Philipp Gaiser: Surface Immobilization of α-[Fe(mcp)L2] for the Investigation of Coupled Electron Transfer Reactions

Abstract

Coupled electron transfer reactions are key steps in many electrocatalytic mechanisms, for example, in the water oxidation reaction. Fundamental understanding of how the electron transfer in such reactions is influenced by parameters like the pH and the supporting electrolyte is crucial to advance the production of green hydrogen by electrocatalytic water splitting. Molecular catalysts serve as well-defined model systems in this endeavour. The surface immobilization of these coordination complexes is essential for investigations into their electron transfer kinetics. This work focuses on surface immobilization methods for the α-[Fe(mcp)L2] complex. Two different approaches are presented: the incorporation in conducting redox polymer (CRPs) as well as the formation of monolayers. The incorporation in CRPs allowed the immobilization on various electrode materials. However, the electrochemistry of the α-[Fe(mcp)L2] pendant group is dominated by the ion transport through the polymer matrix when measuring in aqueous electrolytes, thus limiting their use for the investigation of coupled electron transfer reactions. In a second approach, the α-[Fe(mcp)L2] monolayers were formed on glassy carbon electrodes via the Diels-Alder reaction using a maleimide linker. The electrochemical responses of the obtained monolayers closely follows the redox behaviour of the freely diffusing complex in solution. Aside from proton-coupled electron transfer (PCET) behaviour, an electron transfer induced ligand exchange reaction with the supporting electrolyte anions, which we labelled anion-coupled electron transfer (ACET), is presented. Thermodynamic schemes that allow the rationalization of a PCET occurring in parallel to and ACET were derived. This thesis expands the surface immobilization toolbox for pyridyl amine ligands and their corresponding coordination complexes. This work highlights the critical yet often overlooked role of electrolyte anions in electrochemical reactions and deepens the fundamental understanding of coupled electron transfer reactions.