A cathode is the electrode from which a conventional current leaves a polarized electrical device. This definition is sometimes remembered using the mnemonic CCD for cathode current departs. A conventional current describes the direction in which positive electronic charges move.he flow of electrons is almost always from anode to cathode outside of the cell or device, regardless of the cell or device type and operating mode. An exception is when a diode reverse-conducts, either by accident (breakdown of a normal diode) or by design (breakdown of a Zener diode, photo-current of a photodiode).