Passive water removal in fuel cells by capillary droplet actuation

In this paper, a microstructured flow field for passive water management in proton exchange membrane fuel cells (PEMFC) is presented. It is based on the transport of liquid water droplets by capillary forces. A triangular microchannel forces droplets to detach from a fuel cell's gas diffusion layer (GDL) or membrane electrode assembly (MEA). Thus, it ensures proper oxygen supply of the reactive area. Water droplets are lifted into a secondary channel, and removed from the fuel cell by capillary action. Water formation in the flow field channels has been studied by analytic models and experiments. Three droplet configurations were identified, which show different properties in terms of capillary transport. Preferred shapes cover the GDL only slightly and can be found for contact angles typical for fuel cell materials. The actuation mechanism was studied by simulations for different designs, with varying contact angles and geometries. The new channel design was compared in a test fuel cell to standard rectangular channels, in the initial phase of the cell, at low working temperatures (22–30 °C). The new flow field design stabilized the cell at 95% of its initial performance compared to 60% when using the standard design.