| AVS 65th International Symposium & Exhibition | |
| Processing and Characterization of Air-Liquid, Solid-Liquid and Air-Solid Interfaces Focus Topic | Tuesday Sessions |
| Session PC+AS+BI+EM+NS+PB+SS-TuA |
| Session: | Progress in Industrial Processes and Characterization of Interfaces and Gas-Solid Interfacial Processes and Characterization |
| Presenter: | Axel Knop-Gericke, Fritz Haber Institute of the Max Planck Society, Germany |
| Authors: | R. Mom, Fritz-Haber Institute of the Max Planck Society, Germany L. Frevel, Fritz-Haber Institute of the Max Planck Society, Germany J.J. Velasco-Velez, MPI CEC Mülheim, Germany T.E. Jones, Fritz-Haber Institute of the Max Planck Society, Germany M. Plodinec, Fritz-Haber Institute of the Max Planck Society, Germany R. Schlögl, MPI CEC Mülheim, Germany A. Knop-Gericke, Fritz Haber Institute of the Max Planck Society, Germany |
| Correspondent: | Click to Email |
Green production of hydrogen will be an important building block in the transition to a carbon-balanced economy and could be realized by electrolytic water splitting powered by cheap renewable energy sources. Water electrolysis is currently limited by the oxygen evolution reaction (OER) and development of the associated catalysts is proceeding slowly, mainly due to missing descriptors for activity and stability of working OER catalysts. Herein, we contribute to that emerging field with in situ XPS and NEXAFS on iridium anodes. In our in situ cell the catalyst is probed through a graphene layer, which traps an electrolyte layer around the catalyst and provides electrical contact for separated iridium nanoparticles. In this way we enhance spectroscopic signal from the active surface relative to the bulk of the catalyst and reduce mass transport problems. In taking advantage of these benefits, we found that the two well-known oxidation waves occurring before the OER onset are connected to the development of two different types of electron deficient oxygen species, which are bound to one (µ1) or two (µ2) iridium atoms. It appears that oxygen is not only a “non-innocent ligand”, but rather a protagonist in the catalysis of the OER.
During the electrochemical reduction of oxygen, platinum catalysts are often (partially) oxidized. While these platinum oxides are thought to play a crucial role in fuel cell degradation, their nature remains unclear. We studied the electrochemical oxidation of Pt nanoparticles using in situ XPS. By sandwiching the particles between a graphene sheet and a proton exchange membrane that is wetted from the rear, a confined electrolyte layer was formed, allowing us to probe the catalyst under wet electrochemical conditions. We show that the behavior at the onset of Pt oxidation is influenced by the choice of proton exchange membrane, yet universally involves PtO2 formation. The oxidation process is fast: even bulk oxide growth occurs on the sub-minute timescale. Thus, our observations indicate that PtO2 may take part in the transient processes that dominate Pt electrode degradation.