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

The direct synthesis of ammonia from nitrate (NO 3 – ) 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 NO 3 – and H + are regulated via appropriate electrostatic interactions, thus realizing the priority of NO 3 RR with respect to HER or NO 3 – -to-NO 2 – . As a result, an NH 3 yield rate of 11.01 mmol h –1 mg –1 and a corresponding Faradaic efficiency of 91.0% are attained, and solid NH 4 Cl 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.