Invited Paper SS-ThM9
Functional Molecular Layers for Energy Applications

Thursday, November 1, 2012, 10:40 am, Room 22

Electrode materials for renewable energy applications are largely based on materials such as metal oxides and various forms of carbon because of their intrinsically high stability. However, the properties can be markedly enhanced through the integration of "smart" molecular functionalities. We have been investigating the development and application of new chemistry for fabricating novel types of electrochemically and photoelectrochemically active molecular structures on surfaces of metal oxides and on thin-film diamond. One area of interest has been the use of "click" chemistry as a versatile approach to functionalizing surfaces with redox-active molecules that can be used either as potential catalysts or as light-harvesting molecules. By using complementary functionalization on two different nanostructured oxides, it is also possible to make chemically-assembled oxide-oxide heterojunctions, such as TiO₂/SnO₂. In these cases the formation of a heterojunction can provide a built-in potential to enhance charge transfer at the interface.

A key question in these studies has been understanding how the presence of alkyl chain, ranging from ~4 atoms to ~ 12 atoms, impacts the electron transfer. While most previous work on molecular layers has been performed on densely packed layer on coinage metals such as gold and silver, when molecular layers are tethered to covalent materials such as diamond or metal oxides, the resulting layers have a high degree of disorder due to the mismatch between the native packing of the alkyl chains and the distribution of available surface sites. We have investigated the electron-transfer properties at these functionalized interfaces and find that the electron transfer rates are surprisingly high and only weakly dependent on the length of the alkyl chain, which we explain as a result of the increased conformational disorder. Our data suggest that the"best" molecular layers for electron-transfer applications are those that have a controlled degree of conformational disordered. We demonstrate these effects using recent measurements of electroactive Ru(bpy)-based complexes on diamond and on metal oxides.