About Hydrogen Fuel cell
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Fuel cells generate power efficiently without pollution
- its only by products are heat and water
- Recently more cars are beginning to use fuel cell technology
- A fuel cell converts the chemicals hydrogen and oxygen into water, and in the process it produces electricity.
- It is similar to a battery
- But battery eventually goes dead, and have to be replaced or recharged
- Fuel cells have their chemicals flow into them constantly so it can never go dead.
- As long as the chemicals keep flowing in, the electricity will keep being generated.
- There are several types of fuel cells:
- The Polymer exchange membrane fuel cell (PEMFC)
- Solid oxide fuel cell (SOFC)
- Alkaline fuel cell (AFC)
- Molten-carbonate fuel cell (MCFC)
- Phosphoric-acid fuel cell (PAFC)
- Direct-methanol fuel cell (DMFC)
- The PEMFC is the most likely fuel cell to be used for transportation purposes due to its high power density and low operating temperature, allowing it to warm up quickly and start generating electricity
- How the PEMFC works
- Components
- Anode: The negative post of the fuel cell. The anode conducts the electrons freed so they can be used in an external circuit. The anode has cells etched to 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.
- How it works:
- Pressurized hydrogen gas (H2) enters 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. Bipolar plates are used to connect one fuel cell to another and are subjected to both oxidizing and reducing conditions and potentials. A big issue with bipolar plates is stability. Metallic bipolar plates can corrode, and the byproducts of corrosion (iron and chromium ions) can decrease the effectiveness of fuel cell membranes and electrodes. Low-temperature fuel cells use lightweight metals, graphite and carbon/thermoset composites (thermoset is a kind of plastic that remains rigid even when subjected to high temperatures) as bipolar plate material.