In the charged condition, electrochemical capacitors, like batteries, are in a state of high energy relative to that of the system in the discharged state. Hence there is a 'driving force', corresponding to the free energy of discharge, tending to spontaneously diminish the charge if some mechanism(s) of self-discharge exist. An ideally polarizable (chargeable) capacitor has no self-discharge or current-leakage pathway and hence can remain charged indefinitely. However, practical capacitors, like batteries, suffer appreciable self-discharge over periods of days or month sso that this phenomenon is of major interest in evaluation of capacitor performance and choice of materials to minimize self-discharge. Several mechanisms of self-discharge are distinguished and the resulting forms of the change of potential on open-circuit with time or log time provide a means of identifying the type of self-discharge process that occurs. With RuO_2, some remarkable potential-recovery effects arise following discharge.
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