Generation/collection mode SECM operation

SECM amperometric methods are based on the measurement of electrode currents (tip and substrate, (p and ig, respectively) as a function of various parameters, including tip-substrate distance (d) and tip or substrate potentials (Ej or Eg). Irrespective of the system studied (e.g., an electrode, an inert surface, a catalyst, or a living organism), the probe tip is a necessary component to perform any SECM experiment. In all cases, the amperometric tip is a UME that can be positioned in close proximity to another surface. There are two amperometric operation modes feedback and generation/collection modes. The preparation and characterization of commonly used amperometric tips of different geometries as well as their operation modes will be described in this section. 

The development of SECM, which began in the late 1980s, is mainly credited to A. Bard and his coworkers who first described the technique, coined its name, and also developed the early modes of its operation, namely the feedback and the generation-collection modes, which will be described later. In the course of its nearly 30 years of existence, SECM has established itself as the tool of choice for studying spatially resolved local electrochemical reactivity of surfaces, including the quantitative study of the kinetics of both electrochemical and chemical reactions from microscopic to submicroscopic scales [2, 7]. Indeed, the ability of SECM to... 

Most popular inodes of operation of the SECM. (a) Feedback mode, (b) Generation-collection mode (herein the substrate is generating an electroactive species Ox, which is collected at the SECM probe (tip) by its reduction according to Equation 8.1. (Adapted from Kanoufi, F., Acta Chim., 311,36-48,2007.)... 

A number of SECM modes of operation are possible [28,48]. The tip can be used to detect a species generated at the substrate surface (substrate generation/tip collection mode or SG/TC mode), a method that is particularly useful in corrosion studies. Alternatively, the tip generation/substrate collection (TG/SC) mode is usefiil for kinetic measurements. Additional information may be obtained by... 

To study the kinetics of electron transfer, SECM can be operated in two modes a feedback mode (53, 69) and a substrate generation-tip collection mode (53). In the feedback mode, a mediator redox couple is required to probe the interface. The tip is poised to a potential well above Eredox- The steady-state current observed due to hemispherical diffusion of O toward the tip is expressed as (Figure 9.29a)... 

In addition to the amperometric feedback mode described above, other amperometric operation modes are also possible. For example, in the substrate generation/tip collection (SG/TC) mode, ip is used to monitor the flux of electroactive species from the substrate and vice versa for the tip generation/substrate collection (TG/SC) mode. These operation modes will be described in Section 12.3.1.3 and are useful in studies of homogeneous reactions that occur in the tip-substrate gap (see Section 12.4.2) and also in the evaluation of catalytic activities of different materials for useful reactions, e.g., oxygen reduction and hydrogen oxidation (see Section 12.4.3). In addition to the amperometric methods, other techniques, e.g., potentiometric method is also applicable for SECM and will be discussed in Section 12.3.2. We will also update the techniques suitable for the preparation of SECM amperometric tips in Section 12.3.1.1 and potentiometric probes in Section 12.3.2.2. 

There are several modes of operation of the SECM. In the tip generation/substrate collection (TG/SC) mode, the tip is used to generate a reactant that is detected at a substrate electrode. For example, the reaction O+ne occurs at the tip and the reverse reaction occurs at the substrate. This mode of operation is similar to that at the rotating ring-disk electrode. Similar behavior is observed for a pair of side-by-side microband electrodes and in thin-layer cells. In the SECM,... 

The quantitative scanning electrochemical microscopic (SECM) theory has been developed for various regimes of measurements and electrochemical mechanisms. Different operating modes of the SECM, for example, feedback and generation/collection (G/C) modes, steady-state and transient... 

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