science

Converting Solar Energy to Hydrogen Fuel with the Help of Photosynthesis!

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Global economic growth comes with increased energy demand, but accelerating energy production can be difficult. Recently, scientists have achieved a record efficiency in conversion from solar to fuel. And now they want to involve the photosynthesis mechanism to push this further. The researchers will present their results at the American Chemical Society (ACS) Autumn 2020 Virtual Meeting and Fair.

Dr. LilacAmirav says they want to create a photocatalytic system that uses sunlight to stimulate chemical reactions of environmental importance. ^ In particular, his group at the Israel Institute of Technology is designing a photocatalyst that can split water into hydrogen fuel.

“When we place our rod-shaped nanoparticles in water and shine a light on them, they generate positive and negative electric charges,” Amirav said.

“Water molecules break; negative charges produce hydrogen (reduction), and positive charges produce oxygen (oxidation). Two reactions involving positive and negative charges must occur simultaneously. Without taking advantage of positive charges, negative charges cannot be diverted to produce the desired hydrogen. “

If the positive and negative charges that are attracted to each other manage to reunite, they annihilate each other and the energy is lost. Therefore, to make sure the charges were far enough apart, the team created unique heterostructures consisting of a combination of different semiconductors along with metal and metal oxide catalysts. Using a model system, they studied the reduction and oxidation reactions separately and modified the heterostructure to optimize fuel production.

We turned solar energy into real conversion to fuel

In 2016, the team designed a spherical cadmium-selenide quantum dot heterostructure embedded in a rod-shaped piece of cadmium sulfide. A platinum metallic particle was placed at the tip. While the cadmium-selenide particle attracted positive charges, negative charges accumulated at the tip.

Amirav says that by adjusting the size of the quantum dot and the length of the bar and other parameters, they were able to convert sunlight 100% from water reduction to hydrogen. He also notes that a single photocatalyst nanoparticle can produce 360,000 molecules of hydrogen per hour.

The group published its results in ACS magazine NanoLetters. But in these experiments, they examined only half of the reaction (reduction). For proper function, the photocatalytic system must support both reduction and oxidation reactions.

Amirav said, “We were not yet converting solar energy into fuel. We still needed an oxidation reaction to supply electrons to the quantum point continuously. “

“The water oxidation reaction takes place in a multi-step process and as a result remains a major challenge. Also, derivatives appear to compromise the stability of the semiconductor. ”

Together with their collaborators, the group discovered a new approach that leads them to benzylamine, looking for different compounds that can be oxidized instead of water. Researchers have discovered that they can produce hydrogen from water while simultaneously converting benzylamine to benzaldehyde.

Photocatalytic system


“With this research, we transformed the process from photocatalysis to photosynthesis, the actual conversion of solar energy to fuel,” says Amirav. The photocatalytic system realizes the actual conversion of solar energy into storable chemical bonds with a maximum solar-chemical energy conversion efficiency of 4.2%.

“This data sets a new world record for photocatalysis and doubles the previous record,” he adds. “The US Department of Energy defined 5-10% as the” practical feasibility threshold “for producing hydrogen by photocatalysis. Therefore, we are on the verge of an economically viable conversion from solar to hydrogen, ”he says.

These impressive results motivated the researchers to see if there were other compounds with the high conversion from the sun to the chemical. To do this, the team uses artificial intelligence. Through a collaboration, researchers are developing an algorithm to search for chemical structures for an ideal fuel-producing compound. Additionally, they are exploring ways to improve their photosystems, and perhaps one way is to be inspired by nature.

A protein complex in plant cell membranes, which contains the electrical circuitry of photosynthesis, has been successfully combined with nanoparticles. Amirav says this artificial system has so far proven to be efficient and supports water oxidation and provides a photocurrent 100 times greater than other similar systems produce.

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