Design and evaluation of a passive self-breathing micro fuel cell for autonomous portable applications

Abstract A micro fuel cell system designed to power complex autonomous systems with dynamic pulse-shaped loads like wireless sensor nodes is presented in this work. The requirements posed by the corresponding pulse load profiles are considered for the design of the passive self-breathing micro fuel cell. The performance of the fuel cell is mainly affected by the oxygen and water management which is influenced by the openings in the cathodic current collector. Due to the comparatively low average cell current the performance can be strongly improved by retaining water within the cell using a reduced opening ratio and thus improving the ionic conductivity of the electrolyte. The impact of the opening ratio is studied in the range between 54% and 0.007%. The total active area of the fuel cell is only 0.1 cm 2 . Prototypes are realized using printed circuit board technology and wet chemical etching of the micro-structured current collectors. The cells were characterized with an exemplary load profile with a 10 ms load pulse and a 1 s pulse period. Successful operation was demonstrated for all cells for different current densities. A significant power improvement was achieved by reducing the opening ratio down to 0.3%. Under these circumstances a power density of 220 mW cm −2 could be generated during the pulse. This is more than twice in comparison to cells with large opening ratios of 54% where only approx. 100 mW cm −2 was obtained.