In this paper, we compare the Proton Exchange Membrane Fuel Cell (PEMFC) with non-electrochemical Catalytic Membrane Reactors (CMR). The comparison notably lies on the particular geometry of the membrane vertical bar(electro)catalyst interface in PEMFC, the design of which optimizes the triple ionic-electronic(gas) reactant percolation. Through a selected literature review, we will describe how the performances of practical PEMFC improved following the optimization of (i) the ionomer vertical bar electrocatalyst interface and (ii) the mass-transport processes for reactants and products within the Active Layers (AL). We will also focus (iii) on the possible alteration/modification of the intrinsic catalyst electroactivity of Pt/C materials at the ionomer interface and (iv) on the influence of the membrane vertical bar electrode architecture and composition on the durability of the PEMFC Membrane-Electrodes Assembly (MEA). (C) 2010 Elsevier B.V. All rights reserved.