A transient agglomerate model for simulation and analysis of experimental data, obtained by current interruption on porous molten carbonate fuel cell cathodes, is presented. The initial fast change of the potential after current interruption on a polarized NiO electrode is due to the closed-circuit potential distribution in the electrode. Conventional estimation of the iR corrected overvoltage by current interruption on porous electrodes, with finite electronic conductivity in the solid phase and a finite ionic conductivity of the pore electrolyte, leads to an overcompensation of the external potential drop and an underestimation of the total steady-state overvoltage due to the internal currents passing in the electrode after interruption. The overcompensation of the external potential drop is directly proportional to the geometric current density and to the thickness of the electrode and inversely proportional to the sum df the effective conductivities in the electrode matrix and the pore electrolyte.