| AVS 64th International Symposium & Exhibition | |
| Fundamental Discoveries in Heterogeneous Catalysis Focus Topic | Wednesday Sessions |
| Session HC+NS+SS-WeM |
| Session: | Nanoscale Surface Structures in Heterogeneously-Catalyzed Reactions |
| Presenter: | Jakob Fester, Aarhus University, Denmark |
| Authors: | J. Fester, Aarhus University, Denmark J.V. Lauritsen, Aarhus University, Denmark M. Garcia-Melchor, Trinity College Dublin A.S. Walton, University of Manchester, UK M. Bajdich, Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory A. Vojvodic, University of Pennsylvania Z. Sun, Aarhus University, Denmark J. Rodríguez-Fernández, Aarhus University, Denmark |
| Correspondent: | Click to Email |
Nanostructured cobalt oxides show great promise as earth-abundant and cheap heterogeneous catalysts, in particular for the oxygen evolution reaction (OER) in electrochemical water splitting and low temperature CO oxidation. However, despite the strong potential in this system as catalysts, we still lack basic knowledge on the active sites and the exact reaction pathways as well as an understanding of the underlying principles behind observed synergistic effects with gold.
To study the possible structure and location of catalytically active sites under controlled conditions, we created a model system consisting of 2-dimensional layered cobalt oxide (CoOx) nanoislands supported on Au(111) [1] and Pt(111) [2] substrates. This system offers the possibility to reveal the structures in atomic detail by Scanning Tunneling Microscopy (STM) combined with high-resolution X-ray Photoelectron spectroscopy (XPS).
By recording in-situ STM movies during exposure of Co-O bilayer nanoislands to H2O we showed that H2O dissociates on edge sites of the nanoclusters followed by migration of H to the basal plane which serves as a reservoir [3] . In combination with Density Functional Theory (DFT) calculations, a preferable dissociation pathway was revealed, also highlighting an assisting role of a second water molecule in the dissociation process.
The determining role of edge sites in the nanoparticle reactivity was further emphasized by STM and XPS studies capturing several stages in both of the gradual oxidation- and reduction processes leading to transitions between layered Co-O bilayer and O-Co-O trilayer morhphologies. In particular, atom-resolved STM images showed changes in edge structure and high densities of defect lines prior to the intercalation of oxygen. The onset of the O-Co-O trilayer formation is located at the island edges on both Au(111) and Pt(111), however several substrate effects were observed on the process rate, mechanism and reversibility. In general, the microscopic picture revealed in these studies suggests that special sites at CoOx nanoparticle edges may be important for the integral description of CoOx as a catalyst.
1. Fester, J., et al., Gold-supported two-dimensional cobalt oxyhydroxide (CoOOH) and multilayer cobalt oxide islands. Physical Chemistry Chemical Physics, 2017. 19(3): p. 2425-2433
2. Fester, J., et al., Comparative analysis of cobalt oxide nanoisland stability and edge structures on three related noble metal surfaces: Au (111), Pt (111) and Ag (111). Topics in Catalysis, 2016: p. 1-10
3. Fester, J., et al., Edge reactivity and water-assisted dissociation on cobalt oxide nanoislands. Nature Communications, 2017. 8