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The interface of Cu͑001͒ electrode surfaces in 10 mM HCl solution was studied by in situ surface x-ray diffraction and density functional theory, focusing on the precise structure of the c͑2 ϫ 2͒ Cl adlayer formed at positive potentials. Crystal truncation rod measurements in this adsorbate phase at a potential of −0.20 V Ag/AgCl reveal distinct differences to corresponding data by Tolentino et al. ͓Surf. Sci. 601, 2962 ͑2007͔͒ for the c͑2 ϫ 2͒ Cl structure formed at the Cu͑001͒-vacuum interface. Although in both environments, the atoms in the second Cu layer exhibit a small vertical corrugation, the sign of this corrugation is reversed. Furthermore, also the Cu-Cl bond distance and the average Cu interlayer spacings at the surface differ. Ab initio calculations performed for this adsorbate system reproduce these effects-specifically the reversal of the subsurface second-layer buckling caused in the presence of coadsorbed water molecules and cations in the outer part of the electrochemical double layer. In addition, studies at more negative potentials reveal a continuous surface phase transition to a disordered Cl adlayer at −0.62 V Ag/AgCl , but indicate a substantial Cl coverage even at the onset of hydrogen evolution.

Model experiments, in which active material in the electrode is replaced with insulating ceramic particles, are used to show the importance of pure conductive additives network. Ceramic particles are chosen with particle diameter of 10 and 3 μm. Coatings with similar loading and varying levels of carbon black, graphite and polyvinylidene fluoride are fabricated, analyzed regarding electronic conductivity and investigated with a new "quasi" in-situ SEM compression method. The electronic conductivity strongly depends on porosity, inactive material amount and distribution. SEM/EDX images showed that coatings with 10 μm particles have higher porosity and denser network of conductive additives compared to 3 μm particles. Therefore, the conductive additives and binder amount should be adjusted based on the particle size distribution.

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. Furthermore, we demonstrate that information on the lateral surface morphology and in-plane lattice strain during the electrochemical process can be obtained.

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. Krug et al., Phys. Rev. Lett. 96, 246101 (2006)]. The anomalous behavior is rationalized by a decisive influence of the ordered c(2 × 2)-Cl adlayer on the surface energy landscape, specifically on the effective change in dipole moment during adatom diffusion.

The influence of polyethylene glycol (PEG) on the atomic-scale interface structure and Cu growth behavior of Cu(001) in chloride-containing electrolyte was investigated by in situ surface X-ray diffraction. Studies in Cu-free solution unambiguously verify the presence of the ordered c(2 × 2) chloride adlayer in the presence of the polymer as well as reversible Cl adsorption/desorption and an order-disorder transition in the adlayer. The partially ordered chloride adlayer is found over a wider potential range as compared to PEG-free electrolyte, indicating stabilization of this adsorbate phase. Crystal truncation and superstructure rod measurements reveal that the polymer interacts more strongly with the partially c(2 × 2) Cl covered surface than with the close-packed c(2 × 2) adlayer at saturation coverage. In Cu-containing electrolyte layer-by-layer growth was observed at potentials ≤ −0.35 V vs. Ag/AgCl. The deposition rate was significantly reduced as compared to PEG-free electrolyte, providing clear evidence of inhibition on the atomic-scale. At more positive potentials a crossover to 3D growth and increasing surface roughness is found.

Kinetic roughening during electrodeposition was studied by grazing incidence small angle x-ray scattering for the case of Au(001) homoepitaxial growth in Cl- containing electrolytes. The formation and coarsening of an isotropic mound distribution on unreconstructed Au(001) and of [110]-oriented anisotropic mounds on the "hex" reconstructed surface was observed. The lateral mound coarsening is described by a well-defined scaling law. On unreconstructed Au a transition in the coarsening exponent from ≈1/4 to ≈1/3 with increasing potential is found, which can be explained by the pronounced potential dependence of surface transport processes in an electrochemical environment.

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