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

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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.