Proton-filtering covalent organic frameworks with superior nitrogen penetration flux promote ambient ammonia synthesis

Abstract

The simultaneous achievement of both high ammonia yield and Faradaic efficiency in electrochemical nitrogen reduction is a long-sought-after goal. However, due to the strong competing hydrogen evolution and extremely low solubility of N2 in aqueous systems, thermodynamic modulation at the catalyst level is insufficient, leaving the current performance still far from practical application. Here, we rationally control the diffusion of the reactants to obtain suppressed proton supply and greatly enhanced nitrogen flux using proton-filtering covalent organic frameworks, forcing a highly selective and active nitrogen reduction. In this proof-of-concept system, we achieved a high performance in the electrochemical ammonia synthesis (ammonia yield rate 287.2\u2009±\u200910.0\u2009μg\u2009h−1\u2009mgcat.−1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\rm{mg}}_{\\rm{cat.}}^{-1}$$\\end{document}, Faradaic efficiency 54.5\u2009±\u20091.1%) using a traditional carbon-based catalyst. The proposed strategy successfully optimizes the mass transfer that greatly facilitates nitrogen reduction, providing powerful guidelines for achieving green ammonia production at a more practical level. The simultaneous achievement of both high ammonia yield and Faradaic efficiency in electrochemical nitrogen reduction is a challenging goal. Now, the diffusion of reactants to the catalyst surface is controlled using a covalent organic framework, which results in high-performance electrochemical ammonia synthesis.