1. How does a modern fuel cell work?
Yang LIAO
Department of Mechanical Engineering,
University of Fukui
Good morning.

2. Introduction Fuel cell
A fuel cell is a device that uses hydrogen (or hydrogen-rich fuel) and oxygen to create electricity. Fuel cells are more energy-efficient than combustion engines and the hydrogen used to power them can come from a variety of sources. If pure hydrogen is used as a fuel, fuel cells emit only heat and water, eliminating concerns about air pollutants or greenhouse gases. 2

3. Parts of a Fuel Cell +
The electrodes (anode and cathode), catalyst, and polymer electrolyte membrane together form the membrane electrode assembly (MEA) of a PEM fuel cell.
Anode. The anode, the negative side of the fuel cell, has several jobs. It conducts the electrons that are freed from the hydrogen molecules so they can be used in an external circuit. Channels etched into the anode disperse the hydrogen gas equally over the surface of the catalyst.
Cathode. The cathode, the positive side of the fuel cell, also contains channels that distribute the oxygen to the surface of the catalyst. It conducts the electrons back from the external circuit to the catalyst, where they can recombine with the hydrogen ions and oxygen to form water.
Polymer electrolyte membrane. The polymer electrolyte membrane (PEM)—a specially treated material that looks something like ordinary kitchen plastic wrap—conducts only positively charged ions and blocks the electrons. The PEM is the key to the fuel cell technology; it must permit only the necessary ions to pass between the anode and cathode. Other substances passing through the electrolyte would disrupt the chemical reaction.

4. Polymer electrolyte membrane fuel cells
Fuel cells come in many varieties; however, they all work in the same general manner. They are made up of three segments which are sandwiched together: the anode, the electrolyte, and the cathode. The polymer exchange membrane fuel cell (PEMFC) is one of the most promising fuel cell technologies.

5. Chemistry of a Fuel Cell
Anode side:
2H2 => 4H+ + 4e-
Cathode side:
O2 + 4H+ + 4e- => 2H2O
Net reaction:
2H2 + O2 => 2H2O
It shows 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).

6. How does a modern fuel cell work