A rigorous protocol for measuring electrochemical ammonia synthesis rates

NEWS BRIEF: A paper published this week in Nature addresses the challenge of accurately reporting synthesis rates for electrochemical ammonia production technologies. According to the authors, from Stanford University, the Technical University of Denmark (DTU), and Imperial College London, it is not always clear if new technologies really synthesize ammonia, or if the researchers simply measured contaminants. This is because, at experimental scale, materially significant amounts of ammonia (or other nitrogen-containing molecules) could be present in the air, membranes, catalysts, or simply the researchers’ breath. To support the development of viable electrochemical ammonia synthesis technologies, the authors propose “benchmarking protocols,” and “a standardized set of control experiments.”

The amount of ammonia produced is usually so small that it is difficult to firmly attribute it to electrochemical nitrogen fixation and exclude contamination …

Concerted efforts to develop effective electrochemical nitrogen reduction processes would benefit from benchmarking protocols for the reaction and from a standardized set of control experiments to identify and then eliminate or quantify contamination sources. Here we put forward such a rigorous procedure that, by making essential use of 15N2, allows us to reliably detect and quantify the electroreduction of N2 to NH3.
Chorkendorff et al, A rigorous electrochemical ammonia synthesis protocol with quantitative isotope measurements, Nature, May 2019

According to an accompanying announcement from DTU:

The protocol put forth by the scientists uses Nitrogen-15 (15N2), an isotope that allows them to detect and quantify the electroreduction of N2 to ammonia. Through this method, they are able to separate the effects of spurious contamination from true N2 reduction …

“We are all part of an emerging field that could have a very positive impact on ammonia production and global CO2 emissions. Consequently, we need to be sure that we make good use of our time in the lab — and this research could help us to do so.”
Ib Chorkendorff quoted in DTU announcement, Need for rigorous procedures within electrochemical production of ammonia, ScienceDaily, 05/22/19

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Joe Beach

A researcher discussed the challenges of separating background NH3 signal from electrochemical synthesis signal at the NH3FA conference two years ago, I recall being impressed with her rigor in hunting down the background NH3 sources. I’m glad to see the challenges being addressed in a widely read magazine, it will help keep people from spending time chasing background signal in their measurements. There have been many reports of electrochemical NH3 synthesis at low levels summarized in review articles. This makes me wonder how many of the 1e-10 to 1e-9 mol/(s cm^2) measurements were due to background NH3 instead of electrochemical… Read more »