Cambridge researchers use sunlight to create clean, liquid drop

Motiar Rahaman

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Researchers at Cambridge University in the U.K. have succeeded in replicating the process of photosynthesis to convert carbon dioxide and water into fuel. The highlight of the research is that the fuel can be used as a drop-in fuel for existing vehicles, a press release said.

With countries around the world looking for ways to move away from fossil fuels, electric modes of transportation are being promoted while discouraging the sale of vehicles with internal-combustion engines (ICE). Although the policy has the right intent, a mandatory move to electric vehicles will leave millions of vehicles with ICE in the junkyard while also pumping up demand for rare earth minerals that are needed to make EV batteries.

A non-carbon emitting drop-in fuel could extend the life of ICE vehicles without raising concerns about damaging the environment. The research at Cambridge promises to make this possibility a reality in the near future.

Biofuels such as ethanol have been suggested as a replacement for fossil fuels. Countries have already begun using them as substitutes in smaller proportions. However, the production of biofuels requires the diversion of agricultural land.

With an ever-growing global population, many have questioned the need to convert food into fuel. In the U.S. alone, 45 percent of corn grown is used for ethanol production.

Motiar Rahman

Erwin Reisner and his team of researchers at Cambridge have been looking for ways to generate zero-carbon fuels and have found their answer in the artificial leaf. Just like their natural counterparts, artificial leaves convert carbon dioxide and water into usable chemicals that can be used in the pharmaceutical, plastic, or fuel industry.

The researchers were able to use their artificial leaf to make syngas – a combination of hydrogen and carbon monoxide. However, they needed it to make much more complex chemicals in a single step if the technology had to have practical applications.

The researchers then developed a catalyst using copper and palladium that allowed the artificial leaf to produce complex chemicals like ethanol and propanol. Both of these multicarbon alcohols are also high-density fuels that can be stored and transported easily.

Research from other groups has also led to the synthesis of these alcohol molecules, but the source of energy in their case was electricity. This is the first time only solar energy has been used to synthesize these chemicals.

The device is still in the proof of concept stage. The research team is now working to optimize the light absorbers and the catalyst so that more fuel can be generated, increasing the overall efficiency of the system. Further work will also involve increasing the size of the leaf so that large volumes of fuel can be generated at a time.

The research findings were published today in the journal Nature Energy.

Abstract:

The synthesis of high-energy-density liquid fuels from CO2 and H2O powered by sunlight has the potential to create a circular economy. Despite the progress in producing simple gaseous products, the assembly of unassisted photoelectrochemical devices for liquid multi-carbon production remains a major challenge. Here we assembled a standalone artificial leaf device by integrating an oxide-derived Cu94Pd6 electrocatalyst with perovskite–BiVO4 tandem light absorbers that couple CO2 reduction with water oxidation. The wired Cu94Pd6 | perovskite–BiVO4 device provides a Faradaic efficiency of ~7.5% for multi-carbon alcohols (~1:1 ethanol and n-propanol), whereas the standalone artificial leaf produces ~1 μmol cm−2 alcohols after 20 h unassisted operation under AM 1.5 G irradiation with a rate of~50 μmol h−1 gCuPd−1. This study demonstrates the production of multi-carbon liquid fuels from CO2 over an artificial leaf and therefore brings us a step closer in using sunlight to generate value-added complex products.