A planar, air-breathing, proton-exchange membrane fuel cell (PEMFC) system using a humidified H-2 gas released from the hydrolysis of a stabilized sodium borohydride (NaBH4) solution with a selected solid catalyst is extensively investigated as a promising energy storage system for mobile power sources. In economic terms, the passive air-breathing PEMFC is quite attractive because can its reliability, fuel utilization, and specific energy can be enhanced by removing auxiliary devices such as the air pump and the humidifier. The rate of hydrogen generation can be manually controlled by adjusting the amount of NaBH4 solution passed through the selected catalyst. In this study, the rate of hydrogen generation is varied from 0 to 18 cm(3) min(-1) by controlling the mass transport of stabilized NaBH4 solution. The open-circuit voltage (OCV) and maximum power density are, respectively. 0.9V and 128 mW cm(-2) at ambient temperature and pressure. Assuming a fuel conversion efficiency of 100%, the Faradic efficiency and energy efficiency of this system estimated to be 75% and 46%, respectively. In a planar 8-cell series-connected format, the maximum power density and cathode temperature are 3.1 W (103 mW cm(-2)) at 103 mW cm(-2) and 46 degrees C, respectively. (C) 2008 Elsevier B.V. All rights reserved.