Plants have been producing their own solar energy for half a billion years. Now humanity is catching up on replicating their photosynthetic processes.
Chemists at the University of Illinois have made a breakthrough in artificially replicating the process of photosynthesis in the laboratory. Their research has allowed for the production of liquid fuel, such as propane, from the combination of water, light and carbon dioxide. Ultimately, the researchers hope to replicate plantlife further by producing a substance that would allow solar energy to be efficiently stored - much like as it is within plants.
Within plants, sunlight is used to drive the chemical reaction between flora’s other prime resources - water and carbon dioxide. Ultimately, this reaction results in energy rich glucose, which the plant uses to perform its various functions and grow. It was this process, Prashant Jain, a chemistry professor and co-author of the study published in the Nature Communications journal, hoped to replicate with modern science. The team aimed to use the same green light portion of the visible light spectrum to synthesis water and carbon dioxide and produce liquid hydrocarbons - or fuel. As Jain explained:
"The goal here is to produce complex, liquefiable hydrocarbons from excess CO2 and other sustainable resources such as sunlight. Liquid fuels are ideal because they are easier, safer and more economical to transport than gas and, because they are made from long-chain molecules, contain more bonds -- meaning they pack energy more densely."
Taking a Leaf From Nature's Book
© Prashant Jain (left) and Sungju Yu performing artificial photosynthesis experiments using green light.
In order to achieve this, Jain and co-author Sungju Yu (pictured above) also had to reproduce the elements which allows photosynthesis to work within plantlife. In particular, a substitute for chlorophyll - the natural pigment that captures sunlight - had to be found. The University of Illinois team settled on electron-rich gold nanoparticles to fulfill this function, allowing the metal to act as a catalyst which absorbed the sunlight and facilitated the chemical reaction. Gold was discovered to be particularly effective as it could absorb sunlight readily, did not degrade over time and reacted favourably with carbon molecules. The result was useable liquid fuel.
Of course, the energy potential of this fuel could be released in the conventional method - via combustion in an engine - however, this would ultimately result in more carbon being produced, defeating the point of the endeavour. Instead, the team has hypothesised that the fuel could be used to power fuel cells related to solar energy. Jain continued:
"There are other, more unconventional potential uses from the hydrocarbons created from this process. They could be used to power fuel cells for producing electrical current and voltage. There are labs across the world trying to figure out how the hydrocarbon-to-electricity conversion can be conducted efficiently."
Additionally, such artificial photosynthetic processes could become an important element of carbon capture technology - a pioneering field which hopes to recycle the carbon emitted from industrial process back into fuel. Various approaches have been experimented with to achieve this, however at their core they follow the same process - combining carbon with hydrogen to create hydrocarbons.
Ultimately, however, it might be some time before we see artificial trees lining city boulevards and recycling carbon dioxide into green energy. Although Jaim’s team have proven the process works, it is currently far too inefficient to be immediate practical use. The metal catalysts used in the artificial process, for example, need to be fine-tuned to allow for economic output. The University of Illinois team are also not the only researchers looking to plants for inspiration. In 2017, a German research center also announced progress in unlocking the secrets of photosynthesis - albeit on a small scale.
So, for the time being, it seems, nature is still ahead of humanity in using the power of the sun for fuel. But importantly, we are catching up.