Newly discovered properties of a mixed metal oxide provide insight for catalytic applications

Mixed metal oxides show promise in enhancing catalytic performance for reactions such as water splitting and CO₂ reduction, but the mechanism of enhancement is poorly understood, and optimization and design of these materials remain difficult. The new study by Rodriguez-Fernandez et al. reports their findings on the effect of Fe dopants in CoO bilayers on Au(111), as an effort to better understand the synergistic catalytic properties of these mixed metal oxides.

The researchers used scanning tunneling microscopy to probe the incorporation of iron in cobalt oxide bilayers supported on Au(111). They found that Fe incorporation was possible both during and after synthesis of CoO nanoislands, highlighting its facile integration. Single Fe atoms replaced Co atoms in the basal plane of the nanoislands, up to a Fe to Co ratio of 0.4 to 0.6.

Further analysis using x-ray photoelectron spectroscopy and density functional theory revealed that the Fe dopant assumes a higher oxidation state when embedded in CoO bilayers than in structurally corresponding unary FeO. The single-atom Fe incorporation distorts the local geometry within the oxide, and results in electronic perturbation of the nearest three oxygen and, to a lesser extent, six cobalt atoms, which will likely affect the oxide chemistry.

“The way iron binds to oxygen in the cobalt oxide framework is different than iron in its iron oxide framework,” say Aleksandra Vojvodic, co-author and lead of the computational efforts. “We think the different geometry and electronic structure implies that the catalytic activity will also be different.”

Vojvodic says the next step in the work is investigating how these differences will affect the chemical properties of the material. An atomic-level understanding of Fe-doped CoO will help elucidate design principles of mixed metal oxide catalysts, which can lead to controlled synthesis of optimized materials with desired chemical properties.

Source: “Structural and electronic properties of Fe dopants in cobalt oxide nanoislands on Au(111),” by Jonathan Rodriguez-Fernández, Zhaozong Sun, Liang Zhang, Ting Tan, Anthony Curto, Jakob Fester, Aleksandra Vojvodic, and Jeppe V. Lauritsen, The Journal of Chemical Physics (2019). The article can be accessed at https://doi.org/10.1063/1.5052336 .