N-Heterocyclic Carbene Assemblies for the Electrochemical Reduction of Carbon Dioxide

• Applicant: Dr. Juan Jesus Navarro Ocana
• Subject Area: Physical Chemistry of Solids and Surfaces, Material Characterisation
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 520865477

Mitigating anthropogenic climate change by pursuing carbon neutrality in industrial societies is one of the most important tasks of our time. The electrochemical reduction of CO2 (CO2RR) is a key process to close the carbon cycle by converting residual CO2 into valuable chemical feedstock. This reaction still presents major challenges, such as low selectivity and high overpotentials. A lot of effort has been made to get fundamental insight into this reaction, for example by using single crystal electrodes and a myriad of in situ techniques. Copper has resulted to be the only catalyst able to reduce CO2 into multicarbon products. The functionalization of copper electrodes employing organic molecules has emerged as a promising strategy to tune the selectivity of the CO2RR. At the same time, N-heterocyclic carbenes (NHCs) have opened new avenues in the modification of surfaces. These organic ligands are able to form strong bonds to a variety of surfaces, such as metals, oxide thin films or semiconductors. Herein, the functionalization of Cu surfaces using NHC ligands is proposed as a way to tune the product distribution of the CO2RR. NHCs can influence the intrinsic reactivity of the surface, for example, by modifying adsorption energies or electronic properties. By tuning the substitutional groups of the NHC ligands, it is even possible to control the access of different reactants, such as water molecules, to the surface. In addition, the growth of two-dimensional NHC-based materials on Cu surfaces, including covalent and metal-organic networks, will be pursued to create tailor-made ultra-stable organic layers helping the activation of CO2 molecules. In particular, triazine networks could be grown on Cu surfaces employing NHC-building blocks. Furthermore, triazine has been shown to be effective in CO2 capture and activation. Similarly, metal-organic frameworks have been successfully employed as catalysts for the reduction of CO2 into carbon monoxide or formate. It would be highly desirable to form two-dimensional metal-organic networks on Cu surfaces, by anchoring the layer through the strong carbene bonds. In this case, synergistic effects between the Cu catalyst and the metal-organic layer are expected. To get insight into the intrinsic catalytic activity of metal-organic networks, it is planned to use graphene on transition metals as support. These ideas will be carried out by combining different ultra-high vacuum and electrochemical techniques.

• DFG Programme: Independent Junior Research Groups