Assessment of Technologies for Improving Light-Duty Vehicle Fuel Economy—2025-2035 (2021) / Chapter Skim
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6 Fuel Cell Electric Vehicles
6 Fuel Cell Electric Vehicles
Pages 144-200
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Fuel cells offer an alternative to batteries in difficult-to-electrify applications such as vehicles with heavy payloads or high vehicle miles traveled (VMT) that need lighter weight powertrains, longer driving ranges, and/or quicker refueling times.
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This chapter also provides information on the status of hydrogen refueling infrastructure, plans to accelerate infrastructure development, and R&D efforts to improve hydrogen technologies. The chapter ends with findings and recommendations for automotive fuel cells and hydrogen refueling infrastructure.
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. several types of fuel cells, the proton exchange membrane (PEM)
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Reprinted by permission from Springer Nature Customer Service Centre GmbH: [Springer Nature] PEM Fuel Cell Fundamentals by Yuan and Wang, in PEM Fuel Cell Electrocatalysts and Catalyst Layers, J
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, and the onboard hydrogen storage system. A generic flow schematic showing the basic components of an automotive fuel cell power system is shown in Figure 6.4.
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. Toyota is demonstrating fuel cells in heavy-duty freight handling trucks at the Port of Los Angeles and Long Beach (Toyota USA Newsroom, 2019a)
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. Improvements in FCEV fuel economy and cost depend on technology progress, particularly reducing the size and weight of the fuel cell and hydrogen storage systems and increasing the efficiency of the fuel cell system.
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. The study, which assumed that an affordable hydrogen refueling infrastructure will be available, projected that FCEVs may have a cost advantage over BEVs for larger vehicles like passenger vans and sport utility vehicles (SUVs)
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To assess the status and expected future cost and performance of automotive PEM fuel cells, in 2017 Carnegie Mellon University (CMU) led an expert elicitation assessment of fuel cell system cost, stack durability, and stack power density under DOE's high-volume production scenario of 500,000 units per year (Whiston et al., 2019)
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. FIGURE 6.8 PEM fuel cell polarization curve at 1.5 atm (left)
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-- that is, at part load where most driving takes place -- and then drops in the high-power region of fuel cell operation. Fuel cells operate most effectively at constant load.
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. Additional cost savings will come from sizing the fuel cell, hydrogen storage tank, and battery for various drive cycles (Sundström and
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NOTE: OCV is open circuit voltage -- a figure of merit for fuel cells, defined as the maximum operating voltage of the fuel cell, which occurs when no current is flowing (i.e., when no load is applied)
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. As discussed in FCEV energy management strategies, optimizing the sizing of the fuel cell, hydrogen storage tank, and battery is key to maximizing PFCV performance and durability, and minimizing cost of ownership.
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owing to increased hydrogen storage capacity and enhanced fuel cell performance (Toyota USA Newsroom, 2019b)
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FUEL CELL ELECTRIC VEHICLES 159 2020 -- 2022 2023 -- 2025 2026 -- 2030 2031 and beyond Immediate next steps Early scale-up Diversification Broad rollout Applications Under development (e.g., pilots) or early commercialization Mature market 2050 Transportation Light-duty passenger ambitions fuel vehicles Light commercial vehicles/buses Centralized Medium- and power heavy-duty trucks Rail CCU Pure H2 Steel heating Material handling/ Low carbon Low/ forklifts medium fuel2 Distributed power Blended H2 industrial (other segments)
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Because long-term durability data for automotive fuel cells is lacking, this cost analysis is for a model system meeting beginning-of-life performance requirements. These cost estimates are also for technologies in the pipeline but not yet commercial; therefore, they do not take into account 9 The DOE Fuel Cell Technologies Office recently changed its name to the Hydrogen and Fuel Cells Technologies Office.
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This will be discussed in more detail in the next section on durability. A breakdown of PEM fuel cell stack cost, shown in Figure 6.13, indicates that the catalyst is the largest cost component at both low and high volumes.
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Commercial fuel cells are expected to use PGM-based catalysts in 2025–2035; however, some experts believe that a transition to PGM-free catalysts is needed for FCEV cost competitiveness in the longer term. The balance of plant (BOP)
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Within the United States, DOE supports several R&D efforts aimed at reducing the cost of PEM fuel cells while increasing durability and maintaining or improving performance. These include two consortia led by DOE national laboratories:11 • Fuel Cell Consortium for Performance and Durability (FC-PAD)
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Incomplete oxygen reduction at the cathode can produce significant amounts of hydrogen peroxide, which causes oxidative degradation of the membrane. Thus, there is significantly more research focused on cathode improvements to lower the cost of PEM fuel cells and increase their power density, efficiency, and durability.
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In 2025–2035, automotive fuel cells are likely to see a gradual lowering of Pt content, leading to reduced FCEV cost; however, current PGM-free catalysts are far from meeting automotive performance targets. PGM-free catalysts are unlikely to be in commercial FCEVs in that time frame, and their success beyond that is uncertain.
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. Both proton exchange membrane fuel cells (PEMFCs)
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Significant advances are needed before AEMFCs can be considered a viable alternative to PEMFCs; thus, it is unlikely that they will be in commercial FCEVs in 2025–2035. 6.4.1.3 Gas Diffusion Layers The GDL in the PEM fuel cell is used for optimal distribution of reactants to the catalyst layer and for water management within the MEA (Tomas et al., 2017)
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6.4.1.4 Bipolar Plates BPs are a key component in PEM fuel cells, performing several essential functions. They connect each cell electrically, supply the reactant gases -- hydrogen and oxygen (from air)
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. A comparison of the cost of metallic, carbon composite, and expanded graphite plate materials suggested that metal plates may be the lowest cost pathway, and that achieving the DOE 2020 target may be possible by using lower cost plate material, improving the manufacturing process, and increasing the power density of the fuel cell stack.
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Moving forward, increased manufacturing R&D will be critical to achieving the economies of scale needed to reduce the cost of fuel cell and hydrogen technologies. 6.4.1.7 Onboard Hydrogen Storage Because of the size and weight constraints of LDVs, high volumetric and gravimetric energy densities are important characteristics for LDV fuels.
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FUEL CELL ELECTRIC VEHICLES 171 FIGURE 6.17 Fuel cell stack design with combined GDL and gasket. SOURCE: Freudenberg Sealing Technologies (2018)
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Therefore, R&D activities are under way to lower the cost and reduce the volume of compressed hydrogen tanks, and to develop alternative methods of hydrogen storage to enable affordable, lightweight, and compact hydrogen storage systems for FCEVs. Alternative approaches include liquid, cryo-, or cold-compressed hydrogen; physisorption of hydrogen on materials with a high specific surface area; hydrogen intercalation in metals and hydrides; and chemical hydrogen storage methods.
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Compressed hydrogen tanks are used in commercial FCEVs today and are likely to be the hydrogen storage technology used in 2025–2035 FCEVs. State-of-the-art tanks contain hydrogen gas at 350 or 700 bar in composite overwrapped pressure vessels (COPVs)
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DOE has reported a gravimetric energy density of 1.48 kWh/kg (~4.5 wt%) and a volumetric energy density of 0.83 kWh/L for today's 700 bar compressed hydrogen storage systems.
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Automakers are storing hydrogen in two or three onboard tanks in today's commercial FCEVs. In both the Toyota Mirai and the Honda Clarity, the front hydrogen tank sits beneath the rear passenger seat, while the rear tank is behind the rear passenger seat.
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. indicates that two-tank storage systems are more expensive than single-tank systems primarily owing to a second set of in-tank valves required for the two-tank design.
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Interest in cryo-compressed hydrogen storage is driven by its potential for higher energy density, enabling a smaller tank size than 700 bar compressed hydrogen tanks; a lower cost than full liquefaction and a longer dormancy period than liquid hydrogen; and in some cases, a lower cost than 700 bar compressed hydrogen. For a 500 bar cold-compressed hydrogen system, one study estimated a 30% cost reduction and 38% mass reduction from a 700 bar system through material improvements, composite layup design and cold gas operation, even when the required onboard insulation for cold gas storage is included (Simmons, 2014)
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has been incorporated into the U.S. DOE Hydrogen Storage Materials Database.
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Research is currently directed at lowering dehydrogenation temperatures and improving reaction kinetics. Another type of chemical hydrogen storage is liquid organic carriers -- for example, N-ethylcarbazole and methyl-cyclopentane -- which would enable a liquid refueling infrastructure.
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6.5 HYDROGEN REFUELING INFRASTRUCTURE FOR FCEVS A number of obstacles have limited the development of hydrogen fueling infrastructure for FCEVs. The cost of producing and delivering hydrogen to refueling stations is currently high, primarily owing to low volume demand (CaFCP, 2015; Connelly et al., 2019)
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. California's Low Carbon Fuel Standard Hydrogen Refueling Infrastructure credit program, launched in 2019, has encouraged hydrogen station operators to increase the renewable hydrogen content of their fuel and earn more credits.
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, which envisions 1 million FCEVs and 1,000 hydrogen fueling stations in California by 2030 (CaFCP, 2018)
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. FIGURE 6.27 Hydrogen refueling station cost as a function of capacity and time.
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. The buildout of hydrogen infrastructure is expected to benefit from development of fuel cells for MHDV applications and from fleet vehicles that need constant operation, quick refueling, and/or high daily VMT.
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. Several OEMs and hydrogen providers have noted that deployment of fuel cells in heavy-duty transportation applications -- drayage and long-haul trucks, buses, marine vessels, and large mining vehicles -- will exponentially increase demand and drive down the cost of hydrogen production and distribution.
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(3) Assuming FCEV capex cost reduction owing to fuel cell production at scale, gasoline cost of $3.36/gallon from EIA 2030 outlook, a lifetime of 200,000 miles, ranges based on efficiency for SUV gasoline of 29 MPG (efficiency in 2019)
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Hydrogen demand for fuel cells will continue to increase as markets continue to grow in on-road ve hicles, material handling equipment (forklifts) used in warehouses (Satyapal, 2019)
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• Reducing the cost of hydrogen storage tanks by developing low-cost, high-strength CF and scaling-up manufacturing. • Developing novel liquid and solid carriers for storing hydrogen.
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Three automakers have reiterated plans to continue development of fuel cell technology for the LDV market in the near term. While the shift by some automakers to a short-term focus on MHDV applications for fuel cells introduces uncertainties regarding widespread LDV deployment, the increased focus on those applications will enable continued fuel cell cost reductions, durability improvements, and hydrogen infrastructure build-out.
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$3,383 63% efficiency Small (60 kW max) $2,246 68% efficiency Fuel Cell Stack Midsize (81 kW)
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FINDING 6.4: Materials and design and engineering improvements continue to lower the cost and improve the performance of fuel cell systems, hydrogen storage tanks, fuel cell electric vehicles, and hydrogen stations. The proton-exchange membrane fuel cell, containing platinum and platinum-alloy catalysts and perfluorosul fonic acid type membranes, is expected to be the automakers' technology of choice for 2025–2035 vehicles.
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and hydrogen technologies, yet manufacturing R&D efforts have been limited. Development of low-cost, high throughput manufacturing processes for electrolyzers, fuel cells, and hydrogen storage tanks for all FCEV classes is needed to achieve economies of scale.
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2020. "HyMARC: A Consortium for Advancing Hydrogen Storage Materials." Presented at the DOE Hydrogen Program: 2020 Annual Merit Review.
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2012. Fuel cell electric vehicles and hydrogen infrastructure: Status 2012.
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2017. "Carbon Fiber Composite Material Cost Challenges for Compressed Hydrogen Storage Onboard Fuel Cell Electric Vehicles." Presented at the Fuel Cells Technology Office Webinar.Washington, DC.
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2017. "VII.A.1 Fuel Cell Electric Vehicle Evaluation." 2016 DOE Hydrogen and Fuel Cells Program Annual Progress Report.
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2020. "Can Hydrogen Fuel Cells Solve the Pain Points of Electric Vehicles?
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2016. "Comparison of On-Road Fuel Economy | Fuel Cell Electric Vehicle Composite Data Products." National Renew able Energy Laboratory, Hydrogen and Fuel Cells.
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DOE Hydrogen and Fuel Cells Program, 2019 Annual Merit Review and Peer Evaluation Meeting. https://www.hydrogen.
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2017b. "Target Explanation Document: Onboard Hydrogen Storage for Light-Duty Fuel Cell Vehicles." United States Driving Research and Innovation for Vehicle Efficiency and Energy Sustainability (U.S.
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