Multivariate covalent organic frameworks with tailored electrostatic potential promote nitrate electroreduction to ammonia in acid

The direct synthesis of ammonia from nitrate (NO3-) reduction in acid is a promising approach for industrialization. However, the difficulty arises from the intense competition with the inevitable hydrogen evolution reaction, which is favoured due to the overwhelming protons (H+). Here, we systematically explore and rationally optimize the microenvironment using multivariate covalent organic frameworks (COFs) as catalyst adlayers to promote the nitrate-to-ammonia conversion in acid. With the application of tailored positive electrostatic potential generated over the multivariate COFs, both the mass transfer of NO3- and H+ are regulated via appropriate electrostatic interactions, thus realizing the priority of NO3RR with respect to HER or NO3--to-NO2-. As a result, an NH3 yield rate of 11.01 mmol h-1 mg-1 and a corresponding Faradaic efficiency of 91.0% are attained, and solid NH4Cl with a high purity of 96.2% is directly collected in acid; therefore, this method provides a practical approach for economically valorising wastewater into valuable ammonia.