A counter flow membraneless microfluidic fuel cell is presented, where a non-reacting electrolyte separates the reacting streams. In this fuel cell design, vanadium reactants flow through porous carbon electrocatalysts. A sulfuric acid stream is introduced in the gap between the electrodes and diverts the reactants to opposite and independent outlets. This fuel cell differs from other membraneless designs in its ability to maintain a constant separation between the reactants without diffusive mixing. (C) 2010 Elsevier B.V. All rights reserved.