On the face of things, artificial leaves are a two-pronged weapon in the fight against carbon emissions and global warming. Not only do they convert carbon dioxide (CO2), a damaging greenhouse gas that is noxious to humans, into a usable fuel source, but they also turn water into breathable oxygen to replenish our airways. Even better, all of this is achieved using renewable energy from the sun.
However, as with many forms of engineered nanotechnology, the current setup poses both a problem as well as a solution. At present, the artificial leaves in use are highly inefficient, converting a mere 15% of the CO2 they absorb into fuel and releasing the remaining 85% back into the atmosphere along with the oxygen created from the water. As such, drastic improvements in the system are required to make artificial leaves a realistic weapon against carbon emissions.
Acidic splits
Current forms of artificial leaves function via the use of a photoelectrochemical cell. CO2 enters through the cell&#;s electrolyte component, where it is dissolved and converted into bicarbonate anions. These travel through to the &#;positive&#; side of the leaf, where water is converted into oxygen. However, that latter conversion process has the unwanted side effect of creating acidic electrolytes as well.
When the bicarbonate anions come into contact with the acidic substances, they produce CO2 once more. This is then released along with the oxygen, contributing to the very issue that the artificial leaves were designed to alleviate. Thus, like many other forms of carbon capture technology, the leaves are not yet operating at anything close to peak efficiency.
&#;The artificial leaves we have today aren't really ready to fulfil their promise as carbon capture solutions because they don't capture all that much carbon dioxide,&#; explained Meenesh Singh, author of a new paper investigating the issue. &#;In fact, [they] release the majority of the carbon dioxide gas they take in from the oxygen-evolving &#;positive&#; side.&#;
Solution buffering
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To circumvent the problem, Singh decided to introduce a buffer between the bicarbonate anions and the acidic side of the leaf. Singh serves as assistant professor of chemical engineering at the University of Illinois and has previously implemented similar technology to optimise artificial leaves in a different sense, by endowing them with the capability to absorb CO2 from the atmosphere rather than from pressurised tanks.
Applying the same kind of bipolar membrane, Singh and his colleagues were successful in separating the two parts of the leaf and preventing the chemical reaction which causes the production of CO2. Thanks to their small but significant tweak in the leaf&#;s composition, they were able to boost its carbon-conversion efficiency from just 15% to between 60% and 70%.
Along with Singh&#;s other efforts in adapting artificial leaves to real-world conditions, he is hoping that this latest alteration in their composition will make the technology both implementable and scalable to provide a meaningful contribution towards our CO2 issues.
Spotted: Engineers often look to nature for inspiration, and, when it comes to capturing carbon dioxide, the leaves of photosynthesising plants set the gold standard. Scientists have been trying to recreate the CO2-capturing properties of leaves for some time, but mimicking nature is not always easy.
Now, researchers from the University of Illinois at Chicago have developed an artificial leaf that is both more efficient at capturing CO2 than existing carbon capture systems, and able to capture carbon from more diluted sources &#; such as the flue gases produced by coal-fired power plants.
To develop the leaf, the researchers modified a pre-existing artificial leaf system by adding new, and inexpensive materials, to create a water gradient&#;a dry side and a wet side&#;across an electrically-charged membrane.&#;On the dry side, an organic solvent attaches to available carbon dioxide to produce bicarbonate ions. The negatively charged ions are pulled across the membrane toward a positively charged electrode on the wet side. The electrode is immersed in a liquid solution which dissolves the bicarbonate, releasing the CO2. This can then be collected for fuel or other uses.&#;
Only around 0.4 Kilojoule/hours of electricity is needed to power the reaction &#; less than that used to power an LED bulb. When the researchers tested the system, they also found that is had a 100 times better rate of carbon capture to surface area compared to other systems. They estimate it would take around $145 (around &#;127) per tonne to harvest the CO2.
Meenesh Singh, assistant professor of chemical engineering and corresponding author on the paper also pointed out that this system is very scalable. &#;&#; it has the potential to be stackable, the modules can be added or subtracted to more perfectly fit the need and affordably used in homes and classrooms, not just among profitable industrial organisations.&#;
Globally, there are around&#;50 large-scale carbon capture facilities&#;in operation or under construction as of . But there are also a number of other innovations that hope to improve the scalability or reduce the cost of carbon capture and re-use. Springwise has covered a number of these, including a microporous material that makes sequestration cheaper and more efficient, and &#;liquid trees&#; made from algae to clean urban air.
Written By: Lisa Magloff
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