Oxidative of water

The rates of hydrolysis for the peroxophosphoric acids are more rapid than the corresponding reactions of the peroxosulfiiric acids. The peroxodiphosphate ion is extremely resistant to decomposition by oxidation of water ... 

When a potential is appHed across the ceU, the sodum and other cations are transported across the membrane to the catholyte compartment. Sodium hydroxide is formed in the catholyte compartment, because of the rise in pH caused by the reduction of water. Any polyvalent cations are precipitated and removed. The purified NaOH may be combined with the sodium bicarbonate from the sodium dichromate process to produce soda ash for the roasting operation. In the anolyte compartment, the pH falls because of the oxidation of water. The increase in acidity results in the formation of chromic acid. When an appropriate concentration of the acid is obtained, the Hquid from the anolyte is sent to the crystallizer, the crystals are removed, and the mother Hquor is recycled to the anolyte compartment of the ceU. The electrolysis is not allowed to completely convert sodium dichromate to chromic acid (76). Patents have been granted for more electrolytic membrane processes for chromic acid and dichromates manufacture (86). 

If the potential of a metal surface is moved below line a, the hydrogen reaction line, cathodic hydrogen evolution is favored on the surface. Similarly a potential below line b, the oxygen reaction line, favors the cathodic oxygen reduction reaction. A potential above the oxygen reaction line favors oxygen evolution by the anodic oxidation of water. In between these two lines is the region where water is thermodynamically stable. 

What is the for the light-generated primary oxidant of photosystem II if the light-induced oxidation of water (which leads to Og evolution) proceeds with a AG° of —25 kj/mol ... 

The overall process is metal transfer from anode to cathode via the solution. The form of anode corrosion is important, and materials may be added both to the anode metal and to the electrolyte, to influence it. There are important instances where an insoluble anode is used, and the anode reaction becomes the oxidation of water or hydroxyl ions ... 

There is often an overpotential of about 0 - 5 V before the rate of oxidation of water becomes rapid. 

Chromium plating from hexavalent baths is carried out with insoluble lead-lead peroxide anodes, since chromium anodes would be insoluble (passive). There are three main anode reactions oxidation of water, reoxidation of Cr ions (or more probably complex polychromate compounds) produced at the cathode and gradual thickening of the PbOj film. The anode current density must balance the reduction and reoxidation of trivalent chromium so that the concentration reaches a steady state. From time to time the PbOj film is removed as it increases electrical resistance. 

Systems for the photo-oxidation of water have used Ru(bipy)2+ with [Co(NH3)5C1]2+ as the electron donor and Ru02 as catalyst. 

To reverse this half-reaction and bring about the oxidation of water, we need an applied potential difference of at least 0.82 V. Suppose the added salt is sodium chloride. When Cl ions are present at 1 mol-L 1 in water, is it possible that they, and not the water, will be oxidized From Table 12.1, the standard potential for the reduction of chlorine is Cl.36 V ... 

For the exercises in this section, base your answers on the potentials listed in Table 12.1 or Appendix 2B, with the exception of the reduction and oxidation of water at pH = 7 ... 

Self-Test 15.3B Write the half-reactions and the overall reaction for the oxidation of water by F2. Determine the standard potential and AG° for the reaction. 

In general, we expect that an external potential wiii drive the pair of reactions whose spontaneous reaction has the ieast positive ceii potentiai. In this case, combining the reduction of water to hydrogen and hydroxide with the oxidation of water to H3 O and oxygen gas gives the ieast positive E ° ... 

On account of the reported photocatalytic activity of titania nanosheets in the oxidation of water [290], Yamada et al. [291] attempted to fabricate photoelectrodes responsive to visible light by coating Cd8 electrodes with titania nanosheets. It was considered that since the thickness of a nanosheet is as small as two atomic layers of... 

Ezzaouia H, Heindl R, Parsons R, Tributsch H (1983) Visible light photo-oxidation of water with single-crystal RuS2 electrodes. J Electroanal Chem 145 279-292 Kiihne HM, Tributsch H (1983) Oxygen evolution from water mediated by infrared light on iron doped RuS2 electrodes. J Electrochem Soc 130 1448-1450... 

The chemistry of Co(III) in dilute aqueous acidic solution is complicated by (/) oxidation of the solvent, it) complex formation with counter-ions, Hi) hydrolysis and iv) apparently extensive dimerisation. These phenomena are discussed further in the section on oxidation of water. 

The rate expression for the oxidation of water by silver(II) perchlorate, [Ag(II)] [C104-] ... 

A few data exist on the oxidation of water by Ag(ril) ethylenedibiguanide nitrate . The decomposition is only approximately first-order in oxidant in both water and dilute nitric acid. The activation energies are very different for the two media, (H2O, 27.8 kcal.mole HNO3, 18.65 kcal.mole ). A is about 10 for water and 10 for nitric acid solutions. These data are inadequate for mechanistic interpretation. 

The formation of hydrogen peroxide by anodic oxidation of water has so far not been realized. 

PEMFC)/direct methanol fuel cell (DMFC) cathode limit the available sites for reduction of molecular oxygen. Alternatively, at the anode of a PEMFC or DMFC, the oxidation of water is necessary to produce hydroxyl or oxygen species that participate in oxidation of strongly bound carbon monoxide species. Taylor and co-workers [Taylor et ah, 2007b] have recently reported on a systematic study that examined the potential dependence of water redox reactions over a series of different metal electrode surfaces. For comparison purposes, we will start with a brief discussion of electronic structure studies of water activity with consideration of UHV model systems. 

Two lines on the Pourbaix diagrams (Figure 5.2) deserve reference. These are the sloping dashed lines, and they represent the stability limits for water they are essentially the domain of thermodynamic stability of water superimposed on potential-pH diagrams. At the upper line, oxidation of water goes according to ... 

The photoreaction of oxidation of water was discovered in 1927 by Baur and Neuweiler (76) and investigated later by a number of workers. The analysis of experimental results performed by Korsunovsky (65-68) is based on the exciton mechanism of light absorption. The kinetics of the reaction has been investigated by Grossweiner (77). 

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