Fundamental insight into enhanced activity of Pd/CeO₂ thin films in hydrogen oxidation reaction in alkaline media

Palladium supported on ceria (Pd/CeO₂) has recently raised strong interest as an alternative catalyst to platinum on the anode electrode in anion exchange membrane fuel cells. Herein, we provide new insight into the enhanced activity of Pd/CeO₂ in hydrogen oxidation reaction (HOR) in alkaline media. Using well-defined model thin films, we show that Pd/CeO₂ thin films lead to enhanced activity in HOR compared to pure Pd thin films. In situ characterization using electrochemical quartz crystal microbalance provide in-depth understanding of the role of CeO₂. CeO₂ leads to fundamental differences in adsorption and absorption of key reaction intermediates during HOR. In combination with characterization and theoretical calculations, Pd atoms embedded in CeO₂ are shown to be present on the prepared thin films and active for hydrogen activation but are not able to bind CO during CO-stripping characterization. Finally, an estimation of the source of hydroxyl intermediates provided by CeO₂ - which could be directly participating in the reaction - is presented herein. Fundamental understanding of the Pd-CeO₂ interface in HOR opens new ways to reduce the amount of noble metals in alkaline fuel cells.