Chemists at the University of Kansas and the US Department of Energy’s Brookhaven National Laboratory have taken a major step toward splitting hydrogen and oxygen molecules to produce pure hydrogen — without using fossil fuels.
The results of the pulsed radioactive decay experiments revealed the complete reaction mechanism for an important set of ‘water splitting’ catalysts. KU and Brookhaven’s work means that scientists are one step closer to making pure hydrogen from renewable energy, an energy source that can contribute to a greener future for the nation and the world.
Their findings appear this week in Proceedings of the National Academy of Sciences.
“Understanding how the chemical reactions that make clean fuels like hydrogen work is incredibly challenging — this paper is the culmination of a project I began in my first year at KU,” said co-author James Blackmore, Associate Professor of Chemistry. whose research on Lawrence forms the basis of the discovery.
“Our paper presents hard-won data from specialized technologies to understand how a particular catalyst for hydrogen generation performs this task,” he said. “The techniques that have been used here at KU and Brookhaven are quite specialized. Their implementation has allowed us to get a complete picture of how hydrogen is made from its component parts, protons and electrons.”
Blakemore’s research at KU was the basis for the breakthrough. He took his work to Brookhaven for research using pulsed radiolysis, as well as other techniques, at the Accelerator Center for Energy Research. Brookhaven is one of only two venues in the nation housing equipment that allows pulsed radiolysis experiments.
“It’s very rare that you get a complete understanding of the entire catalytic cycle,” said Brookhaven chemist Dmitry Polyansky, a co-author on the paper. “These reactions go through many steps, some of which are very fast and not easily noticed.”
Blakemore and co-workers made the discovery by studying a catalyst based on the compound pentamethylcyclopentadienyl rhodium, which is [Cp*Rh] For a short period. They focused on the Cp* ligand (CP-pronounced ‘star’) combined with the rare metal rhodium because of hints from previous work showing that this combination would be suitable for the job.
“Our rhodium system has been shown to be a good target for radioactive pulse analysis,” Blackmore said. “Cp* bonds, as they are called, are familiar to most organometallic chemists, and really chemists of all stripes. They are used to support many catalysts and can stabilize a wide variety of species involved in catalytic cycles. One of the main findings of this paper provides insight into how Cp* bonds are involved in catalytic cycles. Cp* ligand is closely involved in the chemistry of hydrogen evolution.”
But Blakemore stressed that the findings could lead to other improved chemical processes besides producing clean hydrogen.
“In our work, we hope chemists will see a study of how a common bond, Cp*, can enable an unusual interaction,” said the KU researcher. “This unusual reaction is very relevant to the story of hydrogen, but it’s actually bigger than that because Cp* is present in so many different catalysts. Chemists usually think of catalysts as being metal-based. With that way of thinking, if you’re making a new molecule, the metal is the main reactant.” That holds component parts together. Our paper shows that this is not always the case. Cp* can be involved in stitching pieces together to form products.”
Blakemore said he hopes this paper will be an opportunity that will lead to improvements in catalysts and other systems that rely on Cp* bonds. The breakthrough, which was supported by the National Science Foundation and the Department of Energy’s Office of Science, could apply more broadly to industrial chemistry. Blakemore is now applying techniques like those used in this work to develop new approaches to nuclear fuel recycling and handling of actinide species.
Kuwait University students at the graduate and undergraduate levels also participated in research that furthered this breakthrough.
“This project was a very important training tool for the students,” Blackmore said. Graduate student Wade Henke, first author, now works at Argonne National Laboratory as a postdoctoral researcher. Graduate student Yun Peng is second author and has begun joint work with Brookhaven; both have now finished their Ph.D. Undergraduates also contributed to this Over the years, he offers new complexes and insights that we have used to frame the story featured in this paper.
“Overall, I consider this a successful project and it has been a real team effort over the years.”