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

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.

This proposal aims to deliver scalable, efficient catalysts for the production of carbon based fuels and feedstocks from carbon dioxide reduction using sunlight as the energy source. The development of an efficient artificial leaf would dramatically change the energy landscape, offering a route to overcoming the intermittent nature of solar energy. In addition to the potential impact on society, likely beneficiaries also include industry and academia world-wide.

Industry: The materials developed in this research will enable the reduction of carbon dioxide to either pure carbon monoxide or a controllable syngas mixture, this important chemical feedstock (e.g. for the Fischer-Tropsch process) is currently produced in vast quantities using energy intensive, non-renewable pathways. The ability to produce high value products from a waste product (carbon dioxide) and an effectively unlimited energy resource (solar) would be of great industrial and commercial significance, particularly to the carbon capture and storage (CCS) industry. CCS is likely to be employed in the UK to meet the ambitious emissions reduction targets. CCS will provide a concentrated source of carbon dioxide which can be reduced to high value products providing an important pathway to offset the high costs of carbon capture which is essential if CCS is to become commercially viable. This proposal concentrates on developing low cost catalysts making the technology extremely attractive to a commercial partner and although the primary research aim is to develop photocatalysts the materials will also be applicable as high surface area electrocatalysts, which would be of significance to other renewable sectors that rely on intermittent resources (e.g. Wind, Solar PV). Therefore it is anticipated that beneficiary sectors will include the CCS and power companies (e.g. SSE/Shell), renewable (Scottish Power, Vestas, BP) and bulk chemical producers (Sasol, Shell)
The development of novel apparatus and methodologies for the study of catalytic reaction mechanisms on surfaces is also of great significance to the industrial sector. The ability to understand the nature of chemical intermediates, identify catalyst poisoning routes and to study the effect of catalyst modifications under operating conditions is highly desirable. The rational design of new catalysts and industrial processes will increase the efficiency of research through decreased lost time and resources in addition to providing lower cost, greener routes to products. The training of PDRA's and students in catalytic reaction mechanism studies will also strengthen the nation's skill base in these areas benefiting the industrial sector.

General Public: A secure, sustainable energy supply for the UK is recognised as a research priority by the EPSRC. Climate change brought about by rising carbon dioxide levels has the potential to affect all of humanity. The UK government has committed to an 80% reduction in carbon dioxide emissions by 2050 which is an ambitious goal that requires a much greater utilisation of renewable energy resources than is currently achieved. This proposal directly addresses the development of solar energy and also impacts upon other intermittent renewables. As outlined above the proposed research also has the potential to negate some of the costs of CCS, which would otherwise be passed onto the consumer.

Academia: The materials, methodologies and spectroscopic tools developed in the proposed programme of work will have a significant impact on a number of academic fields world-wide as outlined in the academic beneficiaries section.