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What Is an Air Cathode?

Zn-air cathode batteries are often used in hearing aids.
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  • Written By: Maggie J. Hall
  • Edited By: Jenn Walker
  • Last Modified Date: 20 December 2014
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An air cathode basically conducts oxygen into an electrolyte, wherein the molecules react with the ions of the anode to generate an electrical current. The energy produced by this reaction exits back out of the air cathode to whatever object or device requires power. The cathode derives oxygen used to initiate the reaction from the air or from an aqueous solution. Manufacturers refer to these types of power sources as air batteries.

Air battery anodes consist of any one of a number of metals, but those most widely used include aluminum, lithium, magnesium or zinc. The electrolyte used between the anode and the cathode must be a substance that is compatible with and successfully conducts ions from the anode. The cathode material most frequently used in this type of battery is carbon. The names of air cathode batteries typically come from the metal that comprises the anode side of the battery combined with the air cathode itself. For example, lithium or Li-air batteries have a lithium anode, and zinc or Zn-air batteries contain zinc anodes; both have a carbon-based air cathode.

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Manufacturers design Zn-air cathode batteries in a variety of sizes, and the smallest is often the circular battery used in hearing aids or watches. Larger versions typically power cameras or other electronic devices. Advantages of this type of power source include an extended shelf life in addition to lasting longer while in actual use. The components of these energy sources are also generally safer for the environment.

Different types of cathodes become negative or positive, depending on specific applications. Negative cathodes comprise electrolytic cells, and positive cathodes comprise galvanic cells. Air cathodes are generally positive, though they absorb oxygen as a potential power source; they emit the byproduct of the chemical reaction as electrical current.

Individuals might easily replicate a simple air cathode by sandwiching paper or cloth saturated with salt-water solution along with a layer of crushed charcoal between two pieces of aluminum foil. The end of one wire typically attaches to a miniature light bulb or motor, while the other end attaches to the foil. The other wire also attaches to the object, while the other end makes contact with the crushed carbon. Pressing down on all layers creates a chemical reaction, and the device receives electricity. Adding hydrogen peroxide to the salt-water solution typically enhances the number of available oxygen molecules and provides more power.

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