Anodic formation mechanisms

The standard potential for the anodic reaction is 1.19 V, close to that of 1.228 V for water oxidation. In order to minimize the oxygen production from water oxidation, the cell is operated at a high potential that requires either platinum-coated or lead dioxide anodes. Various mechanisms have been proposed for the formation of perchlorates at the anode, including the discharge of chlorate ion to chlorate radical (87—89), the formation of active oxygen and subsequent formation of perchlorate (90), and the mass-transfer-controUed reaction of chlorate with adsorbed oxygen at the anode (91—93). Sodium dichromate is added to the electrolyte ia platinum anode cells to inhibit the reduction of perchlorates at the cathode. Sodium fluoride is used in the lead dioxide anode cells to improve current efficiency. 

Yeh LSR, Hudson PG, Damjanovic A (1982) Anodic formation of thin CdS films. I. Kinetics and mechanisms under galvanostatic and potentiodynamic conditions. J Appl Electrochem 12 153-162... 

Fig. 5.4 Voltage-time curve for a p-type silicon electrode anodized galvanostatically at 0.1 mA cm"2 in 10% acetic acid. Silicon electrodes were removed from the electrolyte after various anodization times (filled circles) and the thickness of the anodic oxide was measured by ellipsometry (open circles). The curvature of the sample was monitored in situ and is plotted as the value of stress times oxide thickness (filled triangles). The bar graph below the V(t) curve shows a proposed formation mechanism. Galvanostatically a...

In contrast to p-type electrodes, an n-type electrode is under reverse conditions in the anodic regime. This has several consequences for pore formation. Significant currents in a reverse biased Schottky diode are expected under breakdown conditions or if injected or photogenerated minority carriers can be collected. Breakdown at the pore tip due to tunneling generates mainly mesopores, while avalanche breakdown forms larger etch pits. Both cases are discussed in Chapter 8. Macropore formation by collection of minority carriers is understood in detail and a quantitative description is possible [Le9], which is in contrast to the pore formation mechanisms discussed so far. 

Porous Silicon, including its morphology and formation mechanisms, as well as anodic reaction kinetics... 

Applications of this electrode material include (i) the anodic formation of hydroxyl radicals, (ii) the anodic formation of ozone and peroxo species, (iii) waste degradation in aqueous solution (hazardous and a range of organic wastes have been broken down without toxic intermediates), (iv) as a mechanically robust electrode for solid state electrochemistry or in the presence of power ultrasound, (v) as a dimensionally stable electrode, (vi) as a IR and Vis transparent electrode material, and (vii) as an inert substrate for electro-catalysts. 

The electrochemistry of amino acids has been studied in strong acid solutions. In general, the compounds are decomposed to carboxylic acids, aldehydes, ammonia, and carbon dioxide. The results are reviewed by Weinberg [35]. The anodic oxidation mechanism has been studied in pH 10 buffer solution. Decarboxylation accompanied by C-N bond cleavage is the main reaction process [182]. The synthetically interesting Hofer-Moest decarboxylations of A/ -protected amino acids and a-amino malonic half esters under the formation of A/ -acyliminium ions is treated in the following section. 

These reaction features must be involved in the formation of PS on silicon in HF. However, because of the great complexity of the anodic reactions on sihcon in HF solutions on the one hand and of the extremely rich PS morphology on the other hand, the results from the two research domains, fundamental electrochemistry and PS formation mechanisms, have not been well integrated. 

T. Unagami, Formation mechanism of porous silicon layer by anodization in HF solution, J. Electrochem. Soc. 127, 476, 1980. 

V.M. Dubin, Formation mechanism of porous silicon layers obtained by anodization of monocrystalline n-type silicon in HF solutions, Surf. Sci., 274, 82-92 (1992). 

Tab. 2 Data for net reactions (spaces) and partial reactions (lines) described in the text, ne = number of involved electrons mH+ = number of involved protons. The total cathodic reduction is described for an island mechanism differing from anodic formation. Partial current densities give the local current dependent on the coordinate x. Transference numbers t have to be considered within the oxide, for example, in case of oxide formation i = /i5 = /i6 + (17 = (f+ + t )i = i i4. In case of partial oxidation/reduction of an oxide by a combined ITR/ETR the local current densities of and have to be added i(x) = / is = ii7(x) + inM = ( e(x) + t-(x))/ = /14. Cathodic intercalation of protons takes place by a process analogue to anodic partial oxidation, differing only by the sign of / and the migration of protons instead of -ions...

The 3D formation mechanism of interphase for graphic anode material is not suitable for the Si or the Sn aUoy anode material, since they do not possess a structure for intercalation/de-intercalation therefore, a simple 2D surface reaction is... 

The SEI between the electrodes and electrolyte plays important roles in the Li-ion battery, whose key performances, such as cyclability, temperature dependence, power density, and safety, are close to the nature of the SEI properties. Chemistry, structure, thermodynamics, and formation mechanisms of the interphase between anode and electrolyte are well established via multi-analytical techniques and combination with computational method during the past few decades. 

Based on the understanding of the formation mechanisms of SEI on graphite anode, it is possible to improve performance of lithium-ion battery by tailoring the structure and chemistry of an SEI. The application of additives is the most successful tailoring SEI. Numerous additives which assist in SEI formation process have been extensively explored, and a few of them have been widely utilized in commercial lithium-ion battery. The successful utilization of SEI formation additives boosts the applications of lithium-ion battery technology in our daily life and, the ultimate goal in future, electric vehicles. 

Trucks G, Raghavachaii K, Higashi G et al (1990) Mechanism of HF etching of silicon surfaces - a theoretical understanding of hydrogen passivation. Phys Rev Lett 65 504-507 Unagami T (1980a) Formation mechanism of porous silicon layer by anodization in HF solution. J Electrochem Soc 127 476-483... 

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