Platinum catalysts supported on mixed-phase TiO2 coated by nitrogen-doped carbon derived from NH2-MIL-125 for methanol oxidation

Abstract

Supports play a key role in the performance of platinum-based catalysts. In this work, using NH2-MIL-125 as the precursor, mixed-phase TiO2 coated by nitrogen-doped carbon (TiO2 @NC) is successfully prepared, and used to support platinum (Pt/TiO2 @NC) for methanol oxidation reaction. In 0.5 M H2SO4 solution containing 0.5 M CH3OH, the area specific activity of Pt/TiO2 @NC catalyst (1.186 mA cm-2 Pt) is 4.4 times that of commercial Pt/C (0.272 mA cm-2Pt). At a fixed potential of 0.15 V (vs. Hg/Hg2SO4), the current density of Pt/TiO2 @NC is still 3.6 times that of Pt/C after 3600 s of polarization. Meanwhile, Pt/TiO2 @NC has also a low tafel slope, a large exchange current density and a high charge transfer coefficient. A large number of Ti-OH groups can alleviate poisoning effect caused by the produced "COads" intermediate during methanol oxidation reaction. Nitrogen-doped carbon not only improves the conductivity of TiO2 support, but provides strong anchor sites for the nucleation of Pt nanoparticles, resulting in an enhanced catalytic activity of Pt/TiO2 @NC.