Anyone who needs plants simply uses solar energy

The idea of ​​a man-made device that can convert solar energy into usable fuel has been exciting researchers since the 1970s. With no free lunch, it’s not that easy to create a device that mimics photosynthesis that Mother Nature perfected long ago. Yet researchers at the Department of Energy’s Lawrence Berkeley Lab in California seem to have solved an important part of the artificial leaf challenge.

Solar energy & the artificial leaf of the future

The CleanTechnica radar first crossed the concept of the artificial leaf in 2011 in the form of a map-sized photo-electrochemical cell. Instead of converting sunlight into electricity, the cell acts as a catalyst that uses solar energy to split water into oxygen and hydrogen.

First versions of the device required purified water. By 2013, researchers had figured out how to prevent a film of dirt from covering the solar catalyst so that it could be used in contaminated water.

Around the same time, further improvements to the concept of artificial leaves began to emerge, with a major area of ​​research being to reduce the cost of the solar catalyst. The new iterations also included an artificial leaf that uses sunlight to convert carbon dioxide into carbon monoxide, a ubiquitous chemical building block.

Until 2014, researchers at the Berkeley Lab worked on a “bionic” version of the artificial leaf concept. They focused on hydrogen production through solar energy based on the premise that the energy storage value of hydrogen would help create a low cost route for a commercial version of the artificial leaf.

Just a year later, researchers from Lund University announced an artificial “supersonic sheet” based on artificial molecules that can collect solar energy and act as a catalyst. Again, this version was geared towards hydrogen production, with the potential to add methane to the list.

Why bother synthetic photosynthesis when we have wind and solar power?

Now that wind and solar power are so cheap, one might wonder why researchers are still so keen on making synthetic photosynthesis possible. If hydrogen is to be produced from water, this can be done by using solar energy to operate an electrolysis system that uses electricity to push hydrogen gas out of the water.

For the answer, let’s turn to Purdue University, which published an article last June on the benefits of mimicking photosynthesis over generating electricity from wind turbines and solar panels.

“The closest process to artificial photosynthesis that humans have today is photovoltaic technology, in which a solar cell converts solar energy into electricity. This process is known to be inefficient and can only capture about 20% of the sun’s energy, ”noted Purdue. “Photosynthesis, on the other hand, is radically more efficient; it is able to store 60% of the sun’s energy as chemical energy in associated biomolecules. “

Sad but true. Researchers are constantly developing new solar cells that keep breaking records in converting solar energy. The most efficient have exceeded the 20 percent mark by a large margin, but are nowhere near the 60 percent mark.

Purdue quoted biophysicist and solar energy researcher Yulia Pushkar, who emphasized the benefit of the artificial leaves.

“There are no fundamental physical limitations with artificial photosynthesis,” she said. “It’s very easy to imagine a system that is 60% efficient because we already have a precedent in natural photosynthesis. And if we get very ambitious, we could even imagine a system with an efficiency of up to 80%. “

You can’t fool mother nature (unless you really try)

When a plant processes solar energy, it grows. Unfortunately, when scientists try the same thing with an artificial leaf, it falls apart. That just goes to show how awesome Mother Nature is.

That brings us to the latest development. Earlier this month, the Berkeley Lab discovered that a research team led by scientist Francesca Toma recently had a breakthrough. Your contribution to the field of artificial photosynthesis focuses on the issue of durability.

The weakness of a typical man-made leaf system is the result of using a crystalline form of copper called copper oxide. Copper (I) oxide is a preferred material in photoelectrochemical cells due to its high light reactivity, but it disintegrates after a few minutes when exposed to light.

So why stick with a loss proposal?

“Despite its instability, copper oxide is one of the best candidate materials for artificial photosynthesis because it is relatively affordable and has properties suitable for absorbing visible light,” explains Berkeley Lab.

With this motivation Toma and her team took a new look at the photoelectrochemical reaction. Upon closer inspection, the team found that the perpetrator may not be in the cell itself. Instead, it could be something in the water – literally the water electrolyte used in man-made leaf systems.

“We knew it was unstable – but we were surprised to learn how unstable it really is,” said Toma. “When we started this study, we wondered if the key to a better solar fuel device might not be in the material itself, but in the overall environment of the reaction, including the electrolyte.”

Solar energy & the “Z-scheme”

The team concluded that hydroxides in the water contribute to corrosion. The study also revealed a possible workaround that consists of a photoelectrochemical cell protected by a layer of silver on top and a gold / iron oxide on the bottom.

“This ‘Z-Scheme’, which is inspired by electron transfer in natural photosynthesis, was supposed to create a ‘funnel’ that sends holes of copper oxide into the gold / iron oxide sink,” explains Berkeley Lab.

Do you have it all Well! You can find all the juicy details in the study “Investigation and mitigation of degradation mechanisms in Cu2O photoelectrodes for CO2 reduction to ethylene” in the journal Nature Energy.

“The resulting photocathode shows a stable photocurrent for CO2 reduction with ~ 60% Faraday efficiency for ethylene with an equilibrium of hydrogen over hours, while bare Cu2O is broken down within minutes,” conclude Toma and her team.

Attention Fossil Fuels – The Liquid Sunlight Alliance is here for you

If you got the thing about making ethylene, that’s another potential advantage over electrolysis systems. Let our friends at BMC Biology explain it to us:

“The simple hydrocarbon ethylene (C2H4) is a tiny gaseous molecule of great importance. Ethylene is not only the most commonly produced organic compound in the world (used in the manufacture of numerous products such as rubber, plastics, paints, detergents and toys), but is also an important hormone in plant biology. “

The ability to increase non-fossil production of ethylene could be a determining factor. Fossil industry stakeholders have relied on hydrogen, ethylene, and other petrochemicals to stay afloat as the global economy drifts away from fossil fuels, but now it looks like these routes could also be blocked by solar energy.

With this in mind, let’s take a quick look at the Liquid Sunshine Alliance, the umbrella organization that supports Toma’s team, among others. LiSA was founded in 2020 in the final days of the Trump administration as one of two projects funded by the US Department of Energy through the Fuels from Sunlight Energy Innovation Hub, which dates back to the Obama administration.

“The Liquid Sunlight Alliance is developing the scientific principles with which permanently coupled microenvironments can be jointly designed in order to efficiently and selectively generate liquid fuels from sunlight, water, carbon dioxide and nitrogen,” explains LiSA, and that’s not all.

The mission statement of LiSA positions the solar fuels area as an area that promotes “Diversity, Equity and Inclusion, (DEI) aspects that are essential and fundamental for the expansion of knowledge in science and technology and the development of the scientific staff of the future” which is somewhat ironic considering former President Trump attempted to thwart the federal DEI programs in the final months of his lost candidacy for re-election in 2020.

The other program funded by Fuels From Sunlight in 2020 is CHASE, the Center for Hybrid Approaches in Solar Energy to Liquid Fuels. CHASE’s mission is to “develop hybrid photoelectrodes for fuel production that combine semiconductors for light absorption with molecular catalysts for conversion and fuel production”.

Regarding the role of solar energy in the rapid global decarbonization, you don’t seem to have seen anything, so hold on to your hats.

Follow me on Twitter @TinaMCasey.

Photo: “A model for solar fuel called a photo-electrochemical cell. A research team led by Francesca Toma, a research associate with the Liquid Sunlight Alliance in the Chemical Sciences Division of the Berkeley Lab, designed the model ”(Credit: Thor Swift / Berkeley Lab).

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