Renewable forms of energy have become increasingly more important for a multitude of reasons, including in the sphere of technology. Because of this, there has been a considerable increase in the amount of research invested in renewable energies and CO2 reduction.
Over the last few years, several research teams have put resources into developing devices that can reduce CO2 effectively.
CO2 Reduction without Byproducts
Recently, an international research team headed by researchers from the United States Department of Energy's Lawrence Berkeley National Laboratory and Singapore’s Nanyang Technological University have developed a material that can not only reduce CO2 but also create essential fuels from light with nearly 100% selective production of CO.
The CO2 becomes CO after undergoing a process known as reduction. In order for this to happen, the carbon dioxide needs a catalyst to break down. There are a multitude of catalysts that have been used reduce CO2, but none have been able to completely eliminate the competing chemical reactions that occurred during reduction.
Representation of CO2 reduction. Image courtesy of Deanna D'Alessandro via the University of Sydney
“We show a near 100% selectivity of CO production, with no detection of competing gas products like hydrogen or methane,” said Haimei Zheng, staff scientist in Berkeley Lab's Materials Sciences Division and co-corresponding author of the study. “That's a big deal. In carbon dioxide reduction, you want to come away with one product, not a mix of different things.”
To create the material, the team developed an innovative laser-chemical process instead of using a traditional heating method. The nickel precursors were dissolved into a triethylene glycol (TEG) solution and irradiated by an unfocused infrared laser for three hours. The radiation from the light initiates the reaction between the transition metal ions and the TEG. The end result of the reaction is a series of metal hydroxide composites that are then filtered from the rest of the solution. Comparatively, the traditional heating method involved heating the precursor solution for 48 hours, cleansing it with acetone, and then centrifuging.
Comparison to MOFs (Metal Organic Frameworks)
The resulting photocatalyst structure was similar to that of metal organic frameworks (MOFs). The MOF design was considered due to its ability to capture CO2, notably the tunable pores and high surface area. In traditional MOFs, the structure consists of rigid linkers coordinated with metal ions that create a very organized framework.
Earlier this year, Professor Fernando Uribe-Romo from Central Florida University and his research team released a paper on their own MOF-based device that uses blue LED photoreactors to counteract pollution from fossil fuel power stations.
Dr. Uribe-Romo and his device. Image courtesy of UFC
By comparison, in the new photocatalyst, the rigid linkers are instead replaced with TEG soft linkers of varying length that lack the carboxylic groups that provide the organized framework. Without the carboxylic groups, the MOF crystal growth can be staggered, which results in defects. These defects are intentional as they provide more areas and pores for reactions to take place in.
The material was tested in a chamber filled with CO2 gas and yielded promising results. It was found that 1 gram of the catalyst was capable of generating 400mL of CO in under an hour, and remained stable under extended use.
However, it was noted in the data that increased amounts of the photocatalyst would yield less carbon monoxide, something that would need to be further developed, especially in large-scale production. The material was tested further by enriching it with silver and rhodium nanocrystals, yielding acetic and formic acids. The yield of these two acids marks the first step in producing valuable multicarbon fuels.
The original research article can be found in the Journal of Science Advances.
Featured image credit source: UCF: Bernard Wilchusky.