The laser pump X-ray probe system at LISA P08 PETRA III.

Understanding and controlling the structure and function of liquid interfaces is a constant challenge in biology, nanoscience and nanotechnology, with applications ranging from molecular electronics to controlled drug release. X-ray reflectivity and grazing incidence diffraction provide invaluable probes for studying the atomic scale structure at liquid-air interfaces. The new time-resolved laser system at the LISA liquid diffractometer situated at beamline P08 at the PETRA III synchrotron radiation source in Hamburg provides a laser pump with X-ray probe.

and X-ray Scattering Methods in Electrochemistry and Electrocatalysis.

Electrochemical and electrocatalytic processes are of key importance for the transition to a sustainable energy supply as well as for a wide variety of other technologically relevant fields. Further development of these processes requires in-depth understanding of the atomic, nano, and micro scale structure of the materials and interfaces in electrochemical devices under reaction conditions. We here provide a comprehensive review of and studies by X-ray scattering methods, which are powerful and highly versatile tools to provide such understanding.

scanning tunneling microscopy studies of carbonate-induced restructuring of Ag-decorated Cu(100) electrodes.

Ag-decorated Cu electrocatalysts are of great interest for electrochemical CO reduction, because of an increased yield of multi-carbon products. Here, we present studies of well-defined AgCu electrodes by scanning tunneling microscopy. These bimetallic model electrocatalysts are prepared by electrodepositing submonolayer Ag coverages on Cu(100) in 0.

Photoinduced bidirectional switching in lipid membranes containing azobenzene glycolipids.

Following the reaction of biological membranes to external stimuli reveals fundamental insights into cellular function. Here, self-assembled lipid monolayers act as model membranes containing photoswitchable azobenzene glycolipids for investigating structural response during isomerization by combining Langmuir isotherms with X-ray scattering. Controlled in-situ trans/cis photoswitching of the azobenzene N = N double bond alters the DPPC monolayer structure, causing reproducible changes in surface pressure and layer thickness, indicating monolayer reorientation.

Anodic and Cathodic Platinum Dissolution Processes Involve Different Oxide Species.

The degradation of Pt-containing oxygen reduction catalysts for fuel cell applications is strongly linked to the electrochemical surface oxidation and reduction of Pt. Here, we study the surface restructuring and Pt dissolution mechanisms during oxidation/reduction for the case of Pt(100) in 0.1 M HClO by combining operando high-energy surface X-ray diffraction, online mass spectrometry, and density functional theory.

Influence of coverage on adsorbate diffusion measurements at electrode surfaces by in situ linear optical diffraction.

In situ linear optical diffraction is a new method for studies of surface mass transport in electrochemical environments that is based on the equilibration of coverage gratings in an adlayer on the electrode surface. We, here, discuss the temporal evolution of the diffraction intensity on the basis of experimental data for sulfur adsorbates on Pt(111) electrodes in 0.1M H2SO4 and simulations of the time-dependent diffusion profiles.

Measurement of Surface Diffusion at the Electrochemical Interface by In Situ Linear Optical Diffraction.

A new in situ method for measuring the surface diffusion rates of adsorbates on electrode surfaces in electrolyte solution is presented. The method is based on the generation of a periodic spatial modulation of the adsorbate coverage via interfering laser pulses and subsequent monitoring of the diffusion-induced decay of this pattern using the optical diffraction signal of a second laser. Proof-of-principle measurements of the surface diffusion of adsorbed sulfur on Pt(111) electrodes in 0.

Driving Force of the Initial Step in Electrochemical Pt(111) Oxidation.

The first step of electrochemical surface oxidation is extraction of a metal atom from its lattice site to a location in a growing oxide. Here we show by fast simultaneous electrochemical and in situ high-energy surface X-ray diffraction measurements that the initial extraction of Pt atoms from Pt(111) is a fast, potential-driven process, whereas charge transfer for the related formation of adsorbed oxygen-containing species occurs on a much slower time scale and is evidently uncoupled from the extraction process. It is concluded that potential plays a key independent role in electrochemical surface oxidation.

Structure of the (Bi)carbonate Adlayer on Cu(100) Electrodes.

(Bi)carbonate adsorption on Cu(100) in 0.1 M KHCO has been studied by in situ scanning tunneling microscopy. Coexistence of different ordered adlayer phases with ( ×6 )R45° and (4×4) unit cells was observed in the double layer potential regime.

Role of chemisorbing species in growth at liquid metal-electrolyte interfaces revealed by in situ X-ray scattering.

Liquid-liquid interfaces offer intriguing possibilities for nanomaterials growth. Here, fundamental interface-related mechanisms that control the growth behavior in these systems are studied for Pb halide formation at the interface between NaX + PbX (X = F, Cl, Br) and liquid Hg electrodes using in situ X-ray scattering and complementary electrochemical and microscopy measurements. These studies reveal a decisive role of the halide species in nucleation and growth of these compounds.

Identification of the Reversible Skin Layer on CoO as a Three-Dimensional Reaction Zone for Oxygen Evolution.

Co oxides and oxyhydroxides have been studied extensively in the past as promising electrocatalysts for the oxygen evolution reaction (OER) in neutral to alkaline media. Earlier studies showed the formation of an ultrathin CoO (OH) skin layer on CoO at potentials above 1.15 V vs reversible hydrogen electrode (RHE), but the precise influence of this skin layer on the OER reactivity is still under debate.

Interface Phenomena.

This special collection on Interface Phenomena is dedicated to R. Jürgen Behm on the occasion of his retirement and 70th birthday. Jürgen Behm's research over the past 40 years has addressed a wide variety of interface processes in the fields of growth, corrosion, heterogeneous catalysis, electrocatalysis, and batteries.

Comment on "Bi-layering at ionic liquid surfaces: a sum - frequency generation vibrational spectroscopy - and molecular dynamics simulation-based study" by T. Iwahashi, T. Ishiyama, Y. Sakai, A. Morita, D. Kim and Y. Ouchi, Phys. Chem. Chem. Phys., 2020, 22, 12565.

This Comment raises several questions concerning the surface structure concluded in the paper referenced in the title. Specifically, that paper ignores previous experiments and simulations which demonstrate for the same ionic liquids depth-decaying, multilayered surface-normal density profiles rather than the claimed molecular mono- or bi-layers. We demonstrate that the claimed structure does not reproduce the measured X-ray reflectivity, which probes directly the surface-normal density profile.

Nucleation and Growth of PbBrF Crystals at the Liquid Mercury-Electrolyte Interface Studied by Operando X-ray Scattering.

Detailed studies of electrochemically induced PbBrF deposition at the liquid mercury/liquid electrolyte interface are presented. The nucleation and growth were monitored using time-resolved X-ray diffraction and reflectivity combined with electrochemical measurements, revealing a complex potential-dependent behavior. PbBrF deposition commences at potentials above -0.

Electrochemical Stability of the Reconstructed Fe O (001) Surface.

Establishing the atomic-scale structure of metal-oxide surfaces during electrochemical reactions is a key step to modeling this important class of electrocatalysts. Here, we demonstrate that the characteristic (√2×√2)R45° surface reconstruction formed on (001)-oriented magnetite single crystals is maintained after immersion in 0.1 M NaOH at 0.

Vacancy dynamics on CO-covered Pt(111) electrodes.

In situ video-STM studies of Pt(111) electrodes in CO-saturated 0.1 M H2SO4 solution are presented, which reveal the presence of defined point defects in the CO pre-oxidation regime, where the surface is covered by a highly dynamic apparent (1 × 1)-CO adlayer. These defects are generated at the Pt steps and can switch between a mobile and an immobile state.

Observation of Collective Photoswitching in Free-Standing TATA-Based Azobenzenes on Au(111).

Light-induced transitions between the trans and cis isomer of triazatriangulenium-based azobenzene derivatives on Au(111) surfaces were observed directly by scanning tunneling microscopy, allowing atomic-scale studies of the photoisomerization kinetics. Although the azobenzene units in these adlayers are free-standing and spaced at uniform distances of 1.26 nm, their photoswitching depends on the isomeric state of the surrounding molecules and, specifically, is accelerated by neighboring cis isomers.

The Dynamic Nature of CO Adlayers on Pt(111) Electrodes.

CO adlayers on Pt(111) electrode surfaces are an important electrochemical system and of great relevance to electrocatalysis. The potential-dependent structure and dynamics of these adlayers are complex and still controversial, especially in the CO pre-oxidation regime. We here employ in situ high-speed scanning tunneling microscopy for studying the surface phase behavior in CO-saturated 0.

Norbornadiene-functionalized triazatriangulenium and trioxatriangulenium platforms.

Triazatriangulenium (TATA) and trioxatriangulenium (TOTA) ions are particularly suited systems to mount functional molecules onto atomically flat surfaces such as Au(111). The TATA and TOTA units serve as platforms that absorb onto the surface and form ordered monolayers, while the functional groups are protruding upright and freestanding from the central carbon atoms. Azobenzene derivatized TATA's are known to exhibit extremely fast → isomerization on metal surfaces, via a peculiar non-adiabatic singlet→triplet→singlet mechanism.

Molecular platforms as versatile building blocks for multifunctional photoswitchable surfaces.

Controlled attachment of photoswitchable molecules to solid surfaces is a promising route for the realization of complex machine-like molecular functions. A central next step here is the preparation of adlayers with multiple chemical functions that have defined intermolecular spacings and orientations and interact with each other in a controlled way, resulting in novel advanced system properties. We demonstrate that this is possible using molecular platforms with vertical functional units.

Atomic-Scale Insights into Electrode Surface Dynamics by High-Speed Scanning Probe Microscopy.

Atomic-scale processes at electrode surfaces in liquid electrolytes are central elemental steps of electrochemical reactions. Detailed insights into the structure of these interfaces can be obtained with in situ scanning tunnelling and atomic force microscopy. By increasing the time resolution of these methods into the millisecond range, highly dynamic processes at electrode surfaces become directly observable.

Toward an Atomic-Scale Understanding of Electrochemical Interface Structure and Dynamics.

For the knowledged-based development of electrochemical processes, a better fundamental understanding of the interfaces between electrodes and electrolytes is necessary. This requires insight into the interface structure and dynamics on the atomic-scale, including that of the liquid electrolyte in the near-surface region, i.e.

Formation and Diffusion of Subsurface Adsorbates at Electrodes.

We report direct observation of the formation of a subsurface species at metal electrodes in liquid electrolytes and of its migration within the solid's surface layer, below a chemisorbed electrochemical double layer. Using in situ video-rate scanning tunneling microscopy, we find for adsorbed sulfide on bromide-covered Ag(100) electrodes reversible transitions between adsorption sites on top of the surface and within a vacancy in the first Ag layer. In the latter state, the sulfide surface diffusion can be enhanced by orders of magnitude, which we attribute to vacancy-mediated diffusion underneath the bromide adlayer.

Influence of a Metal Substrate on Small-Molecule Activation Mediated by a Surface-Adsorbed Complex.

Activating small molecules with transition metal complexes adsorbed on metal surfaces is a novel approach combining aspects of homogeneous and heterogeneous catalysis. In order to study the influence of an Au(111) substrate on the activation of the small-molecule ligand carbon monoxide, a molybdenum tricarbonyl complex containing a PN P pincer ligand was synthesized and investigated in the bulk, in solution, and adsorbed on an Au(111) surface. By means of a platform approach, a perpendicular orientation of the molybdenum complex was achieved and confirmed by IRRAS and NEXAFS.