The Role of the U.S. National Innovation System in the Development of the PEM Stationary Fuel Cell

NISTIR 7161
The Role of the U.S. National Innovation System in the Development of the PEM Stationary Fuel Cell

II. Overview of Fuel Cells

This section describes the fuel cell, the different types of fuel cells available, and their commercial applications.

A. Description of Fuel Cells

A fuel cell is an electrochemical device that produces electricity silently and without combustion. A fuel cell consists of two electrodes, an anode and a cathode, with an electrolyte sandwiched in between. Figure 1 is a diagram of a typical fuel cell. Oxygen passes over one electrode and hydrogen over the other, generating electricity, water, and heat. Unlike other electrochemical devices such as batteries, a fuel cell only requires a continuous flow of hydrogen and does not run down or require recharging. It will produce energy in the form of electricity and heat as long as fuel is supplied.

Figure 1 - A fuel cell membrane electrode assembly operation. Adapted from Fuel Cell World Council (1999).
Figure 1 - A fuel cell membrane electrode assembly operation.

Fuel cells thus make usable energy in the form of electricity and heat by combining hydrogen and oxygen from the air in an electrochemical reaction. For stationary applications, hydrogen is typically made on site from natural gas by means of a reformer. Fuel cells are highly energy efficient, extracting two to three times more useful energy from fuels than other generation methods. 1 Since a fuel cell has no moving parts in its core system, its reliability can be high. Because fuel cells do not involve combustion, the device produces no air pollutants when operating with pure hydrogen as a fuel, and greatly reduces air pollutants when operating with reformed hydrogen.

As shown in figure 2, a fuel cell system consists of three main components that work together: a fuel reformer, a fuel cell stack consisting of many membrane electrode assemblies, with gas and water distribution manifolds and electronic controls and power conversion equipment. The reformer is responsible for producing a hydrogen-rich stream, typically from a fossil fuel source, which is then fed into the stack containing the membrane assembly to be combined with oxygen from the air. This catalytic reactive combination of hydrogen and oxygen produces electricity. Reformers can be designed to convert a number of everyday fuels into hydrogen, including natural gas, propane, coal-bed gas (sour gas), landfill decomposition gas, and gasoline. The reformer converts the hydrogen from the hydrocarbon molecule, generally using the steam or heat captured from the operating fuel cell. Alternatively, hydrogen can be produced in bulk at a separate facility and then transported and stored on site in a compressed gas form or bound in a metal hydride.

Figure 2 - Fuel cell system components and flow diagram. Adapted from Fuel Cell World Council ( 1999).
Figure 2 - Fuel cell system components and flow diagram

The heart of the fuel cell is the membrane electrode assembly, composed of an anode, cathode, electrolyte, and associated channels to deliver hydrogen and oxygen and to remove water and heat. The anode and cathode have to be electrically isolated from each other, but with a membrane in between that allows hydrogen ions catalytically produced at the anode to migrate to the cathode to combine with oxygen from the air, producing water. The electric current flows from one electrode to the other thru the electrical load. The fuel cell system (figure 2) contains a fuel cell stack, so called because it is a stack of the fuel cells shown in figure 1. The size of the stack determines how much power and voltage can be produced by the system. The third part of a fuel cell system consists of the electronic controls and power conversion equipment. Integral to efficient design, electronic controls balance the inflows and outflows of fuel, air, and cooling agents. Power conditioning equipment is also needed to convert the direct current (DC) power produced by fuel cells into the U.S. standard 110 V, 12 A at 60 Hz power source (alternating current-AC) required by most residential and commercial users. This process, represented by the inverter box in figure 2, is approximately 96% efficient, causing a slight dip in the overall efficiency of the fuel cell.

B. Types of Fuel Cells

Table 1 lists the different types of fuel cells. The primary difference between each is the type of materials used in the fuel cell stack to generate the chemical reaction (electrolyte) needed to make electricity. Not only do fuel cells emit fewer pollutants than other forms of energy generation, they also have the potential to use 50 % less energy than internal combustion engines and 30 % less energy than conventional gas-fired power plants. 2

Table 1 - Types of Fuel Cells

Type	Electrolyte	Operating temperature (°C)	Commercial applications	Commercialization
Proton Exchange Membrane (PEM)	Solid polymer, proton-conducting electrolyte	50 to 90	Transportation, stationary, portable power	Out of 1 900 small stationary fuel cells deployed as of 2003, 75 % are PEM. Currently, Plug Power has installed over 400 PEM stationary fuel cells for demonstration. Ballard has produced PEM fuel cells for cars and trucks over the last decade.
Direct Methanol	Solid polymer, proton-conducting electrolyte	40 to 100	Portable power, transportation, stationary	Of the 3 500 portable fuel cells deployed so far, about 45 % are fueled with methanol.
Solid Oxide	Yttria-stabilized Zirconia	800 to 1 000	Transportation, stationary, portable power	25 % of the 1 900 small stationary fuel cells deployed as of 2003 are solid oxide.
Phosphoric Acid	Phosphoric acid	190 to 210	Stationary	More than 200 fuel cell systems have been installed worldwide, including at hospitals, hotels, and office buildings.
Molten Carbonate	Potassium carbonate	630 to 650	Stationary	Carbonate fuel cells for stationary applications have been successfully demonstrated in Japan and Italy .

C. Fuel Cell Applications

1. Stationary (Residential Systems 1 kW to 20 kW Units, Target Cost <$1 000 per Kilowatt)

Stationary fuel cells, as their name implies, generate power from a unit that remains in a single fixed location. Stationary fuel cells come in a variety of sizes. The smaller on-site stationary fuel cells (between 1 kW and 10 kW) may power a home, business, or stand-alone remote electric application such as a cell telephone tower. For example, Plug Power's residential fuel cell generates approximately 5 kW of power. Since the technology is modular and easily permits units to be added together, such distributed power units can be used to power hotels, hospitals, or industrial establishments that require hundreds of kilowatts of power. The larger PEM stationary fuel cells generate between 50 MW and 200 MW of power and are more

suitable for central power generation. Any large consumer of electricity may use these fuel cells. One advantage of distributed on-site stationary fuel cells is the capability to sell any extra electricity that is generated but not consumed back to the "grid." To compete with electricity coming from the grid, fuel cell power units have to cost less than $1 000 per kilowatt.

2. Transportation (Target Cost <$50 per Kilowatt)

Ballard fuel cells have powered buses in Canada since 1993. All the major automotive manufacturers have fuel cell vehicles under development and in testing right now-General Motors, Ford, Daimler-Chrysler, Honda, Toyota , Hyundai, and Volkswagen. To compete with the internal combustion engine, fuel cell power trains have to be made small, lightweight, and extremely cost effectively at less than $50 per kilowatt-that is, more than 20 times cheaper than stationary units.

Market penetration of fuel cells likely will begin in markets where cost sensitivity is not as great an issue as it is for vehicles. These new markets will include stationary distributed power units for commercial and residential electricity and micro fuel cells. It is widely speculated that the fuel cell vehicle will not be commercialized until 2010 at the earliest. 3

3. Portable Power (Electric Appliances <1 kW, Target Cost <$3 000 per Kilowatt)

Miniature fuel cells will enable consumers to talk for up to a month continuously on a cellular phone without recharging. Fuel cells will change the telecommuting world, powering laptops and Palm Pilots and other personal digital assistants (PDAs) hours longer than batteries. Many of these miniature fuel cells will run on methanol, an inexpensive alcohol used in windshield wiper fluid. Since consumers pay more than $5 000 per kilowatt for rechargeable batteries with their limited run times, significant markets are expected to develop over the next 10 years, first for micro fuel cells where higher costs per kilowatt can be supported by the market, and then for stationary distributed power as the system cost point comes down to below $1 000 per kilowatt. Stationary and micro-power fuel cells will serve to catalyze the building of a fuel cell manufacturing industry infrastructure that will be important to automotive uses, where far more stringent cost points and robust technology targets need to be met.

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1U.S. DOE (2003), p. 1.

2U.S. DOE (2003).

3This estimate was provided by one of the companies involved in a partnership with the Advanced Technology Program on a fuel cell project. Section IV.C.2 contains a description of ATP and its role in fuel cell technology development.

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Date created: March 29, 2005
Last updated: August 3, 2005

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