Nilay İnoğlu

Universality in Oxygen Evolution Electrocatalysis on Oxide Surfaces

Trends in electrocatalytic activity of the oxygen evolution reaction (OER) are investigated on the basis of a large database of HO* and HOO* adsorption energies on oxide surfaces. The theoretical overpotential was calculated by applying standard density functional theory in combination with the computational standard hydrogen electrode (SHE) model. We showed that by the discovery of a universal scaling relation between the adsorption energies of HOO* vs HO*, it is possible to analyze the reaction free energy diagrams of all the oxides in a general way. This gave rise to an activity volcano that was the same for a wide variety of oxide catalyst materials and a universal descriptor for the oxygen evolution activity, which suggests a fundamental limitation on the maximum oxygen evolution activity of planar oxide catalysts.

Configurational correlations in the coverage dependent adsorption energies of oxygen atoms on late transition metal fcc(111) surfaces

The coverage dependence of oxygen adsorption energies on the fcc(111) surfaces of seven different transition metals (Rh, Ir, Pd, Pt, Cu, Au, and Ag) is demonstrated through density functional theory calculations on 20 configurations ranging from one to five adsorption sites and coverages up to 1 ML. Atom projected densities of states are used to demonstrate that the d-band mediated adsorption mechanism is responsible for the coverage dependence of the adsorption energies. This common bonding mechanism results in a linear correlation that relates the adsorption energies of each adsorbate configuration across different metal surfaces to each other. The slope of this correlation is shown to be related to the characteristics of the valence d-orbitals and band structure of the surface metal atoms. Additionally, it is shown that geometric similarity of the configurations is essential to observe the configurational correlations.

New solid-state table: estimating d-band characteristics for transition metal atoms

A tight-binding model parameterised by a database of density functional theory calculations is presented and used to estimate the d-band characteristics of bulk systems as well as mono- and bimetallic surface structures. The model incorporates the effects of both electronic and geometric contributions. A d-band width formalism relating surface reactivity with the surface electronic structure is presented and it is shown that the proposed model can be used to estimate the surface electronic structure as well as to explain trends in catalytic properties of metal and alloy surfaces in terms of surface and adsorbate orbital properties.

Sulphur poisoning of water-gas shift catalysts: site blocking and electronic structure modification

Density-functional theory calculations were used to study sulphur poisoning of low Miller index surfaces of Cu(111), (100) and (110). The adsorption properties of S on the studied facets were investigated in different adsorption sites and at coverages between 0.25 and 1 ML. The comparison of adsorption energies among different facets showed that S adsorbs most strongly to the most open surface (110) and most weakly to the most close-packed surface (111). We found that the adsorption energy of S generally gets weaker with increasing coverage, and we related the coverage dependence to an adsorbate-induced surface electronic structure modification which broadens the surface d-band and which causes a consequent reduction in the average energy of the d-band centre due to conservation of d-band filling. The combination of site blocking and surface electronic structure modification leads to a reduction in the surface reactivity of the catalyst at higher coverages of S.