The Paris Agreement and the Green Deal have set 2050 as the date for complete decarbonization. In Europe, roughly 25% of carbon dioxide emissions are related to the industrial sector. Among the various activities, there are some particularly energy-intensive and difficult to decarbonize such as iron/steel, cement, ethylene and ammonia. The latter is the building block for synthesizing nitrogen fertilizers such as urea which is the most used fertilizer on Earth. Ammonia production relies on the Haber Bosch process which is responsible for more than 2% of carbon dioxide emissions worldwide. This emission is derived from the usage of methane to produce hydrogen which is a building element of ammonia. Ammonia and carbon dioxide are then the two main ingredients to produce urea using the Bosch Mesier synthetic process. Electrifying this process without the usage of polluting fossil fuels is a promising route to substantially decrease carbon dioxide emissions. It was calculated that the electrochemical production of urea would decrease by 35% the energy used and by 50% the carbon dioxide emitted.
In the mini-review “Urea Electrochemical Production Using Carbon Dioxide and Nitrate: State of the Art and Perspectives ” (doi: 10.1039/D4EE00561A) published in the journal Energy and Environmental Science (Royal Society of Chemistry Impact Factor 32.5, 2022 Journal Impact Factor, Journal Citation Reports (Clarivate Analytics, 2023)), the electrochemical synthesis of urea starting from nitrate and carbon dioxide is presented. Nitrate is preferred over N2 due to the higher solubility and lower bond dissociation energy of N=O compared to that of N≡N. The initial results obtained are presented and are very promising, however, low activity and selectivity still remain challenging. The recent literature, especially in the past three years is discussed. The reaction mechanisms of the urea electrosynthesis starting from CO2 and NO3- are quite complex and debated and, up to now, a selective electrocatalyst with operative durability has not been found. The advancement in electrocatalysis related to this reaction is presented and discussed. This reaction involves 16 electrons and over 70 intermediates, therefore a strong detection method is needed to identify urea but also to analyze and quantify the reaction intermediates. The combination of the in-situ and ex-situ urea detection methods can certainly help to unravel the reaction mechanisms. This mini-review provides a useful overview of the recent achievements in the electrochemical production of urea. Limitations and challenges are highlighted and further steps to enhance the technology readiness level of this technology are discussed.
This mini-review work was carried out by Mr. Mohsin Muhyuddin, Mr. Giovanni Zuccante, Prof. Piercarlo Mustarelli and Prof. Carlo Santoro (Department of Materials Science, University of Milano-Bicocca) in an international collaboration jointly with Jonathan Filippi and Alessandro Lavacchi (CNR-ICCOM, Istituto per la chimica dei composti organometallici), Ms. Yu-Han Chen and Prof. Plamen Atanassov (University of California Irvine) and Prof. Lior Elbaz (Bar-Ilan University).