In Situ X-Ray Techniques for Electrochemical Interfaces.

This article reviews progress in the study of materials using X-ray-based techniques from an electrochemistry perspective. We focus on in situ/in operando surface X-ray scattering, X-ray absorption spectroscopy, and the combination of both methods. The background of these techniques together with key concepts is introduced.

Adsorption, surface relaxation and electrolyte structure at Pt(111) electrodes in non-aqueous and aqueous acetonitrile electrolytes.

In situ electrochemical surface X-ray diffraction was employed to investigate the atomic scale structure of the electrochemical double layer and the relaxation at the Pt(111) electrode surface in non-aqueous and aqueous acetonitrile electrolytes under potential control. The X-ray measurements provide insight into the potential-dependence of the interface structure by combining potentiodynamic measurements (X-ray voltammetry) with potentiostatic measurements (crystal truncation rod data) to probe both the metal and electrolyte sides of the interface. The crystal truncation rod measurements are consistent with the potential dependent reorientation of acetonitrile in the absence of water and a parallel arrangement in the presence of water.

Simulation of Surface Resonant X-ray Diffraction.

We present an ab initio numerical tool to simulate surface resonant X-ray diffraction experiments. The crystal truncation rods and the spectra around a given X-ray absorption edge are calculated at any position of the reciprocal space. Density functional theory is used to determine the resonant scattering factor of an atom within its local environment and to calculate the diffraction peak intensities for surfaces covered with a thin film or with one or several adsorbed layers.

Probing the charge distribution at the electrochemical interface.

The electrode/electrolyte interface is central to many electrochemical systems; however, gaining insight into the electronic structure at the interface is challenging. Due to its buried nature it is difficult to employ traditional techniques that provide spectroscopic information of localised atoms. To gain new insight into the charge distribution at the interface, we used resonant surface X-ray diffraction to select atoms at the interface via the diffraction conditions and obtained spectroscopic information simultaneously.

Colloidal dual-band gap cell for photocatalytic hydrogen generation.

We report that the internal quantum efficiency for hydrogen generation in spherical, Pt-decorated CdS nanocrystals can be tuned by quantum confinement, resulting in higher efficiencies for smaller than for larger nanocrystals (17.3% for 2.8 nm and 11.

Anomalous potential dependence in homoepitaxial Cu(001) electrodeposition: an in situ surface x-ray diffraction study.

Homoepitaxial Cu electrodeposition on Cu(001) in chloride-containing electrolyte was studied by time-resolved in situ surface x-ray diffraction at growth rates up to 38 ML/ min. With increasing Cu electrode potential, transitions from step-flow to layer-by-layer and then to multilayer growth are observed. This potential dependence is opposite to that expected theoretically and found experimentally for the Au(001) homoepitaxial electrodeposition [K.

Studies of electrochemical surface alloying and dealloying by in situ high-speed STM.

The electrochemical formation and dissolution of a lead/copper surface alloy on Cu(100) in chloride-containing electrolyte solutions were studied on the atomic scale by in situ scanning tunneling microscopy with high temporal and spatial resolution. Alloy formation, induced by a negative potential sweep, starts predominantly at the Cu steps, followed by the formation of a novel transient (4 × 3) alloy phase with 0.25 ML Pb coverage, which continuously is transformed into the 0.

Initiation and inhibition of dealloying of single crystalline Cu3Au (111) surfaces.

Dealloying is widely utilized but is a dangerous corrosion process as well. Here we report an atomistic picture of the initial stages of electrochemical dealloying of the model system Cu(3)Au (111). We illuminate the structural and chemical changes during the early stages of dissolution up to the critical potential, using a unique combination of advanced surface-analytical tools.

Inhibited and enhanced nucleation of gold nanoparticles at the water|1,2-dichloroethane interface.

The deposition of gold at the interface between immiscible electrolyte solutions has been investigated using reduction of tetrachloroaurate or tetrabromoaurate in 1,2-dichloroethane, with aqueous phase hexacyanoferrate as reducing agent. In a clean environment without defects present at the interface, the Au(III) complex was reduced to the Au(I) complex, but no solid phase formation could be observed. A deposition process could only be observed through the addition of artificial nucleation sites in the form of palladium nanoparticles at the interface.

High-speed in situ surface X-ray diffraction studies of the electrochemical dissolution of Au(001).

We present in situ X-ray surface diffraction studies of interface processes with data acquisition rates in the millisecond regime, using the electrochemical dissolution of Au(001) in Cl-containing solution as an example. This progress in time resolution permits monitoring of atomic-scale growth and etching processes at solid-liquid interfaces at technologically relevant rates. Au etching was found to proceed via a layer-by-layer mechanism in the entire active dissolution regime up to rates of ∼20 ML/s.

In situ video STM studies of the hydrogen-induced reconstruction of Cu(100): potential and pH dependence.

The surface structure of Cu(100) electrodes in perchloric acid solutions of pH 1 to 3 was studied in the potential range of hydrogen evolution by video-rate scanning tunneling microscopy, focusing on the recently reported hydrogen-induced surface reconstruction [H. Matsushima et al., J.

Reconstruction of Cu(100) electrode surfaces during hydrogen evolution.

Electrochemical hydrogen evolution on (100)-oriented copper electrodes is shown to induce a novel surface reconstruction, which substantially influences the rates of this electrochemical reaction. As revealed by in situ video-STM the formation of this phase starts with lateral displacements of Cu surface atoms from lattice positions, resulting in stripe-like structures, followed by expansion of the surface lattice along the stripe direction.

From ultra-high vacuum to the electrochemical interface: x-ray scattering studies of model electrocatalysts.

In-situ surface X-ray scattering (SXS) has become a powerful probe of the atomic structure at the metal-electrolyte interface. In this paper we describe an experiment in which a Pt(111) sample is prepared under ultra-high vacuum (UHV) conditions to have a p(2 x 2) oxygen layer adsorbed on the surface. The surface is then studied using SXS under UHV conditions before successive transfer to a bulk water environment and then to the electrochemical environment (0.

Portable chamber for the study of UHV prepared electrochemical interfaces by hard x-ray diffraction.

We report on a new electrochemical cell setup, combined with a portable UHV chamber, for in situ x-ray diffraction using synchrotron radiation. In contrast to more traditional electrochemical sample preparation schemes, atomically clean and well-ordered surfaces are routinely prepared by UHV methods, even in the case of reactive elements or alloys. Samples can be transferred from larger UHV systems into the portable chamber without exposure to ambient air.