Efficient Electrocatalytic Nitrate Reduction to Ammonia Over Copper Catalysts on Electron-Delocalized Covalent Organic Frameworks

Abstract

Electrochemical nitrate reduction to ammonia (NRA) has recently emerged as a promising route to convert nitrate in wastewater into high-value-added products. Nevertheless, the development of NRA has been hampered by reaction involves multi-proton and electron transfer, posing a low Faradaic efficiency (FE). Here, we develop a composite catalyst of Cu/Cu2O nanoparticles on covalent organic frameworks (COFs) with highly ordered and porous topological structures. The high electron delocalization feature of COFs arising from their two-dimensional structure and rich π-bond increase the electron density of Cu active site, which is benefit for the adsorption and activation of NO3–. The composite catalyst can deliver a satisfactory FE of 95% and a yield rate of 3.4 mmol h−1 mg−1 for ammonia synthesis. Experimental and theoretical studies both reveals that the COF support can effectively increase the local concentration of NO3– at catalyst surface and decrease the energy barrier, leading to superior NRA performance.

Keywords: covalent organic frameworks, Cu-based catalyst, metal-support interaction, electron delocalization, Electrochemical nitrate reduction