The technology being developed by the EU-funded DIACAT project could help reduce emissions from power stations by capturing the carbon currently emitted as CO2 and transforming it into chemicals such as hydrocarbons or methanol. These could then be used as a fuel, for example to power cars, or as ingredients for new chemicals.
‘At the moment we use fossil fuels to produce chemicals or to fuel our cars or to heat our homes, and that produces as a side product CO2,’ said Professor Anke Krueger from Würzburg University, Germany, who leads the project.
‘The long-term aim is to transform CO2 from the atmosphere or from exhaust gases into something useful.’
The researchers use ultra-thin layers of synthetic diamonds which are placed in a solution. When a particular wavelength of light is shone onto the diamond, it emits electrons which travel to the surface of the diamond in the solution and react with the carbon dioxide, transforming it into another substance.
The process has been described as a type of photosynthesis as it mimics the way that plants transform light energy from the sun into chemical energy to grow.
‘CO2 itself is very difficult to transform into something useful, it’s not very reactive,’ said Prof. Krueger. ‘In the lab that normally requires quite expensive and not easily achievable technologies. You need a lot of energy, you need expensive and rare catalysts, and you need more aggressive, or much less environmentally friendly, solvents.
The Issue
Carbon capture and utilisation (CCU) for the production of fuels, chemicals and materials has emerged as a possible complementary alternative to Carbon capture and storage (CCS). Low-carbon technologies will have a major role to play if the world is to meet the objectives set out in Paris last year during the COP21 climate talks.
Temperatures are already an average of 1 degree Celsius higher than the pre-industrial era, and to keep rises under 1.5 degrees Celsius, significant reductions in CO2 emissions will have to be made. The EU has set itself targets for progressive reductions between now and 2050.
It means we need to advance and invent better technologies that can remove CO2 from industrial and power plants, and vehicle exhausts, within the next few years.
‘We want to do it pretty much like nature, so in water, using sunlight and on the surface of a material that can be easily made and is not harmful to the environment at all - and this is diamond.’
Rough diamonds
The researchers use industrially produced nanodiamonds and diamond membranes, which are created in labs by depositing methane vapour into layers within a cubic lattice to create the structure of a diamond.
Diamonds are normally electrically insulating but, by doping them with boron, Prof. Krueger and the project team are turning them into semiconductors, which can then be used as electrodes within the solution.
The task for the researchers is to work out the best solution to use, as well as the ideal properties of the diamond and the optimal levels of CO2. This is being done by partners from across Europe, including the Fraunhofer Institute in Freiburg, Germany, CEA Saclay in France, University of Oxford, UK, Uppsala University in Sweden and the company IoLiTec.
Their work is being enhanced by a sophisticated technique which enables them to see the diamond emitting the electron in real-time. It was developed by Professor Emad Aziz from the Helmholtz Zentrum in Berlin and Freie Universität Berlin, Germany, who is a partner on the project.
‘Any of these kind of catalytic materials, if you want to develop and optimise it for solar fuel, for reducing the CO2 or doing its function, we have to see the process in reality,’ said Prof. Aziz. ‘This is happening usually quite fast by a small particle called an electron, in femtosecond timescale (a quadrillionth of a second), and happening in a very small area, in a few angstrom (a ten-billionth of a metre).’
The DIACAT researchers are using Prof. Aziz’s specially designed laser lab at the Helmholtz Zentrum to understand more about what happens at the diamond’s surface and tweak the material accordingly.
The femtosecond laser lab was originally developed as part of a project called PORPHDYN, funded by the EU's European Research Council. It was originally designed to view the electronic behaviour of one specific type of material, porphyrins, and has since been expanded to other materials, including nanodiamonds.
“‘The long-term aim is to transform CO2 from the atmosphere or from exhaust gases into something useful.’
Other fundamental knowledge for the DIACAT project was generated in the EU-funded MATCON and EQUIND projects.
Prof. Aziz says that if the DIACAT project works, nanodiamonds will become an attractive resource for solar fuel researchers. ‘It’s a big new book for studying and we will need to give it the time and the focus but I am quite optimistic.’
Visible light
So far, researchers have managed to use ultraviolet light to activate the diamond’s ability to turn carbon dioxide into fuel, but they are now working on a device that can use visible light, such as the sun.
Prof. Krueger says they are also aiming to make the device operate at room temperature, or at as low a temperature as possible, in order to minimise the amount of energy that needs to be used in the process.
The researchers hope to have a demonstration device ready within three years, and then Prof. Krueger estimates it will be another 10 to 20 years before the technology will be available on a commercial scale.
She is optimistic. ‘I cannot promise now what shape the technology will have but we will find a way to make it work.’
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