Biomimetic auxiliary channels enhance oxygen delivery and water removal in polymer electrolyte membrane fuel cells

In this work, we present a novel laser-cut biomimetic flow field for polymer electrolyte membrane (PEM) fuel cells that provides substantial electrochemical performance and liquid water management improvements due to auxiliary channels which offer additional pathways for reactant delivery and product removal. In particular, these auxiliary channels exploit Forchheimer's inertial effect, driving reactants to the catalyst layer (CL) – gas diffusion layer (GDL) interface, thereby reducing the oxygen transport resistance by 91 % and increasing the power density by 29 % compared to the baseline. The auxiliary channels drastically enhance water removal at the CL-GDL interface (observed via operando X-ray radiography) and enable high current density operation critical for heavy-duty operation. Laser-cutting also produces a 79 % reduction in GDL water saturation at high current densities compared to conventionally milled flow fields due to the trapezoidal configuration and hydrophilic channel walls of the laser cut flow field. Where most flow field designs targeted for enhanced water removal suffer from high pressure drops, our novel flow field is particularly attractive for realizing both enhanced reactant delivery and water management concurrently with an unprecedented reduction in pressure drop of 33 % compared to parallel channel flow fields. Furthermore, from a manufacturing perspective, the simplicity and elegance of this design is highly attractive for reducing the cost of next generation fuel cells. • A PEM fuel cell exhibited 54 % less oxygen transport resistance with biomimetic auxiliary channels added to the flow fields. • Operando radiography revealed auxiliary channels enhance water removal and reactant delivery at the CL – GDL interface. • Adding auxiliary channels led to a 29.1 % higher peak power density due to lower oxygen transport resistances. • Biomimetic flow fields reduce pressure drop by 32.8 % and enhance Forchheimer's effect between the flow field and GDL. • Laser-cut parallel flow fields reduce GDL water saturation by 79 % compared to conventionally milled flow fields.