In situ scanning electrochemical probe microscopy for energy applications
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Introduction Increasing concern about the future availability of fossil fuels as the main energy source has spurred renewed interest in the search for alternative energy sources and technologies.1 Examples of such new technologies include (low temperature) fuel cells and new types of batteries and solar cells, which convert chemical or radiant energy into electrical energy for consumption. These technologies, and the associated challenges, are centered on electrochemistry, and electrochemical tools are needed to study these systems. The main challenge in studying many of these new energy systems lies in the complex electrode-electrolyte interface. In particular, the efficiency of such systems is determined by the interplay between the nature (material and structure) of the electrode, mass transport of reactants and products to and from the electrode, and the surface reactivity, all of which are strongly localized on the nanoscale. Traditionally, most electrochemical techniques have been limited to the investigation of the entire electrode-electrolyte interface, such that only average properties can be elucidated. A truly fundamental understanding of these systems can only be gained from localized studies, ultimately with the capability of probing at the nanoscale. The aim of this article is to give an overview of the application of in situ scanning electrochemical probe microscopy (SEPM) techniques used in energy-related studies. This is a broad and rapidly expanding area, and so the particular focus
is on the use of novel SEPM techniques for obtaining fundamental information at the micro- and nanoscale to investigate truly localized processes.
Scanning electrochemical microscopy Since its introduction in the late 1980s, scanning electrochemical microscopy (SECM)2,3 has developed into a powerful technique to probe electrochemical processes, primarily on the microscale for a wide variety of applications.4–7 In brief, SECM employs an ultramicroelectrode (UME), often called “tip” in analogy with other scanning probe techniques, positioned near the substrate of interest. An UME consists of a micro- or nanoscale electrode sheathed in an insulating material to minimize back diffusion, thus making the tip more sensitive to the process occurring at the substrate. A typical SECM setup is described in detail in Reference 2. The electrochemical (typically current) response of the tip is used to provide information on local properties such as topography and/or reactivity. Various modes of operation can be employed (Figure 1a–d).4,5 For the study of electrode surfaces, the UME is typically used to (1) electrochemically detect (collect) the product generated at the electrode (substrate generation/tip collection; SG/TC); (2) generate a reactant for reaction at the substrate (tip generation/substrate collection; TG/SC); or (3) generate a reactant at the tip that can be converted at the substrate and regenerated at the tip (feedback mode). The tip and substrate can also be set to compete for
Stanley C.S. Lai, University of Warwic
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