In this study, a 100-cm2 single-cell and a 10-cell stack PEM electrolyzers are designed and manufactured, and the effects of operating parameters such as temperature, pressure, and feed water flow rate on the performance of the PEM electrolyzer are investigated. The hydrogen production capacity of the 10-cell stack is measured to be 7 NL/min hydrogen at 1 A/cm2 current density and atmospheric pressure. Both the single-cell and the 10-cell stack can directly supply both oxygen and hydrogen gases up to 50 bars. The operating temperature is found to be most important parameter affecting on the performance. An 87% efficiency is achieved in single cell at 80 degrees C and 1 A/cm2 current density. Copyright (c) 2012 John Wiley & Sons, Ltd.