12 - Stack and bipolar plates design for direct methanol fuel cells

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.

<div class="section abstract"><div class="htmlview paragraph">Faced with one of the greatest challenges of humanity – climate change – the European Union has set out a strategy to achieve climate neutrality by 2050 as part of the European Green Deal. Life Cycle Assessment (LCA), which among other aspects identifies climate change effects, is an important tool to assess the environmental characteristic of sustainable technologies or products to fulfill this ambitious target.</div><div class="htmlview paragraph">In this context, research is presented that examines the ecological sustainability impacts of a metallic vs a composite bipolar plate made of innovative graphite-compound based foils for fuel cell applications. A bipolar plate is a central component of the fuel cell stack to ensure efficiency and durability. For this purpose, a LCA is performed for both bipolar plate materials. This assessment follows the methodology of DIN EN ISO 14040/44 and the EU Product Environmental Footprint framework. Focusing on cradle-to-gate system boundary conditions, the research emphasizes the manufacturing processes with the relevant material and energy flows. Dealing with uncertainties in the energy supply chain, a comprehensive sensitivity analysis is conducted defining current and future energy scenarios with various shares of renewable and fossil energy carriers. Furthermore, the impact of different material production locations on the outcome of the LCA is investigated, considering changing geopolitical conditions. To assess also the effect on a fuel cell stack, the study continues with a cradle-to-gate evaluation of the fuel cell system. Afterwards, to also consider the complete lifetime of a fuel cell vehicle, the study is extended to cradle-to-grave system boundary conditions for a C-segment SUV. Besides the evaluation of the global warming reduction potential, the study deals with the impact of the production processes of both bipolar plates on other impact categories like freshwater eutrophication or acidification. The investigations have shown that the use of foil-based graphite-compound bipolar plates can reduce the global warming potential by up to 75% compared to conventional steel bipolar plates.</div></div>

Design and development of modular fuel cell stacks for various applications

Review A Review of Fuel Cell System Technology: From Fuel Cell Stack to System Integration Weiqun Ren 1,*, Jun Shen 2, Xuebing Li 1, and Changqing Du 2 1 Dongfeng Commercial Vehicle Co. Ltd., 10 Dongfeng Avenue, Wuhan, China 2 Wuhan University of Technology, Wuhan, China * Correspondence: renweiqun@tsinghua.org.cn; Tel.: +86-139-1820-4209 Received: 14 October 2022 Accepted: 8 November 2022 Published: 18 December 2022 Abstract: The technology of hydrogen fuel cell vehicles (FCV) is the ultimate direction of clean energy vehicle development, and commercial vehicles are the most important application area for fuel cell commercialization. This paper summarizes the key components, technologies and development trends of the fuel cell stack, fuel cell system and vehicle integration at home and abroad, and points out that key materials (such as bipolar plates and membrane electrodes), key system components (such as air compressors and ejectors), high-power modular integration technologies, and fuel cell control technologies are the main factors influencing the commercialization of FCVs. Particularly, we put the main fouce on variable ejector or multi-stage ejector technology, integrated and optimized control technology, and multi-energy cooperative control technology due to their crucial roles in meeting the industrial development of FCVs in China. Furthermore, some guidance opinions are also provided for reference about the development and industrialization of FCVs.

Proton exchange membrane (PEM) fuel cells generate electric current by means of the reactants hydrogen or methanol and oxygen, emitting only heat and water or water vapor. Fuel cells therefore represent a possible technological option for a CO2-neutral energy supply. A core component of fuel cells are bipolar plates (BPP) which are stacked alternately with membrane electrode assemblies (MEA) to form fuel cell stacks. The BPP must ensure leakage-free supply of the fuel gas and oxidation gas to the MEA and removal of the reaction products (electric current, heat and water). One approach to produce thin BPP sheets with high dimensional fidelity at a high quality and dimensional accuracy is hot pressing of graphite compound which, however, offers only limited productivity due to long process times. This paper presents a proof of concept for pressing thin BPP made of highly filled graphite compound, with wall thicknesses down to 0.3 mm, at a low temperature. For the experimental investigations, a multi-part press tool was developed for bipolar half plates (BP-HP) with a size of 540 × 140 mm and designed for high performance applications. The various challenges for forming with regard to material, BPP and die design as well as first pressing parameters such as pressure and temperature were investigated in a proof of concept.KeywordsPressingBipolar plateFuel cell

The PEM Fuel Cell (PEMFC) performance depends on the operating parameters like temperature, pressure, stoichiometric ratio of reactants, relative humidity, back pressure on anode and cathode flow channels, and the design parameters like rib width to channel width (L:C), channel depth, shape of the flow channel and number of pass on the flow channel. The voltage and power produced by single cell was not enough for practical applications, hence number of cells are connected in series or parallel to generate required current and voltage to form a fuel cell stack. The effective performance of fuel cell stack depends upon the satisfactory operation of individual cells. For effective thermal management, water management and distribution of reactants (H2 and o2) is challengeable task in fuel cell stack. The design of bipolar plate is contributing more in PEM fuel cell stack to meet the above said critical parameters. In this paper numerical investigation of 500w PEM fuel cell stack with each cell of 100 cm2 active area with rib to channel width (L:C-2:2) of single pass, three pass and six pass parallel serpentine flow channel with square channel inlet and outlet were carried out. The three dimensional PEMFC stack with various passes (1,3,6) for serpentine flow channel were modeled by pro-e, meshed by ICEM 14.0 software packages and simulated using CFD Fluent 14.0 under various operating pressure range from 1 bar to 2 bar and flow rate of hydrogen and oxygen as 500ml/min and 250ml/min respectively. The numerical modeling results on performance of PEMFC stack has been studied and compared and the better flow channel design was identified.

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.

Our dependency on road transportation of people and goods is huge. Unfortunately, this transportation is mainly fed by fossil fuels, with as accompanying disadvantages undesired local and global emissions and politically less desired dependencies. Electric propulsion systems can help to cover the disadvantages of fossil fuel based transportation. Still, battery based, grid charged electric vehicles will not provide an overall solution. Charging takes time and puts a signicant demand on the local electric infrastructure. In addition, such vehicles have a modest range. Therefore, our future mobility is expected to be driven by a more diverse palette of energy carriers, including hydrogen. Hydrogen can be provided by renewable sources and fueling a vehicle with hydrogen takes little time. As the energy density of hydrogen is large compared to batteries, also fuel cell hybrid vehicles provide a signicant longer driving range compared to battery only electric vehicles. In addition, local production of hydrogen by electrolysis with electricity from the local grid, provides new possibilities for demand side management. A fuel cell hybrid propulsion system consists of a fuel cell system to convert hydrogen into electricity, a battery to cover variations in the demand for electric power, a DC/DC converter to match the battery and the fuel cell stack voltages, and an electric motor with inverter to propel the vehicle. Apart from the fuel cell stack, the fuel cell system itself comprises a hydrogen tank to store hydrogen under pressure, a control valve to reduce the hydrogen pressure, a recirculation pump to reuse the surplus of hydrogen leaving the fuel cell stack, a humidier to prevent the fuel cells from dehydration, an air compressor to supply oxygen to the stack and a cooling system to keep the stack at the right operating temperature. The fuel consumption of such a fuel cell hybrid propulsion system is determined by the operation of the vehicle, the management of powers from fuel cell stack and battery, and the sizes of the fuel cell stack and battery. The operation of the vehicle depends on its purpose, its dimensions, the trac conditions and how the driver drives the vehicle. Although how to drive the vehicle is up to the driver, the resulting demand for electric power can still be characterized. This study suggests to characterize the power for traction as a normal distribution. Both simulations and measurements support this assumption, but conclusive evidence is not part of this study. The energy management system denes the management of powers from fuel cell stack and battery when driving the vehicle. This study concludes a close to optimal operation of fuel cell stack and battery is achieved, when the point of operation of the fuel cell stack is chosen equal to the average power demand, and when all variations from this average power demand are distributed over fuel cell stack and battery according to the ratio in their internal losses. The real-time implementation of this energy management strategy determines the value of the average power demand on the measured changes in the amount of energy stored in the battery. The resulting feedback loop provides a robust solution against disturbances, model errors and slowly changing parameters due to issues related to aging. The proposed solution to the energy management problem is validated on a full-scale test facility and demonstrated on a fuel cell hybrid delivery van. The found analytic solution to the energy management problem enables the derivation of an expression for the third factor in fuel consumption; the sizes of fuel cell stack and battery. This derivation makes use of the previously mentioned characterization of the power demand as a normal distribution. The resulting relation expresses the fuel consumption in terms of: properties of the driving cycle such as average speed, parameters of the vehicle such as weight and air resistance, and the number of fuel cells and battery cells. The optimum sizes of fuel cell stack and battery are derived from this relation. The resulting expression shows that, to obtain a minimum fuel consumption, the optimum size of the fuel cell stack does not match the average power demand, nor the maximum power demand, two choices commonly observed for prototypes currently available. Under ordinary condition, its optimum size is located between these two extremes. The sensitivity of the fuel consumption on the fuel cell stack size around this optimum value is limited, which makes the choice for the fuel cell stack less critical. The corresponding optimum size of the battery is the smallest size for which fuel cell stack and battery still can provide the maximum in the power demand and absorb the regenerated power when decelerating the vehicle. The optimum sizes found for the fuel cell stack and the battery are veried through brute force computer simulations. Based on an existing fuel cell hybrid vehicle, for dierent driving cycles, the fuel consumption for all feasible combinations of fuel cell stack size and battery size are derived by simulation. The results match the results of the proposed method. This not only substantiates the proposed sizing method, but also supports a normal distributed power demand as suitable characterization when optimizing the sizes of fuel cell stack and battery in terms of a minimum fuel consumption. An important contribution of the study is the analytical approach of both the energy management problem and the sizing problem. This analytical approach provides a solution to the sizing problem. Moreover, it provides an understand ing how parameter values aect the fuel consumption. For example, a reduction of the specic weights of battery cells and fuel cells oers the best opportunity for additional fuel savings, followed by a reduction of the auxiliary power and a reduction of the internal resistance of battery cells and fuel cells. The observation the fuel consumption is not very sensitive against variations in the fuel cell stack size around its optimum value, can help manufacturers of fuel cell stacks and systems to reduce the number of products over a certain power range. Consequently, the turnover per product will increase and production costs per product will reduce. This will help fuel cell hybrid propulsion systems to faster contribute to the desired reduction of our dependency on fossil fuels and to a further reduction of unwanted (local) emissions.

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.

EKPO Fuel Cell GmbH was founded in 2021 by two parent companies, ElringKlinger and Plastic Omnium, whom both are strong and established automotive suppliers with mass manufacturing capabilities and strategic approaches to hydrogen and the fuel cell businesses. The aim of EKPO is the development and production of proton exchange membrane fuel cell stack components and stack modules. Drawing from the experiences of the pilot automated production line since 2016, a fully optimized automated production, with improved production technologies and products, was developed by EKPO in 2021 to achieve an output capability of 10,000 stacks per year. The line was designed with a modular and scalable approach that allows flexibility as well as increased capacity by parallelization. The implementation is successful of producing EKPO’s various stack platforms while maintaining a high level of quality and production standard for the automotive industry.Since EKPO offers a wide range of products, the automated line can cover stack power ranges from 10 kW up to > 200 kW. As a prerequisite for excellent technical performance, in addition to function quality measures were set as key targets from the start of the development. EKPO has thus established consistent and stringent quality process flows and processes for all production steps. These measures include the early involvement of measurability and manufacturability assessment on all process and analysis steps on the different levels (i.e., components and stack). The feedback from each workflow can then continuously improve products, processes, and documentation regarding product specific codes standards and regulations (CSR).The accumulative knowledge from two decades of activity of fuel cell component and stack development enabled EKPO to establish a production range starting from cell and stack components (i.e., bipolar plates, sealings, and plastic end plate modules) to fuel cell stacks and modules produced by fully automated MEA and stack assembly and end-of-line testing. The automated production covers all processes from bipolar plate manufacturing and assembly, CCM and GDL roll good cutting, MEA-assembly, stacking, and the final compression and characterization of the fuel cell stack. The quality matrixes include inspecting performance key figures as well as quality and geometries of the stack and its components. The incoming materials are typically supplied as roll goods, (i.e., GDL, CCM, and metal coil) or as raw material (i.e., plastic granules). As the incoming materials and finished components are very sensitive to environmental conditions and particle contamination, the entire MEA processing and stack assembly process takes place in a cleanroom with controlled climate for maximum process stability and reliability.With a key approach of “design to manufacture” and deep understanding of stack technology and component requirements, EKPO is able to deliver two best in class stacks, namely the NM5 evo and NM12 single and twin platforms.

Toshiba’s Stationary Fuel Cell SystemToshiba Energy Systems & Solutions Corporation is developing hydrogen solution, which is a key technology to achieve carbon neutral. Now we are manufacturing the pure hydrogen fuel cell systems for stationary application. This fuel cell systems have some models up to 100kW, and in order to provide the larger electricity than 100kW, the 100kW system can be operated connecting several units up to 1MW.Toshiba's fuel cell systems have been achieved stable, long-term operation, high durability, and high energy efficiency. These features are realized by internal water management cell stack conflagration using porous carbon bi-polar plates. The porous bi-polar plates can humidify reactant gases supplied as vapor from the surface of the porous bi-polar plates and removes produced water through the porous bi-polar plates by the pressure difference between the reactant gases and the coolant water. This technology realizes ideal conditions in terms of water activity entire active area, suppressing overpotentials due to flooding and temperature and water activity distribution. This technology enables stable continuous operation up to 1 week and design life of 80,000 hours confirmed by demonstration tests, which is one of the highest in the world.Recent trends in fuel cell development include the growing expectation and demand for higher capacity and long durability fuel cell systems for stationary applications such as carbon neutral complexes and data centers, etc. In addition, demand for high power density fuel cell systems for large commercial mobility vehicles, such as buses and trucks, is also increasing. In order to meet this demand, Toshiba is developing elemental technologies for higher performance fuel cells.Development of advanced high performance fuel cellsIn order to improve cell performance, it is necessary to reduce ohmic, activation, and diffusion polarizations. Among these three overpotentials, a reduction of diffusion polarization is particularly important to achieve operation up to the high current density. To reduce diffusion polarization, the flow field of bi-polar plates must be designed to improve the limiting current density by efficient gas supply to the catalyst layer and to reduce mass transport resistance in the gas diffusion layer and catalyst layer.Toshiba has focused on reducing this diffusion polarization and is working on the flow field design using numerical simulation. As an example, Toshiba has developed the advanced numerical simulation by introducing mass transfer models of water evaporation and water absorption on the surface of a porous bi-polar plates into a commercially available electrochemical reaction and thermal fluidics 3D simulator.This porous bi-polar plates model was then used to perform parametric study of the flow field design, and determine parameters in terms of gas diffusivity, electrical resistance, and temperature and humidity distribution. And then, the advanced cell that incorporating designed bi-polar plates, thinner components, and a new catalyst was fabricated and evaluated. Figure 1 shows comparison of cell performance between conventional and advanced cells. The limiting current density of advanced cell is 3.6 times larger than that of conventional cell due to simulation-based flow field design and optimization of operating pressure. The application of these development items and optimization of operating conditions reduced each polarization and achieved a current density twice that of conventional cell. In the future, we aim to achieve even higher performance by improving catalytic activity and reducing cell resistance through thinner components. Figure 1

Within the last decades, fuel cells have become the center of attention of research community, industry, and the general public. This is due to the emphasis on the sustainability of the society and the emerging concept of a hydrogen economy. Proton exchange membrane fuel cells (PEM FCs) represent a mature and established fuel cell technology. The flexibility of operation, the high degree of fuel utilization, and the output power density make them suitable for mobile applications such as hydrogen-fueled vehicles or on-site energy generation. Membrane electrode assembly (MEA) is the mainstay of the PEM FCs. The MEA consists of the proton exchange membrane, catalytic layers, and gas diffusion layers (GDLs). Single MEAs are interconnected by bipolar plates with flow field channels homogenously distributing reactants and realizing easy removal of the generated water. Individual cells are compressed together, forming the fuel cell stack. The GDL plays a three-fold role in the performance of PEM fuel cells. It has to offer good electrical conductivity, ensure good reactant distribution along the reaction zone, and facilitate the removal of the water produced by the fuel cell operation. The optimal combination of these three aspects of GDL allows the FC to achieve high performance. Furthermore, the homogeneous distribution of the reactants is crucial for the durability and lifespan of the FC. The inhomogeneous reactants distribution leads to a local starvation of the electrode, leading to high local overvoltage and thus shortening the lifespan of overloaded parts. Although GDLs play a crucial role in the operation of PEM fuel cells, so far, they have received little attention. Hence, the objective of our study is to compare commercially available GDLs with respect to their properties, namely permeability under conditions close to the operating fuel cell.The approach of combining advanced mathematical modeling with extensive experimental characterization was used to achieve this task. Testing cells allowing precise determination of the in-plane permeability of various GDLs were designed based on the computational fluid dynamics modeling. According to the contemporary literature, two different carbon based GDLs were examined, namely carbon-cloth and carbon-paper, which principally differ in the carbon-fiber orientation in their internal structure. The investigated properties of GDLs thus include thickness, porosity, internal structure, and the presence or absence of microporous layer.The achieved experimental results show that at given compression, thicker carbon paper GDLs are superior to carbon cloth samples in terms of permeability and deformation resistance. The obtained permeability values of GLDs at different degrees of compression were compared with predictions based on the Carman-Kozeny equation to assess the accuracy of this semi-empirical prediction. Finally, the importance of the optimal flow field and GDL combination in terms of reactant distribution in the fuel cell stack of industrial conditions is documented via mathematical modelling based on the obtained experimental data.This work was supported by the European Regional Development Fund-Project “Fuel Cells with Low Platinum Content” (No. CZ.02.1.01/0.0/0.0/16_025/0007414).

Chapter 5 - Modelling of fuel cell stacks

Fiber optic sensors integrated into fuel cell stacks have the potential to significantly enhance the temperature control and health monitoring of fuel cells. Inhomogeneous loading, both within individual cells and across different cells in a stack, leads to the formation of local hotspots that accelerate aging and degrade performance. This study investigates the behavior and feasibility of incorporating polyimide-coated optical fiber sensors into bipolar plates for precise and spatially resolved temperature monitoring. The sensor is successfully integrated into a single cell of a fuel cell stack and positioned on the bipolar plate in direct contact with the membrane electrode assembly. Pre-tests are conducted to thoroughly evaluate the technical properties of the fiber in relation to specific cell requirements. Additionally, a physical prototype featuring the sensor is developed and employed to validate its effectiveness under realistic operating conditions. The temperature measurement obtained via the fiber exhibits a continuous profile throughout the entire length, covering both the active area and distributor region of the cell. Throughout the entire 60 min test period, the measuring system provides continuous and uninterrupted temperature measurements, encompassing the start of the stack, the heating phase, the subsequent stable operating point, and the cooling phase. However, some technical challenges have been identified, as mechanical pressure exerted on the fiber influences the measured temperature. While this work demonstrates promising results, further advancements are necessary to address inhomogeneous loading within fuel cells and hotspot mitigation. The precise monitoring of temperature distribution enables early detection of potential damage, facilitating timely interventions to improve the service life and overall performance of fuel cells.

The commercialization of fuel cell products for a variety of applications including forklifts, buses, cars and heavy duty trucks is well underway. Particularly in the heavy duty fuel cell market, recent studies suggest that in Europe, fuel cell electric buses (FCEB) total cost of ownership (TCO) will breakeven with battery electric buses (BEB) by 2023, and with internal combustion engine buses (ICEB) by 20241. For applications such as long-distance and heavy-duty transportation, the hydrogen route appears the decarbonisation option of choice, and can become cost competitive with internal combustion engines by 20302.Over the past 30 years, Ballard has developed a wide array of technology “building blocks” for Fuel Cell stacks components. The application requirements (duty cycle, speed, vehicle weight, lifetime and environmental exposure) will determine the key stack features and result in customization of components where economically viable. In contrast with fuel cell stacks developed for passenger cars, Fuel Cells for heavy duty vehicles are particularly challenged by high durability requirements3, with MEA attributes such as catalyst loading and peak efficiency point significantly affecting stack and fuel costs.Building on proven and demonstrated stack durability in the field of more than 35,000 hours in heavy duty vehicles4 Ballard’s MEA development activities draw from extensive field experience to support step changes in durability with each subsequent product iteration. The use of an accelerated testing and modeling approach developed and validated over numerous product iterations enables continuous cost decreases and gains in power density, operational robustness and reliability, with a calculated risk tolerance for new technology introduction.Those MEA durability prediction models along with a good understanding of failure mechanisms are a cornerstone to developing the next generation of Fuel Cells for heavy duty vehicles. Of particular importance is the use of the voltage degradation model to evaluate the time to reach the degradation target for heavy duty applications (USDOE Ultimate target of 10% degradation at 30,000 hours5). Simulation results as a function of the electrode composition show the relationship between cathode catalyst loading and lifetime, and assist in making electrode design and composition choices for a successfully durable product. A sharp increase in voltage loss is observed when local oxygen transport resistance becomes limiting once the cathode reaches low surface area. Maximizing beginning-of-life catalyst electrochemical surface area (ECSA) utilization in the electrode structure, as well as optimizing surface area retention, can have significant benefits for lifetime. A combination of design choices or processing parameters during catalyst layer fabrication can be effective ways to optimize the electrode6.The same voltage degradation model is used to demonstrate the relationship between lifetime and the peak operating current density of the product, which limits the stack design power density within the allocated voltage degradation constraints of heavy-duty vehicles.The simulation results demonstrate that the ideal Fuel Cell stack for heavy duty applications is the result of complex trade-offs between cost, stack design attributes (e.g. catalyst loading), active area sizing (peak efficiency point) and durability, with the ultimate goal to achieve an attractive TCO for wide acceptance of the technology. References Deloitte and Ballard. (2020). Fueling the Future of Mobility: Hydrogen and fuel cell solutions for transportation. Volume 1 [White paper]. Deloitte China. https://www2.deloitte.com/content/dam/Deloitte/cn/Documents/finance/deloitte-cn-fueling-the-future-of-mobility-en-200101.pdf McKinsey & Company and Hydrogen Council. (2020). Path to hydrogen competitiveness: A cost perspective. https://www.hydrogen.energy.gov/pdfs/19006_hydrogen_class8_long_haul_truck_targets.pdfMacauley, N., Lauritzen, M., Knights, S. and Kjeang, E., J. Electrochem. Soc., 165(10), F780 (2018).https://www.ballard.com/about-ballard/newsroom/news-releases/2020/01/27/ballard-powers-fuel-cell-electric-vehicles-for-unprecedented-30-million-kilometers-enough-to-circle-the-globe-750-timesUSDOE Hydrogen Class 8 Long Haul Truck Targets https://www.hydrogen.energy.gov/pdfs/19006_hydrogen_class8_long_haul_truck_targets.pdf M. Dutta, A. Young, V. Colbow, J. Bellerive, S. Knights, Examining Catalyst Layer Design Strategies for Improved Fuel Cell Performance and Durability, ECS PRiME 2020