This work is focussed on modelling mass and charge transfer limitations within an active layer considering uniform distribution of catalyst phase (classical model) or a more realistic discrete distribution (modified model). A model is proposed here based on soft-coupled equations describing diffusion, ionic ohmic drop and interfacial charge. It is applied to the practical case of oxygen reduction or hydrogen oxidation for PEM fuel cells. Simulation shows that the modified model has to be used for fast kinetics, that is, when the local limitations become predominant. In contrast, the classical flooded homogeneous model remains suitable when mass and charge transport resistances are negligible at the particle level.