Electrode windows,

Ionic liquid system Cation(sj Anion(s) Working electrode" Window (V) Ref. 

Figure 5.46 shows clearly how the application of potential changes the brightness and thus the workfunction O, of the grounded Pt catalyst-electrode (windows 2 and 3) and of the YSZ surface, (window 1), in accordance to the above discussed alignment (pinning) of the two Fermi levels. 

The necessary thin-layer configuration was obtained by pressing the electrode against the optical window. Different cell constructions have been used. Fig. 1.6 shows a cell similar to one used by Seki et al. [32], The micrometer screw attached to the working electrode allows a reproducible adjustment of electrode-window distances. 

Ionic liquid system Cation(s) Anion(s) Working electrode Window Ref. (V) ... 

Miniaturized systems for performing chemical/biochemical reactions and analysis require cavities, channels, pumps, valves, storage containers, couplers, electrodes, windows and bridges [53]. The typical dimensions of these components are in the range of a few micrometers to several millimeters in length or width, and between 100 nm and 100 pm in depth and height. An extensive set of techniques for fabricating these microstructures is discussed in Sect. 3. 

Figure 9.23 Laser Stark spectroscopy with the sample inside the cavity. G, grating S, Stark electrodes W, window M, mirror D, detector...

Figure 3.6-1 shows the electrochemical window of a 76-24 mol % [BMMIM][(GF3S02)2N]/Li[(GF3S02)2N] ionic liquid at both GG and Pt working electrodes [15]. For the purposes of assessing the electrochemical window, the current threshold for both the anodic and cathodic limits was set at an absolute value of 100 pA cm . ... 

Figure 3.6-1 The electrochemical window of 76-24 mol % [BMMIM][(CF3S02)2N]/Li [(Cp3S02)2N] binary melt at a) a platinum working electrode (solid line), and b) a glassy carbon working electrode (dashed line). Electrochemical window set at a threshold of 0.1 mA cm. The reference electrode was a silver wire immersed in 0.01 m AgBp4 in [EMIM][BF4] in a compartment separated by a Vicor frit, and the counter-electrode was a graphite rod.

As shown in Figure 3.6-1, GC and Pt exhibit anodic and cathodic potential limits that differ by several tenths of volts. However, somewhat fortuitously, the electrochemical potential windows for both electrodes in this ionic liquid come out to be 4.7 V. What is also apparent from Figure 3.6-1 is that the GC electrode exhibits no significant background currents until the anodic and cathodic potential limits are reached, while the Pt working electrode shows several significant electrochemical processes prior to the potential limits. This observed difference is most probably due to trace amounts of water in the ionic liquid, which is electrochemically active on Pt but not on GC (vide supra). 

Ideally, one would prefer to compare anodic and cathodic potential limits instead of the overall ionic liquid electrochemical window, because difference sets of anodic and cathodic limits can give rise to the same value of electrochemical window (see Figure 3.6-1). However, the lack of a standard reference electrode system within and between ionic liquid systems precludes this possibility. Gonsequently, significant care must be taken when evaluating the impact of changes in the cation or anion on the overall ionic liquid electrochemical window. 

Germanium In situ STM studies on Ge electrodeposition on gold from an ionic liquid have quite recently been started at our institute [59, 60]. In these studies we used dry [BMIM][PF<3] as a solvent and dissolved Gel4 at estimated concentrations of 0.1-1 mmol 1 the substrate being Au(lll). This ionic liquid has, in its dry state, an electrochemical window of a little more than 4 V on gold, and the bulk deposition of Ge started several hundreds of mV positive from the solvent decomposition. Furthermore, distinct underpotential phenomena were observed. Some insight into the nanoscale processes at the electrode surface is given in Section 6.2.2.3. 

It was shown some time ago that one can also use a similar thermodynamic approach to explain and/or predict the composition dependence of the potential of electrodes in ternary systems [22-25], This followed from the development of the analysis methodology for the determination of the stability windows of electrolyte phases in ternary systems [26]. In these cases, one uses isothermal sections of ternary phase diagrams, the so-called Gibbs triangles, upon which to plot compositions. In ternary systems, the Gibbs Phase Rule tells us... 

Table 7 lists the electrochemical windows or the anodic stability limits of several nonaqueous electrolytes, or their anodic stabilty, the reference electrodes Rref used, the working electrode material Ew, the experimental conditions, and the references. It shows the following features ... 

FIGURE 4-5 Accessible potential window of platinum, mercury, and carbon electrodes in various supporting electrolytes. 

The limited anodic potential range of mercury electrodes has precluded their utility for monitoring oxidizable compounds. Accordingly, solid electrodes with extended anodic potential windows have attracted considerable analytical interest. Of the many different solid materials that can be used as working electrodes, the most often used are carbon, platinum, and gold. Silver, nickel, and copper can also be used for specific applications. A monograph by Adams (17) is highly recommended for a detailed description of solid-electrode electrochemistry. 

S.2.2 Carbon Electrodes Solid electrodes based on carbon are currently in widespread use in electroanalysis, primarily because of their broad potential window, low background current, rich surface chemistry, low cost, chemical inertness, and suitability for various sensing and detection applications. In contrast, electron-transfer rates observed at carbon surfaces are often slower than those observed at metal electrodes. The electron-transfer reactivity is strongly affected by the origin... 

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