A @F02321@ that corresponds to the reduction or @O04362@ of an @E01940@ formed by a prior @C01033@ from another substance that is not electroactive, and that is partially or entirely controlled by the rate of that reaction. The reaction may be heterogeneous, occurring at an electrode-solution @I03082@ (surface reaction), or it may be homogeneous, occurring at some distance from the @I03082@ (volume reaction).