Carbon Dioxide Guzzlers

Carbon dioxide, the most common greenhouse gas, plays an important role in helping the earth hold on to the energy it gets from the sun by trapping it close to the planet. However, this gas is harmful in excess. Too much carbon dioxide (CO2) in the atmosphere increases the greenhouse effect, contributing to climate change. Scientists are working on ways to not only remove excess CO2 but also to turn this into energy. Ultimately, if we are to make any headway in halting the heating up of the earth, it is not enough to merely reduce our carbon dioxide emissions – we need to actively clean it out of the atmosphere too.

Plants do an amazing job of converting sunlight, water, and carbon dioxide into energy, something which scientists have failed to recreate – until now. Researchers from the University of Illinois at Chicago (UIC) have successfully designed an artificial leaf that can work under real-world conditions, sucking carbon dioxide out of the air and creating oxygen and synthetic fuels. The fact that it can work under realworld conditions is significant, because past versions of artificial leaves were only able to do this under lab conditions.

According to Meenesh Singh, corresponding author of the UIC study, all designs for artificial leaves that have been tested in the lab use carbon dioxide from pressurised tanks. To be implemented successfully in the real world, these devices need to be able to draw carbon dioxide from much more diluted sources, such as air and flue gas, which is the gas given off by coal-burning power plants. Their new artificial leaf design is such a kind of real-world-ready technology, the UIC researchers say. Better still, their design will be as much as ten times more efficient at this process than a natural leaf, the research team touts. The team calculated that in one day, 360 of these leaves could produce half a ton of carbon monoxide and pull ten percent of the CO2 out of the air for about 100 metres around the setup.

The leaf is essentially an artificial photosynthesis unit, wrapped in a transparent capsule. The outer layer is a semi-permeable membrane made of quaternary ammonium resin filled with water. The idea is that when the sun hits the device, the water slowly evaporates out through these pores and, in its place, CO2 is selectively sucked in from outside. That gas is then converted into carbon monoxide by the artificial photosynthesis unit on the inside. This carbon monoxide can be captured and used for a range of purposes, like making synthetic fuels. Oxygen is also a by-product and can either be collected or released back into the outside air, as would be the case with a natural plant.

“By enveloping traditional artificial leaf technology inside this specialised membrane, the whole unit is able to function outside, like a natural leaf,” explains Singh. "Our conceptual design uses readily-available materials and technology that, when combined, can produce an artificial leaf that is ready to be deployed outside the lab, where it can play a significant role in reducing greenhouse gases in the atmosphere."

Researchers at Ulsan National Institute of Science and Technology (UNIST) and Georgia Tech, inspired by the ocean's role as a natural carbon sink, have developed a new system that absorbs CO2 and produces electricity and usable hydrogen fuel. The device, which the team calls a Hybrid NA-CO2 System, is essentially a big liquid battery. Unlike other designs, this one does not release any CO2 as a gas during normal operation.

“Carbon capture, utilisation, and sequestration (CCUS) technologies have recently received a great deal of attention for providing a pathway in dealing with global climate change," says Professor Guntae Kim, lead researcher on the study. "The key to that technology is the easy conversion of chemically stable CO2 molecules to other materials. Our new system has solved this problem.”

While the team says that there is still room for improvement on every component of the new design, what is certainly noteworthy about it is the system's ability to also produce renewable electricity and hydrogen fuel, which could be used, for example, to power hydrogen cars.

While most of the world is moving toward renewables at an increasing pace, there are still hundreds of fossil-fuel-powered plants pumping greenhouse gases into the atmosphere with reckless abandon. Researchers at Oak Ridge National Laboratory (ORNL) have, thankfully, developed a substance that could soak up the carbon from such power plant emissions, and do it using less energy than existing methods.

Underpinning this new technology is a class of organic compounds called bisiminoguanidines (BIGS), which bind to specific anions – negatively charged ions – over others. According to the ORNL researchers, this system uses 24% less energy than existing methods. “The main advantage of our 'organic soda lime' is that it can be regenerated at much lower temperatures and with significantly less energy consumption, compared to inorganic scrubbers," says Radu Custelcean, senior author of the study. "The lower energy required for regeneration is expected to significantly reduce the cost of carbon capture, which is critical considering that billions of tons of CO2 need to be captured every year to make a measurable impact on the climate.”