Noncovalent Immobilization of Electrocatalysts on Carbon Electrodes via a Pyrenyl Ligand

Abstract

There are many problems that need to be overcome if solar energy is to be viable on a global scale. Photons must be harvested and stored in a usable to allow efficient use of energy throughout the day. The functionalization of electrode surfaces with molecular catalysts is an attractive route for assembling (photo)electrochemical devices that convert renewable energy into chemical fuels. This work focuses on one method of noncovalently attaching molecular catalysts to graphitic surfaces. The first part describes the synthesis of a pyrene-appended bipyridine ligand that serves as the linker between the catalysts and the surface. Using this ligand, a rhodium proton-reduction catalyst and a rhenium CO2-reduction catalyst were synthesized in order to study the electrochemistry of the surface-attached species. Electrochemical and spectroscopic analysis confirm catalyst immobilization and electrocatalytically active assemblies. Bulk electrolysis of the surface-attached complexes confirm catalytic turnover formation of H2 for the rhodium complex and CO for the rhenium complex. The second part describes three new complexes utilizing the same pyrene-appended bipyridine ligand. These are [Ru(P)(4,4’-dimethyl-2,2’-bipyridine)2]Cl2, [Cp*Ir(P)Cl]Cl, and [Mn(P)(CO)3Br]. Once again, spectroscopic and electrochemical analyses confirmed successful immobilization of these complexes on high surface area carbon electrodes. The iridium complex was found to be unstable with respect to redox cycling due to ligand exchange. The ruthenium complex exhibited very high stability over long periods of redox cycling. The manganese complex was found to catalytically produce CO during bulk electrolysis.