Monday, March 4, 2019
11:15AM - 11:51AM
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B34.00001: Probing the charge distribution at the electrochemical interface
Invited Speaker:
Yvonne Grunder
In-situ surface x-ray diffraction has enabled an atomic/molecular-level understanding of the interface under reactive conditions, including its potential and time dependence, to be developed. While information about the atomic structure of the electrode surface in electrochemical in-situ cells has been widely investigated, insight into the charge distribution and the structure of the electrolyte at the interface is still lacking. A fundamental understanding of the nature of the charge transfer, especially the influence of the applied potential and the screening by the electrolyte, is a major goal in electrochemistry to better understand electrochemical processes and charge transfer during adsorption and deposition.[1]
In-situ studies of the chemical bonding are rather difficult due to the presence of the electrolyte, as standard characterisation techniques which are mostly UHV based cannot be applied. Thus combining x-ray spectroscopy and x-ray diffraction to gain site specific information about the charge distribution at buried interfaces is a promising tool. [2,3] Examples of how the use of surface x-ray scattering techniques can help to characterise electrochemical interfaces in-situ in order to link, structure, reactivity and stability will be presented. Advances in these directions offer possibilities in elucidating atomic scale models of the electrochemical interface and thus will help to establish structure-stability-reactivity relationships.
References: [1] Y. Gründer, P. Thompson, A. Brownrigg, M. Darlington, and C. A. Lucas, Journal of Physical Chemistry C, 2012,116, 6283 [2] Y. Gründer and C. A. Lucas, Physical Chemistry Chemical Physics, 2017, 19, 8416 [3] Y. Joly et al., J. Chem. Theory Comput,. 2018, 14, 973−980 |
Monday, March 4, 2019
11:51AM - 12:27PM
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B34.00002: Monitoring electrochemical and electrocatalytic interface processes on the atomic and nanometer scale by operando surface X-ray scattering
Invited Speaker:
Olaf Magnussen
The need for sustainable energy, reduction of pollutants, and the environmental benign processing of chemicals has spurred worldwide scientific activities in electrochemical energy science and electrocatalysis. These processes occur at the interfaces of solid electrodes in contact with complex liquid environments under conditions, which are difficult to access by most surface analytic techniques. For a better understanding of structure-property relationships and reaction-induced morphological changes, experimental approaches are required that provide direct insight into the atomic and nanoscale interface structure. Modern synchrotron-based X-ray scattering methods provide unique opportunities for such operando studies. They allow monitoring structural changes at electrode surfaces with high structure sensitivity on (sub-) second time scales. The talk will give an overview of the current state of this field. It will specifically highlight the advantages of using very high photon energies (70 keV) in combination with 2D X-ray detectors. This new approach enables e.g. detailed determination of complex, dynamically changing interface structures and microdiffraction studies of spatially heterogeneous materials. The application of these methods will be demonstrated by studies of Pt oxidation and transition metal oxide catalysts for water splitting. In the first case, a strong dependence of the oxidation mechanism on the Pt surface structure was observed, resulting in pronouncedly different Pt dissolution and nanoscale restructuring. The second example will focus on epitaxial Co oxide thin films, which were monitored in the oxygen evolution regime up to current densities as high as 150 mA cm-2. Whereas CoOOH(001) films were perfectly stable under these conditions, oxygen evolution on Co3O4(111) films occurs on a disordered nm-thick skin layer, which forms highly reversibly at potentials 300 mV negative of the onset of this electrocatalytic reaction. |
Monday, March 4, 2019
12:27PM - 1:03PM
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B34.00003: Transition-metal-oxide/liquid interfaces
Invited Speaker:
Ulrike Diebold
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
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Monday, March 4, 2019
1:03PM - 1:39PM
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B34.00004: Molecular Self-Assemblies as Templates for Electrochemically Deposited Nanostructures
Invited Speaker:
Manfred Buck
Ranging from porous networks to dense layers, the structural and functional versatility of aromatic molecules provides a diversity of options for controlling processes at the liquid/solid interface. This includes the electrochemical interface where the level of control intrinsic to electrochemical processes combines favourably with the control of charge transfer, interfacial energies and chemical functionality by highly organized molecular assemblies. This combination can be taken advantage of for the generation of nanostructures by templated electrodeposition using molecular patterns produced by either bottom-up self-assembly or top down lithography. While structures down to the 20 nm range are relatively straightforward to achieve, progress in the move towards the bottom end of the nanoscale will be critically dependent not only on the precision of template structures but also on the level of control over the dynamics of processes such as diffusion and nucleation which, ultimately, become the limiting factors. To address these issues requires to go beyond the usual application of organized molecular layers to render electrodes electrochemically passive. As illustrated by the electrodeposition of metals, utilising a more varied design than non-functionalized single component layers offers interesting prospects for the generation of ultrasmall structures such as a reduction in the percolation threshold or self-limiting layer formation enabled by coordination controlled deposition.
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