ChBE Seminar Series: YuYe Tong
Tuesday, October 27, 2015
11:00 a.m.-12:15 p.m.
Room 2108, Chemical and Nuclear Engineering Building
Professor Dongxia Liu
Irrelevance of CO Poisoning of Pt in Methanol Oxidation and Unraveling the Mystery of Formic Acid Oxidation
YuYe Jay Tong
Professor and Chair
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) and formic acid oxidation reaction (FAOR), 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 as well as substantially enhanced FAOR. 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 in situ surface enhanced IR reflection absorption spectroscopy (SEIRAS) studies of MOR and FAOR on PtRu electrocatalysts using flow cell and isotope labeling show that the higher activity observed at low anodic electrode potential, i.e., < 0.5V vs RHE, has little to do with eliminating reaction-generated CO on Pt. 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, bifunctional mechanism is the most appropriate one for rationalizing the observed activity enhancements at low anodic potential, let alone for guiding the development of better anode electrocatalysts for direct methanol/formic acid fuel cells. In this presentation, we will discuss ramifications of our SEIRAS observations and propose new mechanisms in both MOR and FAOR.