Syngas from artificial leaf offers sustainable liquid fuels

Researchers have developed a method of making syngas with an ‘artificial leaf’, an advance inspired by photosynthesis that could be used to develop a liquid fuel alternative to petrol.

syngas
This ‘artificial leaf’ uses water, sunlight and carbon dioxide to produce a widely-used gas, inspired by the natural process by which plants use the energy from sunlight to turn carbon dioxide into food (Credit: Virgil Andrei)

The artificial leaf from Cambridge University is powered by sunlight and does not release any additional carbon dioxide into the atmosphere. The results are reported in Nature Materials.

Syngas is made from a mixture of hydrogen and carbon monoxide and is used to produce commodities including fuels, pharmaceuticals, plastics and fertilisers.

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“Being able to produce [syngas] sustainably would be a critical step in closing the global carbon cycle and establishing a sustainable chemical and fuel industry,” said senior author Professor Erwin Reisner from Cambridge’s Department of Chemistry, who has spent seven years working towards this goal.

On the artificial leaf, two light absorbers, similar to the molecules in plants that harvest sunlight, are combined with a catalyst made from cobalt. When the device is immersed in water, one light absorber uses the catalyst to produce oxygen. The other carries out the chemical reaction that reduces carbon dioxide and water into carbon monoxide and hydrogen, forming the syngas mixture. The researchers add that their light absorbers work under the low levels of sunlight or on rainy or overcast days.

The research was carried out in the Christian Doppler Laboratory for Sustainable SynGas Chemistry in the University’s Department of Chemistry and was co-funded by the Austrian government and OMV, a petrochemical company headquartered in Vienna.

“The [Cambridge] team’s fundamental research to produce syngas as the basis for liquid fuel in a carbon neutral way is ground-breaking,” said Michael-Dieter Ulbrich, a senior advisor at OMV.

Other ‘artificial leaf’ devices have also been developed, but these usually only produce hydrogen. The Cambridge researchers say the reason they have been able to make theirs produce syngas sustainably is down to the combination of materials and catalysts they used.

These include perovskite light absorbers, which provide a high photovoltage and electrical current to power the chemical reaction by which carbon dioxide is reduced to carbon monoxide. The researchers used cobalt as their molecular catalyst as it is more economical and better at producing carbon monoxide than other catalysts.

The team is now looking at ways to use their technology to produce a sustainable liquid fuel alternative to petrol.

“What we’d like to do next, instead of first making syngas and then converting it into liquid fuel, is to make the liquid fuel in one step from carbon dioxide and water,” said Reisner. “There is a major demand for liquid fuels to power heavy transport, shipping and aviation sustainably.”