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Diamond materials for the photocatalytic conversion of CO2 to fine chemicals and fuels using visible light

Periodic Reporting for period 3 - DIACAT (Diamond materials for the photocatalytic conversion of CO2 to fine chemicals and fuels using visible light)

Reporting period: 2018-01-01 to 2019-12-31

In DIACAT we propose the development of a completely new technology for the direct photocatalytic conversion of CO2 into fine chemicals and fuels using visible light. The approach utilises the unique property of diamond, widely available at low economic cost, to generate solvated electrons upon light irradiation in solution (e.g. in water or ionic liquids).
The project has achieved the following objectives on the way to the efficient production of chemicals from CO2:
- experimental and theoretical understanding of the principles of production of solvated electrons stemming from diamond
- identification of optimal forms of nanostructured diamond and surface modifications to achieve high photoelectron yield and long term performance
- investigation of optimized energy up-conversion for the direct use of sunlight for the excitation of electrons
- characterisation of the chemical reactions which are driven by the solvated electrons in “green” solvents
- demonstration of the feasibility of the direct reduction of CO2 using visible light in a laboratory environment.

The ultimate outcome of the project is the development of a novel technology for the direct transformation of CO2 into organic chemicals using visible light. On a larger perspective, this technology will make an important contribution to a future sustainable chemical production as man-made diamond is a low cost, environmentally friendly, industrial material.
As an early-stage research project, DIACAT aimed at generating fundamental knowledge and developing a new technology towards the long-term goal of a sustainable conversion of CO2. Our approach lays the foundation for the removal and transformation of CO2 and at the same time a chemical route to store and transport energy from renewable sources. This will have a transformational impact on society as whole by bringing new opportunities for sustainable production and growth.
From the beginning of the project we have worked on the production of novel diamond materials enabling the generation of solvated electrons in solution and the transformation of CO2 into fuels and chemicals. In the 1st period the foundations were laid by the development of analytical methods, production of first materials and the utilization of spectroscopy and computation in search for optimal materials and solvents. In the 2nd period we successfully carried out in-depth investigation of the photoelectrochemical transformation of CO2. Different nanostructured and doped diamond materials with and without surface functionalization have been produced in larger quantity and reproducible quality (WP1,2). I.e. different types of diamond materials have been terminated with hydrogen and fluorine using optimized methods. Photocatalytically active metal complexes and metal oxide coatings have been developed. Synchrotron spectroscopy at BESSY II, other spectroscopic experiments and computations enabled the elucidation of the underlying electronic processes for the generation of solvated electrons (WP3).
In the 2nd period, the systematic study of photocatalytic processes on the different diamond materials has been in the focus (WP4). The project has demonstrated for the first time that a whole range of diamond materials are able to reduce CO2 to fuels using visible light. Investigation of the properties of ionic liquids have permitted the identification of specific design criteria for ionic liquids (mixtures), which both offer commercial viability and large activity enhancements. Combining these findings and the best diamond material the project has demonstrated the highest activities observed by diamond catalysts to date.
In the 3rd period, the partners focused on optimizing the different components of the catalytic system and the construction and optimization of a demonstrator reactor. With in-depth spectroscopic investigation and optimized material combinations the efficiency of the photocatalytic transformation of CO2 was increased by more than 1 order of magnitude.
Several reactor designs for different purposes have been realised and characterized (WP5). A fluidic transport system for the use with a prototype reactor has been completed and an operational demonstrator has been successfully tested.
This project as a whole will initiate a major new line of technology for the use of CO2 as feedstock for chemical processes and energy storage. The developed technology will not only store the emitted CO2 as e.g. in the CCS (carbon (dioxide) capture and storage) approach, but transform it to less oxidized and hence chemically accessible hydrocarbons and their derivatives. The project lays the foundation for the development of the direct use of sunlight in the chemical conversion of CO2.
Furthermore, in the long term, the project’s outcome will help to decarbonize the energy sector. The direct application of sunlight and the generation of solvated electrons in water or ionic liquids make this technology independent from fossil energy sources and hence it will have an important transformational impact on society by shaping of our future energy sources. When electricity from strongly fluctuating renewable resources such as wind or sun is employed, directly or indirectly, the system can be used to store this energy in the form of fuels and chemicals. Such decentralized, mobile and flexible energy storage is one of the components of the strategic energy plan for the European Area (SET-Plan), and DIACAT has contributed towards this goal.
Thus, this project fosters the development of a low-cost technology for the sustainable removal of with secure supply chain even at large scale. Due to the stability and corrosion resistance of diamond, the system will exhibit improved long-term stability - a key factor for the implementation of the technology. Application of sub-bandgap excitation to generate free electrons in the conduction band of diamond is a radically new approach. So far, the optical excitation of electrons in a wide band gap semiconductor like diamond had not been explored. In this light, the project contributed fundamental new knowledge in a technologically important area.
In order to interact with stakeholders and the wider public we publicized the research through social media and the project website to inform interested parties about the progress and achievements of the DIACAT project. A collaboration with artist Pinar Yoldas in the frame of FEAT (Future & Emerging Art and Technology) programme helped to raise awareness on climate change and CO2 and enabled to further publicize our work by means of artistic interpretation.
The participation at a FET Meet&Match Event aimed at connecting with scientists, business stakeholders and early investors as a first step toward future exploitation of project results. DIACAT has been also active in policy work by participating in the P4P validation workshop organised by the EC on how to unlock the potential of novel technologies and to enable a significant reduction of carbon emissions in industry through energy efficiency and carbon capture and utilisation. At the end of the project, an international symposium was organized that showcased the chances and challenges of carbon nanomaterials for the sustainable transformation and storage of energy.
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