Tackling Challenges Related to Thick Electrodes in Platinum Group Metal Free Polymer Electrolyte Fuel Cells

Platinum group metal-free catalysts (PGM-free) are a promising option to counter the high cost of platinum in proton exchange membrane fuel cells (PEMFCs). The recent improvements to PGM-free catalyst activity has allowed us to ad- dress the two primary challenges for PGM-free catalyst PEMFC marketability: durability and resistance. To counter the lower volumetric activity of the PGM-

free catalyst, more is used resulting in a thicker cathode catalyst layer (CCL) and increased resistance. To mitigate this effect, we lessened chemical species resistance by exploring different PGM-free catalyst and ink compositions via electrochemical experiments. For example, optimizing particle size and ionomer content enabled sufficient species transport to achieve state of the art PGM-free MEA performance. Several novel electrodes were designed for water management and oxygen transport improvement, the most effective of which was the non-planar CCL. This work was enhanced and expedited by the use and validation of a two-phase non-isothermal PEMFC model. The model was also used to elucidate relative contributions of different oxygen transport resistances and show that oxygen limited transport is actually caused by fast proton transport

due to increasing temperature instead of flooding. Parametric modeling studies offered insights to further optimizations, such as optimizing thickness to balance oxygen transport and activity, which in turn was realized experimentally.