Connecticut Global Fuel Cell Center

A fuel cell is an electricity generator that converts energy from fuel directly into electrical energy. The fuel cell operates on a continuous basis as long as fuel and oxidant are supplied, unlike batteries that slowly lose their energy or discharge. Hydrogen is frequently used as the fuel so that the products of the fuel cell are only electricity, water, and heat. The fuel cell is a highly efficient, clean, and reliable alternative to conventional electrical generators.

2. How Does a Fuel Cell Work?

A fuel cell consists of two electrodes separated by an electrolyte. Fuel passes over one electrode, the anode, and oxygen over the other, the cathode. For a hydrogen fuel cell using an acid electrolyte, hydrogen on the anode side is encouraged by a catalyst to separate into hydrogen ions (protons) and electrons. The hydrogen ions migrate through the electrolyte to the cathode where they react with oxygen (or air) and electrons to form water. The formation of electrons at the anode and the consumption of electrons at the cathode results in a voltage difference between the two electrodes so that electrical wires can be connected to these electrodes to power electrical devices.

3. What Different Fuels can be used in a Fuel Cell?

Fuel cells can utilize many fuels. Some fuel cells use hydrogen produced from hydrocarbon fuels such as natural gas, methanol and even gasoline or diesel fuel. Some fuel cells consume the hydrocarbon fuels directly. When hydrogen is required, a "fuel reformer" is frequently used to extract the hydrogen from the hydrocarbon. In the absence of fossil fuels, hydrogen can be produced using biomass, wind, and solar energy or other renewable sources.

4. What Types of Fuel Cells Exist?

a.
Low Temperature Fuel Cells are the furthest toward commercialization and can be used in stationary (buildings, industrial and commercial), mobile, or portable applications as follows:

Phosphoric Acid (PAFC). This type of fuel cell is commercially available today at the 200 kw level and operates at about 400 degrees F. These fuel cells are being used in hospitals, office buildings, schools, utility power plants, airports, and nursing homes. Power generating efficiencies using phosphoric acid fuel cells can reach 40%. The on-site waste heat from these cells is used to supply hot water or building heat so that over 85% of the energy in the fuel is used.

Proton Exchange Membrane (PEMFC). This type of fuel cell operates around 180 degrees F and is suited for applications that can utilize the high power density and lower operating temperature. Applications that are ideal for the PEMFC include small portable and mobile devices, small on-site generators, and vehicles. The electrical efficiency is similar to that of the phosphoric acid fuel cell but the waste heat is currently not as useful.

Alkaline (AFC). Alkaline fuel cells use potassium hydroxide as the electrolyte and operate at about 200 degrees F. The primary applications have been in the Apollo moon-landing, the space shuttle program, and submarines. Commercial application of AFC's is hampered by the neutralization of the electrolyte by carbon dioxide that is present in the hydrogen fuel obtained from processed hydrocarbons.

b.) High Temperature Fuel Cells are in a later stage of commercialization and can be used in applications for large scale electricity production by a utility, industry, or building, and possibly some transport applications. The high operating temperature makes cogeneration an important advantage for these fuel cells. They consist of:

Molten Carbonate (MCFC). Molten carbonate fuel cells operate at 1200 degrees F and are best suited for large-scale, stationary applications. Existing molten carbonate fuel cells have been operated utilizing the following fuel types: natural gas, propane, ethanol, landfill gas, marine diesel, and simulated coal gasification products. Natural gas can be reacted directly within the cell to eliminate the conversion of the fuel to hydrogen. Power generating efficiencies for molten carbonate fuel cells is 55% and can be increased to about 75% by the addition of a gas turbine bottoming cycle using the waste heat.

Solid Oxide Fuel Cell (SOFC). Solid oxide fuel cells operate at up to 1800 degrees F and utilize a solid ceramic material as the electrolyte as opposed to a liquid electrolyte. Applications for this technology include large, high power applications such as industrial electricity generating stations and small auxiliary power units in vehicles. Power generating efficiencies using solid oxide fuel cells can reach 60% and be further increased using a bottoming cycle.

5. What are the Benefits of Fuel Cell Technology?

Reliability. Fuel cell technology is expected to be very reliable since few moving parts are used and operating temperatures are lower than those of conventional systems. This reliability has been proven with the PAFC with one unit having operated for 49,000 hours.

Clean Emissions. The byproduct from a hydrogen fuel cell system is only water vapor, which is environmentally benign. Impurities such as sulfur, which contributes to acid rain, must be removed from the fuels prior to processing since they can be harmful to the fuel cell. Fuel cells produce little NOx that also contributes to acid rain. Since fuel cells are very efficient, the resulting carbon dioxide emission is reduced when hydrocarbon fuels are used, resulting in less emission of the gas being attributed to an increased global warming.

Quiet Operations. Some fuel cells are extremely quiet and can be installed indoors with no additional soundproofing requirements.

High Efficiency. Fuel cells operate with efficiencies today that range from 40-70%. A modern combustion combined cycle power plant has an efficiency of about 57%, and a vehicular diesel power plant an efficiency of about 45%. The advantage of a fuel cell is that the efficiency is not a strong function of size so efficient fuel cells can be made smaller in size than conventional gas turbine or steam turbine power plants. Efficiency is also high when the power plant is at partial power, in contrast to the decreasing efficiency of conventional systems. Overall fuel cell system efficiency is further enhanced because the waste heat from on-site power plants can be used.

Reduced Cost. The high efficiency of fuel cell systems and the use of on-site waste heat will result in a reduced operating cost. In areas where grid service is unreliable, cost prohibitive, or unavailable fuel cells offer a viable alternative solution.

6. What are the Opportunities for Fuel Cells?

Many applications are presently seen for fuel cells, with the reliable, efficient, on-site power plant with used waste heat appearing to be one of the best. The integration of fuel cells with all other environmental control devices (air conditioner, heat pump, hot water, emergency power) of a building will provide a significant cost reduction. Other applications that appear favorable cover a range from large dispersed power plants for electrical power generation to miniature portable applications. When fossil fuel usage is being replaced by renewable energy sources, hydrogen will be used as an energy storage medium with fuel cells the preferred means for generating electricity.

7. What are the Costs or Risks Associated with Fuel Cells?

The main obstacle to the commercialization of fuel cells has their initial cost. Projections of costs for mass produced quantities of fuel cells are frequently based on questionable assumptions. This uncertainty and the advancements being made in competing technologies make sales projections uncertain. Varying governmental regulations and subsidies add to this complexity.

8. Where did Fuel Cells Originate?

Sir William Grove in Great Britain invented the fuel cell in 1839. However, many other inventors in various countries were involved in the several types of fuel cells that currently exist. The first major uses of fuel cells were a Proton Exchange Membrane Fuel Cell (PEMFC) cell used in the NASA Gemini program and an Alkaline Fuel Cell (AFC) used in Apollo.

9. Where Does the Hydrogen Come From?

Hydrogen is currently produced primarily from natural gas, resulting in the production of carbon dioxide, a potential greenhouse gas. In the future, hydrogen will be made from sources that do not result in carbon dioxide emissions such as biomass, solar, wind, and nuclear energy.

10. What about hydrogen safety?

Hydrogen can be extremely explosive when mixed with air in the correct proportions. However, hydrogen is a light gas so it rapidly disperses in air, unlike gasoline that is denser than air and forms a dangerous explosive mixture that does not disperse rapidly. The unlikely leakage of hydrogen gas from a fuel cell system is easily detected so the system can be shut down for servicing before a hazard results. Hydrogen-rich gas is currently distributed in some countries in pipelines similar to our natural gas pipelines. Research is underway on techniques for hydrogen storage.