In-situ surface X-ray diffraction is used to characterize the surface oxides on Pt(111) surface in 0.1 M HClO 4. Detailed analysis at two potentials confirms that the surface restructuring at the initial oxidation stages is consistent with a place exchange process between Pt and O atoms, and the exchanged Pt atoms are located above their original positions in the Pt(111) lattice. The (1,1,1.5) reflection is used to dynamically study the surface during cyclic voltammetry. The restructuring associated with the place exchange initiates with the CV peak at 1.05 V, even though multiple cycles to 1.17 V lead to no changes in the CV. The restructuring is reversible below a critical coverage of place exchanged Pt atoms, which we estimate to be between 0.07 and 0.15 ML. Extensive cycling to potentials higher or equal to 1.17 V leads to progressive disordering of the surface.

Room-temperature ionic liquids are of great current interest for electrochemical applications in material and energy science. Essential for understanding the electrochemical reactivity of these systems are detailed data on the structure and dynamics of the interfaces between these compounds and metal electrodes, which distinctly differ from those in traditional electrolytes. In situ studies are presented of Au(111) electrodes in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([BMP][TFSA]) by high-speed scanning tunneling microscopy (video-STM). [BMP][TFSA] is one of the best-understood air and water stable ionic liquids. The measurements provide direct insights into the potential-dependent molecular arrangement and surface dynamics of adsorbed [BMP](+) cations in the innermost layer on the negatively charged Au electrode surface. In particular, two distinct subsequent transitions in the adlayer structure and lateral mobility are observed with decreasing potential.

The surface restructuring of Pt(111) electrodes upon electrochemical oxidation/reduction in 0.1 M HClO4 was studied by in situ grazing-incidence small-angle X-ray scattering and complementary scanning tunneling microscopy measurements. These methods allow quantitative determination of the formation and structural evolution of nanoscale Pt islands during potential cycles into the oxidation region. A characteristic ripening behavior is observed, where these islands become more prominent and homogeneous in size with increasing number of cycles. Their characteristic lateral dimensions primarily depend on the upper potential limit of the cycle and only slightly increase with cycle number. The structural evolution of the Pt surface morphology strongly resembles that found in studies of Pt(111) homoepitaxial growth and ion erosion in ultrahigh vacuum. It can be fully explained by a microscopic model based on the known surface dynamic behavior under vacuum conditions, indicating that the same dynamics also describe the structural evolution of Pt in the electrochemical environment.

The potential dependent surface structure of Pt(111) electrodes in electrochemical environment was studied by in situ crystal truncation rod measurements and in operando grazing incidence small angle X-ray scattering. Determination of the interface structure in the oxidation region reveal a continuous increase of the coverage of place exchanged atoms toward more positive potentials. The resulting oxide consists of an oxygen rich outer and a Pt-rich inner atomic layer. With increasing potential the oxide approaches a more uniform stoichometry. While place exchange on atomically smooth terraces only occurs above 1.05 V, structural changes of 3D Pt islands, grown by repetitive oxidation/reduction cycles, already commence at 0.8 V, which is assigned to oxidation at Pt steps. Evolution of the 3D island distribution occurs in all stages of the cycles: Whereas Pt oxidation leads to narrowing of the lateral size distribution, vertical island growth occurs during the subsequent reduction.

The molecular arrangement and surface dynamics of Au (111) electrodes in 1-hexyl-3-methylimidazolium chloride ([HMIm][Cl]) and 1-hexyl-3-methylimidazolium bis-(trifluoromethylsulfonyl)imide ([HMIm][TFSA]) were investigated by in situ high-speed scanning tunneling microscopy (video-STM). These measurements provide direct insights into the potentialdependent adlayer structure of adsorbed [HMIm] + cations and Cl − anions on the Au (111) surface. At low electrode charge densities highly dynamic structures with only local order are observed. After changing the potential in the negative direction, stripe-like adlayers structures are observed, which are attributed to [HMIm] + in a planar adsorption geometry. These can be described by simple commensurate (√3 × 3) and a (√3 × √13) structures in the presence of Cl − and [TFSA] − counterions, respectively, indicating that the in-plane arrangement of the cations is affected by epitaxial effects and coadsorbed anions. Upon a further decrease in potential, a transition to a more close-packed (√3 × 2) adlayer phase is observed in [HMIm][TFSA], in which the cations are partly oriented away from the metal surface.