Bio-inspired cooperative electrocatalyst design for sustainable CO2 utilisation

• Applicant: Dr. Moritz F. Kühnel
• Subject Area: Inorganic Molecular Chemistry - Synthesis and Characterisation
• Term: from 2013 to 2015
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 235251984

In light of the climatic consequences of increasing atmospheric CO2 concentrations and the impact of surging oil prices on the global economy, the use of CO2 as a C1 feedstock for chemical synthesis is highly attractive. The conversion of thermodynamically and kinetically stable CO2 into products of higher value such as CO consumes energy and requires a suitable catalyst; CO is industrially important and can be converted into liquid hydrocarbon fuels.Natural enzymes like carbon monoxide dehydrogenases (CODHs) are excellent catalysts for the electrochemical reduction of CO2 to CO in terms of selectivity and efficiency and they are based on earth-abundant transition metals. Their efficiency has been ascribed to their degree of specialisation for stabilising the CO2 molecule by a network of outer-sphere interactions. Practical applications of CODHs are precluded by their high cost and fragility. The performance of synthetic CO2 reduction catalysts is still far behind. Most systems are based on precious metals and operate under forcing conditions, i.e. they waste energy because they require a high overpotential. Recent investigations suggest a similarly important role of outer-sphere interactions in synthetic systems, too, but this aspect has not been translated into systematic catalyst design.The aim of this project is to develop bio-inspired electrocatalysts for CO2 to CO reduction. This is to be achieved by functionally mimicking outer-sphere interactions in the protein environment based on constructing novel cooperative ligands in four steps.Initially, a set of bis(imino)pyridine pincer ligands (PDI ligands) with a single peripheral functionality in different orientations will be synthesised; this study will include functionalities such as amino, hydroxyl, and boryl groups. By analogy to the known non-functionalised CO2 reduction electrocatalyst [Ni(PDI)2+], a family of functionalised nickel complexes will be generated from these ligands.Electrochemical evaluation of their electrocatalytic properties will enable us to derive a quantitative measure of the influence of outer-sphere interactions on catalytic performance and the optimum position for each functional group.With this knowledge at hand, the additivity of two or more cooperative functionalities will be investigated. In combination with mechanistic studies and systematic catalyst optimisation regarding the ligand steric and electronic properties as well as the metal centre, we expect this work to result in a significant improvement of the catalyst's selectivity, overpotential and efficiency. Finally, a derivative of the optimised complex bearing an anchoring group will be synthesised and immobilised on a high-surface nanostructured electrode in order to generate a novel heterogeneous high-performance CO2 reduction system towards practical applications.

• DFG Programme: Research Fellowships
• International Connection: United Kingdom
• Host: Professor Erwin Reisner, Ph.D.