TiC electrode

Fig. 35. Cls core level of a TiC electrode as prepared and after electrochemical nolarization at 1.25 Vsce in 0.5 mol L 1 H2SQ4. After [122],...

Figure 6.32 Cyclic voltammogram of a nanocrystalline TiC electrode modified with a electroactive aromatic amine, measured at a scan rate of 2 mV s 1. The electrolyte is acetonitrile containing 0.5 M lithium bis(trifluoromethylsulfonyl)imide. Reprinted with permission from P. Bonhote, E. Gogniat, S. Tingry, C. Barbe, N. Vlachopoulos, F. Lenzmann, P. Comte and M. Gratzel, /. Phys. Chem., B, 102,1498 (1998). Copyright (1998) American Chemical Society...

TiC can be used as electrode of semiconductive SiC because TiC is metallic conductor with low electrical resistivity. In this case also, the gradient bonding is important to prevent cracking. SiC-TiC gradient material reveals the ohmic behavior and has low resistivity. Such a gradiently-bonded TiC electrode may be available for high-temperature application of semiconductive SiC device because TiC is thermally stable as well as SiC. 

It will also be shown that the absolute electrode potential is not a property of the electrode but is a property of the electrolyte, aqueous or solid, and of the gaseous composition. It expresses the energy of solvation of an electron at the Fermi level of the electrolyte. As such it is a very important property of the electrolyte or mixed conductor. Since several solid electrolytes or mixed conductors based on ZrC>2, CeC>2 or TiC>2 are used as conventional catalyst supports in commercial dispersed catalysts, it follows that the concept of absolute potential is a very important one not only for further enhancing and quantifying our understanding of electrochemical promotion (NEMCA) but also for understanding the effect of metal-support interaction on commercial supported catalysts. 

In coulometry, one must define exactly the amount of charge that was consumed at the electrode up to the moment when the endpoint signal appeared. In galvanosta-tic experiments (at constant current), the charge is defined as the product of current and the exactly measured time. However, in experiments with currents changing continuously in time, it is more convenient to use special coulometers, which are counters for the quantity of charge passed. Electrochemical coulometers are based on the laws of Faraday with them the volume of gas or mercury liberated, which is proportional to charge, is measured. Electromechanical coulometers are also available. 

This is comparable to or slightly higher than the values reported for single crystal (11) and polycrystalline Ti02 (12), and much higher than those for the TiC>2 film electrode prepared by other methods such as chemical vapor deposition (13) and oxidation (14) and anodization (15) of Ti metal. The high efficiency of the dip-coated Ti(>2 film may be attributed to the porous nature of the film as described below. 

Figure 5. Length (squared) of the electrode impregnation with acetonitrile vs. time for various carbon materials produced by Skeleton Technologies 1 - C/SiC 2 -C/TiC-1 3 - C/TiC-2 4 - C/Mo2C.

Technical electrodes usually consist of a mixture of Ru02 and TiC>2 plus a few additives. They are called dimensionally stable anodes because they do not corrode during the process, which was a problem with older materials. These two substances have the same rutile structure with similar lattice constants, but RuC>2 shows metallic conductivity, while pure TiCU is an insulator. The reaction mechanism on these electrodes has not yet been established the experimental results are not compatible with either of the two mechanisms discussed above [4]. 

Thus, the polarisation data, cyclic voltammetric results and the a.c. impedance measurements all suggest that, when an Ru02/TiC>2 anode exhibits a high overpotential, this is a direct consequence of the surface depletion of Ru. This is also consistent with the estimated Re values of approximately 20 Q for the failed electrodes, in contrast to the known, much higher specific resistivity of Ti02 of... 

Q.cm. This suggests the absence of any build-up of a TiC>2 layer between the Ti substrate and the Ru/Ti oxide coating with the onset of anode deactivation. Furthermore, the similarity of the frequency response of a failed electrode to that of freshly prepared low at.% (c. 5-10 at.%) Ru electrodes at low frequencies, supports the conclusion of the absence of the build-up of a TiC>2 layer with failed electrodes. 

Direct measurement of the change in interfacial potential difference at the oxide-electrolyte interface with change in pH of solution can be measured with semiconductor or semiconductor-oxide electrodes. These measurements have shown d V g/d log a + approaching 59 mV for TiC (36, 37). These values are inconsistent with the highly sub-Nernstian values predicted from the models with small values of K. (Similar studies 138.391 have been performed with other oxides of geochemical interest. Oxides of aluminum have yielded a value of d t)>q/A log aH+ greater than 50 mV, while some oxides of silicon have yielded lower values.)... 

H. Hidaka, Y. Asai, J. Zhao, K. Nohara, E. Pelizzetti, N. Serpone, Photoelectrochemical decomposition of surfactants on a TiC /TCO particulate film electrode assembly, J. Phys. Chem. 99 (1995) 8244-8248. 

S. Takabayashi, R. Nakamura, Y. Nakato, A nano-modified Si/TiC>2 composite electrode for efficient solar water splitting, J. Photochem. Photobiol. A Chem. 166 (2004) 107-113. 

Electroreduction of aliphatic esters with an Mg electrode, under apro-tic conditions, leads to dimerization... 

Metals, including Ag, Cu, Zn, Cd, and Hg, can be used as indicator electrodes for their aqueous ions. Most metals, however, are unsuitable for this purpose, because the equilibrium M"+ + tic M is not readily established at the metal surface. 

By exciting the red-orange cyclooctatetraene dianion 1 in the presence of cyclooctatetraene in our photoelectrochemical cell (n-TiC>2/NH3/Pt), we were able to observe photocurrents without detectable decomposition of the anionic absorber (2). Presumably, a rapid dismutation of the photooxidized product inhibited electron recombination, producing a stable hydrocarbon whose cathodic reduction at the counter electrode regenerates the original mixture essentially quantitatively (eqn 3). 

Triarylamine is a purely organic molecule which is interesting as a chro-mophore in e.g. display technology. The molecule can be switched between a reduced colourless, and an oxidized blue state. The sensitization to nanos-tructured TiC>2 electrodes provides the substantial surface area required for a strong coloration. It is, however, believed that the electron transfer involved in the redox reaction takes place mainly within the sensitizer layer, and does not involve the substrate. Instead, there is an eventual electrical contact between the back-contact and the sensitizer layer [98]. For a quantum chemical modelling of the system, the inclusion of the substrate is in this case not likely to be essential. For a molecule of this size, it is possible to apply standard quantum... 

Photoswitchable enzymes could have an important role in controlling biochemical transformations in bioreactors. Various biotechnological processes generate an inhibitor, or alter the environmental conditions (pH, for example) of the reaction medium. Photochemical activation of enzymes that adjust environmental conditions or deplete the inhibitor to a low concentration may maintain the bioreactor at optimal performance. More specifically, integration of the photoswitchable biocataly-tic matrix with a sensory electrode might yield a feedback mechanism in which the sensor element triggers the light-induced activation/deactivation of the photosensitive biocatalyst. 

Gold nanoparticles have been used to immobilize micro-peroxidase 11,46 tyrosinase,47 and hemoglobin48 to construct amperometric sensors, while silver nanoparticles have been used to enhance electron transfer of cytochrome c and myoglobin onto pyrolitic graphite electrodes.49 The use of semiconductor and oxide nanoparticles has also been reported, such as horseradish peroxidase (HRP) on TiC>2 nanoparticles,50 as well as Fe304 and MnC>4 nanoparticles to immobilize and facilitate direct electron transfer.51... 

---