While Pt is widely observed to be the best monometallic anode material in electrocatalysis, it is easily poisoned by reaction-generated CO as in methanol oxidation reaction (MOR), which renders it impractical for direct use in fuel cells and had led to the development of many bimetallic systems. For instance, alloying Ru to Pt substantially increases CO tolerance of the latter, leading to the best-performing electrocatalysts for MOR. This has been mainly attributed to the bi-functional mechanism in which the more oxophilic Ru adsorbs oxygen-containing species and enables oxidizing CO adsorbed on Pt at lower potential but to a lesser extent also to weakened Pt-CO bonding by alloyed Ru (the ligand effect). However, our recent <i>in situ</i> surface enhanced IR reflection absorption spectroscopy (SEIRAS) studies of MOR on PtRu electrocatalysts using flow cell and isotope labeling show that the higher activity observed at low anodic electrode potential, i.e., &lt; 0.5V vs RHE, has little to do with eliminating reaction-generated CO. Yet, it is such activity enhancement at low anodic potential that is most desirable to developing economically viable fuel cell applications. Our observations raise a critical question as to whether the aforementioned, though long-held, bi-functional mechanisms is the most appropriate for rationalizing the observed activity enhancements at low anodic potential, let alone for guiding the development of better anode electrocatalysts for direct methanol fuel cells. In this presentation, we will discuss ramifications of our SEIRAS observations and propose new mechanism.

Irrelevance of CO poisoning in methanol oxidation on PtRu electrocatalysts: A re-visit of the bifunctional mechanism

249th National Meeting (2015)

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