A fuel cell is an electrochemical cell that converts a source fuel into an electric current. It generates electricity inside a cell through reactions between a fuel and an oxidant, triggered in the presence of an electrolyte.
Sir William Robert Grove developed the first working prototype in the year 1839 representing the foundation stone for today’s fuel cell technology.
This fuel cell prototype consisted of two platinum electrodes which were separately surrounded by a glass cylinder. One of the cylinders was filled with hydrogen the other with oxygen. Both electrodes were immersed in diluted sulphuric acid -which was the electrolyte- and created the electric connection. At the electrodes voltage was produced. This voltage was very low and therefore Grove linked several of these fuel cells to get a higher voltage.
fuel cell structure
Fuel cell consist tree main layer: anode, cathode and electrolyte. Anode and cathode serve as catalyst. The layer in the middle consists of a carrier structure which absorbs the electrolyte. In different types of fuel cells different substances are used as electrolyte. Some electrolytes are liquid and some are solid with a membrane structure.
The fuel cell reverses the process of electrolysis which is known from school. In the process of electrolysis by applying electric power water is decomposed into the gaseous components oxygen and hydrogen.
The fuel cell takes exactly these two substances and converts them to water again. In theory the same amount of energy which has been used for the electrolysis is set free by this conversion. In practice insignificant losses are caused by different physical-chemical processes.
main types of fuel cells
AFC (Alkaline Fuel Cell)
It is the only type of fuel cell that requires oxygen and hydrogen in purest form because even smallest amounts of dirt would destroy the cell. The electrolyte consists of caustic potash.
PEM (Proton exchange membrane fuel cell)
It is very light, it is very efficient and as reaction gas it requires only atmospheric oxygen instead of pure oxygen. The hydrogen has to be generated in a reformer.
PEM fuel cells are very sensitive to carbon monoxide (CO). This gas might block the anode catalyst and subsequently lead to a reduced performance.
The electrolyte consists of a solid proton exchange membrane (PEM) made from sulphonated polymer.
PAFC (Phosphoric Acid Fuel Cell)
Type of fuel cell which run at a high operating temperature. It is suited perfectly for cogeneration. Highly concentrated phosphoric acid which is bond in a gel matrix serves as catalyst. The PAFC requires atmospheric oxygen and hydrogen as reduction gases.
MCFC (Molten Carbonate Fuel Cell)
The electrolyte in this fuel cell is a salt melting of combined alkali carbonates (Li2CO3 / K2CO3).
Natural gas, coal gas, biogas and synthesis gas can be used directly as fuels. No reformer is needed.
The molten carbonate fuel cell – MCFC operates at high temperature ranges of 580 … 660°C.
SOFC (Solid Oxide Fuel Cell)
Operates with atmospheric oxygen and hydrogen. Its operating temperature is between 800 and 1000°C.
There are two different SOFC designs: planar (shaped like a plane) and tubular (shaped like a tube). With the tubular SOFC cathode, electrolyte and anode are arranged at the inside of a ceramic pipe. The fuel gas is led through the inside of the tube and the atmospheric oxygen is led around the outside.
DMFC (Direct Methanol Fuel Cell)
The only cell which is not using hydrogen but methanol for the eduction.
There are no reformers needed because the cell on its own converts methanol into hydrogen protons, free electrons and CO2. Because of the missing reformer it is best suited for the use in motorcars by coming closest to the ideal of an energy source as simple as possible.
A proton exchange membrane serves as electrolyte.
fuel cells and environment
Depending on the fuel used, environmental performance (CO2 emissions in particular) is vary.
Hydrogen fuel cells are good for the environment because they are the cleanest burning fuels ever developed. Hydrogen is taken out of water and then put into fuel cells as a gas that can power a vehicle. The only emission that comes out of a fuel cell powered vehicle is water vapor.
There are, however, some drawbacks that are associated with hydrogen fuel cells and the environment. A completely efficient system of producing, storing and transporting hydrogen should, in principle, lead to no unwanted emissions of the gas.
The use of nanomaterials makes these membranes more efficient and also serves in the development of light and inexpensive fuel tanks especially for hydrogen storage. So the main concern focuses on the environmental effects of nanoparticles and nanomaterials used in fuel cell manufacturing and operation.
The effectiveness of energy conversion with minimum losses and the reduction of production cost give hopes for a greener environment.