The Reduction of Carbon Dioxide by Enzymes Adsorbed on Electrodes: from Mechanistic Studies to Bioinspired Catalysts

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Carbon dioxide (CO2) is produced by the combustion of carbon-containing molecules, such as fossil fuels, to power industry, for transportation, and in our homes. Burning fossil fuels is not only causing the level of CO2 in the atmosphere to increase (CO2 is a greenhouse gas and a major contributor to global warming) it is also depleting valuable resources that are required for the manufacture of plastics, chemicals, fertilizers - and countless other requirements of modern society. Unfortunately, CO2 is a very stable and unreactive molecule, and the only large scale process known that can remove CO2 from the atmosphere and use it to regenerate a carbon-containing fuel is biological photosynthesis (growing plants and trees). Therefore, an industrial process that could use the energy from sunlight, or a green-electricity source, to take CO2 out of the atmosphere and turn it into a useful fuel or chemical would revolutionise modern society, by supplying both our energy and material demands. Of course, no such process currently exists. The aim of this proposal is to explore a new approach for the development of such a process. Some bacteria use enzymes called formate dehydrogenases (FDHs) to catalyse the oxidation (= burning) of formate to CO2, and extract energy from this reaction in order to survive. Chemically, formate is one of the simplest hydrocarbons - it is already used as a chemical building block (feedstock) in industry, and formate 'fuel cells' are being developed. Turning a formate dehydrogenases 'in reverse' would turn CO2 into formate, a useful product. In fact, a small number of specialised bacteria use special 'tungsten-containing' FDHs to catalyse this reverse reaction - and live off the tiny amount of energy that they extract. In a pilot study we showed that the tungsten FDH from a bacterium called Syntrophobacter fumaroxidans can act as an extremely efficient electrically-driven catalyst for the reduction of CO2 to formate. In this project we aim to find out 'how the tungsten formate dehydrogenase does it'. We will start by looking for and characterising tungsten FDHs from different organisms, to find those that are the best for our experiments. Then we will apply sophisticated biochemical, electrochemical and physical techniques to aim to find out how they work - and why they work so well. Finally, we will compare our biological catalysts with available synthetic catalysts, aiming to find out how to improve the synthetic catalysts, and to develop 'demonstration devices' that show how efficient CO2 reduction catalysts can be powered by solar radiation and used in fuel cells.