Supramolecular Rebound Healing Mechanism Enhances the Performance of Graphitic Hybrid Monomeric and Oligomeric Molecular Anodes for Electrocatalytic Water Oxidation

Abstract

Water-splitting with sunlight for the generation of solar fuels is regarded as a short- to medium-term solution for the mitigation of global warming. Devices for this purpose require robust redox catalysts embedded in electro(photo)anodes and cathodes for the light-induced catalytic oxidation of water to dioxygen, ideally working at neutral pH. Molecular catalysts for water oxidation constitute a very attractive option, given their synthetic versatility that enables the precise tuning of their electronic properties and hence their performance. Heterogenization of robust molecular catalysts into conductive and/or semiconductive solid supports to provide efficient and robust electro(photo)anodes is one of the main challenges in the field together with its fundamental understanding. Here, we present a detailed kinetic and thermodynamic analysis of the supramolecular anchoring via multiple CH-π, anion-π, and π–π interactions of Ru-tda (tda is ([(2,2′:6′,2″-terpyridine)-6,6″-dicarboxylato]))-based monomer and oligomeric complexes using edp ((E)-1,2-di(pyridine-4-yl)ethene) as bridging ligand. We quantify the binding energy to show that the anchoring process is mainly driven entropically via solvation energy. We also explore the relative stability of their high oxidation states and their stabilization on graphitic material. Finally, we show the high stability and efficiency of these molecular hybrid materials as molecular electroanodes for the water oxidation reaction, supported by a rebound mechanism. In the case of the oligomer, we reach over 100 000 TONs at pH 7 with FE close to 100% and practically no change in their current densities for 2 h. The proper understanding of the anchoring phenomenon involved for the molecular catalysts in the graphitic environment sheds light on the optimization of molecular architectures for efficient neutral water oxidation anodes.