Synergistic Application of XPS and DFT to Investigate Metal Oxide Surface Catalysis

Abstract

To investigate metal oxide surface catalysis, determining an appropriate Hubbard U-correction term is a challenge for the density functional theory (DFT) community and identifying realistic reaction intermediates and their corresponding X-ray photoelectron spectroscopy (XPS) shifts is a challenge for experimental researchers, when these methods are used independently. In this study, using CuO as a model transition metal oxide, we demonstrate that when DFT and XPS are applied synergistically, the determination of the U value and the identification of adsorbate/intermediate species on the surface (and their XPS shifts) can be done simultaneously. The experimental O 1s spectra of the as-synthesized CuO 2D-nanoleaves shows the presence of four different peaks with core level binding energies (CLBEs) of 529.7, 531.4, 533.2, and 534.6 eV. DFT is used to calculate the CLBE shifts for probable adsorbed moieties, in various adsorption configurations, on both, clean and vacancy defect containing surfaces. Comparison of experimental and theoretical CLBEs across the entire U value range of 0–9 eV narrows down the list to only four moieties, namely, O2 in the η1(O) configuration, H2O at the surface oxygen vacancy site, and adsorbed HCO3 and HCO2 (resembling adsorbed HCO3). Finally, the U value of 4–4.5 eV reproduces the experimental CLBE shifts correctly and thus, establishes these experimental XPS spectral peaks to the adsorbates and their geometries. The integrated approach elucidated in this article, results in the identification of adsorbates/intermediates (and their CLBEs) for the experimental XPS spectral analysis and the determination of an appropriate U value concurrently, to study metal oxide surface catalysis.

Formation of environmentally persistent free radicals and reactive oxygen species during the thermal treatment of soils contaminated by polycyclic aromatic hydrocarbons

“…This finding might be explained by the highest content in transition metals of the chernozem soil (Table S1). Indeed, as reported previously, transition metal oxides promote the formation of • OH (Amaniampong et al 2018(Amaniampong et al , 2019Trinh et al 2018;Jia and Wang 2013).…”

Revisiting surface core-level shifts for ionic compounds

“…Furthermore, XPS binding energy shift calculations using the slab model approach are common in the literature; Refs. [5,[35][36][37][38][39][40] give representative examples of the use of slab models for XPS. We have shown that the VCA approach represents a safe way to avoid artifacts related to the screening by the added half an electron in the conduction band and we have shown that these artifacts can result in notable errors, ∼0.5 eV in the present case.…”

Sub‐Thick Electrodes with Enhanced Transport Kinetics via In Situ Epitaxial Heterogeneous Interfaces for High Areal‐Capacity Lithium Ion Batteries

“…Comprehensive understanding on the electronic interaction at the interface of the thick electrodes was studied using density functional theory (DFT) calculations. [30,47] The electron density difference (EDD) provided valuable information on the electron interactions within the components of each hybrid. The cluster models of NiO, Ni 2 P, CuO and Cu 3 P for DFT simulations are shown in Figure S7, Supporting Information.…”