Researchers present new and efficient conversion method

Greenhouse gas emissions are known to be the main cause of global warming. According to the Federal Environment Agency, around 666 million tonnes of carbon dioxide were emitted in Germany alone last year. All countries in the world have committed, in various climate agreements, to reducing these emissions to zero in the medium term. But climate scientists are already convinced that this alone is not enough. The CO2 that already floats in the atmosphere must also be recovered, at least in part.

But what should we do about greenhouse gases? Numerous research teams around the world are now working on this. Vietnamese researcher Cao Thang Dinh and his team at Queen’s University have now invented an integrative system that can handle both the capture and conversion of carbon dioxide (CO2). His team promises that their method uses less energy than previous conversion processes.

In recent years, several technologies have been developed that can convert CO2 into other substances. In the “Carbon2Chem” project, for example, useful chemicals are created from carbon dioxide by breaking down the material and processing it further. But CO2 is difficult to split and therefore consumes a lot of energy. This is often energy obtained from fossil fuels and can therefore lead to more CO2 emissions.

Cao Thang Dinh is trying to make this process more efficient. He wants to use electricity to cause a chemical reaction. Carbon dioxide could be converted into carbon-neutral fuels using renewable energy. “In this way, we can store intermittent electricity in the form of gas,” explained the scientist at this year’s Falling Walls Science Summit in Berlin. “We can also convert carbon dioxide into a sustainable polymeric material so that we can permanently store CO2, which is a carbon-negative process.”

The conversion of carbon dioxide requires a reactor in which the molecule goes through different phases: first it is converted into a gas and then into a solution before stabilizing on the surface of the solid, which serves as a catalyst. There, the CO2 molecule is broken down into smaller molecules or atoms. These are then combined with other molecules to obtain various end products.

For the conversion to be particularly climate-friendly, several factors such as energy efficiency, reaction rate or product selectivity must be taken into account. The target end product of Dinh’s experiments is ethylene, an important raw material in the chemical industry. The objective is to stabilize the conversion system so that high selectivity can be maintained over a long period of time. Until now, the best CO2 conversion system only lasted a few hours. Dinh and his team were able to discover the reason for the failure and let the process last longer.

One reason for the short duration of the process is the decomposition of the electrode at which the CO2 molecule is converted. That’s why the team reinvented the electrode structure. “We use a very stable polymer in combination with the active layer of the molecule and then cover this combination with a protective layer,” explains Dinh. With this system, researchers were able for the first time to maintain high ethylene selectivity for around 150 hours.

Dinh’s experiments also show that it is possible to enlarge the reactor to convert more carbon dioxide. In initial studies, the reactor was the size of a Rubik’s cube, capable of converting about a gram of CO2 per day. The Queen’s University team has now managed to build a microwave-sized reactor that can convert up to 2.5 kilograms of CO2 per day. “To date, this is one of the largest electrochemical conversions of CO2 ever demonstrated,” says the chemist.

To convert carbon dioxide, it must be extracted and purified from the atmosphere, exhaust gases or industrial processes, which are also energy-intensive. This happens in nature without human intervention. An apple tree, for example, takes diluted carbon directly from the air and converts the CO2 into carbohydrates, creating an apple without the individual substances having to be cleaned and separated. The Vietnamese scientist is guided by this process.

His research team has been working on a solution for about a year. The starting point for the experiments is concentrated and diluted CO2. This is collected in a solution and then introduced into the reactor as a solution. The gaseous product leaving the reactor is then continuously separated from the liquid. In the end, a concentrated product is created that can reduce energy costs for separation. The electrodes used in the reactor are crucial: depending on the material, reactors can be built that convert as much CO2 as 5 to 10 adult trees.

To convert carbon dioxide on a scale of millions of tons, an efficient and cost-effective system is needed. Dinh’s objective is to increase the selectivity of polyethylene from 75% to 95% and triple energy efficiency.

With its development, Dinh hopes to produce a chemical CO2 conversion system that can be used throughout the world thanks to renewable energy. “If we can do this, not only can we reduce carbon emissions and slow climate change, but we can also give everyone, especially those in least developed countries, the opportunity to have access to clean energy, clean fuel, sustainable materials and obtain sustainable energy. fertilizer.”