Abstract
Employing computer simulations and Poisson-Boltzmann theory, we show that a symmetric electrolyte in an electric condenser undergoes a localisation-delocalisation transition as a function of the external voltage U. The transition occurs at the critical voltage Uc corresponding to the situation where the surface charge density of the plates equals the area charge density of completely charge-separated electrolytes. The average distance of the electrolyte ions to the plates diverges logarithmically for U↙Uc. This transition is expected to be observable in micro-electrodes.