title: Determination of O[H] and CO coverage and adsorption sites on PtRu electrodes in an operating PEM fuel cell.
abstract: A special in situ PEM fuel cell has been developed to allow X-ray absorption measurements during real fuel cell operation. Variations in both the coverage of O[H] (O[H] indicates O and/or OH) and CO (applying a novel Deltamu(L3) = mu(L3)(V) - mu(L3)(ref) difference technique), as well as in the geometric (EXAFS) and electronic (atomic XAFS) structure of the anode catalyst, are monitored as a function of the current. In hydrogen, the N(Pt)(-)(Ru) coordination number increases much slower than the N(Pt)(-)(Pt) with increasing current, indicating a more reluctant reduction of the surface Pt atoms near the hydrous Ru oxide islands. In methanol, both O[H] and CO adsorption are separately visible with the Deltamu technique and reveal a drop in CO and an increase in OH coverage in the range of 65-90 mA/cm(2). With increasing OH coverage, the Pt-O coordination number and the AXAFS intensity increase. The data allow the direct observation of the preignition and ignition regions for OH formation and CO oxidation, during the methanol fuel cell operation. It can be concluded that both a bifunctional mechanism and an electronic ligand effect are active in CO oxidation from a PtRu surface in a PEM fuel cell.
authors.affiliation: Institute for Materials Science, Darmstadt University of Technology, Petersenstrasse 23, D-64287, Darmstadt, Germany. c_roth@tu-darmstadt.de
authors.forename: Christina
authors.initials: C
authors.lastname: Roth
authors.forename: Nathalie
authors.initials: N
authors.lastname: Benker
authors.forename: Thorsten
authors.initials: T
authors.lastname: Buhrmester
authors.forename: Marian
authors.initials: M
authors.lastname: Mazurek
authors.forename: Matthias
authors.initials: M
authors.lastname: Loster
authors.forename: Hartmut
authors.initials: H
authors.lastname: Fuess
authors.forename: Diederik C
authors.initials: DC
authors.lastname: Koningsberger
authors.forename: David E
authors.initials: DE
authors.lastname: Ramaker
mesh_terms: D000497:Alloys / Q000737:chemistry*; D002244:Carbon / Q000032:analysis*; D004566:Electrodes; D008024:Ligands; D008567:Membranes, Artificial; D010084:Oxidation-Reduction; D010100:Oxygen / Q000032:analysis*; D010316:Particle Size; D010984:Platinum / Q000737:chemistry; D011522:Protons; D012428:Ruthenium / Q000737:chemistry; D013499:Surface Properties
chemical_list: D000497:Alloys; D008024:Ligands; D008567:Membranes, Artificial; D011522:Protons; D010984:Platinum; D002244:Carbon; D012428:Ruthenium; D010100:Oxygen