Air electrode
An electrode that uses oxygen from the air in its reaction. It is the positive electrode of metal-air batteries and fuel cells, taking in oxygen on discharge and releasing it on charge.
Because the positive electrode's active material comes from the air instead of being carried inside, the battery can be light and cheap. In return, the electrode has to be a place where gaseous oxygen, liquid electrolyte and solid catalyst all meet, which makes it hard to build.
Hardest of all is running both reactions, taking oxygen in and giving it off, at the same electrode thousands of times. Both are slow and need catalysts. In 2011 a design principle was proposed for predicting how well an oxide will work as a catalyst from the state of its electrons[1]. Damage to the electrode material on each charge is considered a major factor limiting the life of iron-air and similar batteries.
Related terms
- Iron-air batteryA battery that draws electricity as iron rusts in air and turns the rust back into iron when charged. Its materials are extremely cheap, suiting it to storing energy for days.
- Redox reactionA chemical reaction in which electrons pass from one substance to another. Losing electrons is oxidation, gaining them is reduction, and the two always occur together.
- Fuel cellA device that reacts hydrogen with oxygen to produce electricity directly, without combustion. The only exhaust is water.