Ruthenium catalysts can convert ammonia to nitrogen at room temperature while releasing energy, paving the way for carbon-free fuel cells.
A research team at the University of Wisconsin–Madison has identified a new way to convert ammonia to nitrogen gas through a process that could be a step toward ammonia replacing carbon-based fuels.
The discovery of this technique, which uses a metal catalyst and releases, rather than requires, energy, was reported on November 8, 2021, in Nature Chemistry and has received a provisional patent from the Wisconsin Alumni Research Foundation.
“The world currently runs on a carbon fuel economy,” explains Christian Wallen, an author of the paper and a former postdoctoral researcher in the lab of UW–Madison chemist John Berry. “It’s not a great economy because we burn hydrocarbons, which release carbon dioxide into the atmosphere. We don’t have a way to close the loop for a true carbon cycle, where we could transform carbon dioxide back into a useful fuel.”
Nitrogen Energy Economy
To move toward the United Nations’ goal for the world to become carbon-neutral by 2050, scientists must consider environmentally responsible ways to create energy from elements other than carbon, and the UW–Madison team is proposing a nitrogen energy economy based on interconversions of nitrogen and ammonia.
The scientists were excited to find that the addition of ammonia to a metal catalyst containing the platinum-like element ruthenium spontaneously produced nitrogen, which means that no added energy was required. Instead, this process can be harnessed to produce electricity, with protons and nitrogen gas as byproducts. In addition, the metal complex can be recycled through exposure to oxygen and used repeatedly, all a much cleaner process than using carbon-based fuels.
“We figured out that, not only are we making nitrogen, we are making it under conditions that are completely unprecedented,” says Berry, who is the Lester McNall Professor of Chemistry and focuses his research efforts on transition metal chemistry. “To be able to complete the ammonia-to-nitrogen reaction under ambient conditions — and get energy — is a pretty big deal.”
Ammonia has been burned as a fuel source for many years. During World War II, it was used in automobiles, and scientists today are considering ways to burn it in engines as a replacement for gasoline, particularly in the maritime industry. However, burning ammonia releases toxic nitrogen oxide gases.
A Toxic-Free Alternative to Combustion
The new reaction avoids those toxic byproducts. If the reaction were housed in a fuel cell where ammonia and ruthenium react at an electrode surface, it could cleanly produce electricity without the need for a catalytic converter.
“For a fuel cell, we want an electrical output, not input,” Wallen says. “We discovered chemical compounds that catalyze the conversion of ammonia to nitrogen at room temperature, without any applied voltage or added chemicals. This is the first process, as far as we know, to do that.”
“To be able to complete the ammonia to nitrogen reaction under ambient conditions — and get energy — is a pretty big deal.”
John Berry
“We have an established infrastructure for distribution of ammonia, which is already mass produced from nitrogen and hydrogen in the Haber-Bosch process,” says Michael Trenerry, a graduate student and author on the paper. “This technology could enable a carbon-free fuel economy, but it’s one half of the puzzle. One of the drawbacks of ammonia synthesis is that the hydrogen we use to make ammonia comes from natural gas and fossil fuels.”
This trend is changing, however, as ammonia producers attempt to produce “green” ammonia, in which the hydrogen atoms are supplied by carbon-neutral water electrolysis instead of the energy-intensive Haber-Bosch process.
Next Steps Toward a Nitrogen Fuel Future
As the ammonia synthesis challenges are met, according to Berry, there will be many benefits to using ammonia as a common energy source or fuel. It’s compressible, like propane, easy to transport and easy to store. Though some ammonia fuel cells already exist, they, unlike this new process, require added energy, for example, by first splitting ammonia into nitrogen and hydrogen.
The group’s next steps include figuring out how to engineer a fuel cell that takes advantage of the new discovery and considering environmentally friendly ways to create the needed starting materials.
“One of the next challenges I would like to think about is how to generate ammonia from water, instead of hydrogen gas,” Trenerry says. “The dream is to put in water, air and sunlight to create a fuel.”
Reference: “Spontaneous N2 formation by a diruthenium complex enables electrocatalytic and aerobic oxidation of ammonia” by Michael J. Trenerry, Christian M. Wallen, Tristan R. Brown, Sungho V. Park and John F. Berry, 8 November 2021, Nature Chemistry.
DOI: 10.1038/s41557-021-00797-w
This work was supported by the U.S. Department of Energy.
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8 Comments
…and has received a provisional patent from the Wisconsin Alumni [something] Association.”
The USPTO can eat grits, I’m applying to the Alumni Board?!?
Nice green tech.
I apologise, but have to disagree with Christian Wallen in one point
There an ongoing carbon closed loop fully consolidated industry in Brazil
Our country is known for the fuel alcohol gasoline substitution, but there are another unnoticed biofuel massive used in substitution for coal, Eucalyptus firewood which has a LCV around the one of lignite
Since a planted forest requires between six and ten years to be ready to be harvested, you need to have various plots in different stages of growth for the one you are cutting
It means you have to sequester and build up your carbon stock for years before finally have it ready for use, just like a bank savings account
Obviously, this is carbon negative
But in anyway, my congratulations for the discovery
This sounds a real landmark achievement
I can make no sense of this article. I suspect the tech writer didn’t understand the process, or that the process itself is BS. I never suspected that nitrogen, which is the major component of the air we breath, is really a fuel.
The energy sought after is from the fuel cell cracking ammonia and producing nitrogen. It isn’t a combustion energy process, it’s electrical energy produced during the chemical reaction.
There is already a company making ammonia from water, air and electricity this company has a provisional patent on the usa its called FuelPositive
Hydrogen is the fuel component of ammonia not Nitrogen. There is a company with a true carbon to fuel cycle in Canada called Carbon engineering. They capture carbon and instead of storing it convert it to a fuel that has no emissions. Their prototype plant is proof of concept after 7 years in operation. Your writers need to brush up a bit on their knowledge.
This is much more desirable than the CO2 cracking concept producing carbon compounds also described elsewhere.
Very interesting