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Power generation from electrochemical devices based on solid oxide fuel cells (SOFCs) is in great demand for both stationary and automotive applications to achieve carbon neutrality goals by 2050. In particular, SOFCs are known for their fuel-flexible operations; for example, SOFCs can operate on simple and complex renewable fuels (such as ethanol, natural gas, jet fuel, propane, etc.). Unlike H2-based fuel cells, liquid and hydrocarbon fuels in SOFCs adopt the existing fuel infrastructure and contribute to reducing greenhouse gas emissions significantly. This article presents the potential of using metal-based SOFCs (metal cells) as highly performing and durable power generators. The metal cells technology could be the most accessible solution for using SOFCs for versatile industrial needs.

A Metal-Supported-SOFC (MS-SOFC) has been modified by infiltrating a non-noble metal ceria-zirconia supported cobalt (Co/CZ) internal reforming catalyst to improve its reforming activity and inhibit the carbon deposition or coking under ethanol steam reforming conditions. Non-noble metal catalysts can still be deactivated during long-term cell operation in a severe coking-inducing environment. Therefore, an in-situ regeneration procedure was performed by pulsing air into the anode surface to burn the deposited carbon on the anode and catalyst layer during the cell operation. Upon the cell regeneration steps, the cell voltage was recovered to its initial condition at ~0.8 V, while the peak power density of the cell showed up to 116% recovery under H2 and 111% recovery under ethanol. These data show that the air pulsing regeneration steps in the MS-SOFC can improve the lifetime by removing the coking deposit within the anode and further enhancing its electrochemical and catalytic activity.

Stainless steel interconnects in solid oxide fuel cells can lead to chromium poisoning of the cathode, necessitating the use of protective coatings. Electrophoretic deposition is an efficient method to deposit coatings on substrates with complex microstructures. In this study, four spinel coatings; CuMn2O4, CuNi0.2Mn1.8O4, MnCo2O4, and MnFe0.34Co1.66O4, were deposited by direct-current electrophoretic deposition on flat SUS430 stainless steel substrates. The coatings were evaluated on multiple criteria, including microstructural stability, conductivity, Cr gettering ability, and the ability to act as a diffusion barrier at 700°C and 800°C. It was concluded that CuNi0.2Mn1.8O4 is an excellent candidate at temperatures at and below 700oC, while MnFe0.34Co1.66O4 coatings perform better at higher temperatures.

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The metal-supported solid oxide fuel cell (MS-SOFC) is of current research interest in the clean energy field due to its high performance, quick start-up, thermal cycle stability, and lower raw material cost compared to the conventional cermet-based SOFC. To efficiently operate a MS-SOFC using complex hydrocarbon and logistic fuels, it is required to introduce an internal reforming catalyst within the anode metal scaffold. This review article discusses some examples of the performance of MS-SOFCs under hydrocarbon and logistic fuels with and without an additional reforming catalyst. We also discuss the performance improvement of conventional cermet-based SOFCs by adding reforming catalysts via the infiltration method. This information can be directly applied to future MS-SOFC applications. Furthermore, this review article proposes possible novel methods such as direct precursor infiltration, catalyst-anode premixing, and atomic layer deposition methods to introduce the reforming catalyst into a MS-SOFC for improving its initial electrochemical performance and long-term stability under hydrocarbon and logistics fuel.

In this work, praseodymium based double perovskite oxide, PrBa0.5Sr0.5Co1.5Fe0.5O5+ δ (PBSCF) cathode nanofibers were fabricated by electrospinning for intermediate-temperature solid oxide fuel cell (IT-SOFC). The three-dimensional nanofiber network cathode provides high porosity coupled with the large interfacial contact areas, leading to an improved oxygen reduction reaction (ORR) kinetics. The nanofiber cathode showed a polarization resistance of ∼0.025 Ω cm2 at 750 °C. The resulted low resistance is smaller than the commercial LSCF cathode showing polarization resistance of ∼0.041 Ω cm2 at 750 °C. The peak power densities of the PBSCF fibers are ∼2539, 1580 and 993 mW/cm2 at 750, 700, and 650 °C, respectively when compared to LSCF cathode performance of ∼1974, 1304 and 769 mW/cm2 at same temperature. Such promising performance of fiber cathode IT-SOFCs in this study was achieved via careful selection of the catalyst structure and composition, electrode structure for efficient ORR, and through process optimizations. The results obtained in this study illustrates that one-dimensional nanostructures obtained by adopting nanofibers could be an appropriate cathode material choice for intermediate-temperature SOFCs suitable for high power density applications such in automotive, stationary, APU and aviation fields.

The performance of solid oxide fuel cells (SOFCs) can be degraded by “chromium poisoning” where thermally grown Cr2O3 on metallic surfaces forms volatile Cr-containing species that are redeposited on active regions of the cathode. This phenomenon is further exacerbated for porous metallic interconnects and metal-supported electrodes due to their large surface-to-volume ratios. In this study, electrophoretic deposition (EPD) of CuNi0.2Mn1.8O4 spinel powders on porous SUS430 metallic substrates using alternating current (AC) was explored. Two-step densification heat treatment was used to form a thin, uniform, protective spinel coating. The area-specific resistance (ASR) and weight gain were tracked during 100-h oxidation tests at 700°C in air. The results showed that, despite the considerable complexity of the sample shape, AC EPD was able to form a protective coating layer that significantly limited the growth rate of the thermally grown oxide (TGO) by reducing the kg value by a factor of 25.

Solid oxide fuel cells (SOFCs) are a promising solution to a sustainable energy future. However, cell performance and stability remain a challenge. Durable, nanostructured electrodes fabricated via a simple, cost-effective method are an effective way to address these problems. In this work, both the nanostructured PrBa0.5Sr0.5Co1.5Fe0.5O5+δ (PBSCF) cathode and Ni-Ce0.8Sm0.2O1.9 (SDC) anode are fabricated on a porous yttria-stabilized zirconia (YSZ) backbone via solution infiltration. Symmetrical cells with a configuration of PBSCF|YSZ|PBSCF show a low interfacial polarization resistance of 0.03 Ω cm2 with minimal degradation at 700 °C for 600 h. Ni-SDC|YSZ|PBSCF single cells exhibit a peak power density of 0.62 W cm-2 at 650 °C operated on H2 with good thermal cycling stability for 110 h. Single cells also show excellent coking tolerance with stable operation on CH4 for over 120 h. This work offers a promising pathway toward the development of high-performance and durable SOFCs to be powered by natural gas.

MEAs with nanofiber mat electrodes containing Pt/C catalyst and Nafion binder were fabricated and evaluated. The electrodes were prepared by electrospinning a solution of catalyst powder, salt-form Nafion (with Na+, Li+, or Cs+ as the sulfonic acid counterion), and a carrier polymer of either polyethylene oxide or poly(acrylic acid). The carrier polymer was extracted prior to MEA testing by a hot water soaking step. The resulting fibers were 15%–17% porous, with a core–shell-like morphology (a coating of primarily Nafion on the fiber surface). MEAs with anode/cathode catalyst loadings of 0.1 mgPt cm−2 each and a Nafion 211 membrane produced high power at both high and low relative humidity (RH) conditions in H2/air fuel cell tests, e.g., a maximum power density of 919 mW cm−2 at 100% RH and 832 mW cm−2 at 40% RH for a test at 80 °C and 200 kPaabs. The presence of nm-size pores within the fibers trapped water via capillary condensation during low RH feed gas testing, thus maintaining a high proton conductivity of the Nafion binder in the anode and cathode while minimizing/eliminating ionic isolation of catalyst particles in low water content, poorly conductive binder.

Lithium ion batteries have been marked by steady progress over the past few decades owing to their high volumetric and gravimetric energy storage densities. The advent of LIBs resulted in the consistent shift of automotive industry towards hybrid EV's and BEV's. The Nissan Leaf, introduced in Japan and the United States in December 2010, became the first modern all-electric, zero tailpipe emission five door family hatchback to be produced for the mass market from a major manufacturer. Newer models targeted at different customer segments are under development at Nissan and there has been need for more efficient, cost effective and safer LIBs to cater to the needs of the commute. More recently, efforts at Nissan have been diverted towards solid state batteries owing to their ability of surpassing the traditional liquid electrolyte based battery due to higher energy / power densities as well as safety. As a part of Nissan Ambition 2030, research is heavily focused towards development of ASSBs both in terms of chemistry as well as manufacturing technologies. The presentation showcases the efforts of Nissan towards the path of automotive electrification and progress in material, electrode and cell level technologies based on lithium ion batteries and solid state batteries.

Solid oxide fuel cells based on yttria-stabilized zirconia materials have demonstrated a higher level of technology maturity compared to newer materials actively researched to lower the operating temperature. Yttria-stabilized zirconia-based cells can operate around 600 °C and achieve competitive power densities provided the electrolyte can be fabricated relatively thin. In this work, a 2.5-μm thick yttria-stabilized zirconia electrolyte, commercially available, anode-supported solid oxide fuel cell is systematically investigated under various electrochemical conditions, and area of improvements with the electrochemical performance are identified. The cell consists of a Ni-YSZ bulk and functional layer anode, YSZ electrolyte, GDC barrier layer, and LSCF cathode. Using humidified hydrogen, the peak power densities are determined to be 0.31, 0.58, 0.96, 1.41, and 1.78 W/cm2 at 600, 650, 700, 750, and 800 °C, respectively. It is found that the ceria barrier layer is porous; thus, it is not effective to avoid the formation of strontium zirconate. It is therefore expected that the performance can be improved further if a denser ceria barrier layer can be deposited. In addition, energy dispersive spectroscopy analysis revealed significant Ce/Zr interdiffusion between the barrier layer and the electrolyte.

A hybrid Li-ion capacitor represents an emerging class of devices, which results from the coupling of high energy density battery-type electrode materials at one side and high-power EDLC electrode at other side. Here, we develop a simple and scalable method including ball-milling, followed by heating process to synthesize MoS2/graphene composite material. The structural and morphological analyses were carried out by powder X-ray diffraction (PXRD) analysis and scanning electron microscopy (SEM) technique. The composite electrode delivers high specific capacity (725 mAh g−1 at 0.1 A g−1 and 265 mAh g−1 at 5 A g−1). The hybrid device composed of MoS2/graphene composite electrode as negative electrode and commercial activated carbon as the positive electrode exhibits a high energy density of 117 Wh kg−1 at 200 W kg−1 and a maximum power density of 3.9 kW kg−1 at 79 Wh kg−1. The hybrid device showed a long cycle stable Li storage capacity (62% after 5000 cycles at 1 A g−1).

Nitrogen doping and amine-functionalization have previously been used to improve the capacitance of graphene-based materials, however there is a lack of understanding on the mechanisms by which these modifications impact the electrochemical behavior and electrochemical supercapacitor performance, or if these approaches can be combined to achieve synergistic benefits. Herein, we investigate this by synthesizing reduced graphene oxide (HtrGO) with varying degrees of nitrogen-doping (N-HtrGO), amine-functionalization (NH3+-HtrGO), and a hybrid amine-functionalization and nitrogen-doping (N-NH3+-HtrGO). Synthesized materials were systemically investigated to show the effect of nitrogen-doping and amine-functionalization using electrochemical characterization and rigorous physico-chemical analysis. The capacitance performance was increased in the order of NH3+-HtrGO

In this work, praseodymium based double perovskite (PrBa0.5Sr0.5Co1.5Fe0.5O5+𝛿) - PBSCF nanofibers cathodes were fabricated by electrospinning technique for intermediate-temperature solid oxide fuel cells (IT-SOFCs).The optimized three-dimensional nanofiber network cathode provides high porosity coupled with the higher interfacial contact area, leading to a faster oxygen reduction reaction (ORR) kinetics. EIS analysis of the nanofiber structured cathode resulted in a polarization resistance of ~0.025 Ω cm2 at 750 °C. Resulted low resistance is smaller than the commercial LSCF cathode showing polarization resistance of ~0.041 Ω cm2 at 750 °C. The peak power densities of the PBSCF fibers are ~2539, 1580 and 993 mW/ cm2 at 750, 700, and 650 °C, respectively when compared to LSCF cathode performance of ~ 1974, 1304 and 769 mW/ cm2 at same temperature. Such promising performance of fiber cathode IT-SOFCs in this study was achieved via careful selection of the catalyst structure and composition, electrode structure for efficient ORR, and perhaps through process optimizations. The results obtained in this study illustrates that one-dimensional nanostructures obtained by adopting nanofibers can be an appropriate cathode material choice for intermediate-temperature SOFCs suitable for automotive applications.

Water vapor transport through the PEM is one of the key parameters that can help achieve high performance and low-cost fuel cell system. Ex-situ water vapor transport rate (WVTR) measurement is extremely difficult and expensive to measure. This transport depends on many parameters such as ionomer equivalent weight, ionomer type, thickness, reinforcement, and operating conditions. This work presents a simplified and an inexpensive set-up that consists of fuel cell test stand, cell hardware, and a humidity sensor to measure WVTR at PEMFCs operating conditions in order to characterize and compare water transport properties of PEMs. WVTR is found to increase with decrease in EW and decrease in thickness. WVTR shows dependence on flow rates at fixed water vapor activity and increases by almost 2 times at flow rate from 0.1 to 4 L/min. WVTR is strongly dependent on RH% and increases by 4-5 times at RH from 30 to 100%. Overall, a simple and inexpensive set-up is developed which is capable of producing water vapor transport behavior of widely different PEMs.

Membrane-electrode-assemblies with electrospun particle/polymer fiber electrodes produce high power at low Pt loading in a proton exchange membrane H2/air fuel cell, with improved cathode durability as compared to conventional sprayed electrodes [1-5]. This boost in performance has been attributed to inter and intra fiber porosity. The increased porosity of a fiber mat cathode allows for facile removal of product water during fuel cell operation. Porosity within a fiber improves access of reactant gases to catalyst sites and may assist in retaining water during low relative humidity fuel cell operation. Additionally, shear mixing of catalyst and binder during the process of creating an electrospun fiber results in a more uniform distribution of ionomer and catalyst with few, if any, polymer or catalyst aggregates. Previous work on fiber electrodes focused on the use of poly(acrylic acid) (PAA) [1-3, 5] or poly(vinylidene fluoride) (PVDF) [4, 5] as a carrier polymer for Nafion perfluorosulfonic acid during electrospinning. In the present work, poly(ethylene oxide) (PEO) was used as the electrospinning carrier polymer for the fabrication of fiber mat cathodes and anodes, with either Pt/C or PtCo/C as the cathode catalyst and Pt/C as the anode catalyst. PEO carrier polymer was washed out of the fiber mat, resulting in a neat Nafion binder. For a fixed cathode and anode Pt loading of 0.1 mg/cm2, fuel cell tests were performed at 80 °C and 200 kPaabs pressure. In this talk, the effect of carrier polymer on fiber morphology will be discussed using STEM-EDX data collected at Oak Ridge National Laboratory. Beginning-of-life fuel cell power output was measured at feed gas relative humidities from 40% to 100%. The fuel cell polarization results, along with cathode ECSA and mass activity data were contrasted with conventional spray electrode MEAs. Fiber electrode MEAs with Pt/C or PtCo/C cathodes produced very high power at high and low feed gas RH. For example, the maximum power for a Pt/C cathode was essentially constant at 830 mW/cm2 ±5% (experimental error) from 40% RH to 100% RH. Additionally, fiber cathode MEAs exhibited better durability in a load cycling accelerated stress test, e.g., fiber electrode MEAs made with a Nafion/PEO electrospinning ink typically retained ~80% of their initial maximum power vs. 70% retention for a sprayed electrode MEA. This talk will focus on: (i) the methods for fiber electrode electrospinning, (ii) the morphology of the resulting fibers, and (iii) contrasting the performance of fiber electrode MEAs with sprayed electrode MEAs. Acknowledgements This research is supported by the U.S. Department of Energy Fuel Cell Technologies Office, through the Fuel Cell Performance and Durability (FC-PAD) Consortium (Fuel Cells Program Manager: Dimitrios Papageorgopoulos). The work at Vanderbilt University was funded under DOE contract No. DE-EE0007653. References W. Zhang and P. N. Pintauro, ChemSusChem, 4, 1753-1757 (2011). M. Brodt, R. Wycisk, and P. N. Pintauro, J. Electrochem. Soc., 160, F744-F749 (2013). M. Brodt, T. Han, N. Dale, E. Niangar, R. Wycisk, and P. Pintauro, J. Electrochem. Soc., 162, F84-F91 (2015). M. Brodt, R. Wycisk, N. Dale, and P. Pintauro, J. Electrochem. Soc., 163, F401-F410 (2016). J. J. Slack, R. Wycisk, N. Dale, A. Kumar, and P. N. Pintauro, J.Electrochem. Transactions, 80, 829-837 (2017).

Electrospun PFSA-Pt/C nanofiber mats have demonstrated promise as electrodes for PEM fuel cells that are highly scalable and show improved performance and durability compared to traditional sprayed electrodes.1,2 As a result, it is of great interest to understand the underlying mechanisms responsible for these gains, so that these electrode structures may be optimized in order to further increase performance and durability. Neutron radiography was used to measure water formation through the cross-sections of sprayed gas diffusion electrodes (denoted GDE) and electrospun PFSA-Pt nanofiber electrodes (denoted NF) during operation. Both GDE and NF-containing MEAs were assembled in custom hardware specifically designed for use within the neutron beam and operated in a differential cell configuration at 80°C, with variable RH and current density. Initial polarization results (Figure 1a) demonstrated a lower OCV for the NF electrodes, which were attributed to shorting at the through-holes within the active area, specific to the custom-built imaging hardware. Regardless, the performance of NF electrodes is improved at high (2 A/cm2) current densities. Through-thickness water profiles at 0.2 V (Figure 1b) show that the water concentration is around 2x lower within the MEA and GDLs in the NF-containing MEA compared to the baseline GDE. The lower water contents suggests improved performance in the mass transport region, commensurate with the observed polarization curves. Hardware issues are currently being addressed, and further test results exploring effects of RH, current density, and NF composition, will be discussed. Acknowledgements This research is supported by the U.S. Department of Energy Fuel Cell Technologies Office, through the Fuel Cell Performance and Durability (FC-PAD) Consortium (Fuel Cells Program Manager: Dimitrios Papageorgopoulos and Technical Development Manager: Greg Kleen). References P. N. Pintauro, “Fuel Cell Membrane-Electrode-Assemblies with Ultra-Low Pt Nanofiber Electrodes,” Fuel Cell R&D Annual Merit Review Proceedings, 2018. Brodt, R. Wycisk, N. Dale, and P. Pintauro, “Power Output and Durability of Nanofiber Fuel Cell Cathodes with PVDF and Nafion/PVDF Binders”, J. Electrochem. Soc., 163 , F401-F410 (2016). Figure 1

Membrane-electrode-assemblies (MEAs) with particle/polymer nanofiber mat electrodes produce high power and exhibit excellent durability at low platinum loadings in a H2/air proton exchange membrane fuel cell [1-4]. The morphology of an electrospun mat electrode is well-suited for fuel cell applications due to: (1) a high interfacial electrode area, with both inter- and intra-fiber porosity which improves oxygen access to catalytic sites while providing pathways for proton transport, electron conduction, and the removal of product water and (2) a well-dispersed mixture of catalyst and binder along the fiber length and cross-section with a conformal coating of binder on catalyst particles (a consequence of shear mixing, rapid solvent evaporation, and fiber elongation during electrospinning). The focus of this talk is on the design and fabrication of nanofiber-based MEAs (anode, cathode, and membrane) that produce high power at both high and low relative humidity (RH) feed gas conditions. Procedures for electrospinning fiber mat electrodes with low EW PFSA binders will be described and the effect of electrode binder type on power output will be presented. As an example, one nanofiber-based MEA had a 20 μm thick composite membrane (725 EW PFSA with reinforcing PVDF fibers), a 725 EW PFSA binder for the anode and cathode, a Pt/C anode at 0.10 mg/cm2, and a PtCo/C cathode at 0.10 mg/cm2. The measured maximum power density for this MEA in a H2/air fuel cell at 200 kPa pressure, 80oC, and 125/500 sccm H2/air flow rates was 940 mW/cm2 at 100% RH, 924 mW/cm2 at 30% RH, and 804 mW/cm2 at 20% RH. Acknowledgments This work was funded by the Fuel Cell Consortium for Performance and Durability, DOE-EERE FC-PAD Project DE-EE0007653. The authors thank Mike Yandrasits at 3M Co. for providing the 725 EW PFSA ionomer used in the experiments. 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).

Nanofiber electrodes prepared with three different commercial Pt/C catalysts and 1100 EW Nafion® binder were fabricated by electrospinning. The electrodes were further processed into membrane-electrode-assemblies (MEAs) using Nafion 211 as the membrane material. MEAs were evaluated for catalyst activity and power output in a hydrogen/air fuel cell at 80oC. Tanaka Kikinzoku Kogyo (TKK) TEC10E50E (46.1% Pt on Ketjen Black) was more electrochemically active and produced slightly more power than its heat-treated counterpart, TKK TEC10E50E-HT (50.5% Pt on Ketjen Black), and Johnson Matthey HiSpec 4000 catalyst (40% Pt on Vulcan carbon). The nanofiber cathodes were compared to MEAs with standard non-structured gas diffusion electrodes (GDEs) containing the same catalysts, and in all cases, the electrospun fibers generated more power. For example, with a Pt loading of 0.10 mg/cm2, the electrospun TKK TEC10E50E generated 470 mW/cm2 at a 0.65 V vs. 349 mW/cm2 for the GDE-based MEA, an improvement of 35%. The effect of nanofiber composition (the ratio of Pt/C to Nafion) and the effect of fiber diameter on power output were also investigated. In general, such changes had a little or no impact on performance and all the electrospun mats tested yielded MEAs that produced very high power.

A CO2 detection system that enables in-situ and real-time monitoring of CO2 formation from carbon corrosion during start-stop potential cycling was developed. The set-up included a nondispersive infrared (NDIR) CO¬2 detector connected to the fuel cell cathode exhaust. For both Ketjen Black (KB) and Platinum/Ketjen Black (Pt/KB) (50 wt% carbon) cathodes, the amount of CO2 was found to increase with the number of potential cycles (up to 500 cycles) and the carbon loading. Pt was found to increase the initial rate (µg CO2/cycle) of CO2 formation, confirming the findings of earlier studies that Pt accelerates carbon corrosion. Preliminary calculations show that carbon loss is about 30% for both KB and Pt/KB cathodes under the potential cycling protocol used in this study. Pt only acts as a catalyst for the reaction, and it does not significantly affect the total carbon loss which is a function of the amount of corrodible carbon.

An iron based metal-nitrogen-carbon (MNC) type oxygen reduction reaction catalyst was tested for in-situ polarization performance and durability. High open circuit voltage (OCV) of ~0.97 V and high activities were observed. Current density around 750 mA/cm2 was obtained at 0.6 ViR-free/RHE and volumetric current density of 31 A/cm3 was obtained at 0.8 ViR-free. A significant decrease in polarization after start-stop durability test was observed for this catalyst. An attempt was made to recover the in-situ performance after start-stop durability test by running the fuel cell at steady state current density. Partial performance recovery was achieved from the significantly degraded MNC based membrane electrode assembly (MEA). However, performance could not be recovered indefinitely due to eventual carbon loss.

In this paper, equivalent electric circuit models of a commercial 1.2-kW proton exchange membrane (PEM) fuel cell stack are proposed based on AC impedance studies. The PEM fuel cell stack was operated using room air and pure hydrogen (99.995%). Using electrochemical impedance spectroscopy (EIS) technique, impedance data were collected in the laboratory under various loading conditions. Impedance data were analyzed and circuit models developed using basic circuit elements like resistors and inductors, and distributed elements such as Warburg and constant-phase elements. A nonlinear least-square fitting technique is employed to obtain the circuit parameters by fitting a curve to the experimental impedance data. Two circuit models of the fuel cell, one for low and one for high currents are proposed. The average ohmic resistance for the whole stack is estimated to be 41 mΩ. Double-layer capacitances are determined at anode and cathode at various current densities. As expected, cathode charge transfer resistance turns out to be much higher than the anode charge transfer resistance because of slower kinetics of the oxygen reduction reaction. At higher load currents, a significant increase in mass transfer resistance as well as low-frequency inductive effects is observed. These low-frequency inductive effects are recognized and modeled in the fuel cell models of this work. Finally, a semiquantitative analysis was used to determine the contribution of individual performance factors to the overall fuel cell voltage drop. The transient response of the fuel cell circuit models is simulated using MATLAB/Simulink and their performance is validated by comparison with experimental data.

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).

The performance of a 6 kW proton exchange membrane (PEM) electrolyzer was modeled using a semiempirical equation. Total cell voltage was represented as a sum of the Nernst voltage, activation overpotential and ohmic overpotential. A temperature and pressure dependent Nernst potential, derived from thermodynamic principles, was used to model the 20 cell PEM electrolyzer stack. The importance of including the temperature dependence of various model components is clearly demonstrated. The reversible potential without the pressure effect decreases with increasing temperature in a linear fashion. The exchange current densities at both the electrodes and the membrane conductivity were the coefficients of the semiempirical equation. An experimental system designed around a 6 kW PEM electrolyzer was used to obtain the current–voltage characteristics at different stack temperatures. A nonlinear curve fitting method was employed to determine the equation coefficients from the experimental current–voltage characteristics. The modeling results showed an increase in the anode and cathode exchange current densities with increasing electrolyzer stack temperature. The membrane conductivity was also increased with increasing temperature and was modeled as a function of temperature. The electrolyzer energy efficiencies at different temperatures were evaluated using temperature dependent higher heating value voltages instead of a fixed value of 1.48 V.

International audience; A highly active and durable non-platinum group metal (non-PGM) electrocatalyst was synthesized at high temperature from a catalyst precursor involving a ferrous iron salt and a nitrogen-containing charge-transfer salt as a precursor to form a nano-structured catalyst with performance level that makes it suitable for automotive applications. Such precursors have not been previously investigated for non-PGM catalysts. The synthesized material belongs to the class of metal-nitrogen-carbon catalysts and possesses an open-frame structure controlled by the silica-templating synthesis method. Thorough characterization using X-ray photoelectron, Mössbauer and in situ X-ray absorption spectroscopies demonstrates the successful formation of FeNxCy moieties that are active towards the oxygen reduction reaction. We report high kinetic current densities and high power performance in both rotating disk electrode and membrane electrode assembly studies. This Fe-N-C catalyst, jointly investigated by academic and industry partners, has shown high durability under different protocols, including that defined by the US Department of Energy Durability Working Group and Nissan’s load cycling protocol. In summary, the present Fe-N-C catalyst is highly active and durable, making it a viable alternative to Pt-based electrocatalysts for automobile fuel cell applications.

Proton exchange membrane fuel cells (PEMFC) technology is already in commercialization phase for automotive applications. However, the biggest challenges for its successful mass commercialization are cost and durability. Current PEMFC technology can meet the lifetime targets but the cost to achieve it can be very high due to material’s cost and system level mitigation complexities. Understanding of the membrane electrode assemblies (MEA) degradations using relevant durability accelerated tests at early stages of development is essential. PEMFCs for automotive applications goes through thousands of cycles during normal operation of the vehicle over the expected life span of 10 years. These cycles include a combination of load or voltage cycles, start and stop cycles, humidity cycles and temperature cycles. Study have shown that start-stop cycling accounts for 44% of operation mode while load cycling and idling for 28% each (1). Under these cycles, fuel cells suffer from severe degradations of its main components; cathode, anode, membrane and bipolar plates. The PEMFC cathode can degrade during start-stop operation via carbon corrosion (2). Cathode degradation can be mitigated by using stable materials or by applying system mitigations. System mitigation by a voltage limiting control (VLC) can be one of the effective measures (3). The VLC can, however, lead to voltage spikes (high positive potentials) at the anode during fuel cell start-up and shut-down. Moreover, during fuel (H2) starvation conditions, the potential at the anode can give rise to high positive potentials leading to anode catalyst layer degradation. During idling operation mode, PEMFC is at or near open circuit conditions which is known to accelerate proton exchange membrane (PEM) decomposition especially under low humidification (4). Peroxy-radicals originating from hydrogen peroxide produced at the anode catalyst surface cause the PEM degradation (5). Pt band formation in the membrane is also known to promote peroxide formation leading to membrane decomposition (6-7). Several accelerated protocols are currently being used to evaluate the durability of PEMFC. At Nissan, our durability protocols are focused on understanding the material degradation under relevant automotive cycles and correlating single cell durability to the stack level. Start-stop accelerated protocol to evaluate the cathode support durability consist of potential cycling from 1.0 V to 1.5 V using triangular waveform for 1000 cycles with diagnostics conducted intermittently after certain number of cycles. Cathode catalyst durability is evaluated using load cycling accelerated protocol wherein the potential is cycled between 0.6 V to 0.95 V to simulate peak load and OCV/idle using a square wave profile with 3 second hold at each potential. The upper potential is known to have significant impact on catalyst degradation (8). Load cycling is performed for 10,000 cycles with diagnostics conducted intermittently. Anode degradation under cell reversal condition is evaluated using a protocol designed to simulate high voltage spikes at the anode. Cell reversal cycling is performed by applying a load of 0.2 A/cm2 for 1 sec while flowing N2 at the anode and air at the cathode while measuring the cell voltage under the applied load for a total of 200 cycles. Membrane durability is evaluated using humidity cycling (mechanical durability) and potential hold at open circuit (chemical durability). Membrane’s chemical durability is evaluated at 90 °C and 30% RH under hydrogen and oxygen by operating MEA at open circuit. The target of OCV hold test is 500 hrs while maintaining potential above 0.8 V. Mechanical durability of membrane is evaluated by cycling RH to simulate dry condition (0%) and wet condition (100%) for target of 20,000 cycles. All these accelerated tests are performed at ambient pressure and summarized in the Table 1 below. Acknowledgments: The author would like to gratefully acknowledge Nissan Technical Center North America Fuel Cell Research team members (Dr. Amod Kumar, Dr. Ramesh Yadav and Dr. Cenk Gumeci) and Nissan Motor Co. Ltd Japan Fuel Cell research team members (Dr. Atsushi Ohma, Dr. Yoshihisa Furuya) for technical discussions and data. References: R. Shimoi et al., JSAE Spring meeting , April 2009 R. Borup et. al., Chemical Reviews, 107 (10), 3904 (2007) M. L. Perry, T. W. Patterson and C. Reiser, ECS Trans., 3 (1), 783 (2006) S. Sugawara et al., J. of Power Sources, 187 (2009) A.B LaConti et al., Handbook of Fuel Cells, vol 3 A. Ohma et al., ECS Trans., 11 (1), 1181 (2007) A. Ohma et al., ECS Trans., 3 (1), 519 (2006) A. Ohma et al., ECS Trans, 41 (1), 775 (2011) Figure 1

The PEFC cathode can degrade during start-stop operation via carbon corrosion (1). To prevent cathode degradation, a voltage limiting control (VLC) protocol can be one of the effective measures to protect the cathode during cell start-up and shut-down (2). The VLC can, however, lead to voltage spikes (high positive potentials) at the anode during fuel cell start-up and shut-down. Moreover, during fuel (H2) starvation conditions, the potential at the anode can give rise to high positive potentials leading to carbon corrosion and, subsequently, anode catalyst layer degradation. To avoid degradation of the anode catalyst layer during start-up and shut-down with imposed VLC and/or during fuel starvation, a mixed oxide of ruthenium oxide-titanium oxide (RTO) was investigated as a suitable corrosion-resistant replacement for carbon in the anode catalyst. RTO has previously been demonstrated to be an excellent corrosion-resistant support material at the PEFC cathode (3). In this study, 40% Pt/RTO was used as the anode catalyst in a fuel cell and its durability was measured under cell reversal conditions using a protocol designed to simulate high voltage spikes at the anode. The reverse cell potential for the baseline TKK TEC10EA30E reached -2.0 V (MEA failure criteria) well before the target of 200 cycles. The reverse cell potential for the 40% Pt/RTO anode remained steady even after 400 cycles of the cell reversal protocol, indicating higher H2 starvation tolerance for 40% Pt/RTO compared to the baseline TKK TEC10EA30E (Pt/Graphitized Ketjen Black) catalyst, as shown in Figure 1. The reverse cell potential for 40% Pt/RTO did not reach -2.0 V (MEA failure criteria) even after 400 cycles. The high retention in durability of Pt/RTO catalyst compared to TEC10EA30E was attributed to the avoidance of support-corrosion-induced loss and to the excellent activity of RuO2, present in RTO, for the oxygen evolution reaction (OER). From the hydrogen oxidation reaction (HOR) study, the polarization resistance (Rp) of 40% Pt/RTO was found to be higher than that of TEC10EA30E (36.6 mOhm-cm2 compared to 23.9 mOhm-cm2) indicating lower initial HOR activity of 40% Pt/RTO. However, the Rp for HOR of TEC10EA30E increased to 6.6x its initial value after cell reversal cycling, indicating severe degradation of the catalyst layer. The Rp of the 40% Pt/RTO increased to only 1.4x its initial value after cell reversal cycling, which supported the conclusion made earlier that the anode made from 40% Pt/RTO catalyst was considerably more durable than the anode made out of baseline Pt/GKB catalyst. Using limiting current experiments, H2 gas transport resistances were measured in the anode catalyst layer and the resistances: Rdiff (due to diffusion resistance of H2 in the GDL and flow fields) and Rother (arising primarily from H2 gas diffusion in the catalyst layer) resistance values were calculated (4). Rdiff (at 101.3 kPaabs) was found to increase 10 fold for TEC10EA30E anode after durability cycling compared to a 1.3x increase for the 40% Pt/RTO anode. This indicated that the anode GDL could also have corroded under the cell reversal protocol. After durability cycling, the Rother resistance for baseline TEC10EA30E increased by a factor of 12 when compared to 40% Pt/RTO, which retained a relatively constant Rotherdue to its excellent corrosion resistance. Acknowledgments: The authors would like to gratefully acknowledge Guanxiong Wang for synthesizing the catalyst supports and catalysts used in this study and Dr. Ellazar Niangar for research design and planning and helpful discussions. References: R. Borup et. al., Chemical Reviews, 107 (10), 3904 (2007) M. L. Perry, T. W. Patterson and C. Reiser, ECS Trans., 3 (1), 783 (2006) J. Parrondo et.al., Proc Natl Acad Sci USA, 111 (1), 45 (2014) T. Mashio et. al., ECS Trans. 11 (1), 529 (2007) Figure 1

This paper presents the ac impedance study and analysis of a proton exchange membrane (PEM) fuel cell operated under various loading conditions. Ballard’s 1.2 kW Nexa™ fuel cell used for this study is integrated with a control system. The PEM fuel cell stack was operated using room air and pure hydrogen (99.995%) as input. Impedance data were collected for the fuel cell to study the behavior of the stack and groups of cells under various loads. Single cell impedance analysis was also performed for individual cells placed at different locations in the stack. The ac impedance analysis, also known as electrochemical impedance analysis, showed low frequency inductive effects and mass transport losses due to liquid water accumulation at high current densities. Results show that the stack run time to achieve steady state for impedance measurements is important. Using impedance plots, the average Ohmic resistance for the whole stack was estimated to be 41 mΩ, the same value obtained when summing the resistance value of all individual cells. Impedance analysis for groups of cells at different locations in the stack shows changes in both polarization resistance and capacitive component only in the low frequency region. At high frequencies, single cell inductive and capacitive behavior varied as a function of location in the stack. The effects of artifacts on the high frequency loop and on the high and low frequency intercept loops are also discussed.

Impedance characteristics of a 6 kW proton exchange membrane (PEM) electrolyzer stack are presented under various operating conditions. An electrolyzer stack was operated under room temperature and partial current range (0 to 80 A). The whole stack impedance spectrums were measured by three different power supply configurations. The total sweeping frequency range (0.5 Hz to 20 kHz) is divided into low frequency (0.5 to 20 Hz), middle frequency (20 Hz to 1 kHz), and high frequency (1 to 20 kHz). Each frequency range required a different measurement setup to measure the whole stack impedance data. In this study, the partial impedance spectrums at low and high frequency ranges are successfully measured and analyzed. The measured data is verified with Kramers-Kronig relations. Measurement issues at the middle frequency region are discussed.Copyright © 2010 by ASME

This paper describes a system, utilizing the Peltier effect, to reduce and control the dew point of hydrogen gas by water condensation and desublimation using thermoelectric coolers and water cooled heat sinks. The design is compared to a two-tube desiccant-drying system used in some commercial proton exchange membrane electrolyzer systems. The desiccant system in the water electrolyzer consumes roughly 0.2 kg per day of hydrogen product gas (corresponding to 3.4 kWh per kg of hydrogen based on the higher heating value) to maintain the two desiccant beds. Thermodynamic modeling was performed to determine the appropriate sizing for the thermoelectric coolers and water-cooled heat sinks for a 1 Nm3 hr -1 hydrogen flow rate to obtain a theoretical dew point of -35 degC. The potential benefits and energy consumed by the thermoelectric approach (3.05 kWh per kg of hydrogen) is compared to the hydrogen loss of the desiccant system. The thermoelectric cooler-based system has the ability to control the dew point to match the variable flow rate of hydrogen in a renewable electrolysis system.

Wind generated electricity is a variable resource. Hydrogen can be generated as an energy storage media, but is costly. Advancements in power electronics and system integration are needed to make a viable system. Therefore, the long-term goal of the efforts at the University of North Dakota is to merge wind energy, hydrogen production, and fuel cells to bring emission-free and reliable power to commercial viability. The primary goals include 1) expand system models as a tool to investigate integration and control issues, 2) examine long-term effects of wind-electrolysis performance from a systematic perspective, and 3) collaborate with NREL and industrial partners to design, integrate, and quantify system improvements by implementing a single power electronics package to interface wild AC to PEM stack DC requirements. This report summarizes the accomplishments made during this project.

Introduction Conventional carbon supports suffer from catastrophic failure during start-up/shut-down events, which result in high cathode interfacial potentials, which, in turn, lead to carbon corrosion and catalyst degradation. Carbon corrosion is a major problem in fuel cells because it leads to loss of catalyst activity and collapse of electrode structure. Nissan, as an automotive OEM, has always approached the issue of catalyst support durability at the materials level, rather than at the systems-level, since system-level mitigation is an added cost to the balance of plant (BOP), and presents one additional factor that can fail during operation. NTCNA and IIT have been working on the development of high-surface-area, corrosion-resistant non-carbon supports, and we have previously demonstrated a class of highly stable non-carbon supports, e.g. ruthenium-titanium oxide (RTO) (1). In this work, we present the results of our work on a second class of non-carbon supports - tin-doped indium oxide (ITO). Materials and Methods RDE Testing – RDE tests were performed in a 3-compartment electrochemical cell containing 0.1 M HClO4 electrolyte. A glassy carbon disk (0.196 cm2) uniformly covered with Pt/C or Pt/ITO catalyst served as the working electrode. The counter and reference electrodes were Pt foil and RHE, respectively. Membrane Electrode Assembly (MEA) Fabrication - Catalyst inks were prepared by mixing Pt/C or Pt/ITO with water, n-propanol, and a Nafion ionomer dispersion. The mass-based ionomer/support (I/S) ratio in the ink was kept constant at 0.9. The cathode catalyst layers were formed on GDLs using an automated robotic spray system. MEAs (25 cm2) were prepared by hot pressing cathode GDEs (0.35 mgPt/cm2) and commercial anode GDEs (0.4 mgPt/cm2) onto Nafion® NR211 membranes. Results and Discussion Figure 1 shows the RDE performance of Pt/ITO vs. a commercially available Pt/C benchmark catalyst of comparable Pt particle size. The ECA obtained for Pt/ITO (22 m2/gPt) was lower than Pt/C (45 m2/gPt) due to the low surface area of ITO which causes Pt particle agglomeration. Even with a lower ECA, Pt/ITO shows promising performance since its mass activity of ~150 mA/mgPt matches that of the Pt/C benchmark catalyst. However, we have repeatedly observed that Pt/ITO performs very poorly in MEA testing. Figure 2 shows a typical H2/O2 polarization curve obtained for Pt/ITO at a high Pt loading of 0.35 mg/cm2. The only difference between the two MEAs is the cathode catalyst. Other than the dramatic difference between the two polarization curves, it can also be seen that Pt/ITO shows a very high HFR (high frequency resistance) of ~220 mΩ·cm2. The HFR represents the ohmic resistance due to proton transport in the membrane and the electronic contact resistances in the cell. The high HFR is attributed to the poor electronic conductivity of the ITO support since the two MEAs in Figure 2 have the same membrane, cell hardware, and cell components. It is hypothesized that hydroxylated species form on the ITO surface under fuel cell operating conditions. Hydroxide and oxy-hydroxide species may readily form on the surface of ITO due to hydrolysis reactions. Hydroxylated species such as In(OH)3 have low solubilities, hence they may remain adsorbed on the ITO surface, forming a passivating layer that will increase ohmic resistance (2). Furthermore, the Pourbaix diagram for indium shows that under fuel cell conditions, the formation of In3+ is favorable, and it is possible that In3+ can act as a poison that covers the Pt active sites. This is supported by the changes observed in the CV profile in MEA (loss of Hupd features and resistive behavior), suggesting some changes in the chemical properties of ITO and Pt poisoning. The promising RDE results did not translate to good performance in MEA, and this is hypothesized to be caused by cross-over hydrogen in MEA. H2 crossing over from anode to cathode may accelerate the formation of hydroxylated species. Experiments are underway to verify this. References 1. J. Parrondo, T. Han, E. Niangar, C. Wang, N. Dale, K. Adjemian and V. Ramani, Proceedings of the National Academy of Sciences, 111 (2014) 45-50. 2. B. Michael, P. A. Veneman, F. S. Marrikar, T. Schulmeyer, A. Simmonds, W. Xia, P. Lee, and N. R. Armstrong. Langmuir, 23(22), 11089-11099 (2007). Figure 1

The hydrogen/air proton-exchange membrane (PEM) fuel cell is a promising candidate for automotive power plants but Pt/C catalyst electrode cost and durability are still issues that require further study. In a series of previous papers and presentations [1-4], Pintauro and coworkers have shown that an electrospun nanofiber cathode, composed of Pt/C particles and a binder of Nafion + poly(acrylic acid), performs remarkably well in a hydrogen/air proton exchange membrane fuel cell. For example, a nanofiber electrode MEA with a 0.055 mgPt/cm2 cathode and 0.059 mgPt/cm2 anode produced more than 900 mW/cm2 at maximum power in a H2/air fuel cell at 80°C, 100% RH and high feed gas flow rates at 2 atm backpressure. In another study, electrospun nanofiber cathodes exhibited excellent durability, as determined from end-of-life polarization curves after an accelerated start-stop voltage cycling (carbon corrosion) test. For example, after 1,000 simulated start-stop cycles, a nanofiber MEA with Johnson Matthey Pt/C catalyst maintained 53% of its initial power at 0.65 V and 85% of its maximum power, as compared to a 28% power retention at 0.65 V and 58% maximum power for a sprayed electrode MEA. The excellent initial performance of nanofiber fuel cell electrodes was attributed to the unique nanofiber electrode morphology, with inter-fiber and intra-fiber porosity which results in better accessibility of oxygen to Pt catalyst sites and efficient removal of product water. The superior end-of-life performance of the nanofiber MEA after a carbon corrosion test was attributed to the combined effects of a high initial electrochemical cathode surface area, the retention of the nanofiber structure after testing (no collapse of the cathode, as confirmed by SEM imaging), and the rapid/effective expulsion of product water from the cathode which minimizes/eliminates flooding. In this presentation, the performance of Pt-alloy catalysts in electrospun nanofiber fuel cell cathodes will be discussed. The method for creating nanofiber mat cathodes with PtCo and PtNi powders, using a mixture of Nafion and poly(acrylic acid) as the cathode binder, will be described. These cathodes, with a Pt loading of 0.10 mg/cm2 were incorporated into a fuel cell membrane-electrode-assembly (MEA) with a Nafion 211 membrane and a Pt/C nanofiber anode (0.1 mg/cm2). Short-term fuel cell performance was assessed at 80oC with 100% RH using hydrogen and air at flow rates of 500 and 2,000 sccm, respectively. Power output was compared with an MEA containing conventional painted electrode gas diffusion electrodes, with neat Nafion binder and with Nafion + poly(acrylic acid) binder (same as the nanofibers). The performance of nanofiber MEAs was also examined and contrasted with that of a conventional electrode MEA after an accelerated carbon corrosion voltage cycling experiment, with 1,000 voltage cycles between 1.0 and 1.5V. Representative performance results for a nanofiber MEA with a PtCo cathode catalyst at a loading of 0.10 mg/cm2 are shown in Table 1. Under ambient pressure, the nanofiber morphology consistently provides a 25% improvement in power density at both 0.65V and at maximum power. This effect is even greater under backpressure where the improvement is consistently around a 35% increase in power density at both 0.65 and maximum power. In this case at 0.65V a power density above 1W/cm2 has been achieved. Additional results and analyses will be discussed in the presentation. Acknowledgments This work was funded in part by the National Science Foundation (NSF EPS-1004083) through the TN-SCORE program under Thrust 2. Figure 1

Platinum in the form of nanoparticles is the key and most expensive component of polymer electrolyte membrane fuel cells, while trifluoromethanesulfonic acid (CF3SO3H) is the smallest fluorinated sulfonic acid. Nafion, which acts as both electrolyte and separator in fuel cells, contains -CF2SO3H groups. Consequently, research on the electrochemical behaviour of Pt in aqueous CF3SO3H solutions creates important background knowledge that can benefit fuel cell development. In this contribution, Pt electro-oxidation is studied in 0.1 M aqueous CF3SO3H as a function of the polarization potential (E(p), 1.10 ≤ E(p) ≤ 1.50 V), polarization time (t(p), 10(0) ≤ t(p) ≤ 10(4) s), and temperature (T, 278 ≤ T ≤ 333 K). The critical thicknesses (X1), which determines the applicability of oxide growth theories, is determined and related to the oxide thickness (d(ox)). Because X1d(ox) for the entire range of E(p), t(p), and T values, the formation of Pt surface oxide follows the interfacial place-exchange or the metal cation escape mechanism. The mechanism of Pt electro-oxidation is revised and expanded by taking into account possible interactions of cations, anions, and water molecules with Pt. A modified kinetic equation for the interfacial place exchange is proposed. The application of the interfacial place-exchange and metal cation escape mechanisms leads to an estimation of the Pt(δ+)-O(δ-) surface dipole (μ(PtO)), and the potential drop (V(ox)) and electric field (E(ox)) within the oxide. The Pt-anion interactions affect the oxidation kinetics by indirectly influencing the electric field within the double layer and the surface oxide.

Polymer electrolyte membrane (PEM) high performance without external humidification is essential to reduce cost, and simplify design for early commercialization and adoption of fuel cell electric vehicles (FCEVs). Water transport property through PEM is one of the key parameters to design low-cost and high-performance fuel cell system. In this work, a simple and inexpensive water transport measurement set-up has been developed to obtain a water vapor rate (WVR) at PEMFCs operating conditions in order to characterize and compare PEMs. PEM polarization curves have been evaluated at differential relative humidity (RH) to understand effect of water transport and humidification of the anode and cathode. Water transport occurs due to electro-osmotic drag from anode to cathode and concurrent back-diffusion from cathode to anode. This transport depends primarily on thickness, equivalent weight (EW) and operating conditions. New PEMs with low thickness, low EW, and optimal distribution of H+conducting functional groups are being developed to improve water transport and conductivity. These improvements will reduce ohmic losses and allow for FCEV operation at low RH using system-generated water at cathode [1]. Therefore, it is important to measure water transport for new membranes characterization. In PEMFCs without external humidification, system-generated water provides hydration to the membrane mostly on cathode side while the anode side suffers from dehydration because of electro-osmotic drag. Additionally, cathode operation at high RH can cause flooding that limits the performance severely at high current density. Ex-situ water transport measurements, especially at PEMFCs operating condition, are extremely difficult, expensive, and require sophisticated instruments [2-3]. The WVR set-up developed in this work consists of fuel cell test stand, cell hardware, and a humidity sensor near the anode outlet to measure the outlet RH and corresponding dew point. WVR is obtained from the ideal gas law as shown below. WVR = PH2O.V /( R.T.A) [1] Here WVR is in μmol.cm-2.min-1. PH2O is the water vapor pressure at anode outlet dew point, V is dry gas (N2) flow rate at anode outlet, T is system temperature, R is universal gas constant and A is membrane active area. The cathode was supplied with humidified N2 at a target RH and the anode was supplied with dry N2to carry permeated water vapor to the humidity sensor. Stabilized RH and dew point at anode outlet were recorded to obtain water vapor pressure. Fig. 1 shows the WVR results obtained from Eqn. [1] for NR 211 (25μm) and Nafion XL (30μm). As expected, WVR increases by 3 times for cathode RH from 30 to 100% because water transports faster due to increased water activity at cathode. NR 211 showed higher WVR than that of Nafion XL because NR 211 is thinner and non-reinforced. These results suggest that, at same conditions, NR 211 should produce higher IV performance than Nafion XL. IV performance of a Nafion XL CCM was evaluated under differential RH conditions to understand the importance of anode humidification as shown in Fig. 2. The anode and cathode were maintained at unequal RH. It is clear from Fig. 2 that differential RH operation in which the anode is at 100% RH and the cathode at low RH produces similar performance to the anode and cathode both at 100% RH, and higher performance than with the anode at low RH and cathode at high RH. Fig. 2 also shows that anode at high RH provides a greater advantage over low anode RH with increasing current density. These results suggest that anode humidification is important and may require an external humidifier, whereas a cathode external humidifier can be eliminated as it can self-humidify from system-generated water. In this study, WVR across variety of reinforced and non-reinforced PFSA PEMs will be presented to compare their water transport behavior. Polarization curves for variety of PEMs will be discussed to emphasize the importance of water transport and differential RH operation that can help eliminate cathode humidification to simplify FCEVs design. References 1. W. Liu, ECS Trans., 50(2), 51-64 (2012). 2. Adachi et al., J. Electrochem. Soc., 156(6), B782-B790 (2009). 3. Majsztrik et. al., J. Membrane Sci. 301, 93-106 (2007). Fig. 1 Preliminary WVR results as a function of cathode RH. Fig. 2 IV performance of a CCM at differential RH.

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