Oxygen evolution from water

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 enhanced adsorption of anions and other substances that occurs at increasingly positive potentials causes a gradual displacement of water (or other solvent) molecules from the electrolyte layer next to the electrode. This leads to a markedly slower increase in the rate of oxygen evolution from water molecules and facilitates a further change of potential in the positive direction. As a result, conditions arise that are favorable for reactions involving the adsorbed species themselves (Fig. 15.9). In particular, adsorbed anions are discharged forming adsorbed radicals ... 

Oxidation of water to evolve 02 is an important reaction for water photolysis as described in Sect. 2. Oxygen evolution from water by Ru(bpy)f+ oxidation with Ru02 catalyst was studied 41). The authors established an electron relay system for water oxidation (Scheme 3) by the polymer Ru(bpy) + complex and Ru02 catalyst with Pb02 as an oxidant40). 

The coin has its reverse, however. The broadening of the potential window that is often bordered by the solvent electrochemical decomposition potentials (e.g. cathodic hydrogen evolution and anodic oxygen evolution from water) is due to an increase in reactions overvoltage. This may be caused by a diamond s lower electrochemical activity, as compared with the glassy carbon and like electrode materials. On the whole, this conclusion is corroborated by the kinetics studies on diamond electrodes... 

In principle, another anodic reaction can take place instead of semiconductor decomposition (dissolution), for example, oxidation of dissolved substance or oxygen evolution from water. Apparently, in the latter case, the illumination of semiconductor leads to photoelectrolysis of water with the formation of hydrogen and oxygen, that is, conversion of the energy of light into chemical energy of the photoelectrolysis products. 

Continuous and semicontinuous electrochemical reactors are normally employed for effluent metal ion remediation, where the anode reaction is usually oxygen evolution from water [compare with Equation (26.4)]. After the metal contaminant is captured on the cathode, the cathode can be discarded, the collected metal can be resold, or the deposited metal can be chemically or elecfro-chemically etched into a small volume of a suitable leaching liquor (e.g., water) so as to increase its concentration substantially. 

Table 2.3 lists various types of schemes that have been examined to date63 -65,69-74 for light-induced oxygen evolution from water. Photolysis of transition metal ions, as for the case for H2-production, requires UV-photons. Only for the Ce4+ system, the quantum yields are high (

energy storing. Oxy anions such as V02, MnO[Pg.49]

The experimental effects reported above are readily understood in terms of the known photochemical properties of PS II and PS I particles. The l t reaction of PS II particles results in the oxygen evolution from water splitting and the reduction of an elecrron acceptor such as ferricyanide. The l t reaction of PS I particles leads to NADP teduction in the presence of a donor such as DCPIH2. 

Kiwi J, Gratzel M (1978) Oxygen evolution from water via redox catalysis. Angew Chem Int... 

At pH = 0 (Fig. 9.10), the thermodynamic potential of the chlorine-evolving anode is close to -t-1.36 V whereas the thermodynamic voltage of oxygen evolution from water in acidic media is approximately -t-1.23 V. The difference is not very large but the kinetics of the OER are slow and require elevated operation potentials of ca. -1-I.6 V to proceed at a significant rate. Therefore, pure chlorine is evolved at the surface of the DSA. 

Very powerful oxidants like Ag " (2V) and Co " (1-8 V) do actually cause oxygen evolution from water, while agents like MnO (1.5 V), which might be expected to decompose water, do so very slowly at room temperature. Reductants like Na (— 2.7 V) rapidly evolve Hj with water, while Mg ( —2.4 V) requires boiling to give noticeable H2. 

There are many possible reactions leading to the formation of oxygen gas. In the absence of hypochlorite (in the text referred to as the sum of ClOH and QO ), at potentials lower than the reversible potential for chlorine evolution, the main reaction is oxygen evolution from water discharge ... 

The thermostability of PSII were also measured by to other widely used methods the fluorescence rise under low exciting light, Fo (5) and the PSII dependent oxygen evolution of isolated thylakoids (data not shown). Isolated thylakoid were incubated in darkness for lOmin. at various temperatures from 25°C to 45°C and then we measured the PSII dependent oxygen evolution from water to DCPIP at 25°C. Both measurements, Fo rise and PSII dependent oxygen evolution were less sensitive to temperature in the mutant fadSfad7-2fad8. 

Photo-induced oxygen evolution from water... 

SarmaR, Angeles-Boza AM, Brinkley DW, RothJP. Studies of the di-iron(VI) intermediate in ferrate-dependent oxygen evolution from water. J Am Chem Soc. 2012 134 5371-15386. 

---