Hydrogels are used in methanol fuel cartridges to control fuel diffusion from the fuel reservoir to the anode electrode. This ability to control fuel diffusion rates enables the reduction of excess fuel supply that causes fuel crossover through the proton-exchange membrane. Cell performance was increased drastically from 14 to 21.5 m W cm(-2) with higher methanol concentrations using hydrogel fuel cartridges that fulfill the role of a diffusion-rate-controlling agent. This result implies that the hydrogel retards fuel diffusion, even at higher concentrations and suppresses the methanol crossover. (c) 2005 Elsevier B.V. All rights reserved.