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Brennstoffzelle und Elektrolyse
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- Fuel cells and electrolysis When hydrogen and oxygen react with each other, ... ... the result is a violent explosion, because a lot of energy is released.
- As in most chemical reactions, electrons play a key role here. This can be seen here in slow motion. Oxygen attracts electrons more strongly than hydrogen.
- This results in a chain reaction, during which a great deal of energy is suddenly released. The oxyhydrogen gas reaction. The electrons of the hydrogen migrate to the oxygen to form water.
- The resulting radicals ensure that the reaction continues. Reactions involving a transfer of electrons are called redox reactions. The word “redox“ is a combination of the words “reduction” and “oxidation”.
- To put it simply: the oxygen accepts electrons. It is reduced. The hydrogen donates electrons. It is oxidized. Because the oxyhydrogen gas reaction involves both oxidation and reduction, it is referred to as a redox reaction.
- And it can occur explosively. The energy is lost as heat. However, the energy can also be harnessed. In a fuel cell.
- The flow of electrons in the redox reaction can then generate an electrical current. This is achieved by separating the reactants from each other with a membrane. A catalytic coating on the electrode ensures that the hydrogen relinquishes its electrons easily, ...
- ... thus undergoing oxidation. The reacting gases, such as the hydrogen shown here, flow through an electrode layer to the membrane. Oxidation always occurs at the anode.
- The hydrogen molecule releases two electrons – shown here in yellow – ... ...and splits into two hydrogen ions, leaving positively charged protons behind. Here in white. Only the protons are able to pass through the membrane to the other side of the fuel cell.
- The electrons take a detour. They flow through a wire between the electrodes. This is nothing more than electrical current, which can be utilized. When the electrons arrive at the other electrode, they reduce the incoming oxygen molecules.
- Reduction occurs at the cathode. This forms oxygen ions. They are negatively charged and react with the hydrogen ions flowing through the membrane.
- The result is water vapour, which emerges from the fuel cell. The trick of a fuel cell is therefore... ... to separate the reaction of hydrogen and oxygen into individual steps to generate electricity.
- Fuel cells are highly efficient. Theoretically, a fuel cell can harness over 80 percent of the fuel’s energy. In practice, individual fuel cells are packed together into stacks to boost the power output.
- With the electrical current, for example from wind generators or other renewable power sources, ... ... the redox reaction can also be driven in the opposite direction. Hydrogen can then be generated from water. A reaction known as electrolysis.
- Here, electrons are pumped into the water at the cathode. The reduction reaction splits the water. Hydrogen gas forms. At the anode, electrons are removed from the oxygen of the water, which is oxidized. Oxygen gas forms.
- Just as in the oxyhydrogen gas reaction and the reaction in the fuel cell, ... ...the driving force behind electrolysis is the transfer of electrons. Electrochemistry thus forms the basis of a hydrogen economy...
- ...in which we will be able to consume energy without producing the greenhouse gas carbon dioxide.
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