Transition-metal-oxide/liquid interfaces

Transiton metal oxides are promising systems for photo- and electrocatalysis. For a molecular-scale understanding of the underlying mechanisms and processes, experiments on well-characterized samples are necessary, i.e., specific facets of single crystals with a known composition, geometry, and defect structure.
In the talk we will address the question whether the atomic structure of selected oxide surfaces survives the exposure to liquid water. We use a novel apparatus that allows to expose samples to liquids without them leaving the ultrahigh vacuum (UHV) environment [1]. We find that the TiO₂(110) surface maintains its (1x1) termination [2] and that the (2x1) overlayer observed after water exposure in air results in an ordered layer of carboxylates. In contrast, exposure to liquid water lifts the TiO₂(011)-(2x1) reconstruction and results in full hydroxylation [3]. We have also tested the several iron oxide surfaces [4, 5], and find hints that the pairs of dissociated and intact water molecules that form on these [4] and several other metal oxides are present in the liquid phase as well. Magnetite Fe₃O₄ was tested for OER in alkaline conditions, and was found to be stable at the nanoscopic scale, with a facet-dependent reactivity [5].

[1] J. Balajka, et al., Rev. Sci. Instr. 89 (2018) 083906–6. doi:10.1063/1.5046846.
[2] J. Balajka, et al.,, Science. 361 (2018) 786–789. doi:10.1126/science.aat6752.
[3] J. Balajka, et al., J. Phys. Chem. C. 121 (2017) 26424–26431. doi:10.1021/acs.jpcc.7b09674.
[4] M. Meier, et al., P Natl Acad Sci Usa. 115 (2018) E5642–E5650. doi:10.1073/pnas.1801661115.
[5] M. Müllner, et al., J. Phys. Chem. C (2019) doi: 10.1021/acs.jpcc.8b08733