Theoretical insights into effect of surface composition of Pt-Ru bimetallic catalysts on CH3OH oxidation: mechanistic considerations.

A deeper mechanistic understanding on CH3OH oxidation on Pt-Ru alloys with different Ru surface compositions is provided by DFT-based theoretical studies in this paper. The present results show that alloying and surface compositions of Ru can change CH3OH oxidation pathway and activity. The optimal surface composition of Ru is speculated to be ca. 50% since the higher Ru surface composition can lead to formation of carbonaceous species that can poison surface. Our present calculated Ru surface composition of ca. 50% exhibits excellent consistency with experimental studies. The origin of enhanced catalytic activity of Pt-Ru alloys is determined. The significantly decreased surface work functions after alloying suggest more electrons are transferred into adsorbates. The calculated lower electrode potentials after alloying imply that lower overpotentials are required for CH3OH oxidation. The excellent consistency with experimental study on decreased onset potentials after alloying further confirms accuracy of our present calculated results. It is hoped that a systematic understanding of the atomic- and molecular-level processes on CH3OH oxidation mechanisms on Pt-Ru alloys will result in the ultimate goal of the explanation of origin of enhanced electrocatalytic activity and design of improved Pt-based alloy electrocatalysts for DMFCs.