Adsorption of water at the SrO surface of ruthenates

Halwidl, Daniel; Stöger, Bernhard; Mayr-Schmölzer, Wernfried; Pavelec, Jiří; Fobes, David; Jin, Peng; Mao, Zhiqiang; Parkinson, Gareth S.; Schmid, Michael; Mittendorfer, Florian; Redinger, Josef; Diebold, Ulrike

doi:10.1038/nmat4512

Cited by 74 publications

(74 citation statements)

References 51 publications

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“…The dissociation into an (OH) ads fragment, adsorbed on a cation bridge site, and into a proton, adsorbed on a neighboring surface oxygen, was recently observed on the SrO-terminated surface of Sr n+1 Ru n O 3n+1 ( n = 1,2) 19 . There the oxygen octahedra are not tilted with respect to the [001] direction, hence the surface oxygen sublattice is square and all bridge sites are equally spaced from the O surf .…”

Section: Discussionmentioning

confidence: 83%

Ordered hydroxyls on Ca3Ru2O7(001)

et al. 2017

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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.

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Section: Discussionmentioning

confidence: 83%

Ordered hydroxyls on Ca3Ru2O7(001)

et al. 2017

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“…9 A recent scanning tunneling microscopy study also underscored the important role of the RuO 6 octahedra for understanding water molecule adsorption at the ruthenate surfaces. 39 In particular, the structural flexibility or "rigidity" of the octahedra in perovskite oxides was identified as the key factor influencing molecular adsorption. The exact difference between the orthorhombic and tetragonal SRO surfaces at the molecular level is yet to be discovered, in terms of difference in bonding character and possible surface superstructures.…”

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confidence: 99%

Enhanced electrocatalytic activity via phase transitions in strongly correlated SrRuO₃thin films

Lee

Hwang

et al. 2017

Energy Environ. Sci.

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2Transition metal oxides have been extensively studied and utilized as efficient catalysts. However, the strongly correlated behavior which often results in intriguing emergent phenomena in these materials has been mostly overlooked in understanding the electrochemical activities. Here, we demonstrate a close correlation between the phase transitions and oxygen evolution reaction (OER) in a strongly correlated SrRuO3. By systematically introducing Ru-O vacancies into the singlecrystalline SrRuO3 epitaxial thin films, we induced phase transition in crystalline symmetry which resulted in corresponding modification in the electronic structure. The modified electronic structure significantly affect the electrochemical activities, so a 30% decrease in the overpotential for the OER activity was achieved. Our study suggests that a substantial enhancement in the OER activity can be realized even within single material systems, by rational design and engineering of their crystal and electronic structures. 3Transition metal oxides show promising chemical activities that can be applied in solid oxide fuel cells (SOFC), rechargeable batteries, catalytic converters, oxygen-separation membranes, and gas sensors. [1][2][3][4][5] Oxygen evolution reaction (OER, 4OH -→ O 2 + 2H 2 O + 4e -) is one of the most important steps in energy conversion and storage mechanisms, and is the efficiency-limiting process in electrolytic water splitting and metal-air batteries. 6,7 The ultimate goal of OER study is to develop low-cost, highly active, and stable catalysts. 8,9 Recently, perovskite oxides (ABO 3 ), such as Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3-δ , Pr 0.5 Ba 0.5 CoO 3-δ , and LaCoO 3 , have attracted much attention owing to their intrinsically high OER activity. [10][11][12] More interestingly, properties such as surface oxygen binding energy, number of outer shell electrons in the transition metal ion, electron occupancy of the e g orbitals, and the proximity of the oxygen p-band to the Fermi level, have been proposed as descriptors for OER activity. 10,11,13,14 Such approaches, however, have been mainly tested by comparing systems containing different transition metal elements.Unintentionally, such variations in the identity of the elements therein involve commensurate changes in the atomic structures, valence states, electric resistivities, crystalline surfaces, and the overall and specific electronic structures of the materials. Therefore, approaches based on simplified electronic structure may not apply to distinctive material systems, and more carefully controlled study, for example, one using a single-material system, is necessary to precisely understand the effect of the catalyst's electronic structure on the OER. 15In order to probe the link between electronic structure and catalytic activity within a singlematerial system, we exploit the strongly correlated behavior in complex oxides. In particular, the strong coupling among the degrees of freedom of the d-electrons, i.e., charge, spin, orbital, and lattice, in transition...

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“…Water adsorption on other materials, such as TiO 2 , SrO, Al 2 O 3 , and MgO, has been widely reported. Both experimental and theoretical approaches have revealed that there are two different modes through which the water molecule can adsorb on the solid surface: the molecular adsorption and dissociative adsorption .…”

Section: Introductionmentioning

confidence: 99%

“…There is not much information about initial water adsorption on C 2 S surfaces, which is extremely important to better understand the hydration process. 4 Water adsorption on other materials, such as TiO 2 , 10 SrO, 11 Al 2 O 3 , 12 and MgO, 13 has been widely reported. Both experimental and theoretical approaches have revealed that there are two different modes through which the water molecule can adsorb on the solid surface: the molecular adsorption and dissociative adsorption.…”

Section: Introductionmentioning

confidence: 99%

“…14 In cement hydration processes, silicate calcium and water are believed to dissociate into Ca 2+ , OH À , and H 2 SiO 4. [2][3][4][5][6][7][8][9][10][11][12][13][14][15] The released Ca 2+ and OH À promote the formation of Ca(OH) 2 and C-S-H gel. 16 Thus, the dissociative adsorption mechanism of a water molecule is an important aspect in C 2 S hydration.…”

Section: Introductionmentioning

confidence: 99%

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Molecular and dissociative adsorption of a single water molecule on a β‐dicalcium silicate (100) surface explored by a DFT approach

Zhang

et al. 2017

J Am Ceram Soc

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The adsorption of water on a C2S surface initiates belite to hydrate. In the present work, the adsorption behavior of single water molecule on a β‐C2S (100) surface is explored using density functional theory (DFT) due to the lack of alternative approaches for direct observation. Four possible calcium atom sites on the β‐C2S (100) surface slab are considered in our calculations. The results show that water can adsorb on the 2 five‐coordinated calcium sites only via molecular adsorption with adsorption energies of 0.59 and 0.85 eV, respectively, but can dissociate on the other 2 six‐coordinated calcium sites with higher adsorption energies of 0.96 and 0.99 eV, respectively. The energy barriers to the dissociative adsorption of water at the Ca(III) site(0.10 eV) is much lower than that at the Ca(IV) site, indicating that water prefers to adsorb and dissociate on Ca(III) sites. The dissociative adsorption of water causes more obvious surface calcium shifts and Si–O bond length increases than molecular adsorption. The dissociative adsorption of a water molecule changes the electron distribution, and the overlap between Ca 2p and O 2s orbitals leads to new Ca–O bond formations.

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Adsorption of water at the SrO surface of ruthenates

Cited by 74 publications

References 51 publications

Ordered hydroxyls on Ca3Ru2O7(001)

Ordered hydroxyls on Ca3Ru2O7(001)

Enhanced electrocatalytic activity via phase transitions in strongly correlated SrRuO₃thin films

Molecular and dissociative adsorption of a single water molecule on a β‐dicalcium silicate (100) surface explored by a DFT approach

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Adsorption of water at the SrO surface of ruthenates

Cited by 74 publications

References 51 publications

Ordered hydroxyls on Ca3Ru2O7(001)

Ordered hydroxyls on Ca3Ru2O7(001)

Enhanced electrocatalytic activity via phase transitions in strongly correlated SrRuO3thin films

Molecular and dissociative adsorption of a single water molecule on a β‐dicalcium silicate (100) surface explored by a DFT approach

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Enhanced electrocatalytic activity via phase transitions in strongly correlated SrRuO₃thin films