A Fuel Cell (FC) is an electrochemical device which produces electric energy in DC. In order to support design control for the electrical system connected to it, it is necessary to work out a suitable representation of the fast dynamics involved. Therefore, in this work, a mathematical model, based on first principles and including both dynamical equations and algebraic relations, is described for electrochemical reactions, with the related formation of potential differences and anion and cation accumulation phenomena, in a Molten Carbonate Fuel Cell (MCFC). The model is formally consistent and it has been validated against experimental results, such as steady-state power and voltage versus current curves. (c) 2006 Elsevier B.V. All rights reserved.