Polymer electrolyte fuel cells (PEFCs) are a promising clean energy conversion technology to replace the internal combustion engine due to their high efficiency and power density. Platinum catalyst cost can compose up to 40% of the total cost of fuel cell stack. To reduce the cost, there is a need for either substantial reduction of Pt loading in the cathode catalyst layer or use platinum group metal-free (PGM-free) electrocatalysts. Atomically dispersed Fe-N-C electrocatalyst is the emerging advanced type of PGM-free catalyst. Despite substantial advances over the last decade of intensive development, PGM-free electrodes have lower volumetric activity comparing to the traditional Pt-based electrodes due to either lower turnover-frequency or/and lower number of active sites. To compensate for lower volumetric activity, PGM-free electrodes use higher loading of ~4 mg/cm2, resulting in order of magnitude thicker electrodes (~100 µm) compared to conventional Pt/C electrodes. This larger thickness can result in overall mass transport losses. A systematic analysis, both experimental and model-assisted have been performed over three main configurations of PGM-free electrodes in PEFCs: catalyst-coated membrane CCM technology is being compared to gas-diffusion electrode (GDE) method of electrode fabrication and juxtaposed to a hybrid/combined GDE-CCM method of membrane-electrode assembly (MEA) fabrication. The corresponding electrodes were evaluated for their electrochemical performance, modeled and studied with in-situ and operando X-ray computed tomography (X-ray CT). The study establishes that through-thickness inhomogeneities play most important role in water withdrawal / water management and affect most significantly PGM-free PEFC performance. The catalyst integration technique results in formation of interfacial regions with increased porosity and surface roughness. These regions form critical interfaces de-facto responsible for flooding type behavior of the PEFC as shown for a first time by operando X-ray CT. The computational model shows that the PEFC performance critically depends on liquid water formation and transport at cold and wet conditions.

Understanding the role of interfaces for water nanagement in PGM-free electrodes in polymer electrolyte fuel cells

2019 Fall National Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.