Fuel cells are hydrogen batteries. They convert hydrogen (or hydrogen-containing fuels) directly into electrical energy through an electrochemical process. Because hydrogen is converted directly, fuel cells don't have the problems of internal combustion engines such as gasoline or diesel engines in trucks and cars.

The benefits of fuel cell power systems include:

• Fuel cells have no (or few) moving parts, are silent and don't require a lot of repairs and upkeep.
• They can be small enough to fit inside a vehicle or large enough to power a building.
• The efficiency of a fuel cell — its ability to produce usable energy — is much higher than internal combustion engines. Fuel-cell engines for automobiles can generate electric power at an efficiency as high as 50% at full power and 60% at partial power; versus 15% to 20% for most internal combustion engine, or 30% for some advanced diesel engines.
• Fuel cells use fuel in proportion to the load, or amount of electricity required by the electrical equipment it is linked to. When electrical use is low, the amount of fuel used in similarly low.
• Fuel cells can generate electricity all the time using renewable energy sources such as solar, wind and biomass. Because the sun doesn't shine and the wind doesn't blow all the time, solar and wind energy systems require batteries to store electricity for use when no electrical energy is being generated. And the battery power is limited, only up to 250 watts or about the energy needed to operate a small microwave oven. But fuel cells can use electricity from renewable energy sources such as the sun or the wind to create hydrogen through the electrolysis of water. Electrolysis is a chemical process in which electricity splits water atoms — H₂O — to create hydrogen and oxygen. The hydrogen can be stored for use by the fuel cell when electric power is required, even at night or when the wind isn't blowing. New fuel-cell generators using stored hydrogen can produce 250,000 watts of power or more, enough to power lights, machines and other things we use.
• When fuel cells produce electricity, they bind hydrogen and oxygen atoms to create water with no pollution. The only emission from a fuel cell is pure distilled water.

In 1839, British scientist Sir William Robert Grove showed how a fuel cell works and became known as the inventor of the fuel cell. He generated about one volt of electric potential in his "gas chain," an array of platinum electrodes dipped in hydrogen and oxygen in sulphuric acid. (Figure 1)

Technical problems, especially the instability of the materials used, and the development of modern-style rotary electrical generators by Werner von Siemens soon caused scientists to ignore fuel cells. But in the 1960s, space flight revived interest in fuel cell research. NASA used alkaline fuel cells to provide onboard electrical power and drinking water for the Apollo mission. However, alkaline fuel cells cost a lot and don't last very long, so they were used only in space and by the military.

Recently, scientists began working with other types of fuel cells that last longer, are less expensive and produce more electricity. These new fuel cells can produce electricity at nearly the same cost as other ways of generating electricity such as power plants that use coal, natural gas or nuclear power.

Fuel cells produce energy using chemical reactions. A fuel cell, like a flashlight "D" cell, is an electrical cell. Unlike the "D" cell, which relies on chemicals and materials that eventually stop producing electricity, fuel cells can be continuously fed with energy or fuel so that electricity is produced as long as the fuel is provided.

A fuel cell consists of two electrodes bonded to an electrolyte, where the chemical reaction takes place. (Figure 2) The anode is supplied with the fuel (hydrogen or a hydrocarbon like natural gas which contains hydrogen) and the cathode is supplied with the oxidant (oxygen or air). The fuel is oxidized at the anode and releases electrons. The electrons released during oxidation flow from the anode (negative pole) through the external electrical load — the appliances or equipment that need electricity to work — to the cathode (positive pole), producing the electric current. At the cathode the oxidant is reduced by absorbing the returning electrons.

The electrical charge within the fuel cell is effected by the movement of the ions through the electrolyte. A fuel cell supplies electrical energy in the same way as a battery. The key difference is that the electrodes of a fuel cell do not chemically deteriorate and stop functioning. Therefore, if a fuel cell has a constant supply of fuel it can supply continuous electrical energy.

A single fuel cell supplies a direct current, or DC, voltage of less that one volt. If larger voltages are needed individual cells are stacked together in series. Factory-made stacks can produce up to about 200 volts. The maximum current that can be drawn from a fuel cell is proportional to the surface area of the electrodes. The bigger the surface of the electrodes, the more electric current, is produced. Today's fuel cells can generate a current of up to 2 amperes per square centimeter, depending on the kind of cell and operating conditions.

Fuel cells are classified by the type of electrolyte they use. Different electrolytes operate at different temperatures. As you might guess, which kind of fuel cell is best depends on where you are and what you want to do with it.

Fuel cell	Electrolyte	Anode gas	Cathode gas	Operating temperature	Applications
AFC (Alkaline Fuel Cell)	Potassium hydroxide solution	hydrogen	oxygen	up to 100°C	spacecraft submarines
PEMFC (Proton Exchange Membrane Fuel Cell)	Proton-conductive polymer electrolyte	hydrogen/ hydrogen from methanol after reforming	oxygen or oxygen in air	up to 100°C	portable power automobiles cogeneration
DMFC (Direct Methanol Fuel Cell)	Polymer electrolyte	methanol	oxygen in air	90-120°C	portable power automobiles
PAFC (Phosphoric Acid Fuel Cell)	Phosphoric acid	hydrogen/ hydrogen from methanol after reforming	oxygen in air	200°C	cogeneration small power plants
MCFC (Molten Carbonate Fuel Cell)	Molten alkaline carbonates	hydrogen methane coal gas	oxygen in air	650°C	cogeneration small power plants
SOFC (Solid Oxide Fuel Cell)	Ceramic solid electrolyte	hydrogen methane coal gas	oxygen in air	800-1,000°C	cogeneration small power plants

Low-temperature fuel cells include the alkaline fuel cell (AFC), the proton exchange membrane fuel cell (PEMFC) and the phosphoric-acid fuel cell (PAFC). These fuel cells all use hydrogen as a fuel. This hydrogen can be extracted from natural gas, biogas or methanol by a process called reformation (a chemical reaction between hydrocarbon fuels and water vapor), or it can be made from the electrolysis of water.

High-temperature fuel cells include the molten carbonate fuel cell (MCFC) and the solid oxide fuel cell (SOFC). These cells have an advantage in that they can use either natural gas or untreated coal gas as a fuel directly, without the use of a reformer, through a process called "Direct Internal Reforming".

Due to the modular structure of fuel cells, fuel cells can be used for all kinds of power applications — from batteries powering a specific device (producing a few watts) to power plants (generating megawatts). The most intensive research and development is currently focused on fuel-cell stationary power generators and electrically driven automobiles.

Proton exchange membrane (pem) fuel cells are getting a lot of attention among designers and manufacturers now because they can be used almost anywhere and are relatively simple. pem fuel cells run on hydrogen, which can be produced by reforming natural gas or methanol. in a pem fuel cell, hydrogen molecules are oxidized at the anode to create positively charged hydrogen ions (protons), releasing electrons that move to the cathode by way of the external electric device or load. the protons move, or diffuse, through the ion-conducting polymer membrane (electrolyte) to the cathode. at the cathode, the protons react with oxygen and the electrons, to form water.

Anode:		2 H2		—>		4 H+ + 4 e-
Cathode:		O2 + 4 H+ + 4 e-		—>		2 H2O
Overall reaction:		2 H2 + O2		—>		2 H2O

In theory, a single cell's maximum voltage is 1.23 volts. Actual voltages are usually between 0.6 and 0.9 volts for an individual cell due to reaction inhibition, internal resistance or insufficient gas diffusion.

The membrane electrode assembly (MEA) is the heart of a PEM fuel cell. The electrodes are coated with a catalyst containing a precious metal. The most common design has finely distributed platinum deposited onto specially treated carbon mats at 0.1-0.5 milligrams of platinum per square centimer. The carbon mats are then hot-press-bonded with the polymer membrane. As a result, the membrane extends into the porous electrode structures. The catalyst must have simultaneous contact with the gas, the proton conductor (polymer membrane) and the electron conductors (electrodes). The electrochemical reactions take place at these points. (Figure 3)

Stationary power generators range in electrical output from one kilowatt (1,000 watts, to provide power where there are no electric power lines) to several megawatts (1 million watts, for a large industry or business). Conventional power generators, from small internal combustion engine generators to huge power plants that use coal, natural gas, or nuclear power to produce the steam needed to turn turbines and generate electricity, have electrical efficiencies ranging from about 20% to 60%. (Figure 4) Fuel cell electrical efficiency has been commercially demonstrated at about 40% and potentially can approach 65%. (Figure 4)

Up to now, only phosphoric-acid fuel cells (PAFC) have been used for fuel-cell stationary power generation. The primary manufacturer of PAFC stationary power generators is ONSI (a subsidiary of International Fuel Cells Corp., USA). Fuel-cell generators produced by ONSI run on natural gas, generate 200,000 watts of electrical power and 200,000 watts of thermal power at an output temperature of 60°C (at an output temperature of 90°C the thermal power output is 100,000 watts). Because of the large amount of heat produced from PAFC generators, they are most commonly used for applications that require both electric power and heat. Systems that provide both heat and power are termed cogeneration systems (or combined heat and power, abbreviated CHP)

The efficiency of PAFC cogeneration system is 40% electrical and 40% thermal. Thus if all the thermal power produced is used, the total efficiency of the system can be as high as 80%.

A PAFC cogeneration plant using natural gas must have: a reformer (to convert the natural gas into hydrogen); a fuel cell; a heat exchanger (to produce hot water or steam from the exhaust heat of the fuel cell); and an inverter (to convert direct current voltage into alternating current). In the reformer, natural gas (purified to remove traces of sulphur) is mixed with superheated water vapor and converted into hydrogen and carbon monoxide using a catalyst at approximately 800°C. The carbon monoxide gas then reacts with water vapor, using a catalyst, to form carbon dioxide and additional hydrogen at approximately 200°C. The hydrogen gas is then fed continuously into the fuel cell. (Figure 5)

Phosphoric-acid fuel cell generators have already been highly developed. Now engineers aim to cut costs from $4,000/kW at the present time to about $1,500/kW to make them competitive in price with conventional diesel-engine cogeneration plants. PAFC generators offer the advantages of high reliability, silent operation and low pollution (emissions of NOx and SOx are less than 1/100th that of diesel-engine generators, and CO2 emissions are approximately half).

PEM fuel cells are currently being developed for use in generators providing power up to 250,000 watts (sufficient energy to power 50 homes). Since PEM fuel cells operate at a lower temperature than phosphoric-acid fuel cells, they produce less heat and are more suited for applications requiring electricity alone. PEM generators are still under development but are expected to enter the market in 2001, priced at about $1,500/kW, competing in price with diesel-engine generators. The price is expected to drop to about $500/kW by 2010 if sales meet expected targets.

Molten carbonate fuel cells are being developed for power plants providing 250,000 watts to more than 1 million watts. Market introduction of molten carbonate fuel cells is expected within the next few years. These cells will offer the advantage of direct use of fuel without the need of a reformer.

Fuel cells could enable internal combustion engines to be replaced by electric motors, thereby reducing emissions from concentrated mobile sources in metropolitan areas. Since the early 1990s, car makers around the world have been researching and developing fuel cells for use in cars and trucks. The primary developer and manufacturer of PEM fuel cells for transportation applications is Ballard Power, based in Vancouver, Canada.

The advantages of a fuel-cell engine include high efficiency at both full and partial power. PEM fuel-cell engines designed by Ballard Power have an efficiency at full load of about 50% (versus 15-20% for an internal combustion engine). At partial load, the efficiency of a fuel-cell engine will rise as high as 60%. By contrast, the efficiency of an advanced diesel engine at partial load falls to about 17%.

There are currently two potential fuel systems for fuel cell vehicles under development. One is the direct use of hydrogen. This method has been adapted for city buses. Hydrogen is stored in pressurized tanks on the roof of the buses, providing the bus with a range of 350 miles between fillups.

The other method, currently favored for passenger automobiles, is the production of hydrogen from liquid methanol using an onboard reformer. (Figure 6) When using liquid methanol as a fuel, the reformation process is 75-80% efficient, resulting in an overall engine efficiency with reformer of 40% at full load and of 45% at partial load. This higher efficiency enables fuel cell vehicles using methanol to travel as far as internal-combustion vehicles using an equal amount of gasoline despite the lower energy content of methanol. In the future, methanol may be produced from renewable biomass.

Buses, passenger automobiles and trucks will gradually be entering the market over the next few years. City buses are entering the market now. Ballard Power introduced a 40-foot Zero Emission Bus powered by a 275 horsepower (205 kW) fuel-cell engine in 1995. Its range is 400 km (250 miles) before requiring refueling. It is extremely quiet, has good acceleration and produces zero emissions other than water. Three of these prototype buses have been sold to Chicago Transit Authority, for tests on performance, cost and reliability. Three additional buses are currently being tested on the streets in Vancouver. Passenger automobiles and trucks, carrying onboard reformers, are expected to enter the market in 2004.

The primary challenges facing manufacturers for the introduction of fuel-cell vehicles are:

• Costs must be brought down to compete with the price of the internal combustion engine. The 70 horsepower (50 kW) fuel-cell engine designed for automobiles, for example, is expected to have an initial selling price of around $10,600 coming down to around $5,600 by 2005 and $3,400 by 2010. Current prices for an internal combustion engine are $3,000-4,000. As the market develops, the larger demand for fuel cells will introduce mass production techniques and should lead to lower costs.
• The infrastructure system (methanol filling stations) must be developed, and
• The new technology must gain general acceptance.

CONNIHAN, M.: A Dictionary of Energy, Routledge and Kegan Paul, London 1981.

CHEWNING, R. L.: "Energy: Alternative Power Technologies," U.S. and the Americas Investment Research, Morgan Stanley Dean Witter, New York, 0ctober 27, 1997.

COLELL, H.: Solar Hydrogen Technology, Heliocentris, Berlin, Germany, 1997.

KHATIB, H: "Electrical power in developing countries," Power Engineering Journal, IEE, London, October 1998

KORDESH, K. and SIMADER, G.: Fuel Cells and Their Applications, VCH Publishing, New York, 1996.

The guys who helped write this section have different educational and work backgrounds, but both find their work with fuel cells at Heliocentris interesting and challenging.

Henrik Colell received the Ph.D. degree in electrochemistry from Freie Universität Berlin, in 1996. He wrote his thesis on catalysts of fuel cells and electrolysers. In 1995 he co-founded Heliocentris, a company developing and manufacturing low power PEM fuel cells and solar hydrogen systems for the research and educational market.

Brian Cook is a licensed electrical contractor from Vancouver, Canada and is a member of the International Brotherhood of Electrical Workers. He has written several articles on energy efficiency and methods of sustainable energy production. Since March 1998 he has been working as Director of International Marketing and Sales for Heliocentris.

Henrik Colell and Brian Cook can be reached at:

Heliocentris GmbH
Rudower Chaussee 5
12489 Berlin, Germany
Tel: +49 30 6392 6323
Fax: +49 30 6392 6329
E-mail: info@heliocentris.com
Web site: www.heliocentris.com