Catalyzed SnO2 Thin Films: Theoretical and Experimental Insights into Fabrication and Electrocatalytic Properties

SnO2 thin films are studied experimentally and from first-principles as model supports for Pt nanoparticle catalysts in an acidic environment. SnO2 thin film supports are attractive model systems because composition, microstructure, and surface termination can be tailored by varying the deposition parameters. SnO2 films are synthesized by reactive dc magnetron sputtering, and the effects of the deposition conditions on the physicochemical and electrochemical properties are investigated experimentally and theoretically. Variation of the deposition conditions results in limited long-range order SnO or SnO2 films. Annealing in either case leads to well-crystallized SnO2 films, but with different growth directions. Films deposited as SnO2 show only growth along the [110] direction, while SnO2 films formed from deposited SnO show no preferred orientations. Hybrid density functional theory (DFT) suggests that growth along the [110] direction is driven by (110) being the lowest energy surface, while the loss of orientation in the SnO derived films originates from an almost degenerate set of surface energies at the SnO|SnO2 equilibrium. The oxygen reduction reaction activity of Pt nanoparticles depends on the SnO2 film orientation. A 2-fold higher catalytic activity is observed for Pt nanoparticles on the SnO2 film without preferential orientation compared to Pt on SnO2 grown along the [110] direction, pointing to the presence of strong surface-dependent metal–support interaction.