Oxygen Reduction Reaction Activity Enhancement of Dry-Process-Synthesized Pt(111)/Nb:SnO2(101)/Pt(111) Coherent Lattice Stacking Model Catalyst Surface

We synthesized an oxygen reduction reaction (ORR) model catalyst surface of Pt(111)/Nb-doped SnO2(101) (Nb:SnO2) coherent lattice stacking layers on a Pt(111) substrate and investigated the influence of the surface strain of the Pt(111) layer on ORR activity enhancement. The Nb:SnO2 lattice stacking layer was synthesized through arc-plasma deposition (APD) of SnNb on Pt(111) in a vacuum chamber (base pressure <10(-7) Pa), followed by thermal annealing at 823 K for 120 min under 1 atm of dry air. The resulting Nb:SnO2/Pt(111) was then re-introduced into the chamber, and Pt was deposited by using an e-beam deposition method to form Pt/Nb:SnO2/Pt(111) ORR model catalyst surface. The cross-sectional, atomically resolved HAADF-STEM image of Pt/Nb:SnO2/Pt(111) clearly shows that the interfaces between the substrate Pt(111)/Nb:SnO2(101) and the Nb:SnO2(101)/surface Pt(111) match well and generate a single-crystal Pt(111)/Nb:SnO2(101)/Pt(111) ORR model catalyst surface. The synthesized catalyst surface showed ca. 3 times higher activity compared with clean Pt(111). It was estimated by in-plane-XRD that 0.6% of compressive strain worked on the surface Pt(111) layer, which was induced by a lattice mismatch between the surface Pt(111) and the underlaid Nb:SnO2(101). The results suggest that the ORR activity enhancement mechanism of the compressively strained surface Pt(111) lattice can be applied not only to Pt-based alloys of Pt and transition metal elements with smaller atomic radii but also to Pt on ceramic supports, such as SnO2.