Electrochromic materials. Electrochromic materials are those that change color with the passage of an electric current . This induces redox reactions in them that modify the energy bands in which the material interacts with visible light. Its applications include anti-glare mirrors, smart windows and chameleon fabrics.
Summary
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- 1 Antecedents
- 2 Operation
- 1 Counter electrode
- 3 Redox reactions
- 4 Applications
- 1 Other applications
- 5 References
- 6 Fountains
Background
The first electrochromic material was synthesized in the eighteenth century and the first references to this effect date back to the nineteenth century , the detailed study of its properties did not arrive until the sixties of the last century.
During the last years, the development of new electrochromic materials has known an exponential growth. Its applications include smart glasses, display devices and camouflage fabrics.
Functioning
The electrochromic effect was first explained in 1969 . ” [1] Initially it was treated as basic research in materials, but its interest in home automation was soon realized, as EC materials could be excellent candidates for variable transmittance windows in a “smart” building, as well as other applications.
An EC device is a multilayer coating a few um thick, consisting of a pure ionic conductor (electrolyte) located between two layers: one of EC material, and another of another material called a counter electrode. The assembly is in turn inserted between two layers of transparent electrical conductor (typically indium-tin oxides, ITO). [2] When applying tension to the transparent conductors, an electrochemical reaction takes place in which ions are inserted or extracted from the EC layer, which originates a molecular change, which entails a modulation in the spectral dependence of the optical transmittance (in ultimately, in the color of the material). In essence, an oxidation reduction reaction is responsible for the change in properties.
counter electrode
The name counter electrode comes from the fact that each charge that the electrochromic molecules acquire comes from this material.
redox reactions
In response to the application of a small voltage—on the order of a volt—some materials change their color. The electric current induces in them a reaction of reduction (gain of electrons) or oxidation (loss of electrons) that modifies the range of energies in which the compound interacts with visible light. For this reason, such materials are called electrochromic.
The addition of a thin film of electrochromic material to a circuit makes it a color changeable electrochemical cell. The substance can be deposited on one of the electrodes or dissolved in an electrolyte solution. As the circuit is charged and discharged, the oxidation and reduction reactions (collectively called redox reactions) responsible for the color change occur.
Applications
There are currently two applications that have extensive commercial development:
- Rear-view mirrors, specially developed by Gentex in the USA. [3]
- The “smart” window proposed by Flabeg in Germanyin 1999. [4]
Other apps
- On display screens, gogglesand camouflage clothing. Electrochromic substances would also save energy .
- A building with an electrochromic coating on the roof could reduce its energy consumption if in winter it adopts a dark color (which absorbs heat) and, in summer, a light and reflective tone.
- Use in windowsthat reduce the amount of incoming light during the clearest hours of the day.
