Ordered hydroxyls on Ca3Ru2O7(001)

Abstract

As complex ternary perovskite-type oxides are increasingly used in solid oxide fuel cells, electrolysis and catalysis, it is desirable to obtain a better understanding of their surface chemical properties. Here we report a pronounced ordering of hydroxyls on the cleaved (001) surface of the Ruddlesden-Popper perovskite Ca3Ru2O7 upon water adsorption at 105 K and subsequent annealing to room temperature. Density functional theory calculations predict the dissociative adsorption of a single water molecule (E ads = 1.64 eV), forming an (OH)ads group adsorbed in a Ca-Ca bridge site, with an H transferred to a neighboring surface oxygen atom, Osurf. Scanning tunneling microscopy images show a pronounced ordering of the hydroxyls with (2 × 1), c(2 × 6), (1 × 3), and (1 × 1) periodicity. The present work demonstrates the importance of octahedral rotation and tilt in perovskites, for influencing surface reactivity, which here induces the ordering of the observed OH overlayers.

A full monolayer of superoxide: oxygen activation on the unmodified Ca3Ru2O7(001) surface

“…The tilt and rotation of the octahedra leads to a distorted surface oxygen sublattice that was found essential in affecting the ordering of a hydroxyl overlayer on this surface. 29 STM shows alternating bright and dark lines along the [010] direction, see Fig. 1c .…”

“…Also, the appearance in STM of O vacancies created by electron irradiation is known from previous work. 29 …”

“…The van-der-Waals contributions were described by the optB86b 26 , 27 functional which has been employed successfully in previous studies of water adsorption on ruthenate surfaces. 28 , 29 The low-coverage case was described using a (3 × 3) unit cell with one O 2 molecule adsorbed on it, yielding a coverage of 1/9, while the high-coverage model cell consisted of a (2 × 1) surface unit cell with two added O 2 molecules. For the large (3 × 3) unit cell a 2 × 2 × 1 Gamma-centered k -point grid was sufficient to achieve electronic convergence while for the smaller (2 × 1) model a 3 × 6 × 1 Gamma centered mesh was used.…”

Interaction of SrO-terminated SrTiO3 surface with oxygen, carbon dioxide, and water

“…Amongst those phases the most important are the formation of surface carbonates, surface hydroxides, and physisorption or chemisorption of water molecules. [25][26][27] A knowledge of the real surface composition of ABO 3 perovskite air electrodes for solid oxide devices is crucial for the understanding of the chemical activity on the electrode surface and for the further optimization of electrode performance. Theoretical studies on surface termination of perovskites have so far been limited to the chemical composition of the investigated materials.…”

Water adsorption at zirconia: from the ZrO2(111)/Pt3Zr(0001) model system to powder samples

“…on a-Cr 2 O 3 (001), 14 a-Fe 2 O 3 (012), 15 and on oxides of the alkaline earths, 16 including CaO-terminated Ca 3 Ru 2 O 7 (001). 17 On RuO 2 (110), 18 PdO(101), 19 and Fe 3 O 4 (001), 20 water binds to coordinatively unsaturated cations and forms partially dissociated structures stabilized by hydrogen bonds.…”