Converting Solar Energy To Hydrogen Fuel, With Help From Photosynthesis
Global Economic Growth comes with increasing demand for energy, but stepping up energy production are often challenging. Recently, scientists have achieved record efficiency for solar-to-fuel conversion, and now they need to include the machinery of photosynthesis to push it further.
The researchers will present their results today at the American Chemical Society (ACS) Fall 2020 Virtual Meeting & Expo.
“We want to fabricate a photocatalytic system that uses sunlight to drive chemical reactions of environmental importance,” says Lilac Amirav, Ph.D., the project principle investigator.
Specifically, her group at the Israel Institute of Technology is designing a photocatalyst which will break down water into hydrogen fuel. “When we place our rod-shaped nanoparticles in water and shine light on them, they generate positive(+ve) and negative(-ve) electric charges,” Amirav says. “The water molecules break; the negative charges produce hydrogen (reduction), and therefore the positive charges produce oxygen (oxidation). the 2 reactions, involving the positive and negative charges, must happen simultaneously. Without taking advantage of the positive charges, the negative charges can’t be routed to supply the specified hydrogen.”
If the positive and negative charges, which are interested in each other , manage to recombine, they cancel one another , and therefore the energy is lost. So, to form sure the fees are far enough apart, the team has built unique heterostructures comprised of a mixture of various semiconductors, along side metal and metal oxide catalysts. employing a model system, they studied the reduction and oxidation reactions separately and altered the heterostructure to optimize fuel production.
In 2016, the team designed a heterostructure with a spherical cadmium-selenide quantum dot embedded within a rod-shaped piece of sulfide . A platinum metallic particle was located at the tip. The cadmium-selenide particle attracted positive charges, while negative charges accumulated on the tip. “By adjusting the dimensions of the quantum dot and therefore the length of the rod, also as other parameters, we achieved 100% conversion of sunlight to hydrogen from water reduction,” Amirav says. One photocatalyst nanoparticle can produce 360,000 molecules of hydrogen per hour, she notes.
The group published their leads to the ACS journal Nano Letters. But in these experiments, they studied only half the reaction (the reduction). for correct function, the photocatalytic system must support both reduction and oxidation reactions. “We weren’t converting solar power into fuel yet,” Amirav says. “We still needed an oxidation reaction that might continually provide electrons to the quantum dot.” The water oxidation reaction occurs during a multi-step process, and as a result remains a big challenge. Additionally , its byproducts seem to compromise the steadiness of the semiconductor.
Together with collaborators, the group explored a replacement approach — trying to find different compounds that would be oxidized in lieu of water — which led them to benzylamine. The researchers found that they might produce hydrogen from water, while simultaneously transforming benzylamine to benzaldehyde. “With this research, we’ve transformed the method from photocatalysis to photosynthesis, that is, genuine conversion of solar power into fuel,” Amirav says. The photocatalytic system performs true conversion of solar energy into storable chemical bonds, with a maximum of 4.2% solar-to-chemical energy conversion efficiency. “This figure establishes a replacement record within the field of photocatalysis, and doubles the previous record,” she notes. “The U.S. Department of Energy defined 5-10% because the ‘practical feasibility threshold’ for generating hydrogen through photocatalysis. Hence, we are on the doorstep of economically viable solar-to-hydrogen conversion.”
These impressive results have motivated the researchers to ascertain if there are other compounds with high solar-to-chemical conversions. To do so, the team is using AI (artificial intelligence). Through a collaboration, the researchers are developing an algorithm to look chemical structures for a perfect fuel-producing compound. Additionally , they’re investigating ways to enhance their photosystem, and a method could be to draw inspiration from nature. A protein complex in plant cell membranes that comprises the electrical circuitry of photosynthesis was successfully combined with nanoparticles. Amirav says that this artificial system thus far has proven fruitful, supporting water oxidation while providing photocurrent than is 100 times larger than that produced by other similar systems.