Catalysts water cleavage

Frank AJ and Honda K (1982) Visihle-light-induced water cleavage and stabilization of n-type CdS to photocorrosion with surface-attached polypyrrole-catalyst coating. J Phys Chem 86 1933-1935... 

WATER CLEAVAGE USING SIMPLE METAL SALTS AS CATALYSTS 493... 

WATER CLEAVAGE USING METAL COMPLEXES AS CATALYSTS 495... 

One other important criterion for successful water cleavage that must be considered is the solution pH. Although the potential difference between the two half reactions for water decomposition is fixed at 1.23 V and is independent of pH, the half-cell reactions are dependent upon pH (Figure 4). Thus, by altering the pH of a solution it is sometimes possible to alter the half-cell potentials to be compatible with the redox properties of a photosensitizing catalyst. The oxidant must have a redox potential above the oxygen line, whilst the reductant must have a redox potential below the hydrogen line. The effect of pH is illustrated in subsequent sections of this chapter. 

Redox potentials for various different Feu/Fem couples are shown in Table 3 and although [Fe(OH)2] is thermodynamically capable of reducing water to hydrogen and does so at elevated temperatures,39 the rate of the reaction is low. It can, however, be increased by the addition of suitable catalysts, eg. Ni salts,39,40 excess [FeSOJ,40 metals such as Ni,40 Cu,40 Pd,18,41 or colloidal Pt.40 Nevertheless, cyclic water cleavage based on this system is unlikely since [Fe(OH)3] is a. highly stable material. 

Efficient Water Cleavage by Visible Light in Colloidal Solutions of Bifunctional Redox Catalysts... 

Figure 9. Cyclic water cleavage by visible light in the presence of Ru(bipy)i as a sensitizer and bifunctional redox catalyst as an electron relay.

---