Water electrolysis uses electricity to split water into hydrogen and oxygen, but it is not widely used commercially due to practical and environmental concerns. Electrolytes are added to water to allow electrical conduction, and batteries or solar panels are used as power sources. Hydrogen ions form hydrogen molecules at the negative electrode, while hydroxide ions form oxygen and water at the positive electrode. The process is inefficient and costly, and environmental challenges must be addressed before it can be a practical source of energy.
Electrolysis of water is a process that uses an electric current to split water molecules into hydrogen and oxygen. It is often performed as an experiment in high school science labs and has been studied as a method of obtaining hydrogen fuel. As of 2010, however, water electrolysis had not found widespread commercial or industrial use. The process requires three components: an electrical source, two electrodes and water.
Pure water is not used in electrolysis: pure water inhibits electrical conduction. In order for the electric current to pass through the water, substances must be added to it. These substances dissolve to form something called electrolytes.
An electrolyte is any substance that conducts electricity. Electrolytes are able to conduct electricity because they are composed of electrically charged atoms or molecules called ions. Although water is composed of hydrogen and oxygen ions, the water molecule itself has a neutral electric charge. Salt or a few drops of acid or base are commonly added to water to form an electrolyte solution.
Batteries, a direct current (DC) power source, or solar electric panels are commonly used to provide electricity for the electrolysis of water. Two electrodes are connected to the electrical source and immersed in a container of water. When electricity is applied, water molecules begin to split, forming unstable hydrogen (H+) and hydroxide (OH-) ions.
Hydrogen ions, which lack an electron, are positively charged. They migrate to the negative electrode where free electrons flow through the water. Here the hydrogen ions gain an electron to form stable hydrogen atoms. Individual hydrogen atoms combine to form hydrogen molecules (H2), which bubble to the surface. This reaction can be expressed as: 2 H+ + 2 e- → H 2.
Conversely, hydroxide ions carry too many electrons. They migrate to the positive electrode, where the extra electrons are stripped away and drawn into the electrical circuit. This leaves oxygen and water molecules. This reaction can be expressed as: 4 OH-− 4 e- → O2 + 2H2O. Oxygen molecules bubble to the surface.
Although the electrolysis of water has mainly been confined to laboratories, the use of hydrogen as a source of clean energy has attracted renewed interest. Finding a clean energy source to drive the reaction, however, poses practical and environmental concerns. Electrolysis of water is neither efficient nor economical.
Fuel costs have been a major obstacle. The environmental impact of electricity generation is another. In particular, the carbon dioxide emitted by thermoelectric plants should be considered. These environmental and technological challenges may not prove insurmountable. Until they are overcome, however, water hydrolysis remains an impractical source for meeting society’s energy needs.
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