A heat map showing the variation in Faradaic efficiency with LiClO4 concentration and water concentration.
Researchers from Osaka University have used trace water to improve the Faradaic efficiency of nitrogen into ammonia. This work will help optimize the sustainability of a reaction that contributes substantially to global carbon emissions
Osaka, Japan – The Haber–Bosch reaction helps feed the world by converting nitrogen into ammonia, a fertilizer precursor. However, its carbon footprint is huge: this one reaction is the source of nearly 2% of global carbon emissions. Now, in a study recently published in ACS Energy Letters, researchers from Osaka University have helped re-imagine this reaction to improve the sustainability of the chemical industry.
Replacing the Haber–Bosch reaction with a more sustainable alternative has been an active area of research for many years. These efforts have led to a globally well-established electrochemical reaction for ammonia synthesis. However, efforts at optimizing this reaction are hindered by insufficient understanding of how it proceeds. A general consensus is the need to minimize the water concentration in the reaction as much as possible. Revisiting this consensus—with the goal of providing chemical reaction details that will be useful for optimizing ammonia production—is the problem that the researchers sought to address.
"There are various creative ways to improve the Faradaic efficiency by increasing the nitrogen partial pressure or solubility," explains Yu Katayama. "We have complemented these studies by showing that trace water can facilitate the reaction progress."
The researchers report a trace water concentration (ca. 36 millimolar) and a lithium perchlorate concentration (0.8 molar) that results in a Faradaic efficiency of ca. 28% at atmospheric pressure. This selectivity is the highest reported to date at ambient pressure, without using a gas diffusion electrode.
"X-ray photoelectron spectroscopy experiments indicate that the selectivity is attributable in part to the trace water facilitating lithium oxide incorporation into the solid electrolyte interphase," says Katayama. "Higher water concentrations might facilitate hydrogen evolution, an undesired side reaction.” “This surprising result can only be found with help and discussion with researchers from ICL. I believe the outcome emphasizes the importance of research collaboration.”
This work succeeded in improving the Faradaic efficiency of nitrogen reduction into ammonia at ambient pressure by straightforward means and uncovering the chemistry that leads to this result. Fine-tuning chemical process parameters dramatically improved the output of this reaction. Thus, there are many previously discounted electrochemical systems that might be worthwhile revisiting for future research efforts that investigate their detailed mechanisms. Researchers are now closer to optimizing fertilizer precursor synthesis in industry and minimizing the carbon footprint of its production.
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The article, “Water Increases the Faradaic Selectivity of Li-Mediated Nitrogen Reduction,” was published in ACS Energy Letters at DOI: 10.1021/acsenergylett.2c02792
About Osaka University
Osaka University was founded in 1931 as one of the seven imperial universities of Japan and is now one of Japan's leading comprehensive universities with a broad disciplinary spectrum. This strength is coupled with a singular drive for innovation that extends throughout the scientific process, from fundamental research to the creation of applied technology with positive economic impacts. Its commitment to innovation has been recognized in Japan and around the world, being named Japan's most innovative university in 2015 (Reuters 2015 Top 100) and one of the most innovative institutions in the world in 2017 (Innovative Universities and the Nature Index Innovation 2017). Now, Osaka University is leveraging its role as a Designated National University Corporation selected by the Ministry of Education, Culture, Sports, Science and Technology to contribute to innovation for human welfare, sustainable development of society, and social transformation.
Website: https://resou.osaka-u.ac.jp/en
A comparison of the maximum Faradaic efficiencies reported for different strategies at ambient pressure. Each of these systems uses THF as the solvent, and 1% v/v ethanol as a proton source, unless otherwise stated.
