A revolutionary method to extract 99% of CO2 from the air

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Hydroxide exchange membrane fuel cells are currently being investigated as an alternative to traditional fuel cells. They would indeed be more economical and more ecological than the batteries used today. However, they have the disadvantage of being extremely sensitive to carbon dioxide in the air, which reduces their performance. After more than 15 years of research, a group of scientists decides to take advantage of this obstacle and proposes a particularly profitable solution allowing to extract 99% of the CO2 present in the air.

A fuel cell generates an electric voltage thanks to the oxidation of a reducing fuel (for example dihydrogen) coupled with the reduction of an oxidant, such as oxygen from the air. It consists of two bipolar plates (one which distributes hydrogen, the other which distributes oxygen), two electrodes and an ion exchange membrane (which acts as an electrolyte). Additionally, the oxidation is usually catalyzed by platinum. But this metal is rare and expensive, which is why scientists are looking for alternatives.

Unlike traditional batteries whose electrolyte is acidic (H+), hydroxide exchange membrane (HEM) fuel cells involve an alkaline environment that allows more cost-effective catalysts and bipolar plates to be used. However, their operation is largely impacted by ambient CO2, which prevents the battery from operating optimally. This problem induces up to 20% performance drop, according to the researchers. Professor Yushan Yan, and his team at the Center for Catalytic Science and Technology at the University of Delaware, realized that this drawback could actually serve to remove carbon dioxide from the air.

An innovative separation technique

Capturing CO2 from the air via a hydrogen-powered device could not only lead to the development of more environmentally friendly fuel cells, but could potentially help in the fight against global warming. ” We realized that fuel cells captured virtually all the carbon dioxide from the air that entered it, and were very efficient at separating it on the other side “, Explain in a press release Brian Setzler, Assistant Professor for Chemical and Biomolecular Engineering Research and co-author of the research paper.

The phenomenon affects the functioning of the cell, but the team realized that it could therefore act as a carbon dioxide separator – in other words, the cell would effectively extract CO2 from the air. ” It turns out that our approach is very effective. We can capture 99% of carbon dioxide from the air in a single pass if we have the right design and setup “, clarified Yan.

device diagram
The module designed by the researchers absorbs hydrogen and air through two separate inlets, then rejects carbon dioxide and “purified” air (after passing through two short-circuited membranes covered with a catalyst). © L. Shi et al.

To achieve this high level of efficiency, they integrated a short-circuited membrane into the electrochemical system, which conducts both the anions (CO32-) and the electrons. The device is powered by hydrogen, like a fuel cell, but does not require electrical wires, bipolar plates or current collectors, and can therefore be modulated like a typical separation membrane, the team explains in the review Nature Energy.

A very efficient and economical device

Integrating the wires of the device directly inside the membrane has made it possible to develop a more compact module, rolled up on itself – and thus to have a larger exchange surface while limiting the volume. This structure also allows carbon dioxide particles to move more easily from side to side; the module is therefore able to filter larger quantities of air at a time.

The results show that an electrochemical cell with a short-circuited membrane of 25 cm² can eliminate more than 99% of the CO2 present in the air, whose flow rate is 2000 cm³/min, for 450 hours, and can operate efficiently under dynamic load following conditions. An early prototype of the device, the size of a soda can, was found to be able to filter 10 liters of air per minute removing more than 98% of carbon dioxide, the researchers added. For an automotive application, the device would be about the size of a gallon of milk (or about 3.7 liters), Setzler said.

This innovative system therefore appears to be both efficient and profitable for fuel cell applications. In addition, the reduction in the number of components required results in a significant reduction in costs and, above all, makes it possible to envisage a rapid entry into the market. ” Our techno-economic analysis indicates that a compact module capable of removing more than 99% of CO2 costs $112 for an 80 kW HEM cellnet “, Say the authors of the study.

Of course, such a device could also be used to remove carbon dioxide in other contexts. The team notably evokes the possibility of installing it on board spaceships or submarines, where the continuous filtration of the air is essential. It could also be put to good use in airplanes and buildings, where air recirculation is one of the energy saving measures envisaged.

Source : L. Shi et al., Nature Energy

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⇧ [VIDÉO] You might also like this partner content (after ad) Hydroxide exchange membrane fuel cells are currently being investigated as an alternative to traditional fuel cells. They would indeed be more economical and more ecological than the batteries used today. However, they have the disadvantage of being extremely sensitive to carbon dioxide in the…

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