This hydrogen fuel engine can be the ultimate guideline for self-improvement

This hydrogen fuel engine can be the ultimate guideline for self-improvement

Guosong Zeng, a postdoctoral fellow in the Department of Chemical Sciences at Berkeley Lab, is working on testing an artificial photosynthesis device made of gallium nitride. Zeng, along with Berkeley Lab staff scientist Francesca Toma, discovered that the device improves with use. Credit: Thor Swift / Berkeley Lab

Three years ago, scientists at the University of Michigan developed an artificial photosynthesis device made of silicon and gallium nitride (Si / GaN), which uses sunlight in carbon-free hydrogen for fuel cells, with twice the efficiency and stability of some previous technologies.

Now, Department of Energy (DOEs) scientists at the Lawrence Berkeley National Laboratory (Berkeley Lab) – in collaboration with the University of Michigan and Lawrence Livermore National Laboratory (LLNL) – have discovered a surprising, self-improving property in Si / GaN that contributes to to the extremely efficient and stable performance of the material to convert light and water into carbon-free hydrogen. Their findings, reported in the journal Natural materials, can help radically accelerate the commercialization of artificial photosynthesis technologies and hydrogen fuel cells.

“Our discovery is a true changer,” said senior writer Francesca Toma, a personnel scientist in the Department of Chemistry at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab). Usually, materials decay in solar fuel systems, they become less stable and therefore produce hydrogen less efficiently, she said. “But we have discovered an unusual feature in Si / GaN that somehow enables it to become more efficient and stable. I have never seen such stability.”

Previous artificial photosynthetic materials are excellent non-durable light absorbers; or they are durable materials that do not have the league absorption efficient.

But silicon and gallium nitride are plentiful and inexpensive materials commonly used as semiconductors in everyday electronics such as LEDs and solar cells, said co-author Zetian Mi, a professor of electrical and computer engineering at the University of. Michigan who invented Si / GaN artificial photosynthesis devices a decade ago.

When Mi’s Si / GaN device achieved a record-breaking 3 percent solar-to-hydrogen efficiency, he wondered how such ordinary materials could perform so exceptionally well in an exotic artificial photosynthesis device – which is why he Toma asked for help.

HydroGEN: follows a Team Science approach to solar fuels

Mi learned about Toma’s expertise in advanced microscopy techniques to examine the properties of nanoscale (billionths of a meter) of artificial photosynthesis material by HydroGEN, a five-nation laboratory consortium supported by the DOE’s Office of Hydrogen and Fuel Cell Technologies, and led by the National Renewable Energy Laboratory to facilitate collaboration between National Labs, academia and industry for the development of advanced water-splitting materials. “These interactions between supporting industry and academia over advanced water-splitting materials with the capabilities of the National Labs are precisely why HydroGEN was formed – so we can move the needle across clean hydrogen production technology,” said Adam Weber, Berkeley Lab’s Hydrogen and Program Manager of Fuel Cell Technologies Lab and co-deputy director of HydroGEN.

Toma and lead author Guosong Zeng, a postdoctoral fellow in the Department of Chemical Sciences at Berkeley Lab, suspected that GaN may be playing a role in the unusual potential of hydrogen production and stability.

This hydrogen fuel engine can be the ultimate guideline for self-improvement

Guosong Zeng, a postdoctoral fellow, and Francesca Toma, a personnel scientist, both in the Chemical Sciences Division of Berkeley Lab, are testing an artificial photosynthesis device made of gallium nitride. Instead of degrading over time, which is typical of devices that turn water and light into hydrogen fuel, Toma and Zeng discover that this device improves. Credit: Thor Swift / Berkeley Lab

To find out, Zeng conducted a photoconductive atomic force microscopy experiment in Toma’s laboratory to test how GaN photocathodes could efficiently convert absorbed photons into electrons, and then recruit the free electrons to divide water into hydrogen, before material begins to degrade and become less. stable and efficient.

After a few hours, they expected to see a sharp decrease in the photon absorption efficiency and stability of the material. To their surprise, they see a 2-3 order improvement in the material flow of the material coming from small facets along the ‘side wall’ of the GaN grain, Zeng said. Even more confusing was that the material increased its efficiency over time, although the total surface area of ​​the material did not change that much, Zeng said. “In other words, instead of getting worse, the material got better,” he said.

To gather more clues, the researchers recruited scanning transmission electron microscopy (STEM) at the National Center for Electron Microscopy in the Molecular Foundry of Berkeley Lab, and angle-dependent X-ray photon spectroscopy (XPS).

These experiments revealed that a layer of 1 nanometer mixed with gallium, nitrogen and oxygen – or gallium oxynitride – formed along some side walls. A chemical reaction took place that added ‘active catalytic sites for hydrogen production reactions’, Toma said.

Density functional theory (DFT) simulations performed by co-authors Tadashi Ogitsu and Tuan Anh Pham at LLNL confirmed their observations. “By calculating the change in the distribution of chemical species on specific parts of the material’s surface, we found a surface structure consistent with the development of gallium oxynitride as a reaction site for hydrogen evolution,” Ogitsu said. “We hope that our findings and approach – a rigorously integrated collaboration between theory experiments facilitated by the HydroGEN consortium – will be used to further enhance renewable hydrogen production technologies.”

Mi adds: “We have been working on this material for over ten years – we know it is stable and effective. But this collaboration has helped to identify the fundamental mechanisms why it is becoming more robust and effective rather than degrading. The findings from this work will help us build more efficient artificial photosynthesis devices at a lower cost. ‘

Looking ahead, Toma said she and her team want to test the Si / GaN photocathode in a water-splitting photoelectrochemical cell, and that Zeng will experiment with similar materials to gain a better understanding of how nitrides contribute to stability in artificial photosynthesis. devices. —What they never thought would be possible.

“It was completely amazing,” Zeng said. “It did not make sense – but Pham’s DFT calculations gave us the explanation we needed to validate our observations. Our findings will help us design even better artificial photosynthesis devices.”

“It was an unprecedented network of collaboration between National Labs and a research university,” Toma said. “The HydroGEN consortium has brought us together – our work demonstrates how the National Labs team science approach can help solve major problems affecting the entire world.”


Water splitting: nano-level imaging provides important insights


More information:
Development of a photoelectrochemical self-improving Si / GaN photocathode for efficient and durable H2 production, Natural materials (2021). dx.doi.org/10.1038/s41563-021-00965-w

Provided by Lawrence Berkeley National Laboratory

Quotation: This hydrogen fuel engine could be the ultimate guideline for self-improvement (2021, April 5) obtained on April 5, 2021 from https://phys.org/news/2021-04-hydrogen-fuel-machine-ultimate-self-improvement .html

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