This paper describes the numerical modelling of a key material-stability issue within the realm of Molten Carbonate Fuel Cells (MCFC). Differential models have been developed for the 2D and 3D distributions of current density as well as peroxide and carbon dioxide concentrations. By suitable variations of the integration domain - based on the agglomerate concept - one can describe the morphological and attending electrocatalytic evolution of porous NiO electrodes. On the basis of electrochemical data recorded during the operation of a laboratory MCFC, we have shown that this model is able to rationalise the evolution of cathode conditions leading to both improvements of electrocatalytic performance - such as lithiation - and degradation - such as agglomeration -. Copyright (C) 2010, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.