Anode

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Zinc anode 2

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Fig bat Discharge Charge3

Galvanic cell with no cation flow

Charge discharge secondary batterie

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Anode is an electrode through which conventional current flows into a polarized electrical device. The direction of electric current is, by convention, opposite to the direction of electron flow. Therefore, the anode is positively charged in a device that consumes power, and negatively charged in a device that provides power. This definition is widely used in devices such as diodes, electrolytic cells, and batteries. The term was coined by Michael Faraday, deriving from the Greek word anodos, meaning 'way up'.

Function and Operation

In an electrolytic cell, the anode is the electrode at which the oxidation reaction occurs, meaning it gives up electrons to the external circuit and corrodes. In contrast, in a galvanic cell, the anode is the electrode at which the reduction reaction occurs, meaning it gains electrons from the external circuit. This distinction highlights the relative nature of the anode's definition, depending on whether the device is consuming or providing power.

In a rechargeable battery, the anode switches between being the positive and the negative electrode, depending on whether the battery is being charged or discharged. During discharge, the anode undergoes oxidation and releases electrons, while during charging, it undergoes reduction and gains electrons.

Applications

Anodes are crucial components in a variety of applications, including:

• Batteries: Serving as the source of electrons in the discharge cycle.
• Electroplating: Where the anode is made of the metal to be plated onto the object.
• Cathodic protection: Sacrificial anodes made from a more reactive metal are used to prevent corrosion of protected metal structures, such as pipelines and ship hulls.
• X-ray tubes: The anode targets in these tubes are struck by high-speed electrons, producing X-rays.

Materials

The material of an anode depends on its application. For example, in a zinc-carbon battery, the anode is made of zinc, while in a lead-acid battery, it is made of lead. Sacrificial anodes used in cathodic protection are typically made of zinc, magnesium, or aluminum, due to their high position in the galvanic series, which makes them corrode preferentially and protect the structural metal.

Environmental and Safety Considerations

The use of certain materials in anodes, such as lead and mercury, raises environmental and health concerns. Proper recycling and disposal of batteries and other devices containing toxic materials are essential to minimize their environmental impact.

See Also

• Cathode
• Electrolysis
• Galvanic cell
• Electrochemical cell

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