THIS TECHNOLOGY IS extremely interesting to people in all walks of life because it offers a means of making power more efficiently and with less pollution. In technical terms, a fuel cell is an electrochemical energy conversion device. A fuel cell converts the chemicals hydrogen (H) and oxygen (O₂) into water (H₂O), and in the process it produces electricity. The water that is produced is the most pure form of H₂O on earth. But how does it do this?

 

This is not some kind of rocket science; you are very familiar with a similar device that produces electricity by performing some chemical reactions - a battery, yes a hydrogen fuel cell works on a similar track. Similar to any battery the fuel cell produces a DC (direct current) voltage that can be used to power motors, lights or any number of electrical appliances. Fuel cells convert chemical energy into electricity and heat from a variety of fuels. Unlike batteries, fuel cells use an external fuel supply and in principle run so long as fuel is supplied. Compared with internal combustion (IC) engines, fuel cells offer particularly high conversion efficiency (up to 60%) and far lower emissions, since the only waste product of hydrogen oxidation is water. SOx and NOx emissions are barely detectable and CO2 emissions are reduced due to the increased operating efficiency. Thus fuel cells combine the best of both batteries and combustion engines, whilst avoiding most, if not all, of their undesirable characteristics.

 

There are several different types of fuel cells, each using a different chemistry. Fuel cells are usually classified by the type of electrolyte they use. Some types of fuel cells work well for use in stationary power generation plants. Others may be useful for small portable applications or for powering laptops, cars and even submarine.

 

The proton exchange membrane fuel cell (PEMFC) is one of the most promising technologies. This is the type of fuel cell that will 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:

 

 

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.

The catalyst is a special material that facilitates the reaction of oxygen and hydrogen. It is usually made of platinum powder 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.

 

 

The pressurized hydrogen gas (H₂) entering the fuel cell on the anode side. This gas is forced through the catalyst by the pressure. When an H₂ molecule comes in contact with the platinum on the catalyst, it splits into two H⁺ ions and two electrons (e^-). The electrons are conducted through the anode, where they make their way through the external circuit (doing useful work such as turning a motor) and return to the cathode side of the fuel cell.

 

Meanwhile, on the cathode side of the fuel cell, oxygen gas (O₂) is being forced through the catalyst, where it forms two oxygen atoms. Each of these atoms has a strong negative charge. This negative charge attracts the two H⁺ ions through the membrane, where they combine with an oxygen atom and two of the electrons from the external circuit to form a water molecule (H₂O). This reaction in a single fuel cell produces only about 0.7 volts. To get this voltage up to a reasonable level, many separate fuel cells must be combined to form a fuel-cell stack.

 

PEMFCs operate at a fairly low temperature (about 176 degrees Fahrenheit, 80 degrees Celsius), which means they warm up quickly and don’t require expensive containment structures. Constant improvements in the engineering and materials used in these cells have increased the power density to a level where a device about the size of a small piece of luggage can power a car.

 

Many multinational companies including Honda and Toyota have taken huge steps into this field. Knowing all these features of fuel cell, it is yet a dream for most of us due to the very high one time investment cost. Many Government and NGO bodies are taking actions on the path to make it a cost effective technology to harness its power to the fullest.