Diffraction studies, electrode/solution interface

Interfacial water molecules play important roles in many physical, chemical and biological processes. A molecular-level understanding of the structural arrangement of water molecules at electrode/electrolyte solution interfaces is one of the most important issues in electrochemistry. The presence of oriented water molecules, induced by interactions between water dipoles and electrode and by the strong electric field within the double layer has been proposed [39-41]. It has also been proposed that water molecules are present at electrode surfaces in the form of clusters [42, 43]. Despite the numerous studies on the structure of water at metal electrode surfaces using various techniques such as surface enhanced Raman spectroscopy [44, 45], surface infrared spectroscopy [46, 47[, surface enhanced infrared spectroscopy [7, 8] and X-ray diffraction [48, 49[, the exact nature of the structure of water at an electrode/solution interface is still not fully understood. 

Lucas CA, Markovic NM. 2006. In-situ X-ray diffraction studies of the electrode/solution interface. In AUdre RC, Kolb DM, Lipkowski J, Ross PN, editors. Advances in Electrochemical Science and Engineering. Volume 9. New York Wiley-VCH, pp. 1-45. 

As mentioned previously, this can be attributed in part to the lack of structure-sensitive techniques that can operate in the presence of a condensed phase. Ultrahigh-vacuum (UHV) surface spectroscopic techniques such as low-energy electron diffraction (LEED), Auger electron spectroscopy (AES), and others have been applied to the study of electrochemical interfaces, and a wealth of information has emerged from these ex situ studies on well-defined electrode surfaces.15"17 However, the fact that these techniques require the use of UHV precludes their use for in situ studies of the electrode/solution interface. In addition, transfer of the electrode from the electrolytic medium into UHV introduces the very serious question of whether the nature of the surface examined ex situ has the same structure as the surface in contact with the electrolyte and under potential control. Furthermore, any information on the solution side of the interface is, of necessity, lost. 

Figure 2.69 Cyclic voltammograms recorded for a 7500A-thick Ni(OH>2 film on a nickel electrode in 8M KOH. Scan rate=lmVs 1, The periods of ageing are shown in hours. Reprinted from Electrochimica Acta, 31, M. Fleischmann, A, Oliver and J. Robinson, tn situ X-ray diffraction studies of the electrode solution interface, pp. 899-906 (1986), with kind permission from Pcrgamon Press Ltd, Headington Hill Hall, Oxford 0X3 OBW, UK,...

X-ray surface diffraction has been applied in situ to study several processes at the electrode solution interface [13, 14]. An important phenomenon in electrochemistry at Au is surface reconstruction in which a monolayer of atoms on the surface of a single crystal acquires a different arrangement from that of the... 

In-situ X-ray Diffraction Studies of the Electrode/Solution Interface... 

Fleischmann, M., Graves, R, Hill, I.R. et al. (1983) Raman spectroscopic and X-ray diffraction studies of electrode-solution interfaces. Journal of Electroanalytical Chemistry, 150, 33. 

Fleischmann, M., Oliver, A. and Robinson, J. (1986) In situ X-ray diffraction studies on electrode solution interfaces. Electwchimica Acta, 31, 899. 

---