To tackle global warming, we shouldn’t just reduce our carbon emissions. This has led researchers to investigate how to recycle carbon dioxide into carbon-neutral fuel sources. Now, a team from Indiana University led by Professor Liang-shi Li has worked on a way to do it using sunlight and a special chemical molecule.

The molecule is a piece of nanographene with a rhenium atom attached. The nanographene acts as a solar collector by absorbing the energy of sunlight and transmitting that energy to the rhenium, which can break carbon dioxide molecules into carbon monoxide that can be used as fuel. This breakthrough is reported in the Journal of the American Chemical Society.

"Carbon monoxide is an important raw material in a lot of industrial processes," Li said in a statement. "It's also a way to store energy as a carbon-neutral fuel since you're not putting any more carbon back into the atmosphere than you already removed. You're simply re-releasing the solar power you used to make it."

The team looked into rhenium, which is used in bipyridine molecules, because its effects in reducing carbon dioxide were already known. The drawback is that bipyridine can only do that using UV light, which is not ideal. So they came up with the idea of using graphene (which is just a single layer of carbon atoms) to absorb as much sunlight as possible and transfer that energy.

"If you can create an efficient enough molecule for this reaction, it will produce energy that is free and storable in the form of fuels," added Li. "This study is a major leap in that direction."

The nanographene leaf acts as a solar cell. The light generates a current trough the material, with electrons flowing into the rhenium “engine”, which breaks the CO2 molecule and releases carbon monoxide.

The breakthrough is very much a first step, although the team is already busy exploring the next step. They would like the molecule to be more resilient so that it lasts longer and doesn’t have to be in a liquid form. They also hope to find a substitute for rhenium, which is a rare metal. They think manganese, which is cheaper, might just do the trick.