Report

Teaser, summary, work performed and final results

Periodic Reporting for period 3 - Cu4Energy (Biomimetic Copper Complexes for Energy Conversion Reactions)

Teaser

Water oxidation (WO) and oxygen reduction (OR) are crucial reactions to produce and to consume solar fuels. It is important that WO and OR occur with very high catalytic rates with only a very small thermodynamic driving force. In these terms, Natural catalysts perform...

Summary

Water oxidation (WO) and oxygen reduction (OR) are crucial reactions to produce and to consume solar fuels. It is important that WO and OR occur with very high catalytic rates with only a very small thermodynamic driving force. In these terms, Natural catalysts perform significantly better than the artificial systems that are currently employed in fuel cells and electrolyzers. Especially the copper enzyme Laccase operates fast at a low overpotential. In principle one could use the same design principles used in the enzymatic systems to produce artificial catalysts for OR and WO. The aim of the proposal is to significantly increase of fundamental understanding of the design principles for molecular OR and WO catalysts and to deliver new and very active molecular copper catalysts for OR and WO at the end of the project.

Work performed

Due to a very fast equilibrium between coordination and de-coordination of ligands copper(I) and copper(II) complexes are very labile. Formation of small amounts of non-coordinated copper easily leads to formation of copper or copper oxide deposits on the electrode.

Many of the molecular catalysts that were explored during the initial stages of the project resulted therefore in formation of deposits on the electrode, even despite some of these were claimed to be molecular catalysts in literature reports. In addition to these findings, a molecular copper complex was synthesized that:

1) Is stable in solution and doesn’t form any deposits on the electrode

2) With a turnover frequency of 10000 per second is very active, thereby exceeding the turnover frequency of Laccase, albeit at a higher thermodynamic driving force

This catalyst is the prime platform for further studies within this project. Thus far the mechanism of the oxygen reduction reaction is largely solved, and studies to shift the onset for the oxygen reduction reaction to more favorable potentials is ongoing according to various different strategies.

Final results

An extremely fast catalyst for the oxygen reduction reaction has been found and has been explored mechanistically. The bottlenecks of the catalytic reaction has been pinpointed and the catalyst structure will be improved accordingly to remove such bottlenecks. This continuing process should lead to a clear picture what the design-principles are for an efficient molecular oxygen reduction catalyst. Similar studies on the water oxidation reaction are in progress ass well and combined with studies regarding the oxygen reduction reaction should lead to full elucidation of the design principles for an efficient catalysts that can catalyze both the oxygen reduction and the water oxidation reaction efficiently.