Redox reaction
A 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.
When iron rusts, the iron loses electrons (oxidation) and oxygen takes them up (reduction). A battery makes the two halves happen at separate electrodes and sends the electrons the long way round through an outside circuit, which is how it delivers electricity. Charging applies electricity from outside to drive the reaction backwards.
How fast the electrons are handed over affects a battery's power and efficiency. In 1956 Rudolph Marcus, noting that the surrounding molecules have to rearrange as an electron moves, built a theory for calculating the speed of such reactions[1]. It won the 1992 Nobel Prize in Chemistry. For newer batteries such as iron-air, making this reaction fast and repeatable over thousands of cycles is the heart of the development work.
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.
- Air electrodeAn 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.
- Lithium-ion batteryA battery that charges and discharges as lithium ions shuttle between the positive and negative electrodes. Used everywhere from phones to electric cars.