Author: Lawrence Livermore National Laboratory May 24, 2021

The hydrogen gas bubbles escape from the water at the thin layer of gallium oxynitride formed on the surface of gallium nitride. This work proves that the chemical conversion of gallium nitride to gallium oxynitride leads to continuous operation and enhanced catalytic activity, thus showing the promise of the oxynitride layer as a protective catalytic coating for hydrogen evolution. Image source: Illustration by Ella Maru Studios

Three years ago, scientists at the University of Michigan discovered an artificial photosynthesis device made of silicon and gallium nitride (Si/GaN), which can convert sunlight into carbon-free hydrogen for fuel cells, which is efficient and stable Sex is twice that of some previous technologies.

Now, scientists at Lawrence Livermore and Lawrence Berkeley National Laboratories, in collaboration with the University of Michigan, have discovered surprising self-improving properties in Si/GaN that help the material Efficient and stable performance in converting light and water into carbon-no hydrogen. This research published in Nature Materials can help fundamentally accelerate the commercialization of artificial photosynthesis technology and hydrogen fuel cells.  

The materials in solar fuel systems usually degrade and become less stable, so hydrogen generation is less efficient, but the team found that an unusual property in Si/GaN makes it more efficient in some way And stability.

Previous artificial photosynthetic materials were either excellent light absorbers lacking durability, or durable materials lacking light absorption efficiency.

However, silicon and gallium nitride are abundant and inexpensive materials that are widely used as semiconductors in everyday electronic products, such as LEDs (light emitting diodes) and solar cells, said co-author Zetian Mi, professor of electrical and computer engineering at the University of Michigan. The state of Michigan invented Si/GaN artificial photosynthesis equipment ten years ago.

When Mi’s Si/GaN device achieved a record 3% solar-to-hydrogen efficiency, he wanted to know how this ordinary material performed so well in a bizarre artificial photosynthesis device-so he turned to senior authors and Berkeley Lab scientist Francesca Toma asked for help.

With the support of the US Department of Energy's Office of Hydrogen and Fuel Cell Technology, Mi learned of Toma's expertise in advanced microscopy technology that uses HydroGEN to detect the nanoscale (one-billionth of a meter) properties of artificial photosynthetic materials.

HydroGEN is a national laboratory consortium led by the National Renewable Energy Laboratory, which aims to promote cooperation among national laboratories, academia, and industry to develop advanced water-splitting materials.  

Toma and lead author Zeng Guosong, a postdoctoral scholar in the Department of Chemical Sciences at Berkeley Lab, suspect that GaN may play a role in the device's extraordinary hydrogen production efficiency and stability potential.

To find out, Zeng conducted a photoconductive atomic force microscope experiment to test how the GaN photocathode effectively converts the absorbed photons into electrons, and then recruits these free electrons before the material begins to degrade and become unstable and reduce efficiency. Decompose into hydrogen. 

They observed that the material photocurrent from the tiny faces along the "sidewalls" of the GaN grains increased by 2-3 orders of magnitude. Over time, the efficiency of this material has also improved, although the overall surface of the material has not changed much.

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

These experiments show that a 1 nanometer layer of gallium, nitrogen, and oxygen (or gallium oxynitride) is formed along some sidewalls. Toma said that a chemical reaction took place, adding "active catalytic sites for hydrogen production reactions."

Density functional theory (DFT) simulations performed by LLNL co-authors Tadashi Ogitsu and Anh Pham confirmed their observations. "By calculating the changes in the distribution of chemical substances in specific parts of the material surface, we successfully discovered the surface structure related to the development of gallium oxynitride as a reaction site for hydrogen evolution," Ogitsu said. "We hope that our findings and methods-the tightly integrated theory-experimental cooperation supported by the HydroGEN Alliance-will be used to further improve renewable hydrogen production technology." 

Looking to the future, Toma said that she and her team hope to test Si/GaN photocathodes in water splitting photoelectrochemical cells. Zeng will conduct experiments with similar materials to better understand how nitrides can promote the stability of artificial photosynthesis devices. Sex-this is something they never thought of.

"This is totally surprising," Zeng said. "It doesn't make sense-but Pham's DFT calculations provide us with the explanation needed to verify the observations. Our findings will help us design better artificial photosynthesis devices."

References: Guosong Zeng, Tuan Anh Pham, Srinivas Vanka, Guiji Liu, Chengyu Song, Jason K. Cooper, Zetian Mi, Tadashi Ogitsu and Francesca's "Development of photoelectrochemical self-improving Si/GaN photocathodes for efficient and durable H2 production" M. Toma, April 5, 2021, Nature Materials. DOI: 10.1038/s41563-021-00965-w

This work was supported by the HydroGEN Advanced Water Splitting Materials Alliance, which is part of the Energy Materials Network of the Office of Energy Efficiency and Renewable Energy of the U.S. Department of Energy.

So a 3% efficient Si/GaN layer and the need for solar radiation means that the energy density per square meter of land is very low, I guess it might be 1W/square meter. If you want to shock the entire world of hydrogen production, at least give us an estimate of production costs and land use, such as hydrogen production per watt, or in this case per uW of hydrogen. And whether the sun is still intermittent and seasonal, so in the northern part of the world, the overall capacity coefficient will be close to 15%. There is no such thing as 24/365 base load solar radiation.

At the same time, the sulfur-iodine catalyst obtains 50% high-temperature thermal efficiency from the 2GWth 800c reactor plant, which means that a 1GW hydrogen source can be obtained on a small piece of land at a price of about 1B US dollars.

John Jackson...maybe you can realize what you want on a small piece of "sliding" land of your own.

Congratulations to these teams for their breakthrough in hydrogen.

The average energy consumption in the U.S. is about 10KW or 300GJ/yr of primary energy, see Wikipedia. In the northeastern United States, the annual output of a solar panel is only 1 GJ. Hydrogen battery panels will account for a small part of it.

Solar energy, wind energy, and water energy account for approximately 5 watts of land per square meter. Biomass and this hydrogen collection is about 1 watt per square meter of land. See there is a problem here? How much land does each Westerner need to produce all their energy? Only by solar energy, 10,000/5 square meters will be turned into electronic waste in 20 years.

"No Hot Air" is a good book about energy. It explains why we cannot live on the sun at the current population density.

In short, it is related to energy density. We should look for more dense and cleaner energy than fossil fuels, but solar hydrogen enthusiasts want to reduce the density, because the land is free to some extent, plus all that can be Something that covers it.

And it is not cheap without Si GaN. It is cheap enough for LED chips of about 1 square millimeter, but it is not cheap enough for a square meter panel that can only collect watt peaks.

You can also watch "Human Planet", but you may not like it.

When I read it, their initial efficiency was 3%, and the article describes the efficiency improvement. I hope they will publish as low as possible and keep the best estimates for investors and others who sign the NDA.

What i just read

Reply to John Jakson: The world population density will soon stabilize and then gradually decline. At the same time, the world's population is expected to reach 8 billion soon, but "factors" will eventually push this number down to below 5 billion, and it remains to be seen whether the remaining people can live a normal lifespan.

Yes, there are many articles on this site, and others do say so.

As long as there is enough zero carbon dioxide energy and the child mortality rate is controlled within a certain range, the life span can be maintained at today's level, but who knows how it gets paid. The aging problem will become an important part of the economy, and the old will become the new long-term baby.

Why don't they get energy from the air? Copper quality is related to energy input. Many people are confused because the RF patent attempt failed and everyone labeled it as AC. Both ac and rf have the same scientific notation...

I just want to add deuterium to the Mariana Trench. It is infinite, can't we start to use this energy and use it?

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