What exactly is a fuel cell, anyway? Why are governments, private businesses and academic institutions collaborating to develop and produce them? Fuel cells generate electrical power quietly and efficiently, without pollution. Unlike power sources that use fossil fuels, the by-products from an operating fuel cell are heat and water. But how does it do this?

A fuel cell is an electrochemical energy conversion device. A fuel cell converts the chemicals hydrogen and oxygen into water, and in the process it produces electricity.

The other electrochemical device that we are all familiar with is the battery. A battery has all of its chemicals stored inside, and it converts those chemicals into electricity too. This means that a battery eventually “goes dead” and you either throw it away or recharge it.

With a fuel cell, chemicals constantly flow into the cell so it never goes dead — as long as there is a flow of chemicals into the cell, the electricity flows out of the cell. Most fuel cells in use today use hydrogen and oxygen as the chemicals.

 

Polymer Exchange Membrane Fuel Cells

The polymer exchange membrane fuel cell (PEMFC) is one of the most promising fuel cell technologies. This type of fuel cell will probably end up powering cars, buses and maybe even your house. The PEMFC uses one of the simplest reactions of any fuel cell. First, let’s take a look at what’s in a PEM fuel cell:

In Figure 1 you can see there are four basic elements of a PEMFC:

  • The anode, the negative post of the fuel cell, has several jobs. It conducts the electrons that are freed from the hydrogen molecules so that they can be used in an external circuit. It has channels etched into it that disperse the hydrogen gas equally over the surface of the catalyst.
  • The cathode, the positive post of the fuel cell, has channels etched into it that distribute the oxygen to the surface of the catalyst. It also conducts the electrons back from the external circuit to the catalyst, where they can recombine with the hydrogen ions and oxygen to form water.
  • The electrolyte is the proton exchange membrane. This specially treated material, which looks something like ordinary kitchen plastic wrap, only conducts positively charged ions. The membrane blocks electrons. For a PEMFC, the membrane must be hydrated in order to function and remain stable.
  • The catalyst is a special material that facilitates the reaction of oxygen and hydrogen. It is usually made of platinum nanoparticles very thinly coated onto carbon paper or cloth. The catalyst is rough and porous so that the maximum surface area of the platinum can be exposed to the hydrogen or oxygen. The platinum-coated side of the catalyst faces the PEM.

Fuel Cell Efficiency

If the fuel cell is powered with pure hydrogen, it has the potential to be up to 80-percent efficient. That is, it converts 80 percent of the energy content of the hydrogen into electrical energy. However, we still need to convert the electrical energy into mechanical work. This is accomplished by the electric motor and inverter. A reasonable number for the efficiency of the motor/inverter is about 80 percent. So we have 80-percent efficiency in generating electricity, and 80-percent efficiency converting it to mechanical power. That gives an overall efficiency of about 64 percent. Honda’s FCX concept vehicle reportedly has 60-percent energy efficiency.

If the fuel source isn’t pure hydrogen, then the vehicle will also need a reformer. A reformer turns hydrocarbon or alcohol fuels into hydrogen. They generate heat and produce other gases besides hydrogen. They use various devices to try to clean up the hydrogen, but even so, the hydrogen that comes out of them is not pure, and this lowers the efficiency of the fuel cell. Because reformers impact fuel cell efficiency, DOE researches have decided to concentrate on pure hydrogen fuel-cell vehicles, despite challenges associated with hydrogen production and storage.

Benifits of Fuel Cell Technology

  • Efficiency: Facilities managers are drawn to DFC fuel cell power plants primarily due to their highly efficient use of natural gas and inherent Low Heating Value (LHV) efficiency. DFC’s offer clear efficiency advantages in comparison to other forms of distributed power generation. DFC power plants are 47% efficient in the generation of electrical power and, depending on the application, up to 90% efficient overall in Combined Heat and Power (CHP) applications when the byproduct heat is used.  Typical fossil fuel-powered plants operate at about 35% electrical power generation efficiency.
  • Environmental Impact: Amid the increasing energy demand and cost, and growing public awareness for energy conservation, fuel cell power plants are becoming the choice for on-site power. With low emissions of pollutants such as nitrogen oxides (NOx), sulfur oxides (SOx), and particulate matter as well as dramatically lower emissions of carbon dioxide (CO2), fuel cell power plants qualify under several environmental certifications established by the government, such as the Leadership in Energy and Environmental Design (LEED) program and Renewable Energy Standards (RES). DFC power plants also have been designated as “Ultra-Clean” by the California Air Resources Board (CARB), and exceed all 2007 CARB standards. FuelCell Energy’s power plants eliminate emissions generated by fossil-fuel-based backup generators.
  • Reliability: By locating the power plant on-site, and implementing real-time monitoring capability, end-users are assured of increased reliability, a necessary requirement for applications such as hospitals, hotels,universities and manufacturing facilities. Unlike wind and solar technologies, which generally have an overall availability of 35%, FuelCell Energy products operate independently of the grid, and have an availability of about 90%.
  • Fuel Flexibility: A number of industrial, agricultural plants and wastewater treatment facilities generate renewable biogas as part of the manufacturing process. Fuel cell power plants can harness the methane in this byproduct, and use the gas to power the system in lieu of natural gas, making it a renewable energy source. In many places where digester gas production volume is variable, DFC plants are designed to operate with automatic blending with natural gas.

Courtesy: howstuffworks.com, fuelcellenergy.com

Posted by

Mahesh.P

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