SubProject 1: Supramolecular water oxidation catalysts

Mononuclear Ru or Ir water oxidation catalysts is attached via a supramolecular linkage based on donor-acceptor interactions to a framework that is equipped with -PO3H2 –SH or - COOH functionalities for interfacing to Si nanowire electrode surfaces and supramolecular antenna charge separator dyes and dendrimers for extended charge transfer. Initially we aim for the optimization of [IrCp*(OH)2(Me2-NHC)] that has been shown to be catalytically active without any signs of catalyst deactivation over two hours and more than 2000 turnovers under the oxidative conditions applied, into a supramolecular framework.

Critical factors are catalyst activation for PCET, redox leveling and thermodynamic stabilization of intermediates in the 4-electron process, variation of the bite angle for accessibility of a second water molecule to avoid that structural rearrangements become rate-limiting instead of the PCET steps.

The optimization will be evidence-based, and are performed in close collaboration with the time resolved laser and freeze hyperquenching NMR analysis projects that are fed into the constrained molecular modeling of catalysis mechanisms. The supramolecular catalyst are then incorporated into the semiconductor heterojunction tandem device that is the focus of artifical leaves.

During the second stage of the project, focus will shift to multinuclear cobalt based water oxidation catalysts that have multicompartimental NHC ligands, since cobalt is much cheaper and abundant compared to its ruthenium and iridium counterparts. Since we use a multicompartimental ligand, the same supramolecular linkage system can be used as developed for the precious metal based catalysts described above. Facilitated by the predictive range obtained from the analysis and constrained modeling, multinuclear catalyst optimization will proceed via a converging evidence-based “plug- and-play” approach, without any alterations to the basic setup of the device engineering platform.

The project will be a success if a device compatible supramolecular framework is obtained that allows for variation of the catalyst and optimization of activation, redox leveling, and water accessibility for PCET, while avoiding wasteful or damaging side-reactions, and its catalysis function is demonstrated, both in homogeneous catalysis and immobilized on an electrode for incorporation in a tandem heterojunction device.

The work in this project is primarily done at the Supramolecular & Homogeneous Catalysis department of the van ‘t Hoff Institute for Molecular Sciences, Science Park Amsterdam, Amsterdam University.

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