Electrochemical processes electrode performance determinants

Sol-gel films can be used to immobilize biomolecules. For example, Dong etal. developed thin sol-gel films on electrodes in which enzymes horseradish peroxidase (HRP) and glucose oxidase (GOD) were used to determine enzyme substrates [12]. A vapor-deposition sol-gel process [13] featuring a thin film of aqueous HRP solution into which titanium isopropoxide vapor was diffused to form a Ti02 sol-gel film incorporating HRP prevented denaturation of the enzyme. Surfactants were used in preparation of sol-gel films incorporating redox proteins on electrodes to improve porosity and electrochemical and catalytic performance [14]. 

There are some major differences between electrochemical engineering and classical electrochemistry. In conventional electrochemistry the mechanism of the electrode process and its kinetics are often the factors of major concern whereas in electrochemical engineering the actual mechanistic details of the process are usually less important than its specificity or process efficiency. The rate of the process defined either as current efficiency or as a general measure of reactor efficiency, the space-time yield are the main performance criteria. This latter factor determines whether a process is economically or commercially viable since it can be used to compare performance of different electrode designs as well as comparing an electrochemical process with the space-time yields for alternate non-electrochemical technologies. 

Nevertheless, the overall performance of electrochemical processes is established by the complex interaction of different parameters that may be optimized to obtain an effective and ecmiom-ical mineralization of pollutants. The principal parameters that determine an electrolysis performance are (i) electrode potential and current density, (ii) current distribution, (iii) mass transport regime, (iv) cell design, (v) electrolysis medium, and (vi) electrode materials. Even if we still remain far from meeting all the requirements needed for an ideal anode, significant steps have been made toward the production of better electrode materials [3]. 

With a strong emphasis on the development of electrochemical membrane processes, e.g., water electrolysis and fuel cells, electrode performance must be well characterized electrochemically. Use of a hydrogen pump concept can provide insight into anode and/or cathode electrode electrochemical characteristics. Furthermore, the method can also be utilized to determine the back diffusion of hydrogen through the membrane [5, 25]. 

Another electrochemical technique used for the determination of antioxidant capacity is amperometry (Milardovic et al., 2006 Intarakamhang and Schulte, 2012). The current utilized in this technique is selected after a voltammetric analysis. Milardovic et al. (2006) determined the antioxidant activity of eight samples of different types of tea, wine, and other beverages. The amperometric method is based on the electrochemical reduction of DPPH at a glassy-carbon electrode. Initially, the voltammetric study of different standard antioxidants (caffeic acid and Trolox) was performed to obtain their respective reduction potentials. The potential selected for the analysis was 140 mV, to avoid possible interference from electrochemical processes of caffeic acid and Trolox. The concentration of DPPH significantly decreased after the antioxidant addition. The results were expressed as Trolox equivalents. 

Recently the proposed Oz evolution mechanism was supported by the results of a DEMS (Differential Electrochemical Mass Spectrometry) study performed by Wohlfahrt-Mehrens and Heitbaum [71] on Ru electrodes. Using this mass spectroscopic technique and lsO labeling for the determination of reaction products during 02 evolution, it could be verified that the oxygen of the oxide formed on Ru takes part in the 02 evolution process. The same observation was made for Ru02 electrodes when using labeled H2lsO. 

In general, the electrochemical performance of carbon materials is basically determined by the electronic properties, and given its interfacial character, by the surface structure and surface chemistry (i.e. surface terminal functional groups or adsorption processes) [1,2]. Such features will affect the electrode kinetics, potential limits, background currents and the interaction with molecules in solution [2]. From the point of view of electroanalysis, the remarkable benefits of CNT-modified electrodes have been widely praised, including low detection limits, increased sensitivity, decreased overpotentials and resistance to surface fouling [5, 9, 11, 17]. 

The electrochemical behavior of Np ions in basic aqueous solutions has been studied by several different groups. In a recent study, cyclic voltammetry experiments were performed in alkali ([OH ] = 0.9 — 6.5 M) and mixed hydroxo-carbonate solutions to determine the redox potentials of Np(V, VI, VII) complexes [97]. As shown in Fig. 2, in 3.1 M LiOH at a Pt electrode Np(VI) displays electrode processes associated with the Np(VI)/Np(V) and Np(VII)/Np(VI) couples, in addition to a single cathodic peak corresponding to the reduction of Np(V) to Np(IV). This latter process at Ep —400 mV (versus Hg/HgO/1 M NaOH) is chemically irreversible in this medium. Analysis of the voltammetric data revealed an electrochemically reversibleNp(VI)/Np(V)... 

Electrochemical deposition of lithium usually forms a fresh Li surface which is exposed to the solution phase. The newly formed surface reacts immediately with the solution species and thus becomes covered by surface films composed of reduction products of solution species. In any event, the surface films that cover these electrodes have a multilayer structure [49], resulting from a delicate balance among several types of possible reduction processes of solution species, dissolution-deposition cycles of surface species, and secondary reactions between surface species and solution components, as explained above. Consequently, the microscopic surface film structure may be mosaiclike, containing different regions of surface species. The structure and composition of these surface films determine the morphology of Li dissolution-deposition processes and, thus, the performance of Li electrodes as battery anodes. Due to the mosaic structure of the surface... 

If a reaction path is predominant and one of its elementary step is rate determining, the Tafel slope will be characteristic of this step. Thus, electrochemical measurements performed on rotating disk electrode can provide a first solution to elucidate the mechanistic behavior of oxygen reduction reaction on a catalyst. Par-sons has demonstrated that, in a several step electrode process,... 

---