Three-electrode cells comprise (1) an indicator (or test) electrode or a @W06686@, at the surface of which processes that are of interest may occur, (2) a @R05229@ and (3) a third electrode, the auxiliary or counter electrode, which serves merely to carry the current flowing through the cell, and at the surface of which no processes of interest occur. If processes of interest occur at both the @A00370@ and the @C00905@ of a cell (as in differential amperometry or controlled current potentiometric @T06387@ with two indicator electrodes), the cell should be said to comprise two indicator (or test) working electrodes.
Orange Book, 2nd ed., p. 59 [Terms] [Book]