As platinum group metal-free (PGM-free) catalysts make significant advances in their acidic oxygen reduction reaction activity when evaluated at low current, it is important to establish electrode designs capable of meeting automotive polymer electrolyte fuel cell (PEFC) demands for power density. Unfortunately, cathode-level transport losses can impose a tremendous penalty on PGM-free catalyst performance in PEFCs. The lower volumetric activity (A/m³) of PGM-free cathodes versus Pt/C cathodes requires cathodes thicknesses on the order of 0.1 mm, or roughly 10 times the thickness of Pt/C cathodes. That extreme thickness combined with hydrophilic, functionalized carbon surfaces, yields a cathode that is highly sensitive to liquid water flooding and large proton conduction Ohmic losses.

This talk will overview methods in the field developed for characterizing electrode-level losses in PGM-free electrodes and identifying the underlying mechanisms that hinder transport and limit high power density. The overview will include methods we have recently applied to Fe-N-C PGM-free catalysts synthesized from polyaniline and cyanimide (Fe-CM-PANI). As the figure illustrates, these methods include electrochemical measurements, nano-scale X-ray computed tomography (nano-CT) of 3D pore and ionomer morphology¹, particle-scale simulation², and PEFC simulation and optimization³. These studies are then subsequently applied to advancing electrode performance as well as guiding targets for future catalyst synthesis.

References

1. S. Komini Babu, H.T Chung, P. Zelenay, ACS Appl. Mater. Interfaces, 2016 8 (48), pp 32764–32777.

2. S. Ogawa, S. Komini Babu, H.T. Chung, P Zelenay, S Litster, ECS Trans 75 (14), pp 139-146.

3. S. Komini Babu, HT Chung, G Wu, P Zelenay, S Litster, ECS Trans. 64 (3), pp 281-292.