Water has a paramount importance in chemical, biochemical and electrochemical processes. However, very little information is known about the microscopic mechanism by which water affects these processes. This is due to the fact that water in the condensed phase shows ultrafast (sub-picosecond) molecular dynamics and forms an extremely inhomogeneous system. Femtosecond pump-probe mid-infrared spectroscopy is ideally suited to distinguish different types of water molecules and it also provides sufficient time resolution to resolve the translational and orientational dynamics of water molecules. The essence of this technique is the excitation of a selected type of molecules by a pump pulse, and the subsequent analysis of its relaxation and molecular motions by a probe pulse at varying time delays. This technique has been applied successfully to water and aqueous solutions. The challenge presented here is to apply this technique, for the first time, to the study of the behavior of water at electrified interfaces under potential control. For this purpose, it is crucial to develop an adequate experimental set-up that allows probing preferentially interfacial water. In this regards, the use of the surface enhancement effect in ATR-SEIRAS (Attenuated Total Reflection-Surface Enhanced IR Absorption Spectroscopy) is specially promising. It should be stressed that the excellent experience of the candidate in the study of metal|water interfaces and the impressive achievements of the host institution in femtosecond mid-infrared spectroscopy of water, makes this project unique and unprecedented. The results of this project will constitute a breakthrough in the molecular-level understanding on the role of water in electrochemical reactions. In turn, this information will be also invaluable for the understanding of the general effect of electrocatalysis. For this reason, the present project can play a very important role in the development of electrochemical technologies.