COLLOIDAL NANOCRYSTALS AND HYBRID NANOSTRUCTURED MATERIALS FOR ENERGY CONVERSION AND STORAGE

Room Temperature Ionic Liquids (ILs) have been intensively investigated as promising materials for applications in the field of energy conversion and storage. Furthermore, Polymeric ionic liquids (PILs) are a relatively new class of polyelectrolytes, merging peculiar physical-chemical features of ionic liquids with flexibility, mechanical stability and processability typical of polymers. The combination of ILs or PILs with colloidal semiconducting nanocrystals leads to novel nanocomposite materials with high potential for batteries and solar cells. Here the results of a spectroscopic study focused on the interactions between titanium dioxide nanorods and imidazolium-based ionic liquids are reported. TiO2 nanoparticles are unquestionably the most used material for the fabrication of sensitized solar cells and batteries, in which ILs are being used in order to replace conventional electrolytes. Anatase TiO2 rod-like nanocrystals, synthesized by means of a colloidal synthetic procedure, have been dispersed in a series of alkyl-substituted imidazolium based ILa, in order to investigate the interactions between the organic and inorganic moieties and the effects induced by different anions and alkyl chain lengths. Time-resolved spectroscopic measurements have highlighted significant differences in the recombination decay of ILs in presence of TiO2 nanorods. Such a behaviour can be reasonably ascribed to charge-transfer phenomena from photo-excitedTiO2 nanocrystals to imidazolium-based ILs. Also hybrid nanocomposites made of colloidal luminescent CdSe nanocrystals incorporated in a novel imidazolium-based PIL functionalized with a thiol end-group have been investigated. A capping exchange procedure has been implemented for replacing the pristine organic capping molecules of the colloidal CdSe nanocrystals with inorganic chalcogenide ions, aiming to disperse the nano-objects in the PILs, by using a common polar solvent. Spectroscopic measurements highlight the beneficial effect of the thiol functionality at the termini of PIL chains in completely retaining the optical properties of the CdSe NCs. In addition, the possible coordination of PIL functionalities to the NC surface favors the occurrence of charge transfer processes from SH-PIL to the CdSe NCs emitting states. The obtained results are of considerable interest for designing batteries and solar cells based on nanostructured materials and ionic liquids and can represent the starting point for developing innovative electroactive nanocomposite hybrid materials for the fabrication of electrochemical devices and actuators.