Abstract
Nitrogen-doped ordered mesoporous carbon (NOMC) is studied as the support to synthesize a Pt/CN-doped catalyst for methanol oxidation reaction (MOR). The effects of carbon dimension and metal loading are investigated by nitrogen ad/desorption isotherms, transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and electrochemical methods. Both TEM and XRD results show that platinum nanoparticles (Pt NPs) are highly dispersed on NOMC with a uniform and narrow distribution, while the dimension of NOMC has a considerable effect on the dispersion of Pt. For 10wt% metal loading, the average diameter of Pt NPs on 2D-NOMC is 1.40nm; smaller than that on 3D-NOMC (1.90nm). XPS results reveal that a strong electronic interaction exists between Pt and NOMC, indicating the formation of Pt–N bonds at the interface. Such an interaction gets more pronounced in the case of low Pt loadings and low-dimensional supports; the reason is that the 2D support is more accessible to load Pt and the metal-support interface is better developed at low metal loadings.The electrochemical results are well correlated with the physiochemical characterizations. 1) The electrochemically active surface area of Pt is higher on the 2D-support than that on the 3D-one, confirming the better dispersion of Pt on NOMC-2D. 2) A positive shift in the potential is observed for the adsorption of oxygen-containing species onto Pt, which is indicative of the charge transfer from Pt to the support and the formation of Pt–N bonds. 3) Both onset and peak potentials are negatively shifted by ca. 50mV for MOR on 10wt% Pt/NOMC-2D, as compared with the commercial Pt/XC-72. The ratio of forward to backward current, a measure of poisoning tolerance, is 1.1 on Pt/NOMC-2D and 0.80 on Pt/XC-72R. This enhancement can be attributed to the bifunctional mechanism at the Pt/CN-doped interface. In MOR, CO-like intermediate species on Pt can be effectively stripped off by the adjacent active –OH species on carbon, generated at lower potentials.
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