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This work aims to demonstrate that chronoamperometry is a valuable tool for determining diffusivities in all‐solid‐state nanometer‐thick cells. The transient current in chronoamperometry of electrochemical cells under constant voltage is described by firstly considering purely capacitive processes, defined by RC circuit equations, and then purely diffusive processes, by Cottrell's equations. The physical meaning of the equations has been amply described in liquid cells with porous electrodes but scarcely in solid‐state cells. Thus, we studied Metal/Insulator/Metal nano‐cells with Ru and Au electrodes, Yttria Stabilized Zirconia (YSZ) electrolyte at temperatures between 50 and 170°C and voltages between 0.5 V and 1.5 V, where non‐Faradaic processes occur. The calculated diffusive and capacitive contributions at different temperatures obey the Arrhenius law. The activation energy was associated with vacancies, the major carrier during electrical transport. The analysis discusses other parameters, such as capacitance, effective concentration, and leakage current. The experimental diffusivity of YSZ electrolytes was compared with diffusivity values obtained by the statistical moment method. [ABSTRACT FROM AUTHOR]