^ Inexpensive, small-scale and decentralized fertilizer production would especially help farmers in remote, rural areas. The image shows a bio-organic market garden in the Netherlands where SSWN’s editor volunteers most Saturday mornings.
Article by David Sear
In a step toward small-scale fertilizer production, the research team at MIT (Massachusetts Institute of Technology) has devised a way to combine hydrogen and nitrogen using electric current to generate a lithium catalyst, where the reaction takes place.
“In the future, if we envision how we want this to be used someday, we want a device that can breathe in air, take in water, have a solar panel hooked up to it, and be able to produce ammonia. This could be used by a farmer or a small community of farmers,” says Karthish Manthiram, an assistant professor of chemical engineering at MIT and the senior author of the study.
Graduate student Nikifar Lazouski is the lead author of the paper, published in Nature Catalysis. Other authors include graduate students Minju Chung and Kindle Williams, and undergraduate Michal Gala.
“Encouraging results have been achieved using a stainless steel mesh electrode”
For more than 100 years, fertilizer has been manufactured using the Haber-Bosch process, which combines atmospheric nitrogen with hydrogen gas to form ammonia. Using this process, manufacturing plants can produce thousands of tons of ammonia per day, but are expensive to run and emit a great deal of carbon dioxide.
The MIT team set out to develop an alternative that could reduce emissions and facilitate decentralized production. “The ideal characteristic of a next-generation method of making ammonia would be that it’s distributed. In other words, you make ammonia close to where you need it,” Manthiram says. “And ideally, it would also eliminate the CO2 footprint.”
While the Haber-Bosch process uses extreme heat and pressure to force nitrogen and hydrogen to react, the MIT team decided to try using electricity to achieve the same effect. Previous research has shown that applying electrical voltage can shift the equilibrium of the reaction so that it favors the formation of ammonia. However, it has been difficult to do this in an inexpensive and sustainable way, the researchers say.
Most previous efforts to perform this reaction under normal temperatures and pressures have used a lithium catalyst to break the strong triple bond found in nitrogen gas molecules. The resulting product, lithium nitride, can then react with hydrogen atoms from an organic solvent to produce ammonia.
The MIT team came up with a way to use hydrogen gas as the source of hydrogen atoms. They designed a meshlike electrode that allows nitrogen gas to diffuse through it and interact with hydrogen, which is dissolved in ethanol, at the electrode surface.
This stainless steel, mesh structure is coated with the lithium catalyst, produced by plating out lithium ions from solution. Nitrogen gas diffuses throughout the mesh and is converted to ammonia through a series of reaction steps mediated by lithium. This setup allows hydrogen and nitrogen to react at relatively high rates. “This stainless steel cloth is a way of very effectively contacting nitrogen gas with our catalyst, while also having the electrical and ionic connections that are needed,” Lazouski says.
In most of their experiments, the researchers used nitrogen and hydrogen gases fl owing in from a gas cylinder. However, they also showed that they could use water as a source of hydrogen, by first electrolyzing the water and then fl owing that hydrogen into their electrochemical reactor.
The overall system is small enough to sit on a lab benchtop, but it could be scaled up to produce larger quantities of ammonia by connecting many modules together, Lazouski says. Another key challenge will be to improve the energy efficiency of the reaction.
The research was funded by the National Science Foundation and the MIT Energy Initiative Seed Fund. Prior research which was foundational for the present work was supported by MIT’s Abdul Latif Jameel Water and Food Systems Lab (J-WAFS).