Spectroscopy-driven design of an efficient photocatalyst for carbon dioxide reduction

地球上每年发生的太阳能事件是全球人类一年能源需求量的8000倍，但太阳能的间歇性使其储存成为实际使用的必要性。利用太阳光作为能源的催化剂(光催化剂)还原二氧化碳提供了一条清洁的路线，可获得一系列碳基燃料和化学原料，如甲醇、甲烷和一氧化碳。当这个过程与光驱动的水分分解结合在一起时，它可以被认为是一种人工光合作用。人们一直对开发用于从二氧化碳生产太阳能燃料的新型光催化剂产生浓厚兴趣，因为高效的人工光合作用将彻底改变能源格局，提供一种安全、可再生的燃料路线。在短期内，二氧化碳的光催化还原和电催化还原还具有提供高价值工业产品(例如一氧化碳)的巨大潜力，这将是使碳捕获技术在经济上可行的重要因素。一种提出的高效利用太阳能减少二氧化碳的途径是将吸收光能的固体半导体材料耦合到分子催化剂上，分子催化剂可以进行复杂的多步骤二氧化碳还原。这是一种非常有希望的方法，但最有效的分子催化剂使用稀有金属元素，其成本将阻碍其广泛使用。伦敦帝国理工学院化学系的一项工作计划将开发新的低成本材料，将二氧化碳还原为具有重要工业意义的原料一氧化碳。将开发一系列以镍和锰为中心的催化剂，并将其固定在光吸收半导体上。虽然第一代低成本材料的成功开发将代表着朝着高效光驱动二氧化碳还原迈出的重要一步，但要实现可扩展的光催化，合理开发这些新材料将是必要的。为了指导合成发展，将进行一系列使用瞬变振动光谱的研究。由于催化剂的性质可以随环境的变化而变化，因此有必要在操作条件下，即结合到半导体表面上对其进行研究。将采用选择性探测界面区域的实验，如催化剂表面的物种，这允许检测即使是低浓度的结合物种，否则其信号将被主体材料和溶剂掩盖。瞬变测量将提供电子运动和发生化学反应机理的快照，为指导新材料的合理设计提供精致的细节。开发高效的自然光合作用模拟是一个具有挑战性的目标，但它将消除我们对化石燃料资源的依赖，并且人造叶子效应的潜在全球影响不可低估。本文概述的光谱技术可用于在操作条件下研究一系列多相催化反应，而不需要目前经常需要的严格的采样要求。对催化反应机理的更好理解将导致开发新的改进的催化剂，这不仅从经济上而且从环境的角度来看都是必不可少的。

The annual solar energy incident on the earth is 8000 times greater than the entire global energy requirements for humankind in a year; however the intermittent nature of solar energy makes its storage a necessity for practical use. The reduction of carbon dioxide by catalysts using sunlight as the energy source (photocatalysts) offers a clean route to a range of carbon based fuels and chemical feedstock's such as methanol, methane and carbon monoxide. When this process is combined with light driven water splitting it can be considered as a form of artificial photosynthesis. There has been intense interest in developing new photocatalysts for the production of solar fuels from carbon dioxide as efficient artificial photosynthesis would revolutionise the energy landscape, offering a secure, renewable route to fuels. In the short term the photo and electro-catalytic reduction of carbon dioxide also has great potential for providing high value industrial products (e.g. carbon monoxide) which will be important in making carbon capture technology economically viable. One proposed route to efficient reduction of carbon dioxide using solar energy is to couple solid semiconductor materials, which absorb the light energy, to molecular catalysts which can carry out the complex multi-step reduction of carbon dioxide. This is a highly promising approach however the most efficient molecular catalysts use rare metallic elements, the cost of which will prevent their widespread use. A programme of work in the Chemistry Department at Imperial College London will develop new low cost materials for the reduction of carbon dioxide to the industrially important feedstock, carbon monoxide. A series of catalysts based around Nickel and Manganese centres will be developed and immobilized on light absorbing semiconductors.Whislt the successful development of this first generation of low cost materials would represent a significant step towards efficient light driven carbon dioxide reduction, to achieve scalable photocatalysis it will be necessary to rationally develop these new materials. To guide synthetic developments a series of studies using transient vibrational spectroscopies will be carried out. As the properties of the catalyst can be changed by its environment it is essential that it is studied under operating conditions i.e. bound to the semiconductor surface. Experiments that selectively probe interface regions, such as the species on a catalyst surface will be employed, this allows for the detection of even low concentrations of bound species whose signals would otherwise be masked by the bulk materials and solvents. The transient measurements will provide snapshots of both the movement of electrons and of the chemical reaction mechanisms occurring offering exquisite details to guide the rational design of new materials.Developing an efficient mimic of natural photosynthesis is a challenging goal but it would remove our reliance on fossil fuel resources and the potential global impact of an effect artificial leaf cannot be underestimated. The spectroscopic techniques outlined here can be used to study a range of heterogeneous catalytic reactions under operating conditions without the stringent sampling requirements that are often currently required. An improved understanding of catalytic reaction mechanisms will lead to the development of new improved catalysts which is essential not just economically but also from an environmental viewpoint.