The humble leaf is an unbelievable little machine, changing carbon dioxide and sunlight into energy for a plant. Synthetic versions could be valuable renewable energy sources, or even used to generate fuels. Currently, researchers from the University of Cambridge have developed an artificial leaf that can produce synthetic gas (or syngas) without discharging carbon dioxide.
Syngas is made from hydrogen and carbon monoxide, occasionally with a bit of carbon dioxide thrown in. While it can precisely be burned to produce electricity or for gas heating and lighting, it more frequently acts as an intermediate step in making products, including fertilizers, plastics, and fuels like diesel. Regrettably, producing it can emit carbon dioxide into the atmosphere.
“You may not have heard of syngas itself but each day, you consume products that were made using it,” says Erwin Reisner, senior writer of the study. “Being able to produce it sustainably would be a vital step in finishing the global carbon cycle and forming a sustainable fuel and chemical industry.”
To enable that, the Cambridge team developed an innovative artificial leaf prototype that can make syngas through photosynthesis. The new device comprises two light absorbers made of perovskite and a cobalt catalyst. When these are positioned in water, one side produces oxygen, while the other reduces carbon dioxide and water into carbon monoxide and hydrogen. Those last two gases can then be integrated into syngas.
The team demonstrated that the technology can still work even in reasonably low light, like that on cloudy or rainy days. The perovskite was selected because it’s good at absorbing light and generating a voltage, which is why it’s presenting in solar panels so much recently. For now, the cobalt in the catalyst is lower cost and more effective at generating carbon monoxide than other materials.
That said, the transformation efficiencies are still quite low – the new design currently generates hydrogen at an efficiency of 0.06 percent and carbon monoxide at 0.02 percent.
The new device enters a range of artificial leaf designs that are being developed to create an array of useful products, like drugs, electricity, fertilizers, and hydrogen fuel. Eventually, the team hopes to be able to miss the middleman syngas stage.
“What we’d like to do next, rather than first making syngas and then changing it into liquid fuel, is to make the liquid fuel in a single step from carbon dioxide and water,” says Reisner. “There is a key demand for liquid fuels to operate aviation, heavy transport, and shipping sustainably.”
The research was issued in the journal Nature Materials.