Molecular level, metal-electrolyte interface

In-Situ Fourier Transform Infrared Spectroscopy A Tool to Characterize the Metal-Electrolyte Interface at a Molecular Level... 

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. 

In the next section a brief layout of simulation methods will be given. Then, some basic properties of the models used in computer simulations of electrochemical interfaces on the molecular level will be discussed. In the following three large sections, the vast body of simulation results will be reviewed structure and dynamics of the water/metal interface, structure and dynamics of the electrolyte solution/metal interface, and microscopic models for electrode reactions will be analyzed on the basis of examples taken mostly from my own work. A brief account of work on the adsorption of organic molecules at interfaces and of liquid/liquid interfaces complements the material. In the final section, a brief summary together with perspectives on future work will be given. 

Understanding the structure and dynamics of pure water on a molecular level is only the beginning. Simulations of electrolyte solutions near metallic interface are much more demanding in terms of computer time than those of bulk water, because the relatively small number of ions even in a highly concentrated electrolyte solution mandates the treatment of systems with a much larger total number of particles than in pure water for a longer time span. Furthermore, as was discussed in section 3, much less is known from quantum chemistry about nature and strength of the ion-metal interaction than about the water-metal interactions, so that the interpretation of the results obtained from the simulations is less clear. 

Characterization of electrode-solution interfaces at the molecular level comparisons of metal-electrolyte with metal-gas and metal-UHV systems. 

The time of wetness is obviously strongly dependent on the critical relative humidity. Apart from the primary critical humidity, associated with clean surfaces, secondary and even tertiary critical humidity levels may be created by hygroscopic corrosion products and capillary condensation of moisture in corrosion products, respectively. A capillary condensation mechanism may also account for electrolyte formation in microscopic surface cracks and the metal surface-dust particle interface. Other sources of surface electrolyte include chemical condensation (by chlorides, sulfates, and carbonates), adsorbed molecular water layers, and direct moisture precipitation (ocean spray, dew, rain). The effects of rain on atmospheric corrosion damage are somewhat ambiguous. While providing electrolyte for corrosion reactions, rain can act in a beneficial manner by washing away or diluting harmful corrosive surface species. 

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