Combined Experimental and Theoretical Investigation of Nanosized Effects of Pt Catalyst on Their Underlying Methanol Electro-Oxidation Activity

Abstract

The nanosized effects of Pt catalysts in terms of surface coverage, electrochemical response, and reaction kinetics during the electro-catalytic methanol oxidation reaction (MOR) have been extensively investigated by the systematic electrochemical measurements, in situ electrochemical FTIR spectroscopy (EC-FTIRS) technique and Density Functional Theory (DFT) computational approaches. In contrast to bulk Pt, a relatively higher COads coverage on the nanosized Pt catalyst was observed at the end of forward sweep (+1.0 V/RHE) from the in situ EC-FTIR investigations. From the DFT calculations, it was demonstrated that the reaction barrier of COads + OHads → COOHads is higher on the edge site of a Pt55 cluster (55 Pt atoms) than that on the facet site of a slab Pt model. The IR observations resulted from the fact that the electro-catalytic MOR appears to be diffusion-controlled on the bulk Pt catalyst, whereas on the nanosized Pt catalyst, it was kinetic-controlled due to both the higher kinetic barrier of COads + OHads reaction and lower diffusion resistance. The surface coverage models of the electro-catalytic MOR on the bulk and the nanosized Pt catalysts have been reasonably proposed via the combined understanding of the in situ EC-FTIR and DFT computational results. The proposed models can reasonably be further elaborated and explained by the systematic electrochemical measurements.