Fuel Cells Fuel cells are the most efficient devices for extracting from . Capable of running on a variety of fuels, including , natural , and , fuel cells can provide clean power for applications ranging from less than a to multiple megawatts. Our transportation—including personal , trucks, buses, marine vessels, and other specialty vehicles such as lift trucks and support equipment, as well as auxiliary power units for traditional transportation technologies—can be powered by fuel cells. They can play a particularly important role in the future by enabling replacement of the we currently use in our and trucks with cleaner, lower-emission fuels like cells directly convert the in hydrogen to , with pure water or . and potentially useful as the only byproducts. Hydrogen-powered fuel cells are not Stationary fuel cells can be used for only pollution-free, but also can have more than two the efficiency of traditional backup power, power for remote technologies. locations, distributed power generation, and (in which excess heat efficient. The can use , where a catalyst causes the hydrogen released during is 60% of the fuel’s energy—correspond- to separate into and used for other applications). They can ing to more than a 50% reduction in fuel . The membrane allows only the take advantage of inexpensive natural gas consumption compared to a conventional protons to pass through it. While the pro- and low- fuels like biogas, enabling significant efficiency improvement and with a internal combustion tons are conducted through the membrane gas reduction when compared . When using hydrogen produced to the other side of the cell, the stream of to combustion-based power generators. from natural gas, fuel cell vehicles are ex- negatively-charged electrons follows an pected to have well-to- greenhouse external circuit to the . This flow of Fuel cells can power almost any portable application that typically uses batteries, gas emissions less than half that of current electrons is electricity that can be used to from hand-held devices to portable gasoline-powered vehicles. do , such as power an . generators. In addition, fuel cells operate quietly, have On the other side of the cell, air flows fewer moving parts, and are well suited to a through channels to the cathode. When Why Fuel Cells? variety of applications. the electrons return from doing work, they Fuel cells directly convert the chemical Excess power produced by intermittent react with in the air and the protons energy in hydrogen to electricity, with pure renewable sources like solar and wind can (which have moved through the membrane) water and potentially useful heat as the only be stored in the form of hydrogen, and either at the cathode to form water. This union is byproducts. Hydrogen-powered fuel cells fed back into the when needed or an exothermic reaction, generating heat that are not only pollution-free, but they can used to power fuel cell electric vehicles. In can be used outside the fuel cell. also have more than two times the efficien- this way, fuel cells could play an important The power produced by a fuel cell depends cy of traditional combustion technologies. role in aiding the widespread deployment of on several factors, including the fuel cell A conventional combustion-based power clean renewable power sources. type, size, temperature at which it operates, plant typically generates electricity at and pressure at which are supplied. efficiencies of 33 to 35%, while fuel cell How Do Fuel Cells Work? A single fuel cell produces roughly 0.5 to can generate electricity at ef- A single fuel cell consists of an 1.0 , barely enough for even the ficiencies up to 60% (and even higher with sandwiched between two , smallest applications. To increase the volt- cogeneration). an anode and a cathode. Bipolar plates age, individual fuel cells are combined in series to form a stack. (The term “fuel cell” The gasoline engine in today’s typical on either side of the cell help distribute is often used to refer to the entire stack, as is less than 20% efficient in converting the gases and serve as current collectors. In a well as to the individual cell.) Depending chemical energy in gasoline into power that Electrolyte Membrane (PEM) fuel on the application, a fuel cell stack may moves the vehicle, under normal driving cell, which is widely regarded as the most contain only a few or as many as hundreds conditions. Fuel cell vehicles, which use promising for -duty transportation, of individual cells layered together. This electric motors, are much more energy hydrogen gas flows through channels to the FUEL CELL TECHNOLOGIES OFFICE

“scalability” makes fuel cells ideal for a place in the fuel cell, the temperature identifying and developing new materials wide variety of applications, from vehicles range of operation, and other factors that that will reduce the cost and extend the life (50-125 kW) to computers (20-50 determine its most suitable applications. of fuel cell stack components including W), homes (1-5 kW), and central power membranes, catalysts, bipolar plates, and generation (1-200 MW or more). Challenges and Research membrane- assemblies. Low-cost, Directions high- manufacturing processes will Comparison of Fuel Cell Reducing cost and improving durability also help to make fuel cell systems cost Technologies are the two most significant challenges competitive with traditional technologies. In general, all fuel cells have the same basic to fuel cell commercialization. Fuel cell configuration — an electrolyte and two systems must be cost-competitive with, and For More Information electrodes. But there are different types of perform as well or better than, traditional More information on the Fuel Cell fuel cells, classified primarily by the kind of power technologies over the life of the Technologies Office is available athttp:// electrolyte used. The electrolyte determines system. Ongoing research is focused on www.hydrogenandfuelcells.energy.gov. the kind of chemical reactions that take Comparison of Fuel Cell Technologies Electrical Fuel Cell Common Operating Typical Stack Efficiency Applications Advantages Challenges Type Electrolyte Temperature Size (LHV) • electrolyte • Backup power 60% direct reduces corrosion Polymer • Portable power • Expensive catalysts H ;i & electrolyte Electrolyte Perfluoro 2 • Distributed • Sensitive to fuel <120°C <1 kW - 100 kW 40% management problems Membrane generation impurities reformed • Low temperature (PEM) • Transportation fuelii • Quick start-up and • Specialty vehicles load following Aqueous potassium • Wider range of stable • Sensitive to CO2 in fuel hydroxide • Military materials allows lower and air Alkaline soaked in a • cost components • Electrolyte management <100°C 1 - 100 kW 60%iii (AFC) porous matrix, • Backup power • Low temperature (aqueous) or alkaline • Transportation • Quick start-up • Electrolyte conductivity polymer (polymer) membrane Phosphoric 5 - 400 kW, acid soaked in • Suitable for CHP • Expensive catalysts Phosphoric 100 kW module a porous matrix • Distributed • Increased tolerance to • Long start-up Acid 150 - 200°C ( PAFC); 40%iv or imbibed generation fuel impurities • Sulfur sensitivity (PAFC) <10 kW (polymer in a polymer membrane) membrane Molten lithium, • High temperature • High efficiency sodium, and/ • corrosion and breakdown Molten • Fuel flexibility or potassium 300 kW - 3 MW, • Distributed of cell components 600 - 700°C 50%v • Suitable for CHP , 300 kW module generation • Long start-up time (MCFC) • Hybrid/gas soaked in a • Low cycle porous matrix • High efficiency • High temperature • Auxiliary power • Fuel flexibility corrosion and breakdown Solid • Electric utility Yttria stabilized • Solid electrolyte of cell components 500 - 1000°C 1 kW - 2 MW 60%vi • Distributed zirconia • Suitable for CHP • Long start-up time (SOFC) generation • Hybrid/ • Limited number of cycle shutdowns

i NREL Composite Data Product 8, “Fuel Cell System Efficiency,” http://www.nrel.gov/hydrogen/docs/cdp/cdp_8.jpg ii Panasonic Headquarters News Release, “Launch of New ‘Ene-Farm’ Product More Affordable and Easier to Install,”http://panasonic.co.jp/corp/news/official.data/data. dir/2013/01/en130117-5/en130117-5.html iii G. Mulder et al., “Market-ready stationary 6 kW generator with alkaline fuel cells,” ECS Transactions 12 (2008) 743-758 iv Doosan PureCell® Model 400 System Specifications, http://www.doosanfuelcell.com/en/solutions/system.do v FuelCell Energy DFC300 Product Specifications,http://www.fuelcellenergy.com/assets/DFC300-product-specifications1.pdf vi Fuel Cells Gennex Product Specifications,http://www.cfcl.com.au/Assets/Files/Gennex_Brochure_ %28EN%29_Apr-2010.pdf

For more information, visit: hydrogenandfuelcells.energy.gov

November 2015 Printed with a renewable-source ink on paper containing at least 50% wastepaper, including 10% post consumer waste.