Three years ago, scientists at the University of Michigan discovered an artificial photosynthesis device made of silicon and gallium nitride (Si/GaN), which converts sunlight into carbon-free hydrogen for fuel cells. Its efficiency and stability are Twice the previous technology.
Now, scientists from the Lawrence Berkeley National Laboratory (Berkeley Laboratory) of the Department of Energy (DOE) in collaboration with the University of Michigan and Lawrence Livermore National Laboratory (LLNL) have discovered the surprising self-improving properties of Si/GaN. It helps the material convert light and water into high-efficiency and stable performance without hydrocarbons.Their findings, published in the magazine Natural materialsIt can help fundamentally accelerate the commercialization of artificial photosynthesis technology and hydrogen fuel cells.
Francesca Thomas, a senior scientist in the Department of Chemical Sciences at Lawrence Berkeley National Laboratory (Berkeley Lab) of the Department of Energy, said: “Our discoveries are truly game-changers.”
Previous artificial photosynthesis materials were either excellent light absorbers lacking durability, or light absorbers. Or they are durable materials that lack light absorption efficiency.
However, silicon and gallium nitride are cheap and inexpensive materials that are widely used as semiconductors in everyday electronic products, such as LEDs (light emitting diodes) and solar cells. The state of Michigan invented the Si/GaN artificial photosynthesis device ten years ago.
When Mi’s Si/GaN device achieved a record-breaking 3% solar conversion efficiency, he wanted to know how this ordinary material could perform so well in an unusual artificial photosynthesis device, so he asked Toma for help.
HydroGEN: Using team scientific methods to study solar energy
Mi has mastered the expertise of advanced microscopy technology through Tone. The technology is supported by the DOE Hydrogen and Fuel Cell Technology Office and led by the US Department of Energy, the five national laboratory alliance HydroGEN to detect the nanoscale of artificial photosynthetic materials. (One billionth of a meter) characteristic. Renewable Energy Laboratory to promote cooperation between national laboratories, academia and industry to develop advanced water-splitting materials. “These interactions that support the use of advanced water-splitting materials by industry and academia and the functions of national laboratories are what formed Hydrogen-so that we can transfer needles to clean hydrogen production technology,” said Hydrogen and Berkeley Labs. Project Manager of Fuel Cell Technology Laboratory and Deputy Director of HydroGEN.
Toma and lead author Zeng Guosong, a postdoctoral scholar in the Department of Chemical Sciences at Berkeley Labs, suspected that GaN may have extraordinary potential in the efficiency and stability of hydrogen generation by the device.
To find out, Zeng Qinghong conducted a photoconductive atomic force microscope experiment in the Toma laboratory to test how the GaN photocathode effectively converts the absorbed photons into electrons, and then absorbs these free electrons to split water into hydrogen, and then the material begins to degrade and change. less. Stable and efficient.
They predict that after only a few hours, the photon absorption efficiency and stability of the material will drop sharply. To their surprise, they found that the photocurrent of the material was increased by 2-3 orders of magnitude. This light came from the tiny facets on the “sidewalls” of the GaN grains. Even more confusing is that even if the overall surface of the material does not change much, this material has improved efficiency over time. He said: “In other words, the material will not be worse, but better.”
To gather more clues, the researchers recruited scanning transmission electron microscopes (STEM) and angle-dependent X-ray photon spectrometers (XPS) at the National Electron Microscopy Center at Berkeley Laboratory’s Molecular Foundry.
These experiments show that a 1nm layer mixed with gallium, nitrogen and oxygen (or gallium oxynitride) is formed along some of the sidewalls. Toma said that chemical reactions have already taken place, adding “active catalytic sites for hydrogen production.”
Co-authors Tadashi Ogitsu and Tuan Anh Pham conducted density functional theory (DFT) simulations at LLNL to confirm their observations. Ogitsu said: “By calculating the changes in the distribution of chemical substances in specific parts of the material surface, we successfully discovered a surface structure that is related to the development of gallium oxynitride as a reaction site for hydrogen release.” “We hope our findings. And methods (closely integrated theoretical and experimental cooperation realized by the HydroGEN consortium) will be used to further improve renewable hydrogen production technology.”
Mi added: “We have been working on this material for ten years and we know it is stable and effective. However, this collaboration helps to determine that it becomes more powerful and efficient rather than degraded. The basic mechanism behind it. The discovery of this work will help us build more efficient artificial photosynthesis equipment at a lower cost.”
Toma said that looking forward to the future, she and her team hope to test Si/GaN photocathodes in water splitting photoelectrochemical cells. Zeng will also try similar materials to better understand how nitrides can promote the stability of artificial photosynthesis devices. . -This is something they never thought of.
Zeng Qinghong said: “This is completely surprising.” “It doesn’t make sense-but Pham’s DFT calculation provides us with the explanation needed to verify the observations. Our findings will help us design better artificial photosynthesis devices.”
Toma said: “This is an unprecedented network of collaboration between national laboratories and research universities.” “The HydroGEN consortium brings us together-our work proves how the national laboratory’s team scientific methods can help solve problems that affect the entire world. Major issue.”
Breaking down the water: Nano-scale imaging yields key insights
Development of photoelectrochemical self-modified Si/GaN photocathode for efficient and long-lasting H2 pcs produce, Natural materials (2021). dx.doi.org/10.1038/s41563-021-00965-w
Courtesy of Lawrence Berkeley National Laboratory
Citation: This hydrogen fuel engine may be the final guide for self-improvement (April 5, 2021). The guide will be available from https://phys.org/news/2021-04-.html on April 5, 2021.
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