Air Depolarised Cells and Other Cells of Interest

Abstract

Some mention was made in chapter 1 of the air depolarised cell; it is certainly worth considering in a book on fuel cells since, although the ‘fuel’ used—the metal electrode—is not at all a conventional fuel, there are nevertheless considerable resemblances. It was pointed out in chapter 1 that one of the important characteristics of a fuel cell was that the material used up in the operation of the cell was almost entirely supplied to it and was not built in at the time of construction, whereas other kinds of galvanic cells usually could only operate on the materials actually put into the cell during its manufacture. The air depolarised cell occupies an interesting position in between these extremes; the oxygen or air electrode clearly operates from material supplied during operation, while the fuel electrode is a metal one manufactured as part of the cell and converted to oxide or other products during its life. The simplest and most well-known air depolarised cell is the zinc-air cell with an alkaline electrolyte:

$$Zn\left( s \right)|{K^ + }O{H^ - }\left( {aq} \right)|{O_2}\left( g \right)|C\left( s \right)$$

which has a cell reaction

$$2Zn + 4KOH + {O_2} \to 2{K_2}Zn{O_2} + 2{H_2}O$$

the potassium zincate being of course an oxidation product of the zinc electrode.