Stability and Activity of Core-Shell and Alloy Catalysts for Proton Exchange Membrane Fuel Cells (PEMFC)

Abstract

State-of-the-art PEMFC use platinum-based catalysts as cathodes. The high cost of Pt and tendency for catalyst degradation at the cathode is the principal reason for devising ways of minimizing the amount of Pt used and ways to enhance catalyst activity and durability. Approaches used to decrease the Pt loading include alloy formation and forming core-shell catalyst with non-noble metal as the core. Alloying as well as the formation of core-shell catalyst alters both the thermodynamics (specifically the chemical potential of Pt) as well as the activity for the oxygen reduction reaction. Extensive literature exists on the processing and characterization of alloy catalysts and core-shell catalysts. The activity as well as the stability of the catalyst also depends on the nature of the support. For instance, it is known that the stability of the catalyst depends on whether or not the support surface is functionalized with certain groups. The stability of the catalyst depends on the nature of the environment it is exposed to, the composition and structure of the catalyst, particle size distribution, the operating cell voltage, and the type and the nature of the support. Virtually all aspects of the stability of the catalyst can be described in terms of classical thermodynamics and the role of coupled transport through the catalyst support and aqueous/ionomer medium. The main objective of this presentation is to demonstrate the role of classical thermodynamics and the kinetics of coupled transport in designing stable and highly active catalysts as cathodes for PEMFC.