A novel air management system was developed to control diffusion for higher performance cylindrical fuel cells. A passive cylindrical fuel cell with expanded graphite diffusion media was constructed and operated with hydrogen. Very stable open circuit potential was obtained with this volume efficient self-sealing construction. Temperature differences on the surface and fuel outlet were determined. Modifications to the diffusion media and good contact between the components were necessary for higher performance and stable power output. Proposed design helps to realize "Replaceable Cartridge Fuel Cell" concept. The mathematical relationship between porosity of the structure and maximum current density was determined based on an assumed diffusion coefficient value with fixed porosity through the body and varying tortuosity through the thickness of the diffusion media. Assumptions favor cylindrical design approach over flat design for smaller, volume efficient construction. (c) 2007 Elsevier B.V. All rights reserved.