UREAlity Check: Approaching the Rising Field of Electrofertilizers

sı Supporting Information I n the past few years, the direct electrochemical synthesis of urea (E-UREA) has been attempted using different carbon and nitrogen sources. 1,2Similarly, photocatalytic processes have been reported. 3,4Regardless of the energy input and the feedstock, E-UREA is in its infancy, and the state of the art lacks several key elements for a proper assessment of its figures of merit.In the present Viewpoint, the author will focus on the process that seemingly holds better promise to a carbonneutral and fossil-fuel-free synthesis of urea, i.e., the combination of electrochemical CO 2 reduction (CO 2 RR) and nitrate reduction (NO 3 RR) reactions.To date, the coreduction of CO 2 and nitrate to urea has been (qualitatively) proven almost only in batch systems that operate at very low current densities and with nonscalable cell designs.Together with the use of biased urea quantification methods, the race to achieve ever-increasing efficiency (i.e., Faradaic Efficiency, FE) in these difficult-to-scale systems has raised several criticalities.This focus on FE Urea , hampered by the real risk of false positives and overestimations, comes at the expense of pursuing a comprehensive understanding of the coreduction process and generally overlooks the importance of meeting industrial relevance.All in all, the author is particularly concerned with the unlucky conjunction in the middle of which E-UREA lies: from one side, the misleading outcomes of CO 2 RR testing in batch systems (e.g., H-cells); 5 from the other, the troubled history of false positives that has flanked the field of nitrogenous compound reductions (N 2 RR in the lead 6,7 ).Recent reviews have discussed the progress in CO 2 RR, 8 NO 3 RR, 9-12 and E-UREA 2,13-15 from the catalytic design standpoint.Differently, this Viewpoint will provide guidelines for implementing both setups and methods to enhance urea production and improve detection/quantification accuracy.In the author's opinion, the broader context is very important when tackling a rather unexplored and complex field of research such as E-UREA.To this extent, a concise but all-rounded introduction to the fertilizers' production is laid out in Nitrogen Fixation in the Supporting Information.In a nutshell, we must be aware that urea is currently produced on a Mtons/year scale; 16-18 therefore, any attempt to decarbonize its synthesis should be validated under readily scalable conditions.Thus, in the case of E-UREA, the FE Urea is not the sole process parameter to take into account.For instance, E-UREA should also achieve high current densities (i.e., high productivity), high voltage/energy efficiency, and high single-pass conversion.For these purposes, it is easy to envisage the use of prototypical electrolyzers, not different (in the notion) from those designed for water splitting and/or CO 2 RR.With this Viewpoint, the author hopes to convince the community that E-UREA studies cannot refrain from (i) the implementation of ad-hoc setups, approaching industrially relevant conditions (Flow Systems for E-UREA); (ii) a proper electrolyte choice/engineering (Electrolyte Engineering for E-UREA); and (iii) accurate detection/quantification tools for both urea and all CO 2 RR/NO 3 RR byproducts (Urea Detection).