Three-Dimensional Microstructure of PEFC Electrodes: Activity and Durability

Abstract

Large-scale deployment of PEMFCs based on catalysts synthesized using non-precious metals (non-PGM) is facing a major challenge: the need for increased lifetime. One way to improve durability is to maintain the chemical makeup and integrity of the pore structure, thereby increasing the effectiveness of the catalyst layer over the lifetime of the fuel cell. The durability of non-PGM catalyst layers is directly related to the interaction of catalyst with ionomer and ionomer dispersion. Composition of the catalyst from both chemical speciation and morphology (porosity, roughness, texture), will determine the interaction between the catalyst and ionomer. Additionally, the pore structure is critical to the transport of oxygen to active sites and removal of water. The change in pore-structure induced by the chemical changes introduced during fuel cell operation has to be understood in order to design non-PGM electrocatalysts with longest possible lifetime. In this work, we will employ focused ion beam/scanning electron microscopy (FIB-SEM) sectioning to obtain a visual 3D representation of catalyst layer morphology. These 3D reconstructions will be used to generate detailed estimates of the evolution of structural parameters such as: specific surface area, total porosity, connectivity of pores, and others as a result of degradation studies. These analyses will be supported by the chemical post-mortem analysis obtained with high-resolution X-ray Photoelectron Spectroscopy. Structural metrics obtained from different components of MEA and chemical metrics obtained from XPS will be linked directly to the properties of the catalyst itself facilitating the design of highly durable fuel cells. Figure 1