(Invited) Fuel Cells for Heavy Duty Vehicles

Towards a CO2 free energy supply, hydrogen plays an important role as a chemical energy storage capable of storing renewable energy in large dimensions. In this context, fuel cells, such as e.g. polymer electrolyte membrane fuel cells (PEMFC) are going to evolve to a key technology for the conversion of the chemically stored energy back to usable electric energy. Therefore, after decades of fuel cell research, the phase of industrialization of fuel cells has begun recently to provide fuel cells in large quantity for a variety of applications, such as e.g. to power heavy duty vehicles, ships and even airplanes or as stationary power plants.For PEMFC mass production, the optimization of the manufacturing process of fuel cells is important to decrease the manufacturing time and costs. One of the most time and cost consuming steps during the production of fuel cells is the first time activation. During the so-called break-in, the fuel cell is operated for the first time in order to activate the membrane electrode assembly (MEA). During break-in, the proton conductivity of the membrane is established and the catalyst is activated, but also chemical residues of the production of the fuel cell components were removed. This procedure is necessary for a fuel cell stack to provide its maximum power output and maximum robustness of all single cells. Furthermore, the successful activation of the PEMFC strongly affects the overall lifetime of a fuel cell stack.To date, a typical break-in of a fuel cell stack takes in between 2 and 8 hours of time, in which a considerable amount of hydrogen and air is required. Thereby, the stack is commonly operated at a high relative humidity doing several cycles of current ramps from minimum to medium or high load interrupted by shutdowns, whereby the first current ramp is usually performed very slowly. Besides the media consumption, the rather long state-of-the-art break-in time calls for a high degree of parallelization of break-in stations at each production line to reach a reasonable output of fuel cell stacks, which is related to high investment costs. An optimization of the break-in process in respect to the necessary time and media consumption significantly reduces the production costs of a PEMFC stack. In this work, several new approaches to activate PEMFCs were introduced in order to decrease the duration and media consumption of the break-in process. Thereby, the common break-in doing several current ramps was replaced by more efficient and promising approaches, such as e.g., hydrogen starvation events or hydrogen pumping. This break-in experiments were performed in short stacks of small scale as well as automotive scale. Finally, the influence of each break-in variation on the performance and durability of the PEMFC was investigated.

Fuel cell vehicles have recently entered the market place (1). Future increases in technology adoption are dependent on concurrent cost reduction and improved durability (2). This is a major challenge because membrane/electrode assemblies based on low platinum catalyst loadings have shown inferior durability (3). Many processes limit the proton exchange membrane fuel cell (PEMFC) durability including the presence of contaminants in ambient air. Although a filter is added at the air intake to remove particulates and undesirable gaseous species, contaminant slippage, missed replacements after the filter has reached its end of life and other failures increase fuel cell exposure risks. A strategy relying on the understanding of contamination mechanisms is expected to result in a more robust system with the development of mitigation, recovery and maintenance procedures that supplement the air filter. Such a strategy is necessary because the impact of many contaminants is still unknown (4). Furthermore, relatively little contaminant related information is available for low platinum catalyst loadings (5-7). In this tutorial, focus will be given to recent contamination results and fundamental understanding obtained with a low cathode platinum loading of 0.1 mg cm-2, a value consistent with the United States Department of Energy 2020 target of 0.125 mg cm-2 for the sum of anode and cathode catalyst loadings. All tested contaminants are organic and representative of alcohols (iso-propanol), alkenes (propene), alkynes (acetylene), esters (methyl methacrylate), halocarbons (bromomethane), nitriles (acetonitrile), and polycyclic aromatics (naphthalene). The impact of catalyst loading and contaminant on cell performance, contaminant hydrophobicity on liquid water transport, a long duration contaminant exposure on degradation, a fuel cell stack compatible recovery procedure on cell voltage losses sustained during contamination, and a contaminant mixture on the synergy between species and cell performance will be discussed and contextualized with the relevant literature. All these contamination aspects have either not been explored or been insufficiently documented. Acknowledgments Authors are grateful to the Office of Naval Research (award N00014-13-1-0463), the Department of Energy (award DE-EE0000467), the National Institute of Standards and Technology (neutron imaging beam time), and the Hawaiian Electric Company for their ongoing support to the operations of the Hawaii Sustainable Energy Research Facility.

This study presents a comparative evaluation of Molten Carbonate Fuel Cell (MCFC) and Solid Oxide Fuel cell (SOFC) stacks coupled with a micro gas turbine (MGT). For the analysis, it is assumed that the fuel supply to the stacks is constant in all the analyzed conditions. The components of the system have been sized using the first law of thermodynamics to meet the thermal conditions required to maintain fuel cell stack operation, while an exergetic analysis has been implemented in order to assess the components in terms of irreversibilities. Furthermore, an economic analysis to estimate the Levelized Cost of Electricity (LCOE) has been carried out to indicate the most feasible option between the two analyzed systems. The capacity of the fuel cell stacks is 500kWdc operating at 350 kPa and 600 °C/650 °C. The results indicate that MCFC stacks are more efficient than SOFC stacks, but are considerably more expensive. Nevertheless, the SOFC/MGT system has a global efficiency higher than that of the MCFC/MGT; also its Total Capital Investment (TCI) is 2.5–3.5 times lower, thus making the SOFC/MGT coupling more attractive. The only product considered coming out from the systems to determine the LCOE is electricity. The LCOE for the SOFC/MGT system is 0.339–0.402$/kWh and for the MCFC/MGT is 0.875–0.897$/kWh, which for both configurations is still higher than the current electricity prices. One aspect that increases the investment and consequently the LCOE is the high cost of the stacks and their replacements which is around 19 % and 10 % of the total Purchased Equipment Cost (PEC) for MCFC and SOFC stacks, respectively.

Improvements in the chemical durability of polymer electrolyte membrane fuel cells (PEMFCs) via the addition of cerium-based (Ce) chemical stabilizers are essential to maximize operational membrane lifetimes in heavy duty transportation. Chemical stability of a state-of-the-art mechanically supported, perfluorosulfonic acid (PFSA), thin (12 µm) membrane with an antioxidant (9.7 µg/cm2 Ce loading) is investigated by analyzing fluoride emission rates (FER) measured in in-cell and ex-situ hydrogen peroxide tests.1,2 Separate correlations are developed for anode FER in terms of the selectivity (moles of fluoride released per mole of crossover oxygen) and for cathode FER in terms of cathode potential. Both also depend strongly on temperature, water activity in membrane, and Ce loading.Transport models defined in physics-based modeling software are developed to determine gradients in water activity and Ce segregation in the membrane in operating differential cells. Greater water production at high current density is found to increase water activity at cathode and anode interfaces of the membrane. Diffusion limits Ce retention in the membrane to <72% near open-circuit voltage (OCV); electromigration further lowers it to <5% at 1.5-2.5 A/cm2 (0.6 V). For the same current density, retention is smaller under drier conditions. Ce migrates from the membrane to the cathode electrode under applied potential, segregating at the cathode interface at low current density before depleting with further increase in current density. Ce depletes faster at the anode interface, especially under drier conditions. Ce segregation and water gradient in the membrane enhance FER at low relative humidity and high operating pressure, temperature, or cell voltage; the enhancement is more pronounced for low Ce loading in the membrane. Under baseline conditions (2.5 bar, 90°C, 21 mol% O2, 9.7 µg/cm2 Ce), FER is higher at the anode interface for cell voltages below 0.9 V and at the cathode interface for cell voltages above 0.9 V. FER is comparable at the two interfaces at 0.9 V, albeit higher at the cathode for operating pressure below 2 bar and at the anode for pressure above 2 bar.The combined transport and FER model is used to construct operating maps for 25,000-h membrane lifetime in differential cells as limited by chemical degradation. These maps are derived from parametric studies which define the combinations of cell voltage, gas relative humidity, and temperature at 2.5-bar operating pressure that lead to membrane failure in different scenarios. This model enables predictive analysis and design optimization of membrane applications in PEMFCs. The actual lifetime may be further limited by contaminants, synergistic mechanical stresses and manufacturing defects. Additional work is underway to extend these results to drive cycles for Class-8 heavy duty trucks and to refine the model based on the inclusion of experimental FER measurements under varying operational parameters. Acknowledgements This work was supported by the U.S. Department of Energy, Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office (HFTO) through the Million Mile Fuel Cell Truck (M2FCT) Consortium. Argonne National Laboratory is managed for the U.S. Department of Energy by the University of Chicago Argonne, LLC, under contract DE-AC-02-06CH11357. References Coms, F. D., Liu, H. & Owejan, J. E. Mitigation of Perfluorosulfonic Acid Membrane Chemical Degradation Using Cerium and Manganese Ions. ECS Meet. Abstr. MA2008-02, 1057–1057 (2008).Xu, H., Mittelsteadt, C. K., McCallum, T. & Coms, F. Novel H2O2 Vapor-Based System for Proton Exchange Membrane Degradation. ECS Meet. Abstr. MA2011-02, 1144–1144 (2011).

It is of utmost importance to develop light weight fuel cell stacks and find the ways to integrate these to light weight and low temperature fuel cell systems. In order to meet the future energy demands non-polluting, compact, transportation and portable applications are required. Current energy systems have lower power density (kW/kg) resulting in optimized power only at higher overall weight. Systems with higher power density demands higher initial setup costs. Low temperature PEMFC, on other hand offers various advantages but fails to provide the required output without exceeding the weight of the fuel cell stack and thereby fuel cell systems. A fuel cell system consists of a fuel cell stack, compressed gas in cylinder, pressure relief valves, regulators, water pump, sensors and cvm. A fuel cell stack is the main component consisting of one of the devices with maximum weight and cost contribution. In such case, developing a system with stack having higher power density reduces overall weight and increases power density (kW/kg). PowerUP Energy Technologies has developed light weight fuel cell stack to achieve higher power density. Experiments considering flow field designs, recirculation strategy, different anode configuration has been a subject of study. Dead-end anode, closed cathode configuration of fuel cell stack further improves fuel utilization. Recirculation line of hydrogen if further added can improve in overall fuel utilization. Counter flow arrangement for reactant distribution further removes the necessity of humidifying the gases. This result in removal of humidifiers and thereby reducing the weight of the fuel cell system in total. Portable fuel cell systems have flexibility for ease in transportation and stationery solutions. Furthermore, lighter fuel cell stacks add advantage for higher output power at lower overall weights. This stack developed is further optimized with improved flow field designs and design of manifold. These fuel cell stacks are used in PowerUP’s portable fuel cell electric generators that are more efficient and sustainable than the currently used fossil fuel based solutions.

Fuel cell stacks produce a DC output with a 2:1 variation in output voltage from no load to full load. The output voltage of each fuel cell is about 0.4 V at full load and several of them are connected in series to construct a stack. An example 100 V fuel cell stack consists of 250 cells in series and to produce 300 V at full load requires 750 cells stacked in series. Since fuel cells actively convert the supplied fuel to electricity, each cell requires proper distribution of fuel, humidification, coupled with water/thermal management needs. With this added complexity stacking more cells in series decreases the reliability of the system. For example, in the presence of bad or mal-performing cell/cells in a stack, uneven heating coupled with variations in cell voltages may occur. Continuous operation under these conditions may not be possible or the overall stack output power is severely limited. In this paper a modular fuel cell powered by a modular DC-DC converter is proposed. The proposed concept electrically divides the fuel cell stack into various sections, each powered by a DC-DC converter. The proposed modular fuel cell powered by modular DC-DC converter eliminates many of these disadvantages, resulting in a fault tolerant system. A design example is presented for a 150 W, three section fuel cell stack and DC-DC converter topology. Experimental results obtained on a 150 W, three section PEM fuel cell stack powered by a modular DC-DC converter are discussed.

The high costs of fuel cell stacks are often prohibitive for research applications. Instead, researchers tend to either perform tests on individual cells under emulated load conditions, or they use model-based emulated fuel cell stacks to test realistic loads. This paper presents an alternative technique that allows the simultaneous investigation of both cell and hardware. In this technique, an amplifier takes as input the voltage of a reference fuel cell and reproduces the “scaled-up” voltage that would be provided by a stack of similar cells. The output terminals of this simulated stack can be connected to realistic loads, which are series connected with the reference cell to maintain a one-to-one correspondence of cell and load currents. This technique allows the simultaneous investigation of stack/load interactions, stack electrochemical performance characteristics, and stack durability under load. The amplifier electronics are independent of the fuel cell allowing its use with all fuel cell types, e.g., solid oxide fuel cells (SOFCs) or proton exchange membrane fuel cells. We demonstrate the emulator using a single planar SOFC and under several real loads. The data collected reveal good steady-state and dynamic accuracy, and the observed electrical interactions highlight the utility of the emulator in cell and hardware-in-the-loop testing. Ultimately, this technique provides fuel cell system researchers and developers a low-cost, easily implemented tool for rapid assessment of novel fuel cell technologies under real-world loading conditions.

Design and development of modular fuel cell stacks for various applications

This report summarizes the experience and early results from the American Fuel Cell Bus Project, a fuel cell electric bus demonstration funded by the Federal Transit Administration (FTA) under the National Fuel Cell Bus Program. A team led by CALSTART and SunLine Transit Agency developed a next-generation fuel cell electric bus for demonstration. The 40-foot ElDorado National transit bus features a BAE Systems series hybrid propulsion system powered by a Ballard Power Systems fuel cell and lithium iron phosphate batteries. The National Renewable Energy Laboratory (NREL) has been tasked by FTA to evaluate the buses in service. This report documents the early development and implementation of the buses and summarizes the performance results through February 2013.

A fuel-cell hybrid electric vehicle is an advanced type of hybrid vehicle that utilizes a combination of fuel-cell technology and electric propulsion for improved efficiency. The fuel cell generates electricity through a chemical reaction using hydrogen as the fuel source. This electricity powers the vehicle’s electric motor, while a battery system stores excess energy, provides additional power during acceleration, and stores regenerative braking energy. To improve the performance of fuel cell hybrids, designing and developing efficient energy management strategies is an urgent need for current automotive manufacturers. From the perspective of energy consumption, the main work is to reduce hydrogen consumption. In recent years, energy management strategies based on intelligent connected vehicle technology have also received extensive attention. Most fuel cell vehicles are classified as zero- emission vehicles that emit only water and heat. Compared with internal combustion vehicles, hydrogen vehicles centralize pollutants at the site of hydrogen production. In an electric drive vehicle, the low-voltage auxiliary battery provides electricity to start the engine before the traction battery is engaged, it also powers vehicle accessories. This high-voltage battery stores energy from regenerative braking and provides supplemental power to the electric motor. The DC converter converts higher voltage to lower voltage DC power which is needed to run the vehicle and recharge the auxiliary battery. Using power from the fuel cell and the traction battery pack, the motor drives the vehicle’s wheels. A fuel cell stack is an assembly of individual membrane electrodes that use hydrogen and oxygen to produce electricity. So the fuel cell electric vehicle is the best option to simultaneously reduce air pollution, greenhouse gas emissions, and the consumption of fossil fuels Key Words: Battery(auxiliary), Battery pack such as petroleum and natural gas., DC/DC Converter, Electric traction motor(FCEV), Fuel cell stack, Fuel filler, Fuel tank(hydrogen), Power electronics controller, Thermal system(cooling), Transmission(electric)

Fuel cells (FC) are power sources that convert electrochemical energy into electrical energy in a clean and efficient manner. FC technology presents one of the most promising solutions to reduce fossil fuel consumption. FC simulators are expected to play a key role in the development of FC systems due to their low cost and flexibility. This paper presents the development of a stand-alone FC simulator based on a low cost digital signal processor (DSP). The proposed fuel cell simulator emulates the electrical dynamic behavior of a direct methanol fuel cell (DMFC) stack. This is achieved via a power converter with a robust control strategy with fast dynamic response. The reference signal for the power converter that represents the dynamic behavior of the FC is generated from an experimental model of the DMFC that can be extended to other FCs. The output of the FC simulator is a reproduction of the dynamic behavior of DMFC model, thus emulating a FC stack. Test results of the FC simulator and the actual FC are compared and discussed. From the viewpoint of educational purposes, the proposed FC simulator provides a flexible solution at a low cost for student and engineers in training. In addition, the proposed simulator can be used for the design and development of FC power electronics

The efficiency and durability of proton exchange membrane fuel cells has come to the forefront of research and development efforts as sustainable transportation applications shift from passenger to heavy duty vehicles. Complementary research expertise and advanced instrumentation are required to accelerate materials discovery and degradation mitigation of fuel cell components, with significant attention on catalysts, ionomers and membranes. The scanning transmission electron microscope (STEM) is among the key characterization techniques for accelerating materials and device development, providing key insights into atomic scale structure. Automating STEM data acquisition and analysis enables large data sets with improved statistical relevance and throughput will expand the impact of this method in the rapid materials and accelerated stress test development.We will show how the latest instrument developments in automation and high speed detectors enable new insights into catalyst structure and electrode layer degradation. This includes correlative, multimodal STEM techniques, such as aberration-corrected imaging, secondary electron detection, energy dispersive X-ray spectroscopy, cryogenic microscopy and 4D-STEM, to build a more comprehensive view of the effect of particle size and composition on surface strain and durability. These results will be correlated with information obtained from X-ray scattering techniques and fuel cell performance testing to understand the type and degree of degradation occurring during accelerated stress tests under development for heavy duty applications. The prospect of automated electron tomography coupled with identical location (IL)-STEM to provide detailed three-dimensional information on catalyst-support interactions will also be discussed.This material is based on work performed by the Million Mile Fuel Cell Truck (M2FCT) Consortium, technology managers Greg Kleen and Dimitrios Papageorgopoulus, which is supported by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office. Electron microscopy research was supported by the Center for Nanophase Materials Sciences (CNMS), which is a US Department of Energy, Office of Science User Facility at Oak Ridge National Laboratory. The X-ray scattering experiments were performed at beamline 9-ID-C at the Advanced Photon Source (APS) at Argonne National Laboratory (ANL). Use of the APS, an Office of Science user facility operated by ANL, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AS02-06CH11357

Stringent reliability and durability requirements for fuel cells in heavy duty vehicles demand highly durable ionomer membranes. Fuel cell membranes degrade chemically and mechanically during operation, which can lead to membrane thinning, pinhole and crack formation and eventual failure due to hydrogen leaks. The chemical portion of degradation can be suppressed with the use of radical scavenging agents such as cerium oxide. In order to implement extended durability solutions in actual field operation, however, aptly designed accelerated durability tests and empirical models are needed to predict membrane lifetime under various operating conditions, while also considering additive stability over time. Here, an empirical membrane lifetime model recently developed for transit bus applications is modified and demonstrated to predict membrane lifetime with cerium oxide incorporated into the membrane electrode assembly as a chemical stabilizer. The lifetime prediction approach utilizes laboratory scale experimental data from an accelerated membrane durability test complemented by measured cerium washout rates. Provided that the cerium washout rates were relatively low, the predicted membrane lifetime of cerium supported membranes was found to significantly exceed the ultimate 25,000 h heavy duty durability target.

Proton Motor, Škoda Electric collaborate on fuel cell electric buses

The objective of this project is to develop a proton exchange membrane (PEM) fuel cell powered scooter with a designed digital controller to regulate the air supply to PEM fuel cell stack. A 500-Watt (W) electric power train was chosen as a platform for the scooter. Two 300 W PEM fuel cell systems, each containing 63 cells, were used to charge 48-Volt batteries that powered an electric motor. The energy carrier (hydrogen) was stored in two metal hydride tanks, each one containing 85 gs of hydrogen pressurized to 250 psig. The output hydrogen pressure from each tank was maintained at 5.8 psi by a two-stage pressure regulator, and then delivered to each fuel cell stack. To regulate the voltage of each PEM fuel cell under different load conditions, two step down DC/DC converters were used. These converters were connected in series to power the motor controller and charge the batteries. The batteries then supplied power to the 500 W brushless motor mounted to the hub of the rear wheel to save space. After all modifications were completed, most of the parts of the scooter stayed the same except for the panel under the seat—where larger space is needed for accommodating the hydrogen tanks. The weight of the scooter did not change significantly, because the weight of the hydrogen tanks (6.5 kg each) and fuel cell stacks (1.7 kg each) was partially compensated by replacing the batteries from the old ones that weighed 17.5 kg to new ones that weighed 9 kg.