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

二氧化碳(CO2)是由化石燃料等含碳分子燃烧产生的，用于电力工业、交通运输和我们的家庭。燃烧化石燃料不仅导致大气中的二氧化碳水平增加(二氧化碳是一种温室气体，也是全球变暖的主要原因)，还在消耗宝贵的资源，这些资源是制造塑料、化学品、化肥以及现代社会无数其他需求所必需的。不幸的是，二氧化碳是一种非常稳定和无反应的分子，唯一已知的能够从大气中去除二氧化碳并用它来再生含碳燃料的大规模过程是生物光合作用(生长植物和树木)。因此，一种工业过程可以利用来自阳光的能量，或绿色电力，从大气中提取二氧化碳，并将其转化为有用的燃料或化学品，通过提供我们的能源和物质需求，将彻底改变现代社会。当然，目前还不存在这样的过程。这项提议的目的是为发展这一进程探索一种新的办法。一些细菌使用被称为甲酸脱氢酶(FDHS)的酶来催化甲酸盐氧化为二氧化碳，并从这个反应中提取能量以求生存。在化学上，甲酸盐是最简单的碳氢化合物之一--它已经被用作工业中的化学构件(原料)，甲酸盐“燃料电池”正在开发中。反转甲酸脱氢酶可以将二氧化碳转化为甲酸盐，这是一种有用的产物。事实上，一小部分特殊细菌使用特殊的“含钨”外佣来催化这一逆反应--并依靠它们提取的极少量能量生存。在一项初步研究中，我们发现一种名为延胡索酸合成杆菌的钨FDH可以作为一种非常有效的电力驱动催化剂，用于将二氧化碳还原为甲酸盐。在这个项目中，我们的目标是找出甲酸钨脱氢酶是如何做到这一点的。我们将从寻找不同生物体中的钨外佣开始，并对其进行表征，以找到最适合我们实验的外佣。然后，我们将应用先进的生化、电化学和物理技术，旨在找出它们是如何工作的--以及为什么它们工作得这么好。最后，我们将把我们的生物催化剂与现有的合成催化剂进行比较，目的是找出如何改进合成催化剂，并开发“演示设备”，展示如何利用太阳辐射驱动高效的二氧化碳减排催化剂，并将其用于燃料电池。

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.