BU-210: How does the Fuel Cell Work?

Explore the development of the fuel cell and study the different systems.

A fuel cell is an electrochemical device that combines hydrogen fuel with oxygen to produce electricity, heat and water. The fuel cell is similar to a battery in that an electrochemical reaction occurs as long as fuel is available. The hydrogen fuel is stored in a pressurized container and oxygen is taken from the air. Because of the absence of combustion, there are no harmful emissions, and the only by-product is pure water. So pure is the water emitted from the proton exchange membrane fuel cell (PEMFC) that visitors to Vancouver’s Ballard Power Systems were served hot tea made from this clean water.

Fundamentally, a fuel cell is electrolysis in reverse, using two electrodes separated by an electrolyte. The anode (negative electrode) receives the hydrogen and the cathode (positive electrode) collects the oxygen. A catalyst at the anode separates hydrogen into positively charged hydrogen ions and electrons; the oxygen is ionized and migrates across the electrolyte to the anodic compartment where it combines with hydrogen. A single fuel cell produces 0.6–0.8V under load. To obtain higher voltages, several cells are connected in series. Figure 1 illustrates the concept of a fuel cell.

Concept of a fuel cell

Figure 1:
Concept of a fuel cell

The anode (negative electrode) receives the hydrogen and the cathode (positive electrode) collects the oxygen.

Source: US Department of Energy, Office of Energy Efficiency and Renewable Energy

Fuel cell technology is twice as efficient as combustion in turning carbon fuel to energy. Hydrogen, the simplest chemical element (one proton and one electron), is plentiful and exceptionally clean as a fuel. Hydrogen makes up 90 percent of the universe and is the third most abundant element on the earth’s surface. Such a wealth of fuel would provide an almost unlimited pool of clean energy at relatively low cost. But there is a hitch.

Hydrogen is usually bound to other substances and “unleashing” the gas takes energy. In terms of net calorific value (NCV), hydrogen is more costly to produce than gasoline. Some say that hydrogen is nearly energy neutral, meaning that it takes as much energy to produce as it delivers at the end destination. (See BU-1007: Net Calorific Value.)

Storage of hydrogen poses a further disadvantage. Pressurized hydrogen requires heavy steel tanks, and the NCV by volume is about 24-times lower than a liquid petroleum product. In liquid form, which is much denser, hydrogen needs extensive insulation for cold storage.

Hydrogen can also be produced with a reformer by means of extraction from an existing fuel, such as methanol, propane, butane or natural gas. Converting these fossil fuels into pure hydrogen releases some leftover carbon, but this is 90 percent less harmful than what comes from the tailpipe of a car. Carrying a reformer would add weight to the vehicle and increase its cost. Reformers are also known to be sluggish.

The net benefit of hydrogen conversion is in question because it does not solve the energy problem. With the availability of hydrogen through extraction, the fuel cell core (stack) to convert hydrogen and oxygen to electricity is expensive and the stack has a limited life span. Burning fossil fuels in a combustion engine is the simplest and most effective means of harnessing energy, but this contributes to pollution.

Sir William Grove, a Welsh judge and gentleman scientist, developed the fuel cell concept in 1839, but the invention never took off. This was during the development of the internal combustion engine (ICE) that showed promising results.  It was not until the 1960s that the fuel cell was put to practical use during the Gemini space program. NASA preferred this clean power source to nuclear or solar power. The alkaline fuel cell system that was chosen generated electricity and produced the drinking water for the astronauts.

High material costs made the fuel cell prohibitive for commercial use. This did not discourage the late Karl Kordesch, the co-inventor of the alkaline battery, from converting his car to an alkaline fuel cell in the early 1970s. He mounted the hydrogen tank on the roof and placed the fuel cell and backup batteries in the trunk. According to Kordesch, there was enough room for four people and the dog. He drove his car for many years in Ohio, USA. Here are the most common fuel cell concepts.

Proton Exchange Membrane Fuel Cell(PEMFC)

The proton exchange membrane, also known as PEM, uses a polymer electrolyte. PEM is one of the furthest developed and most commonly used fuel cell systems; it powers cars, serves as a portable power source and provides backup power in lieu of stationary batteries in offices. The PEM system allows compact design and achieves a high energy-to-weight ratio. Another advantage is a relatively quick start-up when applying hydrogen. The stack runs at a moderate temperature of 80C (176F) and is 50 percent efficient. (The ICE is 25–30 percent efficient.)

The PEM fuel cell has high manufacturing cost and a complex water management system. The stack contains hydrogen, oxygen and water. If dry, water must be added to get the system started; too much water causes flooding. The stack requires pure hydrogen; lower fuel grades can cause decomposition and clogging of the membrane. Testing and repairing a stack is difficult, given that a 150V stack requires 250 cells.

Freezing water can damage the stack and heating elements may be added to prevent ice formation. Start-up is slow when cold and the performance poor at first. Excessive heat can also cause damage. Controlling temperatures and supplying oxygen requires compressors, pumps and other accessories that consume about 30 percent of the energy generated.

If operated in a vehicle, the PEMFC stack has an estimated service life of 2,000–4,000 hours. Wetting and drying caused by short distance driving contributes to membrane stress. Running continuously, the stationary stack is good for about 40,000 hours. Stack replacement is a major expense.

Alkaline Fuel Cell(AFC)

The alkaline fuel cell has become the preferred technology for aerospace, including the space shuttle. Manufacturing and operating costs are low, especially for the stack. While the separator for the PEM costs between $800 and $1,100 per square meter, the same material for the alkaline system is almost negligible. (The separator for a lead acid battery costs $5 per square meter.) Water management is simple and does not need compressors and other peripherals. A negative is that AFC is larger in physical size than the PEM and needs pure oxygen and hydrogen as fuels. The amount of carbon dioxide present in a polluted city can poison the stack.

Solid Oxide Fuel Cell (SOFC)

Electric utilities use three types of fuel cells, which are molten carbonate, phosphoric acid and solid oxide fuel cells. Among these choices, the solid oxide (SOFC) is the least developed but has received renewed attention because of breakthroughs in cell material and stack design. Rather than operating at the very high operating temperature of 800–1,000°C (1,472–1,832°F), a new generation of ceramic material has brought the core down to a more manageable 500–600°C (932–1,112°F). This allows the use of conventional stainless steel rather than expensive ceramics for auxiliary parts.

High temperature allows direct extraction of hydrogen from natural gas through a catalytic reforming process. Carbon monoxide, a contaminant for the PEM, is a fuel for the SOFC. Being able to accept carbon-based fuels without a designated reformer and delivering high efficiency pose significant advantages for this type of fuel cell. Cogeneration by running steam generators from the heat by-product raises the SOFC to 60 percent efficiency, one of the highest among fuel cells. As a negative, high stack temperature requires exotic materials for the core that adds to manufacturing costs and reduces longevity.

Direct Methanol Fuel Cell (DMFC)

Portable fuel cells have gained attention and the most promising development is the direct methanol fuel cell. This small fuel cell is inexpensive to manufacture, convenient to use and does not require pressurized hydrogen gas. The DMFC has good electrochemical performance and refilling is by squirting in liquid or replacing the cartridge. This enables continued operation without downtime.

Manufactures of small fuel cells admit that a direct battery replacement is years away. To bridge the gap, micro fuel cell serves as a charger to provide continuous operation for the onboard battery. Furthermore, methanol is toxic and flammable and there are limitations as to how much fuel passengers can carry on an aircraft. In 2008 the Department of Transportation issued a ruling to permit passengers and crew to carry an approved fuel cell with an installed methanol cartridge and up to two additional spare cartridges of 200 ml (6.76 fl. Oz.). This provision does not yet extend to bottled hydrogen.

Figure 2 shows a micro fuel cell by Toshiba and Figure 3 demonstrates refueling with methanol that is 99.5 percent pure.

Micro fuel cell Toshiba fuel cell with refueling cartridge
Figure 2: Micro fuel cell. This prototype micro fuel cell is capable of providing 300mW of continuous power.

Courtesy of Toshiba

Figure 3: Toshiba fuel cell with refueling cartridge. The fuel in a 10ml tank is 99.5 percent pure methanol.

Courtesy of Toshiba

Improvements are being made and Toshiba unveiled prototype fuel cells for laptops and other applications generating 20 to 100 watts. The units are compact and the specific energy is comparable with that of a NiCd battery. Toshiba has given no indication as to when the product could be available. Meanwhile, Panasonic claims to have doubled the power output from 10 watts to 20 watts with similar size. Panasonic specifies a calendar life of 5,000 hours if the fuel cell is used intermittently for eight hours per day. The low longevity of these fuel cells has been an issue to be reckoned with.

Attempts are made with small fuel cell running on stored hydrogen. Increased efficiency and smaller size are the advantages of pure hydrogen over methanol. These miniature systems have no pumps and fans and are totally silent. A 21cc cartridge is said to provide the equivalent energy of about 10 AA alkaline batteries with a runtime between refueling of 20 hours.

Military and recreational users are also experimenting with the miniature fuel cell. Figure 4 illustrates a portable fuel cell made by SFC Smart Fuel Cell. The EFOY fuel cell comes in different capacities that ranges from 600 to 2160 watt hours per day.

Portable fuel cell for consumer market Figure 4: Portable fuel cell for consumer market

The fuel cell converts hydrogen and oxygen to electricity and clean water is the only by-product. Fuel cells can be used indoors as an electricity generator.

Courtesy of SFC Smart Fuel Cell AG

Table 5 describes the applications and summarizes the advantages and limitations of common fuel cells. The table also includes the Molten Carbonate (MCFC) and Phosphoric Acid (PAFC), classic fuel cell systems that have been around for a while and have unique advantages.


Type of Fuel Cell


Core temp.



Proton Exchange Membrane (PEMFC)

Portable, stationary and automotive

80°C typical;
35–60% efficient

Compact design, long operating life, quick start-up, well developed

Expensive catalyst, needs clean fuel, complex heat and water control


Space, military,  submarines, transport

60% efficient

Low parts and, operation costs; no compressor; fast cathode kinetics

Large size; sensitive to hydrogen and oxygen impurities

Molten Carbonate

Large power generation

45–50% efficient

High efficiency, flexible to fuel, co-generation

High heat causes corrosion, long startup, short life

Phosphoric Acid

Medium to large power generation

40% efficient

Good tolerance to fuel impurities; co-generation

Low efficiency; limited service life; expensive catalyst

Solid Oxide (SOFC)

Medium to large power generation

60% efficient

Lenient to fuels; can use natural gas, high efficient

High heat causes corrosion, long startup, short life

Direct Methanol

Portable, mobile and stationary use

20% efficient

Compact; feeds on methanol; no compressor

Complex stack; slow response;
low efficiency

Table 5: Advantages and disadvantages of various fuel cell systems
The development of the fuel cell has not advanced at the same pace as batteries; a direct battery replacement is not yet feasible.


The fuel cell requires improvements to resolve slow start-up times, low power output, sluggish response on power demand, poor loading capabilities, narrow power bandwidth, short service life and high cost. Similar to batteries, the performance of all fuel cells degrades with age, and the stack gradually loses efficiency. Such performance losses are not visible with the ICE.

The relatively high internal resistance of fuel cells poses a challenge. Each cell of a stack produces about one volt in open circuit; a heavy load causes a notable voltage drop. Figure 6 illustrates the voltage and power bandwidth as a function of load.

Power band of a portable fuel cell

Figure 6: Power band of a portable fuel cell

High internal resistance causes the cell voltage
to drop rapidly with load. The power band is limited to between 300 and 800mA.

Courtesy of Cadex

Fuel cells operate best at a 30 percent load factor; higher loads reduce efficiency. A load factor approaching 100 percent, as is common with a battery and the ICE is not practical with the fuel cell. In addition, the fuel cell has poor response characteristics and takes a few seconds to react to power demands. Rather than serving as a stand-alone engine, as the developers had hoped, the fuel cell works in a support function, or a charger, to keep the batteries charged.

Paradox of the Fuel Cell

The fuel cell enjoyed the height of popularity in the 1990s when scientists and stock promoters envisioned a world running on a clean and inexhaustible resource – hydrogen. They predicted that cars would run on fuel cells and that household electricity would also be generated by fuel cells. The stock prices skyrocketed but marginal performance, high manufacturing costs and limited service life moderated the hydrogen dream.

It was said that the fuel cell would transform the world as the microprocessor did. There was hope that using the inexhaustible source of hydrogen would improve quality of life and solve the environmental consequences of frivolously burning fossil fuels. From 1999 through 2001, more than 2,000 organizations got actively involved in fuel cell development, and four of the largest public fuel cell companies in North American raised over a billion dollars in public stock offerings. What went wrong?

Hydrogen is not a source of energy per se but a medium to transport and store energy similar to electricity that charges a battery. By envisioning “burning an endless supply of hydrogen,” the fuel must first be produced because hydrogen cannot be pumped from the earth as is possible with oil. While fossil fuel lends itself well to producing hydrogen, taking this valuable fuel to unleash hydrogen makes little sense when it costs as much or more for extraction than burning it directly. The only benefit appears to be reduced greenhouse gases.

Just as the attempt to fly airplanes on steam failed in the mid-1800s, it is conceivable that the fuel cell will never become the powerhouse that scientists had hoped. It is our sincere hope, however, that economic applications can be found with minimal government intervention in the form of subsidies.

There is renewed interest for the fuel cell in the automotive field in Japan. Large 40,000kW fuel cells are in operation to generate electricity in remote locations. Fuel cells also replace battery banks and diesel generators in office buildings, as they can be installed in tight storage places without exhaust and on rooftops with minimal maintenance. Fuel cells also allow continuous and pollution-free operation of forklifts. 

Last updated 2015-08-21

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On June 4, 2011 at 7:52am
hugh spalding wrote:

Does adding water to sealed car batteries prolong battery life?

On October 14, 2011 at 8:17am
Al wrote:

As a fairly off-topic point, functional steam airplanes did exist in the 1930’s. The United States Post Office owned one. http://www.rexresearch.com/besler/beslerst.htm and a video here: http://www.archive.org/details/BeslerCo1932

On November 15, 2011 at 10:22pm

Very good but more latest fuelcells which can produce more power in terms of KW may be introduced

On November 15, 2011 at 10:23pm

micro grids may be introduced

On November 15, 2011 at 10:24pm

microbial fuel cells may be introduced

On November 15, 2011 at 10:25pm

microgrids interfacing fuel cells may be introduced

On January 18, 2013 at 3:29am
J wrote:

The price on energy, that will move us from one point to another, is rising and this energy source (fossil fuels)is also causing global warming and melting the ice.

The last couple of years I have seen an increase of renewable energy sources, wind and solar, but these will only give you heat or electricity to your house. There are systems for storing this energy in large tanks with liquid, you can later use it to heat your house and maybe with some kind of stirling engine produce electricity. The other option to store energy is to send it out the power grid and get payed or pay for your net power consumption.
One of the problems with solar energy is also that you dont need the energy when the sun shines (cold countries).
Would it be possible to create hydrogen if you had electric energy? You could making your own fuel at home.

On March 8, 2014 at 7:39pm
Michael Price wrote:

The text and first diagram are inconsistent.  The text says the oxygen ion migrates across the electrolyte whereas the diagram shows the hydrogen ions migrating.  Text is wrong?

On April 6, 2014 at 3:26pm
pinakin wrote:

good topic ilearn

On June 17, 2014 at 10:05am
Manuel wrote:

Dear Sirs

Good day, we need to buy:

Litium batteries 60ah
Quantity: 03 units

I await your prompt response.

More information on our:
Name: SAC Famelect
Ruc: 20551448003
Address. AV. Alfredo Mendiola No. 3913 - Los Olivos
City: Lima
Country: Peru

Thanks for your reply.

best regards

Manuel Serna

On June 21, 2014 at 3:42am
Hari Narayan wrote:
On February 14, 2015 at 12:35pm
Jan Bentz wrote:

The large amount of H2 needed for vehicle fuel cells could be made availiable by utilizing nuclear power plants extra capacity in off peak hours.  Water, for a raw material is essentially free and, the process is non- polluting.  If only we could get over our irrational fear of nuke plants.

On March 29, 2015 at 2:26pm
A. D. Kutluk wrote:

Instead of pressurazing hydrogen, it can well be produced from water (H2O) by way of hydrolize. ( A technic which was used in 1950s and forgetten for long but reinvogorated few yerars ago and now being used over 7000 cars as fuel supplement lowering level of consumption between 20-40% in Turkey)