Hydrogen is conventionally derived from natural gas through a process called methane steam reforming, but splitting water through an electrochemical process is cleaner and more sustainable. That process uses catalysts, which are substances that increase the rate of a chemical reaction without themselves undergoing any permanent chemical change. However, the cost of the greener technique has been a barrier in the marketplace.
Now a team of researchers led by Oregon State University (OSU) has shown that hydrogen can be cleanly produced with much greater efficiency and at a lower cost than is possible with current commercially available catalysts. The new findings, which describe ways to design catalysts that can greatly improve the efficiency of the clean hydrogen production process, were published in Science Advances and JACS Au.
The research team used the resources of the Advanced Photon Source (APS), a U.S. Department of Energy (DOE) Office of Science user facility at DOE’s Argonne National Laboratory, to test and confirm their findings.
In facilitating reaction processes, catalysts often experience structural changes, according to Zhenzing Feng, a chemical engineering professor at OSU who led the research. Sometimes the changes are reversible, other times irreversible, and irreversible restructuring is believed to reduce a catalyst’s ability to affect chemical reactions.
Feng, OSU Ph.D. student Maoyu Wang and collaborators studied the restructuring of catalysts in reaction and then manipulated their surface structure and composition at the atomic scale to achieve a highly efficient catalytic process for producing hydrogen. The new catalysts based on amorphous iridium hydroxide were 150 times as efficient as the original structures they were adapted from, and close to three orders of magnitude better than the common commercial catalyst, iridium oxide.
“We found at least two groups of materials that undergo irreversible changes that turned out to be significantly better catalysts for hydrogen production,” Feng said. “This can help us produce hydrogen at $2 per kilogram and eventually $1 per kilogram.”
DOE has made hydrogen the first of its “Energy Earthshots” — an initiative that aims to accelerate breakthroughs of more abundant, affordable, and reliable clean energy solutions — setting a goal of reducing the cost of clean hydrogen by 80% to $1 per 1 kilogram in one decade (“1 1 1”). The infrastructure bill signed into law in November 2021 authorizes an $8 billion DOE program to support the development of at least four regional clean hydrogen hubs to network hydrogen producers, storage, offtakers and transport infrastructure.
Feng and his team confirmed their findings using several X-ray techniques at the APS. Work was done at beamlines 9-BM and 4-ID-C, where the research team was able to observe the electrochemical process as it happened, getting information about changes to the catalyst in real time.
“Materials that are good catalysts are often unstable,” explained John Freeland, an Argonne physicist and co-author on the Science Advances paper. “When a material is active, it’s difficult to tell whether that material is a good catalyst and giving you the result you want, or if it is being consumed as it releases hydrogen. If it’s being consumed, eventually you will have no catalyst left.”
That’s where the APS comes in. Scientists can use its ultrabright X-rays to get both chemical and structural information at very small scales, and can not only see inside materials as they undergo reactions, but can get insight into what is happening on the surface of the materials, to see if they are eroding or transforming.
“X-ray absorption spectroscopy allows us to look at the atomic structure and see how it is changing,” said George Sterbinsky, an Argonne physicist and a co-author on the Science Advances paper. “It is well suited to giving us chemical and structural information so we can understand the catalytic process.”
A fuller understanding is important, since the materials often used in catalysis (such as iridium) can be expensive. The APS has been working with catalysts for many years, Freeland said, and can offer research teams the experience to make sure their experiments are successful.
“It’s nontrivial to do it right,” he said. “You can do it wrong in a lot of ways. We can help researchers get the data they need.”
The APS is undergoing a massive upgrade that will increase the brightness of its X-ray beams by up to 500 times, and Freeland noted that catalysis research will only get better once the upgraded facility is online. The brighter X-ray beams will enable researchers to take these experiments to smaller scales, using microscopic catalyst samples and getting even better structural and chemical information from them.
The water electrolysis technology for clean hydrogen production that Feng’s group is focused on uses electricity from renewable sources to split water to make clean hydrogen. However, the efficiency of water splitting is low, he said, mainly due to the high overpotential — the difference between the actual potential and the theoretical potential of an electrochemical reaction — of one key part of the process.
“Catalysts are critical to promoting the water-splitting reaction by lowering the overpotential, and thus lowering the total cost for hydrogen production,” Feng said. “Our first study in JACS Au laid the foundation for us, and as demonstrated in our Science Advances article we now can better manipulate atoms on surface to design catalysts with the desired structure and composition.”
Co-authors on the papers include scientists from the University of Texas, Peking University, Pacific Northwest National Laboratory, Northwestern University, South China University of Technology, the University of Cambridge, the University of California, Berkeley and Singapore’s Nanyang Technological University.
Source/Credit: Argonne National Laboratory / Steve Lundeberg and Andre Salles