Redox Reactions in Transition Metal Oxide Gels

Transition metal ions are known to exhibit several oxidation states so that redox reactions can take place during the sol-gel synthesis of the corresponding oxides. The reduction of molecular precursors increases the size of the metal cation, favoring coordination expansion and the formation of condensed species. Electron delocalization through the oxide network is responsible for the electrical, optical, and electrochemical properties of transition metal oxide gels. Moreover the large surface/volume ratio-due to the small size of the solid particles-leads to a whole range of ion and electron exchange reactions at the oxidehvater interface of transition metal oxide colloids.