Metals commonly used as anodes include aluminum, brass, bronze, copper, lead, lithium, magnesium, nickel, silver, titanium, zinc and alloys of them. Non-metals also used as anodes include carbon, graphite and silicon. Each of these has a particular set of characteristics that make it better or worse suited for use in different devices and for specific uses. In practice, metal anodes are categorized according to how, and for what purpose, they are used. Electrical conductivity, thermal conductivity, structural strength, durability and resistance to corrosion typically are among the characteristics taken into consideration when particular metal anodes are chosen.
Perhaps the most familiar use of metal anodes is in galvanic cells, otherwise known as batteries, where an electric current flows between metal cathodes and anodes immersed in an electrolyte that carries electric current between them. Early batteries used in space missions used silver for metal cathodes and zinc for metal anodes. More recently, rechargeable nickel-cadmium batteries have been used to power many electronic devices. Iron and cadmium serve in this way. Light in weight, lithium is also used for metal anodes in rechargeable batteries that are found in portable consumer electronic devices, such as cell phones and portable computing devices. Thanks to advances in technology, lithium also has been used for anodes in lithium ion batteries to power hybrid and all-electric vehicles.
Another common use of metal anodes is to protect metals or other materials from rust or corrosion. For example, sacrificial and offshore sacrificial anodes, which are also known as galvanic anodes, are meant to protect a cathode, typically another metal that needs to be preserved for as long a period as possible, from rust or corrosion. The anode is made from a metal or alloy that corrodes more easily than the cathode. Such is the case with zinc and iron, where zinc, or a zinc alloy, is layered on top of the iron.
With exposure to the elements — air, saltwater or freshwater — oxidation will occur, and electrons will move from the sacrificial anode, the zinc or alloy, to the iron, protecting it from oxidation. By definition, this makes the iron a cathode. Another example of this is the hot water heater anode, where one or more rods of magnesium or aluminum are layered around a steel core, protecting it and the metal outer casing of the tank from the rust or corrosion that would result from regular contact with heated water.
