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It has long been conceived that in equilibrium electrode surfaces in contact with electrolytes remain highly dynamic, exhibiting steady processes such as detachment and adsorption of surface atoms. Importantly, some of those microstate fluctuations play an essential role on formation of surface structure and composition, and ultimately affect the functionality of electrodes. Surface-sensitive techniques, like STM and surface x-ray scattering (SXS), have become invaluable to unraveling electrode surface structures under changing electrochemical environments. Measurements on surface dynamics, however, remain challenging for electrochemical systems [[1]]. In this talk, we will report on the study of Au (111) surface dynamics by coherent surface x-ray scattering (CSXS). A brief introduction will be given for implementation of CSXS and ISXS for electrochemical studies. Time-resolved capability of CSXS will be highlighted. To elucidate factors that could influence surface dynamics, Au (111) electrode surfaces are systemically tailored by varying electrochemical conditions. Phase transition in Au (111) electrode surface had been well characterized by SXS, with structural changes that were shown to be both dependent on potentials and solution chemistry [[2]]. A sharp drop in x-ray scattering intensity around 0.12 V, shown in Fig. 1 (black curve), marks phase transition from (p x√3) to (1x1), which then can be reconstructed back to form a (p x√3) structure in a reverse potential scan. A similar potential dependence is found with increasing chloride concentration as shown in Fig. 1 (red curve). Careful comparison of the hysteresis loops, presented in Fig. 1, additionally reveals that chloride concentration influences the kinetics of phase transition in Au (111) surfaces. In additional to structural details, we have also attained some preliminary results on the dynamics of Au (111) surfaces from CSXS experiments. In the present work, surface dynamics are quantified in terms of correlation time, a parameter that describes the temporal separation between two configurations that are no longer resemble each other due to microstate fluctuations. Correlation time in relation to surface structure will be shown and discussed as a function of applied potential and chloride concentration. A comprehensive analysis on surface dynamics will be performed to help establish its relations with surface structure and solution chemistry. [1] M. Pierce, V. Komanicky, A. Barbour, D. C. Hennessy, C. Zhu, A. Sandy, H. You, Phys. Rev. B 86, 085410 (2012). [2] J. Wang, B.M. Ocko, A. J. Davenport, H. S. Isaacs, Phys. Rev. B 46 10321 (1992). Figure 1

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