Electrooxidation of Methanol at SnOx-Pt Interface: A Tunable Activity of Tin Oxide Nanoparticles

Tin oxide nanoparticles supported on polycrystalline Pt exhibit a size-dependent promoting effect for the methanol oxidation reaction (MOR). We find that the deposition of 2 nm SnO2 nanoparticles on Pt electrode surfaces results in an activity increase for the MOR up to 40 times over bare Pt electrodes. Increasing the size of the SnO2 nanoparticles reduces the MOR activity enhancement, and at a size similar to 20 nm, the SnO2 NPs show a negligible effect on the activity of bare Pt surfaces. Density functional theory calculations suggest that the catalytic activity of SnO2/Pt surfaces is strongly affected by the binding energy of adsorbed OH species on the SnO2 nanoparticles. In particular, a weaker OH-Sn interaction on the small, Pt-supported SnO2 NPs favors the release of adsorbed OH species for effectively oxidizing COads, the blocking intermediate in the MOR on Pt, making this combination an excellent catalyst. These results illustrate the importance of size-dependent chemical properties of nanostructured tin oxides in the catalytic performance of tin-oxide-promoted Pt electrocatalysts.