Thursday, 5 October 2017: 10:00
Chesapeake I (Gaylord National Resort and Convention Center)
There are very few techniques that lend themselves to rigorous requirements, where the individual role of different transition metal components of nano-phasic materials can be investigated in both amorphous and crystalline forms. We have developed a new analytical technique along with theoretical calculations, which enables the amount and specific adsorption site of species such as H, OH, O, CO, other C1 moieties and even anions such as bisulfate to be determined in situ
on a transition metal surfaces using synchrotron XANES data. This technique, commonly called the ‘Delta Mu (∆μ) Technique’ can be taken in situ
in both electrochemical cells and operating fuel cells, and can be obtained from a wide variety of transition metal surfaces and alloys, including non-Pt based metal electrocatalysts with element specificity. EXAFS data taken concurrently provide information on the changes in short range atomic order around the absorber atom thereby providing structural information such as bond distances and coordination numbers (thereby information on average cluster size, homogeneity and surface segregation etc.).
In this presentation among other things we will show in-situ XAS study of group of (Metal-Nitrogen-Carbon) MNC catalysts from perspective of metal center. We will demonstrate the presence of ORR active bio-mimetic porphyrin-like FeNx functionalities (Fig.1), as well as other forms of the metal which indicate no catalytic activity. The XAS in-situ studies will be combined with electroanalytical evaluations using cyclic voltammetry (CV) and square wave voltammetry (SWV) as well as in situ Raman spectroscopy. Further the factors governing the ORR activity at MNC centers, such as the Lewis basicity of the carbon support and the accompanying changes in the redox potential of the metal center will be discussed. This presentation will bring together electrochemistry and XAS spectroscopy (including ∆μ) on effect of pH (inner and outer sphere charge transfer) and aqueous vs. non-aqueous electrolyte (concerted vs. non concerted charge transfer).