Title:	Atomic and electronic structure of ultrathin cobalt oxides
DNr:	SNIC 2022/5-232
Project Type:	SNIC Medium Compute
Principal Investigator:	Lindsay Richard Merte <lindsay.merte@mau.se>
Affiliation:	Malmö universitet
Duration:	2022-04-28 – 2023-05-01
Classification:	10304 10403 10402
Keywords:

Abstract

Ultrathin and two-dimensional oxides of cobalt, nickel and iron are active materials for catalysis and electrocatalysis, and are attractive promoters or replacements for more scarce and expensive materials like platinum. The small thickness—one or a few layers—presents challenges for characterization, however, particularly under reaction conditions. Our project is focused on the application of synchrotron X-ray methods to characterize mono- and few-layer oxides under ambient pressure conditions in order to 1) identify the actual structural motifs exhibited by these materials, and 2) relate the structures identified with the materials’ performance. Most experimental methods applicable to these systems give only partial or indirect information about the structures, and accurate interpretation depends upon close coupling of experiments with simulations based upon structures optimized with DFT. For some recent examples see: (Merte et al., J. Chem. Phys. (2020), doi:10.1063/1.5142558; Gajdek et al. J. Phys. Chem. C (2022) doi: 10.1021/acs.jpcc.1c10284; Olsson et al. Phys. Rev. B (2020) doi: 10.1103/PhysRevB.101.155426). DFT calculations also provide insight into the physical mechanisms driving formation of the structures involved and into the chemical processes taking place on the materials. We have recently performed surface X-ray diffraction, grazing incidence X-ray absorption spectroscopy, and (X-ray) diffraction anomalous fine structure measurements for 1-, 2- and 3-layer cobalt oxides grown on platinum surfaces, using instruments at MAX IV and the Diamond Light Source (UK). Here, we plan to use DFT to produce optimized structure models for comparison with our experiments as well as to simulate X-ray absorption spectra. Continuation of the project, for which preliminary experiments have begun and synchrotron proposals have been submitted, involves investigation of mixed 2D oxides of cobalt and iron. The increase in complexity for the mixed system increases the need for theoretical support for experiments still further, and we plan to investigate the stability of various configurations of the different metals in 2-dimensional films, making use of novel structure search algorithms (see e.g. Merte et al. Angew. Chem. Int. Ed. (2022) doi:10.1002/ange.202204244). For structural optimization we will utilize VASP, while for simulations of X-ray spectra we will use the FDMNES code (http://fdmnes.neel.cnrs.fr/).