Artificial leaf can capture CO2 to make fuel without using any electricity

This approach allowed researchers to cheaply create methanol gas


Researchers have found a way to capture and convert harmful CO^^2 gas into methanol by mimicking a tried-and-tested natural process: photosynthesis.

This process could help automotive, aviation, and chemical production industries reach carbon neutrality by enabling them to convert CO^^2 into methanol gas to be used as a form of alternative fuel or as a way to produce plastics and fibers found in our day-to-day products. This reduction in emissions from such industries would be an important step forward towards curbing damaging environmental effects globally and could ultimately even be a more viable economic choice as well.

In research published Monday in the journal Nature Energy, researchers describe their approach to what has largely been an underdog technique in the world of CO^^2 conversion. Artificial leaves using electricity (also called photovoltaic-electrolysis) have been growing in popularity, but the authors write that their approach, called photocatalysis, had seen little success since its initial proposal in 1978, despite having the potential to be cheaper and more efficient than electricity-based models of CO^^2 conversion.

Previous failures-to-launch for this technology have come down to poor stability and the high-cost of elements necessary for production, the authors write.

But that is about to change, Yimin Wu, an engineering professor at the University of Waterloo who led the research, tells Inverse. Their study’s use of a new photocatalytic compound, cuprous oxide, to spark the conversation reaction allows for efficiency and price that could rival electric-based approaches.

“Our discovery is an inexpensive, simple, efficient way to convert CO^^2 into liquid fuel methanol using sunlight and H^^2^^O,” Wu says. “This is unlike other artificial leaves which use electricity [because] our method does not need any electricity. This gives two major advantages, one it is a simpler infrastructure to scale up, and the other is it directly converts the energy contained in sunlight into fuels, without intermediary conversion into other refillable chemicals, heat or electricity.”

Pictured above, the process of creating the cuprous oxide catalyst in the lab

University of Waterloo

Their artificial leaf works adding the red, powdered cuprous oxide to water and exposing it to white light. This exposure to light jump-starts a reaction in which oxygen is created and CO^^2 derived from the powdered compound and water is converted into methanol, which is collected as it evaporates from the heated solution.

The study reported an internal yield of methanol creation of about 72 percent, which they write is comparable to other electricity-based approaches which have yielded between 50 and 60 percent in previous studies. The study also reports a conversion efficiency of about 10 percent, which Wu tells Inverse is 10 times that of natural photosynthesis, which has an efficiency of about one percent.

While the researchers write that this approach will be scalable in the future, and in particular could be tweaked to create gas other than methanol, Wu says there is still a long road ahead before they can begin thinking about commercializing this approach. Namely, a need for increased efficiency and improving the methanol yield.

“[M]ore efficient artificial leaves can be developed along these lines to bring this research to the commercial space with partnership with industry partners,” Wu says.

But when those advances in efficiency and yield are made, Wu says that a handful of different industries have the potential to benefit and even potentially close their carbon-cycles in the process.

“Many industries have the demand for reducing CO^^2 emissions, such as the automobile industry, the steel industry, and the oil drilling industry. This approach can provide solutions to these demands by providing this carbon-neutral method,” says Wu. “[And] other industries, like the aircraft industry [and] automobile industry, look for alternative fuels to gasoline. This approach can provide them clean and sustainable fuels.”

As industries such as aviation and automotive slowly work to overcome their dependency on nonrenewables, an artificial approach to fuel consumption that restricts the creation of extra CO^^2 emissions could be a good place to start.

Read the abstract here:

Atomic-level understanding of the active sites and transformation mechanisms under realistic working conditions is a prerequisite for rational design of high-performance photocatalysts. Here, by using correlated scanning fluorescence X-ray microscopy and environmental transmission electron microscopy at atmospheric pressure, in operando, we directly observe that the (110) facet of a single Cu2O photocatalyst particle is photocatalytically active for CO2 reduction to methanol while the (100) facet is inert. The oxidation state of the active sites changes from Cu(i) towards Cu(ii) due to CO2 and H2O co-adsorption and changes back to Cu(i) after CO2 conversion under visible light illumination. The Cu2O photocatalyst oxidizes water as it reduces CO2. Concomitantly, the crystal lattice expands due to CO2 adsorption then reverts after CO2 conversion. The internal quantum yield for unassisted wireless photocatalytic reduction of CO2 to methanol using Cu2O crystals is ~72%.