INTERNATIONAL COLLABORATION IN CHEMISTRY ENHANCING DIRECT PHOTOELECTROCHEMICAL CONVERSION OF CO2

通过光对半导体色散的作用，水分解成氧和氢，通常被称为光电分解或光电催化，这是一个非常重要的发现，它导致了大量针对水分解和二氧化碳还原的活动。分散半导体驱动这种氧化还原过程的能力是由与氧化还原过程的电化学电位相比较的带边位置决定的。尽管这些工艺确实有效，而且应用起来成本低廉，但迄今为止，产品的产量还不足以导致技术突破。尽管如此，对光电催化过程的早期研究实际上已经取得了一些非常重要的技术成果，包括自清洁窗口，具有整体氧化还原穿梭的Grtzel太阳能电池和废物的光催化修复。化石燃料转化产生的二氧化碳排放量为每年2.5 × 10^10公吨二氧化碳，由于其与全球变暖的关系，对21世纪构成了重大的环境挑战。《京都议定书》签署后，许多国家政府承诺减少温室气体排放；然而，全球能源需求正在增加，二氧化碳水平很可能会实际增加。二氧化碳封存是一种解决方案，但它可能要付出能源效率成本。通过物理化学手段将二氧化碳转化为有用的燃料和化学原料，不仅可以减少大气中的二氧化碳，还可以减少对化石碳的依赖，从而提高能源安全。这个团队的成员之前已经报道了光电催化将溶解的二氧化碳还原为一系列一碳和二碳产品，旨在开发一条从太阳能合成燃料的可能途径。在二氧化碳分子中加入一个电子会产生一个二氧化碳自由基阴离子。这一种可能被质子化导致甲酸；它可能与一氧化碳和碳酸盐不成比例，也可能二聚形成草酸盐。因此，有一系列可能的机制可以将二氧化碳转化为液体燃料。通过甲酸的路径必须涉及水；然而，在以前的光电催化还原实验中，已经观察到CO和二聚化产物在还原过程中不需要水的参与。还有一些关键问题需要解决，我们寻求在我们的合作项目中分享新的概念和材料来解决这些问题。

The splitting of water to form oxygen and hydrogen by the action of light upon a semiconductor dispersion, often termed photoelectrolysis or photoelectrocatalysis was a very important discovery , which lead a great deal of activity aimed at water splitting and CO2 reduction . The ability of a dispersed semiconductor to drive such redox processes is determined by the positions of the band edges in comparison to the electrochemical potentials of the redox processes. Although these processes do work and would be cheap technologies to apply, the yields of products have so far been insufficient to lead to a technological breakthrough. Despite this, early research on photoelectrocatalytic processes has in fact led to some very major technological achievements including self-cleaning windows , the Grtzel solar cell with integral redox shuttle and photocatalytic remediation of wastes .CO2 emissions from fossil fuel conversion amount to 2.5 x 10^10 metric tons of CO2 per annum yielding a significant environmental challenge for the 21st century due to its association with global warming. Following the Kyoto agreement many Governments were committed to a reduction in Greenhouse gas emission; however, energy demands are increasing globally and it is likely that CO2 levels will actually increase. CO2 sequestration is one solution, but it is likely to have an energy efficiency cost. Conversion of CO2 by physio-chemical means to useful fuels and chemical feedstocks, not only reduces CO2 in the atmosphere it reduces dependency on fossil carbons, increasing energy security. Members of this proposed team have previously reported the photo-electrocatalytic reduction of dissolved carbon dioxide to a range of one and two carbon products , aiming to develop a possible route to synthetic fuels from solar energy. The addition of one electron to a carbon dioxide molecule produces a carbon dioxide radical anion. This species may be protonated leading to formate; it may disproportionate to carbon monoxide and carbonate or it may dimerise giving oxalate. Consequently there are a range of possible mechanisms by which the CO2 may be converted to liquid fuels. The paths via formate must involve water; however both CO and dimerization products that do not require involvement of water in the reduction process have been previously observed in photo-electrocatalytic reduction experiments . There are still a number of key issues to be solved, and, we seek to address each of these sharing new concepts and materials in our collaborative programme.