Three years ago, scientists at the University of Michigan discovered an artificial photosynthesis device made of silicon and gallium nitride (Si/GaN) that harnesses sunlight into carbon-free hydrogen for fuel cells with twice the efficiency and stability of some previous technologies.
Now, scientists at Lawrence Livermore and Lawrence Berkeley national laboratories – in collaboration with the University of Michigan – have uncovered a surprising, self-improving property in Si/GaN that contributes to the material’s highly efficient and stable performance in converting light and water into carbon-free hydrogen. The research, reported in Nature Materials, could help radically accelerate the commercialization of artificial photosynthesis technologies and hydrogen fuel cells.
Materials in solar fuels systems usually degrade, become less stable, and as a result produce hydrogen less efficiently, but the team found an unusual property in Si/GaN that somehow enables it to become more efficient and stable.
Previous artificial photosynthesis materials are either excellent light absorbers that lack durability or they are durable materials that lack light-absorption efficiency.
But silicon and gallium nitride are abundant and cheap materials that are widely used as semiconductors in everyday electronics such as LEDs (light-emitting diodes) 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 extraordinarily well in an exotic artificial photosynthesis device – so he turned to senior author and Berkeley Lab scientist Francesca Toma for help.
HydroGEN: Taking a team science approach to solar fuels
Mi had learned about Toma’s expertise in advanced microscopy techniques for probing the nanoscale (billionths of a meter) properties of artificial photosynthesis materials through HydroGEN, supported by the DOE’s Hydrogen and Fuel Cell Technologies Office.
HydroGEN is a national lab consortium led by the National Renewable Energy Laboratory to facilitate collaborations between national labs, academia, and industry for the development of advanced water-splitting materials.
Toma and lead author Guosong Zeng, a postdoctoral scholar in Berkeley Lab’s Chemical Sciences Division, suspected that GaN might be playing a role in the device’s unusual potential for hydrogen production efficiency and stability.
To find out, Zeng carried out a photoconductive atomic force microscopy experiment to test how GaN photocathodes could efficiently convert absorbed photons into electrons, and then recruit those free electrons to split water into hydrogen, before the material started to degrade and become less stable and efficient.
They observed 2-3 orders of magnitude improvement in the material’s photocurrent coming from tiny facets along the “sidewall” of the GaN grain. The material also had increased its efficiency over time, even though the overall surface of the material didn’t change that much.
To gather more clues, the researchers recruited scanning transmission electron microscopy (STEM) at the National Center for Electron Microscopy in Berkeley Lab’s Molecular Foundry, and angle-dependent X-ray photon spectroscopy (XPS).
Those experiments revealed that a 1 nanometer layer mixed with gallium, nitrogen, and oxygen – or gallium oxynitride – had formed along some of the sidewalls. A chemical reaction had taken place, adding “active catalytic sites for hydrogen production reactions,” Toma said.
Density functional theory (DFT) simulations, carried out by co-authors Tadashi Ogitsu and Anh Pham at LLNL confirmed their observations. “By calculating the change of distribution of chemical species at specific parts of the material’s surface, we successfully found a surface structure that correlates with the development of gallium oxynitride as a hydrogen evolution reaction site,” Ogitsu said. “We hope that our findings and approach – a tightly integrated theory-experiments collaboration enabled by the HydroGEN consortium – will be used to further improve the renewable hydrogen production technologies.”
Looking ahead, Toma said that she and her team would like to test the Si/GaN photocathode in a water-splitting photoelectrochemical cell, and that Zeng will experiment with similar materials to get a better understanding of how nitrides contribute to stability in artificial photosynthesis devices – which is something they never thought would be possible.
“It was totally surprising,” Zeng said. “It didn’t 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.”
Reference: “Development of a photoelectrochemically self-improving Si/GaN photocathode for efficient and durable H2 production” by Guosong Zeng, Tuan Anh Pham, Srinivas Vanka, Guiji Liu, Chengyu Song, Jason K. Cooper, Zetian Mi, Tadashi Ogitsu and Francesca M. Toma, 5 April 2021, Nature Materials.
This work was supported by the HydroGEN Advanced Water Splitting Materials Consortium, established as part of the Energy Materials Network under DOE’s Office of Energy Efficiency and Renewable Energy.
So 3% eff Si/GaN layer and requires solar radiation means very low energy density per sq m of land, I’m guessing maybe 1W/sq m. If you are going to rock the entire world of hydrogen production at least give us an estimate of production costs and land use, say per W of hydrogen output or in this case per uW of hydrogen. And isn’t the sun intermittent still and seasonally variable too so overall capacity factor will be terrible closer to 15% in the northern part of the world. There is no such thing as 24/365 base load solar radiation.
Meanwhile Sulfur-Iodine catalyst gets 50% eff with high temp heat from a 2GWth 800c reactor plant means a 1GW hydrogen source for about $1B on a tiny slither of land.
Glad that’s happening.
John Jakson…maybe go do the idea you want, on your own tiny “slither” of land.
Congrats to these teams on Hydrogen breakthroughs.
US per capita energy use is about 10KW of primary energy or 300GJ/yr, see Wikipedia. One solar panel makes barely 1GJ/yr in the US NE. A hydrogen panel will make a fraction of that.
Solar, wind, hydro make about 5W/sq m of land. Biomass and this hydrogen harvesting is about 1W/sq m of land. See a problem here? How much land does every westerner need to produce all their energy needs just from the sun, 10000/5 sq m of what will become eWaste in 20 years.
“Without The Hot Air” is a good book on energy that explains why we can’t live off the sun at current population densities.
In a nutshell, it’s about energy density, we should be looking for energy sources much denser and cleaner than fossil fuels, but the solar hydrogen fans want to go orders less dense because land is somehow free plus all the stuff that will cover it.
And no Si GaN isn’t cheap either, it’s cheap enough for LED chips of a sq mm or so, but not for sq m size panels that will gather barely a watt peak.
You could watch Planet of the Humans too, but you probably wouldn’t like it.
As I read it, they started at 3% efficiency and the article describes gains in efficiency. I would expect that they would try to publish low numbers and save the best estimates for investors and others who sign an NDA.
What did I just read
Reply to John Jakson: World population density will soon be leveling off and then decreasing. In the meantime world population is expected to reach 8 Billion soon, but “factors” will eventually push that figure down below 5 Billion and whether those left will have normal life spans remains to be seen.
All true, there’s plenty of articles on this site and others saying exactly that.
As long as there is plenty of zero CO2 energy and child mortality is kept at bay, lifetimes can remain at todays levels but how does it get paid for, who knows. Aging issues is going to become a much bigger part of the economy, the old will become the new long term babies.
Why don’t they just get energy from the air. Copper mass is relevant to energy input. So many are confused bc the tricked everybody by labeling it AC because of failed RF patent attempts. Both ac and rf have the same scientific symbol…..
I just wanna add Deuterium in Mariana Trench. It’s unlimited, can’t we start harnessing this energy and use it?