anode
An anode (from Greek ἄνοδος ánodos “ascent”, literally “way up”) is an electrode that, for example, takes free electrons from a vacuum or discharges anions from an electrolyte while absorbing electrons or generates cations , i.e. allows oxidation reactions to take place. An anode thus corresponds to an electron acceptor or behaves formally like an oxidizing agent .
The counter electrode of the anode is the cathode on which reducing processes take place. Anions migrate to the anode and cations to the cathode. The polarity of an anode can be positive or negative when electrochemical processes are taking place, see below . In earlier years the anode of an X-ray tube was also called an anticathode .
In electroplating , electricity is sent through an electrolytic bath. At the positive pole (anode) is the metal that is to be applied (eg., Copper or nickel), the negative terminal (cathode) of the article to be coated.
chemistry
In chemistry , especially electrochemistry , an anode is the electrode on which an oxidation reaction takes place. Electrons from the chemical reaction are absorbed and released via the electrical connection. An electrochemical reaction always takes place at the phase boundary between an electrode and an electrolyte solution, an ion-conducting solid or melt . Therefore the anode is the positive electrode in electrolysis . (Electrolysis requires electrical energy.)
In the case of electrochemical elements that generate electrical energy, oxidation processes take place at the anode. This means that the anions coming from the electrolyte are discharged or neutral atoms become cations. If the anode and cathode are now connected to form a circuit, electrons flow to the cathode via this external connection; in this external circuit the anode then acts as a negative pole (e.g. in batteries and fuel cells ).
In the case of rechargeable batteries ( secondary element , accumulator ) the same electrode can alternately work as an anode or cathode, depending on whether the battery is being charged or discharged.
So-called sacrificial anodes made of a relatively base metal serve as corrosion protection, whereby they are dissolved themselves.
Electrical engineering
In the electrical engineering , the anode is an electrode of a cathode ray tube , fluorescent lamp , LED , fuel cell , lead storage battery and so on. The anode is the electrode at which electrons pass from the surrounding medium (electrolyte, vacuum, silicon ) to the electrode and then flow through the external electrical circuit to the cathode. Since the reference direction for the current flow relates to positive charge carriers and is thus opposite to the direction of movement of electrons, the current flows in the external circuit from the cathode to the anode. Within the component under consideration, the current flows from the anode to the cathode; the circuit is closed.
This statement has nothing to do with whether the potential of the anode is higher or lower than the potential of the cathode (in other words: whether the voltage from anode to cathode is positive or negative). There are the terms positive pole and negative pole; the potential of the positive pole is always greater than the potential of the negative pole. Therefore the voltage from the positive pole to the negative pole is always greater than zero. The positive pole and negative pole thus indicate the direction of voltage, while the anode and cathode indicate the direction of the current.
In the case of components where the anode has positive voltage compared to the cathode, electrical energy is converted into another form of energy (heat, chemical energy, ...), e.g. B. in a tube diode , a cathode ray tube or an accumulator that is charged. In the case of components in which the anode has negative voltage compared to the cathode, electrical energy is given off to the external electrical circuit at the expense of another form of energy (e.g. chemical energy), e.g. B. in a fuel cell or an accumulator that is being discharged.
history
For the naming by Michael Faraday see Faraday's laws .
Web links
- The International Electrotechnic vocabulary (IEV) of the International Electrotechnical Commission (IEC) on the Internet
- About the polarity of the anode
Individual evidence
- ^ Wilhelm Gemoll : Greek-German school and hand dictionary. 9th edition. Freytag, Munich a. a. 1965.
- ↑ Electrical pole the positive pole (positive pole, short plus, sign + or anode) is mostly assigned to the color coding "red"