Electrochemical window defined

Another point is that the reduction and oxidation potential limits (electrochemical window) are defined as the potentials at which the current density reaches a predefined value that is arbitrarily chosen [40, 48], Ue et al. also mention that the same problem arises in the choice of the sweep rate [40]. For example Egashira and coworkers obtained a log I- U line shifted to a higher position at a faster potential scan in comparison to a slower scan because of non-Faradaic currents such as the larger charging currents of the double-layer, and the decomposition of impurities [41]. The last factor affecting the electrochemical window is the electrode itself, its composition and its morphological surface structure, which defines the electrocatalytic properties [40]. 

Decomposition potential (voltage) — The onset voltage for electrochemical decomposition of the electrolytic solution or the electrodes. The decomposition can take place due to either oxidation or reduction, or both. The decomposition potentials define the electrochemical window of the system. Its value depends on the salt, solvent, electrode material, temperature, and the existence of materials that can catalyze decomposition reactions, such as Lewis acids. Exact decomposition voltages are hard to reproduce as the onset current of the process is very sensitive to the experimental conditions (e.g., scan rate, temperature, type of electrode, etc.). Decomposi-... 

Electrochemical window — In electrochemical experiments the range of potentials that is accessible without appreciable current flow, i.e., the potential range in which the electrode may be considered perfectly polarizable . Electrochemical windows depend on the - electrode material, the - solvent, and the - electrolyte. There is no strict definition for the current density defining the potential limits of the electrochemical window. That depends on the experiment, i.e., the signals to be measured. For highly sensitive measurements of very low current densities, the acceptable current densities at the potential limits are much smaller than in cases where high current density signals are measured. The electrochemical window also depends very much on impurities, e.g., traces of water in nonaqueous solvents, or traces of transition metal ions in aqueous electrolyte solutions. The... 

A possible solution to these problems could be to replace the aqueous deposition media by room temperature ionic liquids (RTILs). These are defined as liquids consisting of molecular cations and anions that have a melting point below 100 °C. Due to the size of the molecular ions and the fact that the charge is delocalized through the molecule, these liquids have large electrochemical windows. Another potential benefit is that RTILs have high degradation temperatures and low vapor... 

The unique property profile of ionic liquids (ILs), which are commonly defined as organic salts that are liquid at temperatures below 100 °C or even at room temperature, renders them attractive candidates for manifold applications. Due to their negligible vapor pressure, excellent solvating properties, low flammability, frequently high thermal stability, ionic conductivity, and usually broad electrochemical window, ILs are widely applied as solvents, in catalysis, and as electrolytes in electrochemical devices. " ... 

Direct comparison of the electrochemical window of different ILs is difficult for several reasons. Firstly, the reference electrode is different during the measurement of the electrochemical window since some reference electrodes such as Ft and Ag are only quasi reference electrodes and the standard redox potential is difficult to define. Secondly, the working electrodes are usually not the same and the decomposition potentials at different electrode surfaces are not the same. Thirdly, even when the same working and reference electrodes are used, the content of impurities in the IL is uncertain. Electroactive impurities such as halide ions or water significantly reduce the electrochemical stability of ILs. 

Aliphatic ketones, in general, do not exhibit well defined reduction waves or peaks within the potential window of aprotic solvents. Their reduction is strongly affected by protons, due to the protonation steps involved, and most electrochemical measure-... 

The potential window over which the electrolyte is electrochemically stable may be estimated using a polarizable (blocking) electrode, such as platinum. The current is monitored as a function of the electrode potential, and the zero-current region (or nearly zero-current) defines the domain of electrochemical stability of the electrolyte. Of course, this potential range will depend mainly on the nature and the surface of the electrode (roughness). 

An electrochemical stability window is defined as the potential range in which an electrode can be polarized in a solution without the passage of substantial Faradaic currents. This definition is only a practical one, as it is impossible to define a precise value for the term substantial. ... 

The samples with porous layers were fabricated by electrochemical anodic etching of p-type, 12 Ohmcm and n-type 0.01 Ohmcm monocrystalline silicon wafers in 48 % water solution of HF at the current density of 50 mA/cm2. The anodized area of 1 cm in diameter was defined by the window in a Si3N4 thin film mask deposited onto the wafers. The anodization time was chosen in the range of 15-90 min in order to get porous layers of a thickness from 30 to 180 pm. The integral porosity was estimated by gravimetry to be of about 60 %. 

In this section we briefly discuss the surface expansion of the group IB metals, Cu, Ag and Au, focusing on the close-packed (111) surfaces as they have been studied in the most detail (in fact there have been no published SXS studies of the Cu(lOO) and Cu(llO) surfaces in the electrochemical environment). In terms of surface expansion effects, the IB metals are more difficult to study than Pt as no Hupd is formed, and so it is difficult to correlate stmctural changes with weU-defined adsorption processes. Furthermore, the Au(hkl) surfaces reconstruct at negative potential, which limits the potential window where the surfaces are in the unreconstructed state. Despite these difficulties, relaxation at the Au(lll) surface was recently studied by a combination of SXS and surface stress measurements. For potentials on the positive side of the potential of zero charge (pzc), where the surface is unreconstructed, increasing positive surface charge... 

Some mixed conductors, i.e. electronic and ionic, into which ions can be rapidly and reversibly inserted can undergo a colour change. This is, for example, the case of the hydrogen bronzes , mentioned earlier in this book. The colour change can be either from transparent to coloured or from one colour to another. This phenomenon, which can be produced electrochemically, is called electrochromism. It is broadly defined as the production of an absorption band in a display material caused by an applied electric field or current. Such a property is currently under intensive study because of its potential use for passive information display glare-free rearview mirrors for automotives " , solar control windows or smart windows " , thermal sensors and projection systems if matrixable. 

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