(Invited) Engineering the Microstructure and Atomic Arrangement of Pt-Based ORR Catalyst for High Activity and Durability

Abstract

Polymer Electrolyte Membrane Fuel Cells (PEMFC) have been developed for passenger vehicle applications for several decades. The durability and activity of the Oxygen Reduction Reaction (ORR) catalysts is one of the main obstacles to be overcome to make PEMFC vehicle commercially viable. Efforts have been focused on: 1) Developing non-precious metal catalysts. 2) Reducing the Pt loading and modifying the d-band structure of Pt by forming nano-sized core-shell structures on various cores including metallic materials, oxides, carbides and borides, and/or alloying Pt with transition metals (Cr, Ni, Co, Mn, etc.). 3) Stabilizing the Pt nano-particles by growing them larger and making the particle size more uniform. 4) Atomically engineering the Pt environment by using hybrid support of conductive metal oxide and carbon. Worldwide efforts have greatly improved the durability of the ORR catalysts, extending the life time of PEM fuel cell vehicles to about 2000 hours, which is still less than half of the required commercialization target of more than 5000 hours. Pt-based ORR catalysts still dominate in PEMFC. The main requirements for an effective ORR catalyst are low Pt loading, high activity and durability. We used a PVD based method to engineer the microstructure and atomic arrangement of Pt into a 2-D connected network on worm-shaped islands of conductive metal oxides, which are deposited on graphitic carbon. A model catalyst was first developed on flat surface graphene, and it showed much improved activity and durability. Later, this desired Pt 2-D structure and morphology was replicated onto graphitic carbon powders. In this talk, we will discuss the catalyst, its development, and structural and electrochemical characterization using RDE and in-situ single cell experiments. A mechanistic understanding for the improvement in both activity and durability will be discussed.