CarBioRed

The use of carbon dioxide as a feedstock for fuel production is a highly desirable goal, both in the context of finding alternatives to fossil fuels and to limit the greenhouse effect. Although the direct hydrogenation of CO2 to methanol or methane is a possibility, the electro- and photo-catalytic reduction processes remain the focus of much interest. These reactions are difficult to control as they do not only involve the transfer of several electrons, but are often coupled to protonation. Resulting competitive pathways are thus commonly observed, leading to various products. CO or formate are often formed, though with poor energetic efficiency, and are of interest for Syngas or Formic Acid economies. By contrast alcohols (methanol and ethanol) or hydrocarbons are only formed in low amounts. CarBioRed aims at developing efficient and selective, non-noble metal based molecular electrocatalysts for carbon dioxide reduction, and at gaining some insights into their reaction mechanisms. By contrast with previous studies, a bioinspired approach will be followed for selecting the metals and ligands as part of new catalysts. Based on the knowledge of the structure and reactivity of metalloenzymes dealing with CO2 (CO Dehydrogenase, Formate Dehydrogenase), synthetic molecular mimics of the active sites will be synthesised: mononuclear complexes based on Mo, W with sulphur rich ligands mimicking the natural pterin-dithiolene cofactor and dinuclear Ni-M (Fe,Ru,Mn) clusters with sulphur rich coordination spheres (Task 1). In parallel, we will also use polyoxometalates (POMs), whose structural analogies with the coordination sites found in some metalloenzymes have been underlined, as new type of multidentate and all-inorganic ligands (Task 2). Transition metal substituted POMs (TMSPs) as inorganic Synzymes could provide multifaceted electrocatalysts for CO2 reduction, at least as electron and proton reservoirs. Our consortium will implement the analytical and electrochemical methodologies to assess the performances of our complexes in electroassisted CO2 reduction, in particular in terms of overpotential requirement, turnover frequency, stability and selectivity (Task 3). A particular attention will be paid to the adjustment of the distinct electrolysis conditions (solvent, nature of the electrodes, proton sources…) in order to improve their activity. Simultaneously, a particular focus will be set on the elucidation of the catalytic mechanisms, through the investigation of likely intermediates by in-situ solution spectroelectrochemical studies and a back and forth interplay with theoretical studies (Tasks 3 & 4). This should in return help to synthetically tune the properties of the catalyst, in terms of both selectivity and performance, a clear asset of the molecular chemistry approach. The consortium set up for this project will finally allow to go one step further towards valorisation by the development of modified electrodes and electrolysis cells (Task 5), a step rarely tackled in other molecular studies. Analysis of the performances of these supported systems will benefit from the expertise acquired from homogeneous studies (Task 3).