A new type of planar fuel cell based on printed circuit board (PCB) technology has been developed. This planar design consists of an open cathode side which allows a completely passive, self-breathing operation of the fuel cell. Power densities of 100 mW/cm(2) at 500 mV with hydrogen were achieved. Long-term operation for more than 1500 h has been demonstrated. The operation behavior of planar hydrogen in free-breathing PEMFC concerning stability, water management and temperature distribution are examined. The effects of diffusion layer thickness and cathode opening ratios on the performance of this fuel cell type were characterized. Moreover, the amount of water removed from the anode and the temperature distribution of the cathode side were determined. (C) 2003 Elsevier Science B.V. All rights reserved.