C16H34 (a model compound for diesel fuel, cetane number = 100). This is the first extensive study reported in the literature in which n-hexadecane is used directly as the fuel. Measurements were made to obtain both polarization curves and time-on-stream results. Because deactivation was observed hydrogen polarization curves were measured before and after n-hexadecane experiments, to determine the extent of deactivation of the membrane electrode assembly (MEA). By feeding water-only (no fuel) to the fuel cell anode the deactivated MEAs could be regenerated. One set of fuel cell operating conditions that produced a steady-state was identified. Identification of steady-state conditions is significant because it demonstrates that stable fuel cell operation is technically feasible when operating a PAFC with n-hexadecane fuel.

Optimization of perfluorosulphonic ionomer amount in gas diffusion electrodes for PEMFC operation under automotive conditions

ABSTRACT Perfluorinated sulphonic acid (PFSA) polymers such as Nafion® are widely used for both electrolyte membrane and ionomer in the catalytic layer because of their high proton conductivity (σH) as well as chemical and thermal stability. When PFSA polymers alternative to Nafion® with a different EW are used, it is necessary to optimize the composition of the catalytic ink, considering the different ionomer characteristics. Moreover, fuel cell operating conditions play an important role regarding the catalytic layer optimization. In this work, the influence of ionomer amount in the catalytic layer was evaluated. The electrochemical studies were carried out in a single cell in H2–O2 at intermediate temperatures (80 °C–130 °C) by using a fumapem® F-950 membrane as an electrolyte. A hydro-alcoholic dispersion of fumion® F was also used as an ionomer in the electrode catalytic structure with an amount ranging from 30 to 60%. Under operating conditions finalised to automotive applications (intermediate temperature, low relative humidity and low pressure of gases) an improvement of performance in terms of maximum power density was obtained by using optimized ionomer content.

In situ heater design for nanoscale synchrotron-based full-field transmission X-ray microscopy.

The oxidation of nickel powder under a controlled gas and temperature environment was studied using synchrotron-based full-field transmission X-ray microscopy. The use of this technique allowed for the reaction to be imaged in situ at 55 nm resolution. The setup was designed to fit in the limited working distance of the microscope and to provide the gas and temperature environments analogous to solid oxide fuel cell operating conditions. Chemical conversion from nickel to nickel oxide was confirmed using X-ray absorption near-edge structure. Using an unreacted core model, the reaction rate as a function of temperature and activation energy were calculated. This method can be applied to study many other chemical reactions requiring similar environmental conditions.

Elementary Kinetic Numerical Simulation of Ni/YSZ SOFC Anode Performance Considering Sulfur Poisoning

An elementary kinetic model is developed and applied to explore the influence of sulfur poisoning on the behavior of solid oxide fuel cell (SOFC) anodes. A detailed multi-step reaction mechanism of sulfur formation and oxidation at Ni/YSZ anodes together with channel gas-flow, porous-media transport and elementary charge-transfer chemistry is established for SOFCs operating on H2/H2O mixtures with trace amounts of hydrogen sulfide (H2S). A thermodynamic and kinetic data set is compiled from various literature sources. The derived chemical model, validated against sulfur chemisorption isobars taken from literature, is used to analyze performance drops of SOFCs working under typical fuel cell operating conditions. Electrochemical results show that at relatively low H2S concentrations SOFC button-cell performance can be interpreted using chemical sulfur formation. However, when the concentration is sufficiently high, the inclusion of second stage degradation and triple-phase boundary reconstruction is necessary to describe the performance decrease. Additionally, it is shown that the sulfur surface coverage increases with increasing current density. In order to shed more light on advanced fundamental understanding of cell poisoning, sensitive analyses toward total anode resistance and sulfur coverage for different operating conditions were performed.

Towards fuel cell membranes with improved lifetime: Aquivion® Perfluorosulfonic Acid membranes containing immobilized radical scavengers

A facile synthesis, based on a wet impregnation technique and a thermal treatment, of a novel silica-supported cerium-oxide-based radical scavenger bearing sulfonic acid functionalities is presented. This material is loaded as a filler in ePTFE reinforced membranes (called R79-02S) prepared starting from Aquivion® Perfluoro-Sulfonic Acid (PFSA) dispersions. The aim is to mitigate the peroxy radicals attack to the polymeric membrane under fuel cell operating conditions. These membranes show much longer (7 times more) life-time in Accelerated Stress Tests (AST) and reduced fluoride release (about one half) in Fenton's tests than the radical scavenger-free membrane without any loss in electrochemical performance. Scavenger-free Aquivion® PFSA-based membrane durability is about 200 h in AST whereas the same membrane containing the newly developed radical scavenger exceeds 1400 h. These results confirm the stability of the modified membranes and the excellent activity of the composite scavenger in mitigating the polymer electrolyte degradation.

A Versatile Preparation of Highly Active ZIF-Based Non-PGM Catalysts through Solid State Synthesis

Current proton exchange membrane fuel cell uses precious metal such as platinum as the catalyst to promote electrochemical reactions at both electrodes, which presents a significant cost barrier for large scale fuel cell commercialization. To replace precious metal with other low cost, earth-abundant materials represents a critical yet incredible challenging area in future fuel cell research. To compete with the precious metal based catalyst, the non-platinum group metal (non-PGM) materials must have higher active site density and improved turn-over-frequency. In this report, we discuss a new method of preparing “support-free”, low-cost non-PGM catalysts produced by using “one-pot” synthesized metal-organic frameworks. The new approach led to the formation of catalysts with high-density of active site and high efficiency towards the oxygen reduction reaction in the acidic medium, measured by rotating disk electrode in oxygen saturated electrolyte and under single fuel cell operating condition.

A New Family of Proton-Conducting Conducting Materials in Layered Oxides

To identify a good ionic conducting material for use as electrolyte for intermediate temperature solid oxide fuel cells (IT-SOFCs) remains a big challenge. In this report, we demonstrate that good proton conductor can be obtained in transition element rich intercalation materials such as LixAl0.5Co0.5O2. OCV of 1.0 ~ 1.1V was observed for a H2/air fuel cell at temperature 475 – 575 °C indicating it is nearly a pure ionic conductor under fuel cell operating conditions. A power density of 173 mW cm-2 has been achieved at 525 °C with a thick electrolyte (0.79 mm thick) when silver was used as both cathode and anode. The ionic conductivity of LiAl0.5Co0.5O2 was 0.1 S/cm at 500 °C, deduced from the series resistance of the H2/air fuel cell. This is the highest among known poly-crystalline proton-conducting materials. This study will provide a new approach to discover new proton conducting materials for use in IT-SOFCs. It is expected that an ideal proton-conducting oxide may be identified in layered oxides.

Effect of Au and Ru in Au@Pd and Ru@Pd Core@Shell Nanoparticles for Direct Formic Acid Fuel Cells

The study of Pd-based core@shell bimetallic catalysts with Pd as the shell and another transition metal as the core has generated great interest in the field of PEM fuel cells because their electronic and chemical properties are completely different from pure Pd. As the anode catalyst in direct formic acid fuel cells (DFAFCs), an enhanced activity has been obtained for these Pd-based core@shell nanoparticles compare to pure Pd for formic acid oxidation [1,2]. However, there is a lack of understanding of how these added transition metals interact with Pd, namely by influencing their electronic structure and chemical property toward electrochemical oxidation of formic acid. It is important to fill this knowledge gap and find out a trend between the effect of the transition metals and the activity. This will help developing more efficient and less cost DFAFCs.In this study, Au@Pd and Ru@Pd core@shell nanoparticles with same thickness of Pd are synthesized via a two-step process. Non-supported nanoparticles are used for TEM and X-ray photoelectron spectroscopy (XPS) analysis. TEM is used to characterize the structure and morphology of the nanoparticles. XPS is used to differentiate the chemical shifts due to charge transfer between Pd and Au (or Ru). XPS analysis shows a different binding energy shift for Pd peak of Au@Pd and Ru@Pd compare to that of pure Pd nanoparticles. In addition, a change of the XPS valence band shape and down-shift of the d-band center are also observed. This different binding energy shift indicates that Au and Ru core interact with Pd shell and significantly influence the electronic structure of Pd. Electrochemical measurements (cyclic voltammetry and chronoamperometry) are used to investigate the electrochemical activity of carbon supported Au@Pd and Ru@Pd core@shell nanoparticles toward formic acid oxidation. The Pd loading of the carbon supported samples is 40wt%. Based on CV results shown in Figure 1, Au@Pd shows the best activity toward formic acid oxidation, which is about twice higher than that of Pd/C. The relationship between the electronic perturbation and electrochemical activity will be elucidated in this paper. Furthermore, a real direct formic acid fuel cell test will be also operated with these Au@Pd and Ru@Pd core@shell nanoparticles under the various fuel cell operating conditions.

New Developments in Electrospun Nanofiber Electrodes for Hydrogen/Air Fuel Cells

The hydrogen/air proton-exchange membrane (PEM) fuel cell is a promising candidate for automotive power plants due to its high power output, moderate operating temperature, and quick start-up. The commercialization of such devices is hindered by the high price and inadequate durability of the platinum catalyst electrodes. Recent R&D efforts have been directed at reducing Pt loading and fabricating catalysts with supports that can withstand the harsh automotive operating environment. Work in this area includes the investigation of metal alloys, core-shell nanostructures, and metal oxide supports. Work on non-platinum group metal catalysts for the oxygen reduction cathode in a hydrogen/air fuel cell has also been reported. The creation of particle/polymer nanofiber mat electrodes via electrospinning represents an entirely different strategy for lowering cathode catalyst loading while maintaining high power output in a hydrogen/air fuel cell. A nanofiber electrode morphology with intra and inter-fiber porosity is advantageous because: (i) it increases catalyst contact with reactant gases, (ii) it provides a sufficient number of pathways for effective proton and electron conduction, and (iii) there is sufficient inter-fiber porosity for release of cathode product water. Previously, we have shown that more power was generated from nanofiber electrode MEAs than a conventional MEA with decal electrodes [1,2]. For example, the maximum power density for a H2/air fuel cell with a nanofiber cathode and anode (at loadings of 0.065 mgPt/cm2 and 0.10 mgPt/cm2, respectively) was 437 mW/cm2 vs. 400 mW/cm2 for a decal MEA with a cathode containing 40% more Pt (a loading of 0.104 mgPt/cm2) and an anode loading of 0.10 mg/cm2. In these experiments, the nanofiber catalyst binder was a mixture of Nafion® and poly(acrylic acid), the binder used in decal electrodes was neat Nafion, and the membrane was Nafion 212. The fuel cell operating conditions were: 80oC, 1 atm (ambient) pressure, 125 sccm H2, and 500 sccm air. As another example, an electrospun cathode with a Pt loading of 0.055 mg/cm2 produced a maximum power density of 906 mW/cm2 at 80°C and 3 atm pressure with 2000 sccm fully humidified air and 500 sccm H2. Additionally, the mass activity (0.16 A/mgPt at 0.9 V) and electrochemical surface area (~41 m2/g) of nanofiber cathodes containing Johnson-Matthey HiSpec™ 4000 catalyst were found to be very high and electrospun cathodes exhibited less degradation than a conventional decal cathode in an accelerated voltage cycling durability test.In this presentation, new catalyst/binder electrode formulations will be discussed, in terms of the conditions required to electrospin well-formed fibers and the performance of the fiber mats as cathodes in a hydrogen/air fuel cell operating at 80oC. MEAs are assessed in terms of the initial power density at high and low humidity operation and the changes in power output during voltage cycling Pt dissolution and carbon corrosion durability experiments. All anode and cathodes were prepared with Johnson Matthey HiSpec 4000 catalyst (40% Pt on Vulcan carbon), at a Pt loading of 0.10 mg/cm2. Acknowledgments This work was funded by EMD Millipore and the NSF-funded TN-SCORE program, NSF EPS-1004083, under Thrust 2. References W. Zhang and P. N. Pintauro, ChemSusChem, 4, 1753-1757 (2011).M. Brodt, R. Wycisk, and P. N. Pintauro, Journal of the Electrochemical Society, 160, F744-F749 (2013).

O2 Reduction at Se Modified Surfaces: Characterization by SPM and DEMS

Metal chalcogenides have been extensively studied as catalysts for oxygen reduction reactions, due to their tolerance for small organic molecules especially in relation to fuel cell applications. We have recently reported that also adsorption of Se on polycristalline Ru leads to an increased activity as compared to Ru.[1]. A theoretical study also showed that intermediate surface contents of Ru or Rh by Se or S lead to an increased activity.[2] However, fundamental studies on well-defined rhodium (Rh) single-crystal surfaces modified with chalcogenides (Se) are very rare. Here, irreversible adsorption of Se on Rh(111) was examined by voltammetric technique. Surface structure characterization of Se modified Rh(111) substrate was achieved using cyclic voltammetry and in situ STM and AFM. STM images also show a roughening starting at step edges for Se adsorption at certain potentials, similar to the roughening transition observed on Au(111) surface for S and Se adsorption [3][4] or As on Pt(111)[5], suggesting the formation of an. Se–Rh intermetallic compound. Results on the effect on oxygen reduction activity will be presented. It was observed that chalcogenides usually stripped off under fuel cell operating conditions [6] and also electrochemical hydrogen selenide formation at lower potentials [7].Here, we used differential electrochemical mass spectrometery (DEMS) for an additional quantitative characterisation of Se adlayers via reductive desorption on model fcc metal surfaces like [Rh(111), Pt(111) and Au(111)] References [1] N. Bogolowski, T. Nagel, B. Lanova, S. Ernst, H. Baltruschat, K. Nagabhushana and H. Boennemann, J. Appl. Electrochem., 37 (2007) 1485 [2] Tritsaris, G. A.; Nørskov, J. K.; Rossmeisl, J.; Electrochim. Acta 56 (2011) 9783.[3] C. Wei, N. Myung, K. Rajeshwar, J. Electroanal. Chem. 375 (1994) 109.[4] T.A. Sorenson, K. Varazo, D.W. Suggs and J.L. Stickney, Surf. Sci., 470 (2001) 197.[5] X.Y. Xiao and H. Baltruschat, Langmuir, 19 (2003) 7436.[6] D. C. Papageorgopoulos, F. Liu and O. Conrad, Electrochimica Acta 52 (2007) 4982.[7] M. O. Solaliendres, A. Manzoli, G. R. Salazar-Banda, K. I. B. Eguiluz, S. T. Tanimoto and S. A. S. Machado, J. Solid State Electrochem. 12 (2008) 679.

Enhanced Oxygen Evolution Activity of 3D Nanostructured Cobalt Oxides through Doping with Various Transition Metal Oxides

Photoelectrochemical water-splitting is one of the most renewable and clean ways to produce hydrogen by water electrolysis [1]. However, the oxygen evolution reaction (OER) in anode side of photoelectrochemical water-splitting system shows sluggish kinetics with the high polarization loss due to the 4-electron pathway likewise oxygen reduction reaction (ORR) in fuel cell operating conditions [2-5].Up to now, noble metals, such as iridium, ruthenium and platinum, have still used as OER catalysts [6]. In comparison with these noble metal catalysts, studies of transition metal oxide catalysts (TMOCs) for photoelectrochemical water-splitting systems have not carried out intensively, although they have similar (or more active) properties about OER [7, 8]. In addition, various state-of-art nanotechnologies for fabricating TMOCs may contribute to improve OER properties significantly for water-splitting [9, 10].In this work, a variety of nanostructured cobalt oxides (NCOs) are synthesized by the hydrothermal method using urea, hydrogen peroxide and polyvinylpyrrolidone. Then, various transition metal oxides are doped to NCO matrix during hydrothermal reaction. Their physicochemical properties were confirmed by using various analytic techniques such as SEM, TEM, BET, and XRD.For electrochemical characterizations, a rotating disk electrode system is adopted with an Ag/AgCl reference electrode and a Pt counter electrode in 0.1 M KOH electrolyte. A pretreatment where cyclic voltammetry (CV) post-purging nitrogen gas in the potential range of 0.05 – 1.2 V versus reversible hydrogen electrode (RHE) conducted at a scan rate of 100 mV s-1 for 50 cycles is used for activation of catalyst surface. The OER activity is measured by linear sweep voltammetry (LSV) from 1.2 to 1.7 V at a scan rate of 5 mV s-1 and is compared the oxygen evolution activity at specific current density. J. Jhang, K. Sasaki, E. Sutter, R. R. Adzic, Science, 315, 220 (2007).Y. Liang, Y. Li, H. Wang, J. Zhou, J. Wang, T. Regier, H. Dai, Nature Materials, 10, 780 (2011).J. Suntivich, K. J. May, H. A. Gasteiger, J. B. Goodenough, Y. Shao-Horn, Science, 334, 1383 (2011).J. Suntivich, H. A. Gasteiger, N. Yabuuchi, Y. Shao-Horn, Nature Chemistry , 3, 546 (2011).I. C. Man, H. Y. Su, F. C. Vallejo, H. A. Hansen, J. I. Martínez, N. G. Inoglu, J. Kitchin, T. F. Jaramillo, J. K. Nørskov, J. Rossmeisl, ChemCatChem, 3, 1159 (2011)T. Reier, M. Oezaslan, P.Strasser, ACS Catal., 2, 1765 (2012).Y. J. Sa, K. Kwon, J. Y. Cheon, F. Kleitz, S. H. Joo, J. Mater. Chem. A, 1, 9992 (2013).J. Y. Cheon, C. Ahn, D. J. You, C. Pak, S. H. Hur, J. Kim, S. H. Joo, J. Mater. Chem. A, 1, 1270 (2013).C. A. Wang, S. Li, L. An, Chem. Comm., 49, 7427 (2013).X. Rui, H. Tan, D. Sim, W. Liu, C. Xu, H. H. Hng, R. Yazami, T. M. Lim, Q. Yan, J. Power Sources, 222, 97 (2013). * Corresponding authors: jyoung@sejong.ac.kr (J.-Y. Park)

Effect of Organic Model Compound Contaminants on Platinum Catalysts

Polymer electrolyte membrane fuel cells (PEMFCs) hold great promise for providing clean energy without the use of fossil fuels. A major obstacle that must be overcome before PEMFC’s can successfully compete in a commercial market is durability [1]. The oxygen reduction reaction (ORR) occurring at the cathode is the limiting process in PEM fuel cell performance due to its high activation energy and slower kinetics compared to the hydrogen oxidation reaction at the anode [2]. The catalyst layer facilitating the reaction is typically composed of carbon supported platinum or platinum alloy and is highly susceptible to poisoning from contaminants either entering through the fuel or air streams or being introduced internally through system component degradation [3]. Thus, recognizing potential catalyst contaminants, understanding their adsorption characteristics and mitigating their subsequent performance effects are crucial to improving durability and enabling commercialization of fuel cells. Research has shown through studies involving commercial membranes and model compounds that when perfluorinated sulfonic acid (PFSA) membranes are exposed to hydroxyl radicals during fuel cell operating conditions, severe chemical decomposition products can be generated [4]. The main membrane degradation compounds of Nafion and 3M commercial membranes were identified by Zhou et al. [4]. Along with losses in membrane conductivity and structural integrity, such degradation products may also adsorb onto the Pt based electrocatalyst, possibly leading to a loss in catalyst electrochemical surface area (ECA), ORR activity, or both. To date, little effort has been reported on the impact PFSA degradation compounds have on catalyst performance.This work investigates adsorption characteristics and effects from several model compounds, representing PFSA membrane chemical degradation species, on ECA and ORR activity for platinum based electrocatalysts including polycrystalline Pt, high surface area carbon supported Pt, and extended surface Pt. Adsorption properties due to carboxylate and sulfonate functional groups, fluorocarbon chain length, and model compound concentration were investigated using a variety of electroanalytical techniques including cyclic and linear sweep voltammetry and electrochemical quartz crystal microbalance (EQCMB) will be reported.A rotating disk electrode electrochemical setup utilizing 0.1 M perchloric acid electrolyte (diluted from 70% HClO4 double distilled veritas grade, GFS Chemical) was used to study the effects of the several model compounds on the ORR activity of polycrystalline Pt as well as commercially available carbon supported Pt electrocatalysts. After injecting the model compound into the electrochemical cell and determining the effects on ECA and ORR activity, the electrode was then analyzed in clean electrolyte in order to monitor the recoverability of the activity loss for the Pt catalyst. EQCMB was used to measure the change in mass of the electrode as a function of potential, after the organic compound was added to the perchloric acid electrolyte.This work on the effect of membrane decomposition products on Pt ECA and ORR activity is part of a larger DOE-funded system contaminants project. To better understand the potential adverse effects that system contaminants may have on the fuel cell performance and durability and to lower the cost of balance of plant (BOP) components, the larger project studies families of BOP materials including structural materials, hoses, elastomers for seals and (sub)gaskets, and assembly aids (adhesives, lubricants). For more information, please see http://www.nrel.gov/hydrogen/contaminants.html.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 3M and GM. Membrane degradation products for this study were provided by 3M.

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.