Nitric acid and ammonia electrosynthesis

March 05, 2019

Nitric acid and ammonia are the two important reactive forms of nitrogen, which are widely used in human life and production. In 2017, the worldwide production of HNO3 and NH3 was estimated to be 50 and 150 million metric tons, respectively. At present, the commercial nitric acid is produced through the oxidation of ammonia, which is called Ostwald process. And the ammonia is synthesized through the conventional Haber-Bosch method. Both of these industrial process are energy-inefficient and discharge large amount of greenhouse gas. Otherwise, the traditional centralized mode of production and transformation always consumes plenty of energy and thus leads to the waste of fossil fuels.

In this regard, searching novel solutions that allow energy-efficient and environmentally friendly synthesis of HNO3 and NH3 at distributed sources is urgently needed. In a new research article published in National Science Review, the Zhang group at the Department of Chemistry in Tianjin University present the latest advances in electrochemical synthesis of nitric acid and ammonia. The potentially alternative strategies they proposed are taking advantage of abundant air and waste nitrate combined electrocatalytic process to prepare HNO3 and NH3. Of note, present nitrogen fixation is focused on preparing NH3 through the reduction of pure dinitrogen, which is produced by the energy-intensive air-separation process. And it is also restricted by the accompanying hydrogen evolution reaction.

Therefore, the Zhang group proposed two novel strategies. Strategy I is the electrocatalytic oxidation of N2 to HNO3 by using air as nitrogen source, and strategy II is the electrochemical reduction preparation of ammonia from residual nitrate ions (NO3-) contamination in water. The catalyst for nitrogen oxidation is platinum foil with 1.23% Faradaic efficiency at +2.19 V vs. RHE (the reversible hydrogen electrode), and Co3O4 nanorod arrays catalyst is adopted for nitrate reduction to ammonia with ammonia selectivity of 33.6% at -0.65 V vs. RHE. Furthermore, the isotope labeling experiments confirm the origin of nitrogen for obtained nitric acid and ammonia. These findings point to new opportunities for manipulating the reactive nitrogen species in an "economic" and "clean" way, especially once the electrocatalysis reaction is driven by renewable energy.
See the article:

Electrochemical synthesis of nitric acid from air and ammonia through waste utilization
Yuting Wang, Yifu Yu, Ranran Jia, Chao Zhang, Bin Zhang
Natl Sci Rev, 2019, doi: 10.1093/nsr/nwz019

The National Science Review is the first comprehensive scholarly journal released in English in China that is aimed at linking the country's rapidly advancing community of scientists with the global frontiers of science and technology. The journal also aims to shine a worldwide spotlight on scientific research advances across China

Science China Press

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