Electrochemical stability window

Show possibly broad electrochemical stability window at an interface of carbon electrode ... 

It can be seen that an energy of ca. 150 kJ/kg, comparable to that accumulated in Pb02-Pb or Ni-Cd batteries, can be obtained at voltages of 4V. Somewhat lower energy (100 kJ/kg) is accumulated at a voltage of 3V. Consequently, the searched system carbon/electrolyte should be characterised by (i) specific capacity. > 160 F per gram of activated carbon and (ii) electrochemical stability window at the level of ca. >3V. 

It is essential from the point of view of high power-density to ensure the electrochemical stability of the system at possibly high voltages. Broad electrochemical stability windows are typical if ionic liquids, however, the... 

Table 5. Electrochemical stability window of ionic liquids (IL) at the glassy carbon (potentials [V/ expressed versus Ag/Agf 0.01M in DMSO reference) [26 /.

Table 5 shows cathodic and anodic limits of electrochemical stability windows of a number of ionic liquids. The cathodic limit of the stability window of the ILs based on the EMIm+ and BMIm+ cations, investigated at the glassy carbon electrode, is -2.1 V against the Ag/Ag+ (0.01M in DMSO) reference. The BMPy+ cation is reduced at the glassy carbon at considerably more positive potential, at ca. -1.0 V. 

We have also demonstrated that well-behaved quantized charging of gold MPCs is possible in air- and water-stable room-temperature ionic liquids, such as 1-hexyl-3-methylimidazolium tris(penta-fluoroethyl)-trifluorophosphate (HMImEEP), Fig. 30c, d [334, 335]. As ionic liquids have very attractive features, including nearzero vapor pressure, considerable thermal stability, and an electrochemical stability window that often exceeds 4 V, this demonstration is particularly significant from a technological point of view. 

The anodic limit for the electrochemical stability of these carbonate mixtures has been determined to be around 5.5 V in numerous studies.Thus, new electrolyte formulations are needed for any applications requiring >5.0 V potentials. For most of the state-of-the-art cathode materials based on the oxides of Ni, Mn, and Co, however, these carbonate mixtures can provide a sufficiently wide electrochemical stability window such that the reversible lithium ion chemistry with an upper potential limit of 4.30 V is practical. 

Unfortunately, these aza-ethers showed limited solubility in the polar solvents that are typically preferred in nonaqueous electrolytes, and the electrochemical stability window of the LiCl-based electrolytes is not sufficient at the 4.0 V operation range required by the current state-of-the-art cathode materials. They were also found to be unstable with LiPFe. Hence, the significance of these aza-ether compounds in practical applications is rather limited, although their synthesis successfully proved that the concept of the anion receptor is achievable by means of substituting an appropriate core atom with strong electron-withdrawing moieties. 

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. ... 

In general, the electrochemical stability window for a solution-electrode system is limited by the electrochemical stability of the salt or the solvent or by the dissolution or degradation of the electrode. 

The electrochemical stability window of electrolyte-solution systems, as... 

In some cases, the electrode material is the limiting factor of the electrochemical stability window. In a metal salt solution, underpotential deposition (UPD) may occur. In some examples, such as gold or platinum electrodes in the presence of lithium ions, the UPD appears at potentials that are substantially higher than the bulk metal deposition [4-6], In addition, some metals may possess catalytic activity for specific reduction or oxidation processes [7-12], Many nonactive metals (distinguished from the noble metals), including Ni, Cu, and Ag, which are commonly used as electrode materials, may dissolve at certain potentials that are much lower than the oxidation potentials of the solvent or the salt. In addition, some electrode materials may be catalytic to certain oxidation or reduction processes of the solution components, and thus we can see differences in the stability limits of nonaqueous systems depending on the type of electrode used. 

It is well known that catalyst support plays an important role in the performance of the catalyst and the catalyst layer. The use of high surface area carbon materials, such as activated carbon, carbon nanofibres, and carbon nanotubes, as new electrode materials has received significant attention from fuel cell researchers. In particular, single-walled carbon nanotubes (SWCNTs) have unique electrical and electronic properties, wide electrochemical stability windows, and high surface areas. Using SWCNTs as support materials is expected to improve catalyst layer conductivity and charge transfer at the electrode surface for fuel cell oxidation and reduction reactions. Furthermore, these carbon nanotubes (CNTs) could also enhance electrocatalytic properties and reduce the necessary amount of precious metal catalysts, such as platinum. 

Table 5. Electrochemical stability window of ionic liquids (IL) at the glassy carbon...

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