Tuning Vacancy in Metal Oxide Support to Enhance Activity and Durability of Pt Catalysts for the Methanol Oxidation Reaction

Abstract

Coupling Pt with metal oxides has been shown to be an effective approach for catalyst durability enhancement in the methanol oxidation reaction (MOR). Here, we report tuning valence in niobium oxide (NbO_x) as a support by tin oxide (SnO₂) as a promoter to mediate the Pt electrocatalysis in MOR. The catalyst was designed to consist of Pt supported on SnO₂-modified NbO_x coated on carbon black (Pt-TNb/C), which shows significantly enhanced electrochemical durability and activity in MOR that are better than the catalyst without SnO₂ modification (Pt-Nb/C) and those reported in the literature. Electron diffraction pair distribution function analysis showed an increase in the Nb–Nb bond length after SnO₂ incorporation, from 3.80 to 3.84 Å, indicative of a tuning effect. X-ray photoelectron spectroscopy further confirmed valence mediation in the Pt-TNb/C catalyst, as evidenced by the positive binding energy peak shifts of 0.49 and 0.66 eV in Nb 3d_5/2 and Nb 3d_3/2, respectively, as compared to those of the Pt-Nb/C catalyst. The Pt-Nb/C catalyst has MOR peak currents of 2.71 A/mg-Pt at the beginning and 1.94 A/mg-Pt at the end of 1000 cycles in 1.0 M methanol in 0.5 M H₂SO₄ electrolyte, corresponding to a 28.41% activity loss. However, the Pt-TNb/C catalyst with SnO₂ tuning has a much smaller loss at only 3.77%, with MOR peak currents of 3.45 A/mg of Pt at the beginning and 3.32 A/mg of Pt at the end under the same test conditions. The high durability and activity of the new catalyst are attributed to the effect of valence tuning of the niobium oxide, in addition to a bifunctional effect from tin oxide.