Colorimetric correction of electrocatalytic urea quantification.

Abstract

As a feasible path for the green and sustainable synthesis of urea, electrochemical C-N coupling reactions have attracted considerable attention. To achieve high catalytic coupling performances, efficient electrocatalysts are indispensable. Notably, precise quantification of urea serves as the cornerstone for assessing catalyst performance. Urease can catalyze the decomposition of urea into ammonium (NH₄⁺), and this process is widely used in the quantification of electrocatalytic urea synthesis via calculating the increase of NH₄⁺ concentration. Unexpectedly, NH₄⁺ impurities are present in all four commercial ureases, posing a substantial risk of false-positive of urea concentration. Even when using the urease with the lowest content of NH₄⁺ impurity, the false-positive production rate of urea can exceed most reported performance thus far in electrocatalytic urea synthesis. Therefore, we recommend a simple procedure that adds NH₄⁺ impurity of commercial ureases as a subtractive term into the equation of conventional urease method for reliable urea quantification. The accuracy of the refined urease method is validated in previously reported CO₂/NO₃^- system, thereby ensuring reliable development in urea electrosynthesis.