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

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.