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Fuel Cells are electrochemical devices that can convert a fuel into electricity.
A fuel cell is neither a battery nor an internal combustion engine, however to understand exactly what a fuel cell does, it is helpful to think of a fuel cell as a mixture of both technologies:
- A fuel cell is like a battery, as the output from the Fuel Cell is ELECTRICITY, and there are no moving parts to a fuel cell.
- A fuel cell is similar to an internal engine, as it requires a constant flow of FUEL to work
The basic fuel cell uses Hydrogen as the fuel, and is based upon the reaction that takes place when Hydrogen (H2) and Oxygen (O2) combine to make water (H20). In this process, electricity is released which can be harnessed by the fuel cell. A catalyst, applied to the electrodes is used to speed up the reaction. One of the best catalysts available today is Platinum.
All types of fuel cells have similarities. There are two electrodes - an Anode and a Cathode, sandwiched around an electrolyte (liquid or solid). The electrolyte carries electrically charged particles between the two electrodes. There is an external circuit that connects the two electrodes together, and this carries a flow of electrons around the circuit, which creates the current.
Different types of fuel cells use different fuels, and have different electrolytes. For explanatory purposes, consider the PEM (Polymer Electrolyte Membrane, also called Proton Exchange Membrane) fuel cell:
Hydrogen (the fuel) arrives at the Anode. Here it is split by the catalyst into Protons and Electrons, with the following equation:
Hydrogen Atoms »» Hydrogen Protons + Electrons
2H2 »» 4H+ + 4e-
The electrolyte is a material that conducts protons, but does not conduct electrons. The protons move through the electrolyte towards the Cathode. This creates a positive charge at the Cathode. To balance out both sides, the electrons move around the external circuit. Here they are reunited with the protons (H+), and Oxygen. All combine to form water (H20). This process can be summarised with the following equation:
Oxygen + Hydrogen Protons + Electrons »» Water
O2 + 4H+ + 4e- »» 2H2O
The overall equation therefore is:
Hydrogen + Oxygen »» Water + Energy
2H2 + O2 »» 2H2O + energy |
