New developments in the (photo)oxidation of water to oxygen

This lecture is the counterpart of the previous one in that it concerns the photoanode of the same photoelectrochemical cell. However, there are currently very few bioinspired molecular systems (based on non-noble metals such as manganese) satisfactory for water photooxidation. The few examples based on cobalt polyoxometalate or manganese tetranuclear complexes (chemical model of the photosystem II active site), combined with Ru(diimine_)3-type photosensitizers, are presented. It is shown that the materials to be considered for the development of a photoanode are solid materials with semiconducting properties. The best-known and most widely developed is _TiO2 oxide, but this only absorbs in the UV range. As the solar spectrum requires absorption in the visible range, the oxide most currently being studied is iron oxide _Fe2O3. Its properties can be enhanced by : (i) doping; (ii) nanostructuring; (iii) association with a catalyst to optimize the use of "holes" for water oxidation. Although iridium oxide _IrO2 is a very good catalyst, it has the disadvantages of noble metals (availability and price), and a great deal of research is currently focusing on cobalt oxides or manganese oxides.