Toward geometrical design improvement of membraneless fuel cells: Numerical study

In this paper, the geometry and operation of membraneless laminar flow-based fuel-cells (LFFC) is analyzed. Three different fuel cell geometries are studied, these are: the conventional rectangular cell, a cylindrical cell and a star shaped cell. The geometries are derived from the principle of design of increasing the effective area of cathode while conserving the same volume-to-length ratio. Since the mixing and depletion widths are major factors that determine the cell performance, maximum Reynolds and Péclet numbers as well as fuel utilization are considered as variables of comparison. Furthermore, electrical characteristics as current density and total extracted current have been considered as well. Using finite element simulations, it is shown that for a HCOOH-O₂ cell, improved fuel utilization of 89% and 68.2% can be obtained with star and cylindrical geometries respectively, in comparison to conventional rectangular geometry (42.4%). Moreover, the total extracted current is also improved, reaching percentages greater than 1200% and 400% for the star and cylindrical designs respectively. It is shown that moving liquid-liquid interface, it is possible to further increase the current density of the designs and therefore the total extracted current.