Self-reduction semiconductors

The reduction of CO2 at metallic cathodes has been studied with almost every element in the periodic table °. This reaction can be driven electrochemi-cally or photochemically " and semiconductors have been used as cathodic materials in electrochemical or photoelectrochemical cells . The aim of these studies has been to find cathodes that discriminate against the reduction of H2O to H2 and favor the reduction of CO2 and also to find a cathode selective for one product in the reduction of CO2. A fundamental requirement is that the latter process occurs at a lower overpotential on such electrodes. However the purposes mentioned before in metallic cathodes depends on a series of factors such a solvent, support electrolyte, temperature, pressure, applied overpotential, current density, etc. (we will see the same factors again in macrocyclic electro-catalysis). For instance when protons are not readily available from the solvent (e.g., A,A -dimethylformamide), the electrochemical reduction involves three competing pathways-oxalate association through self-coupling of COj anion radicals, production of CO via O-C coupling between and COj and CO2, and formate generation by interaction of C02 with residual or added water. ... 

Besides inhibiting oxygen reduction, another role of the self-assembled monolayer is to improve the adhesion of the polymer film to the surface under mechanical strain, which of course also plays a role in slowing down coating delamination. Usually, it is assumed that it is the covalent bond of the head group of the molecules to the surface and the tail group to the polymer that is responsible for the improved mechanical stability. From many applications, it is known that this is not the main factor. For instance, in order to protect microelectronic devices, especially microchips, from harmful environmental influences, more than 90% of all semiconductor devices are encapsulated with polymeric compounds. 

---