It’s Like a Leaf, But Better
By: Madison Hunter
Tags: Climate Change, Sustainability, Technology, Environment, Future

The field of chemistry has already had prior success in engineering artificial photosynthetic systems that can be used in tandem with carbon capture technology to turn carbon dioxide into usable fuels.

The first photosynthetic biohybrid system was produced in 2015. The system developed at UC Berkeley used semiconductors and live bacteria to produce a photosynthetic reaction that would use solar energy to produce liquid fuels using carbon dioxide and water. At the time, it was predicted that if the technology improved, it may become the future of energy. The process involves catalysts harvesting solar energy to generate charge which is then transferred to bacteria. The bacteria use the electric charge from the catalysts to instigate a chemical reduction reaction that turns carbon dioxide into liquid fuel. Butanol, acetate, polymers, and pharmaceutical precursors were produced as a result of this experiment. Furthermore, it was found that this first artificial photosynthetic system had a solar-to-chemical conversion efficiency of 0.38%, which is comparable to the efficiency of a natural leaf.

The innovation didn’t stop there though.

A year later at McGill University in Montreal, Canada, the chemical transformation of carbon dioxide into fuels was achieved using metal-nitride nanowires as a catalyst to overcome the eventual efficiency bottleneck that can occur when using conventional photocatalytic technologies. While the typical conversion process of carbon dioxide into fuel requires high temperatures, high pressures, and/or extremely reactive reagents, the metal-nitride nanowire photocatalyst developed allows the process to be completed more stably and efficiently, while also occurring at room temperature. The result: solar fuels generated using an efficient artificial photosynthetic system that can be used to pull carbon dioxide out of the atmosphere, bringing society closer to a net-zero future.

UC Berkeley and McGill University aren’t alone in developing this groundbreaking technology. Just a few years later, another breakthrough came in the world of artificial photosynthetic systems.

In a 2019 report published in the American Chemical Society journal of Sustainable Chemistry and Engineering, the solar-to-fuel efficiency of an artificial photosynthetic (AP) system was evaluated. The study looked directly at how the AP system can capture carbon dioxide directly from the atmosphere and can then convert it into fuel using sunlight. The report concludes that a modern, fully integrated AP system could reduce the carbon dioxide levels in the surrounding air by 10% during steady-state operation, which makes it fourteen times more efficient than natural leaves.

This report was analyzing a study conducted by the Department of Chemical Engineering from the University of Illinois, who had successfully produced fuels using water, visible light, and carbon dioxide using artificial photosynthesis. Scientists conducting the study developed an artificial photosynthesis process that used the same visible green light portion of the electromagnetic spectrum used by plants during natural photosynthesis to convert carbon dioxide and water into fuel. The process used a plasmonic excitation of gold nanoparticles (used as a catalyst) to produce a rich, electrically-charged environment at the gold particle-carbon dioxide solution interface which is conducive to carbon dioxide activation. From there, an ionic liquid stabilizes the charged intermediates that formed on the surface of the interface which begins to facilitate a multi-step chemical reduction reaction coupled with carbon coupling. Multi-carbon chains can be produced, resulting in the formation of methane, ethylene, acetylene, propane, and propene.

The University of Illinois chemists who conducted the study wanted to focus on creating liquid fuels because they are easier, safer, and more economical to store and transport than regular gasoline. Furthermore, liquid fuels are comprised of long-chain molecules containing more bonds than regular gasoline, giving them a higher energy density. While the goal of the study was to learn how to use catalysts to increase the efficiency of the chemical reactions undergone during the carbon dioxide-to-fuel conversion experiment, the chemists of the study agree that the hard work will begin when they start determining how they can scale up the process.