Tools and Electrochemical In Situ and On-Line Characterization Techniques for Nanomaterials

Abstract

In the last century, progress in electrochemistry and electrocatalysis was very spectacular due to the remarkable evolution in surface science, chemistry, and physics. Electrochemical study of perfect smooth or bulk materials was the usual way to understand the interaction between the surfaces of such materials with their close environment. Therefore, any modification of the surface structure or composition provides change in the material behavior and the nature of the adsorbed species or near. Usually, the modification of smooth surface consists in the increase of its roughness factor through the deposition of sublayer or layer of metal particles. The deposition can be done on a well-defined surface (model electrode with a known crystallographic structure) [1]. Then, surface modification becomes a way of creating new active sites to enhance the reactivity of molecules. The development of nanoscale materials has changed the approach of studying and identifying active sites in heterogeneous catalysis, and particularly in electrocatalysis. Indeed, electrocatalysis uses the surface of a material, which is submitted to an electrode potential, as the reaction site. Therefore, the material structure, morphology and its composition are the key parameters to control the electrochemical process [2]. The nature of the active site depends on these parameters. Furthermore, the assessment of the nature of the active site before, during, and after the electrocatalytic reaction becomes a huge challenge. Thereby, electrochemical tools like cyclic voltammetry, underpotential deposition of a monolayer of a species [3–5], the specific adsorption of species or molecule, and CO stripping [6] were the first approaches. It is the basic measurement of the electrons flow through the surface per unit of time during the reaction at the surface. Therefore, the electric current per area unit represents the charge transfer reaction that occurs at a metal-solution interface. Since the middle of the last century, an increase in the development of several in situ spectroscopic techniques was observed due to the need of understanding the structure of the interface between electrodes and solutions. Indeed, coupling the electrochemistry measurements to other techniques such as Fourier Transform Infrared Spectroscopy (FTIRS), X-Ray Diffraction (XRD) [7, 8], Transmission Electron Microscopy (TEM) [9], Scanning Tunneling Microscopy (STM) [10], Surface-Enhanced Raman Scattering (SERS) [11] becomes a suitable approach to assess in real time at the electrified interface electrode-solution; some relevant data on electrocatalysts structure, morphology, composition, and stability of materials; and on the reaction intermediates and products. The identification of the surface state in addition to that of adsorbed species, intermediates, and products of the reaction process have permitted to determine a mechanistic pathway which is essential for enhancing the material performance and selectivity. It appears obvious that the identification of surface state of a nanomaterial under realistic electrochemical reaction conditions represents a noble scientific breakthrough. In the present chapter, for the first time some techniques coupled with electrochemistry able to characterize nanomaterials as electrodes will be extensively addressed. This chapter will also show the progress in in situ electrochemical approaches. One motivated approach is to be able to characterize electrochemically and experimentally the surface of the nanoparticle. Therefore, in the first part of the chapter, an example of a pure electrochemical tool, which permits to probe the nanoelectrocatalyst surface, is discussed. Although the progress in nanotechnology increases rapidly, various tools have been developed in electrochemistry for understanding the reaction pathway, intermediates, and products formation.