PARTIAL CURRENT (DENSITY)

"The two current densities at which the electrode reaction is proceeding in the anodic and cathodic directions at an electrode potential. The actual (net) current density is the algebraic sum of the two partial current densities (one is considered positive the other negative). Electrode reactions are typically ""chemically"" reversible, that is, they can proceed both in forward and reverse direction. At equilibrium, the reaction is proceeding at equal rate in both directions (see exchange current density): the ""anodic partial current density"" and the ""cathodic partial current density"" are equal and the net current density is zero. When the electrode is polarized, the partial current densities are unequal and the net current density is not zero. If the electrode is negatively polarized, the cathodic reaction speeds up (compared with its rate at equilibrium), while the anodic reaction slows down and a net cathodic current density results (and vice versa for anodic polarization). "