Reduced graphene oxides with engineered defects enable efficient electrochemical reduction of dinitrogen to ammonia in wide pH range. (February 2020)

• Record Type: Journal Article
• Authors: Zhang, Mingli; Choi, Changhyeok; Huo, Rupeng; Gu, Geun Ho; Hong, Song; Yan, Chao; Xu, Suying; Robertson, Alex W.; Qiu, Jieshan; Jung, Yousung; Sun, Zhenyu
• Is Part Of: Nano energy. Volume 68(2020)
• Publication Date: 2020-02
• Subjects: Nitrogen reduction -- Defect -- Metal-free catalysis -- Electrocatalyst; Nanoscience -- Periodicals; Nanotechnology -- Periodicals; Nanostructured materials -- Periodicals; Power resources -- Technological innovations -- Periodicals; Nanoscience; Nanostructured materials; Nanotechnology; Power resources -- Technological innovations; Periodicals; 621.042
• DOI: 10.1016/j.nanoen.2019.104323
• Languages: English
• ISSNs: 2211-2855

Abstract

Abstract: Electrochemical nitrogen fixation under mild conditions is highly demanded yet remains a grand challenge. Herein we report metal-free electrocatalysis of aqueous N2 reduction to produce NH3 over reduced graphene oxide (DrGO) with tuned defects. The defect sites in DrGO, consisting of unsaturated carbon [single vacancy (SV), double vacancy (DV), and –COOH], were examined, and showed an improved NH3 selectivity due to the strong binding of N2 instead of H. In addition to improved selectivity, the calculated free energies for N2 reduction reaction at DrGO-COOH and DrGO-DV sites suggest that the thermodynamic overpotentials of these metal-free catalysts are comparable to the most efficient transition metal-based catalysts reported thus far. Our nonmetallic and dopant-free catalysts can convert N2 to NH3 at a faradaic efficiency of up to 22.0% at −0.116 V (versus the reversible hydrogen electrode vs . RHE) in 0.1 M HCl and 10.8% at −0.166 V ( vs . RHE) in 0.1 M KOH, surpassing most earlier reported catalysts. An NH3 formation rate exceeding 7.3 μg h −1 mg −1 was achieved at low overpotentials in both acidic and alkaline environments, comparable to the values shown by metal electrocatalysts under similar conditions. Graphical abstract: The potential role of defects in reduced graphene oxide on its N2 activation was elucidated by density functional theory calculations and verified experimentally, evidenced by remarkably enhanced electrocatalytic reduction of N2 to NH3 in a wide pH range over reduced graphene oxide with engineered defects. Image 1 Highlights: We demonstrate ambient electrochemical N2 reduction in a wide pH range over reduced graphene oxide with tailored defects. A joint computational-experimental study shows that the defects of rGO facilitate the binding and activation of N2 . The metal-free catalysts provide an NH3 faradaic efficiency of 22.0% and an NH3 yield rate of 8.5 μg·h -1 in 0.1 M HCl.