Atomistic Insights into the Hydrogen Oxidation Reaction of Palladium-Ceria Bifunctional Catalysts for Anion-Exchange Membrane Fuel Cells

Abstract

Hydrogen oxidation reaction (HOR) is one of the critical processes in clean and sustainable energy conversion devices such as anion-exchange membrane fuel cells (AEMFCs). There is significant interest in the design of highly active anode catalysts for such fuel cells. Here, we present the results of an ab initio study that explores the mechanism of HOR for palladium-ceria anode catalysts. This combination of materials has been shown to display excellent HOR performance experimentally. We use density functional theory with exchange–correlation functionals described by the generalized gradient approximation and the necessary Hubbard corrections. This allows us to accurately capture the electronic structure and the associated functional properties of all the components of the catalyst. The computations are carried out for multiple palladium concentrations on ceria surfaces. The reaction pathway for HOR is investigated via the Tafel reaction for the dissociation of hydrogen molecules and Volmer reaction for the formation of water molecules. Our findings show that palladium-ceria bifunctional systems have improved HOR activity compared to their individual components. Specifically, an enhanced catalytic activity is predicted for 10 at. % (7 wt %) palladium on ceria. We explain this behavior using multiple activity descriptors including hydrogen, OH, and H2O binding energies, and hybridization and charge transfer between the catalyst, the substrate, and adsorbents. The results suggest that the high HOR activity can be attributed to the delicate balance between the H and OH interactions with the palladium-ceria support as well as the interaction between the individual components that make up the heterostructure. The detailed ab initio analysis provides invaluable insights toward electronic, atomistic, and molecular mechanisms of HOR and paves the way for the development of catalysts that use significantly reduced amounts of precious metals.