@misc{KrammHerrmannGeppertFiechteretal., author = {Kramm, Ulrike Ingrid and Herrmann-Geppert, Iris and Fiechter, Sebastian and Zehl, Gerald and Zizak, Ivo and Dorbandt, Iris and Schmeißer, Dieter and Bogdanoff, Peter}, title = {Effect of iron carbide formation on the number of active sites in Fe-N-C catalysts for the oxygen reduction reaction in acidic media}, series = {Journals of materials chemistry A}, journal = {Journals of materials chemistry A}, number = {8}, issn = {2050-7488}, doi = {10.1039/c3ta13821f}, pages = {2663 -- 2670}, language = {en} } @misc{KrammLefevreBogdanoffetal., author = {Kramm, Ulrike Ingrid and Lef{\`e}vre, Michel and Bogdanoff, Peter and Schmeißer, Dieter and Dodelet, Jean-Pol}, title = {Analyzing Structural Changes of Fe-N-C Cathode Catalysts in PEM Fuel Cell by M{\"o}ßbauer Spectroscopy of Complete Membrane-Electrode-Assemblies}, series = {The Journal of Physical Chemistry Letters}, volume = {2014}, journal = {The Journal of Physical Chemistry Letters}, number = {5}, issn = {1948-7185}, doi = {10.1021/jz501955g}, pages = {3750 -- 3756}, abstract = {The applicability of analyzing by M{\"o}ßbauer spectroscopy the structural changes of Fe-N-C catalysts that have been tested at the cathode of membrane electrode assemblies in proton exchange membrane (PEM) fuel cells is demonstrated. The M{\"o}ßbauer characterization of powders of the same catalysts was recently described in our previous publication. A possible change of the iron species upon testing in fuel cell was investigated here by M{\"o}ßbauer spectroscopy, energy-dispersive X-ray cross-sectional imaging, and neutron activation analysis. Our results show that the absorption probability of γ rays by the iron nuclei in Fe-N-C is strongly affected by the presence of Nafion and water content. A detailed investigation of the effect of an oxidizing treatment (1.2 V) of the non-noble cathode in PEM fuel cell indicates that the observed activity decay is mainly attributable to carbon oxidation causing a leaching of active iron sites hosted in the carbon matrix.}, language = {en} }