Multivariate covalent organic frameworks with tailored electrostatic potential promote nitrate electroreduction to ammonia in acid
Qiyang Cheng, Sisi Liu, Yanzheng He, Mengfan Wang, Haoqing Ji, Yunfei Huan, Tao Qian, Chenglin Yan, Jianmei Lu
Abstract
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. Ammonia electrosynthesis from nitrate reduction direct in acid is restricted by intense competition with hydrogen evolution. Here, a heterogeneous catalyst adlayer composed of multivariate covalent organic frameworks is reported to regulate the microenvironment and promote acidic nitrate reduction.