Scientists at Rice University have used graphene quantum dots combined with nitrogen atoms to transform CO2 into liquid fuel.
Described in the journal Nature Communications, the nitrogen-doped graphene quantum dots (NGQDs) act as an electrocatalyst, converting the greenhouse gas into small batches of ethylene and ethanol. Although the researchers say they don’t fully understand the mechanism at work, the NGQDs are as efficient a catalyst as copper, which is also being tested to turn CO2 into complex hydrocarbons. Furthermore, the quantum dots also retain their catalytic activity for a long time.
“It is surprising because people have tried all different kinds of catalysts, and there are only a few real choices such as copper,” said Rice materials scientist Pulickel Ajayan, who led the research.
“I think what we found is fundamentally interesting, because it provides an efficient pathway to screen new types of catalysts to convert carbon dioxide to higher-value products.”
The quantum dots are atom-thick sheets of carbon which have been split into particles about a nanometre thick and just a few nanometres wide. Adding nitrogen atoms enables various chemical reactions to take place when an electric current is applied and a feedstock like carbon dioxide is introduced. In lab tests, NGQDs were able to reduce carbon dioxide by up to 90 per cent, converting 45 per cent into either ethylene or alcohol.
“Our findings suggest that the pyridinic nitrogen (a basic organic compound) sitting at the edge of graphene quantum dots leads the catalytic conversion of carbon dioxide to hydrocarbons,” said Rice postdoctoral researcher Jingjie Wu, co-lead author of the paper.
“The next task is further increasing nitrogen concentration to help increase the yield of hydrocarbons.”
While the electrocatalysis can easily be performed in the lab, industry generally uses scalable thermal catalysis to produce fuels and chemicals. As a result, said Ajayan, the process is unlikely to be adopted in the near future for commercial purposes.
Last paragraph is a bit of a bombshell. The rest of the article describes a really interesting technology… “but this isn’t a lot of use.”
Surely there’s some expectation for it somewhere, e.g. where there’s electrical power but not heat? What about energy storage at a wind farm, for example? I’m sure the inventors would have better ideas; it would be good to hear their view.
It really depends on whether the quantities scale up to the macro world, or if nothing more than nanomoles of product are ever made. If the reaction can be “tweaked” by adding more nitrogen to the quantum dots, perhaps yield goes up. Next question is how many durable quantum dots can be packed in a reactor?
Maybe I miss the point. “Qdots convert CO2 into fuel” sounded too good to be true. The story is that electrical energy can reduce the CO2 into something less oxidised that can subsequently burn (i.e. re-oxidise). Clearly the process is not 100% efficient and so as a means of producing fuel it is perhaps most useful if used to convert surplus green energy for storage.
Given the other storage technologies which are far more developed, have likely far higher round trip efficiencies and lower maintenance costs I’m not sure the suggestion of using this concept to store energy is viable.
The useful thing about liquid fuels is the energy density, a tank of liquid fuel is still one of the most compact ways to carry enough energy to hurtle around the planet in a variety of vehicles.
If you want carbon neutral plane travel, this idea might work, but then, as the article says thermal catalysis scales better and there’s more waste heat about.
Maybe space travel?