Fused Heterocyclic Molecule-Functionalized N-Doped Reduced Graphene Oxide by Non-Covalent Bonds for High-Performance Supercapacitors

Abstract

Indole molecules with fused heteroaromatic structures can be adsorbed on the N-doped graphene surface through the π−π interaction. Therefore, the indole-functionalized N-doped graphene (InFGN) with mesopores is successfully fabricated by a simple hydrothermal method and subsequent vacuum freezedrying process. The microstructure, thickness, element composition, pore structure, and electrochemical performance of InFGN are analyzed via SEM, TEM, AFM, BET, UV−vis, FT-IR, XPS, Raman, XRD, and electrochemical technologies. Since the fivemembered aromatic heterocycles are electron-rich, the indole molecules fixed on the N-doped graphene surface can repair the structural defects generated by N doping. Electrochemical measurements show that the InFGN electrode highlights an excellent capacitance of 622.3 F g −1 at 2 A g −1 and a durable cycling life of 100.5% after 5000 charging/discharging cycle times. For further practical application, a symmetric device has been assembled by using InFGN electrodes, which realizes high-power and energy densities (18.8−20.6 Wh kg −1 at 800−8000 W kg −1 ). This study provides a shortcut for building green supercapacitors with enhanced energy storage performance.

Revisiting Charge Storage Mechanism of Reduced Graphene Oxide in Zinc Ion Hybrid Capacitor beyond the Contribution of Oxygen‐Containing Groups

“…[7][8][9] Particularly, aqueousbased hybrid devices composed of two types of electrodes involving the charge storage mechanisms of electrochemical redox reactions and electrostatic adsorption/desorption possess the merits of battery-like energy density and capacitorlike fast charge/discharge capability. [10][11][12][13] Regarding anode material, metallic Zn is deemed as an ideal candidate due to its superior theoretical capacity of 823 mAh g −1 , appropriate redox potential (−0.76 vs. standard hydrogen electrode), [14][15][16] as well as natural abundance. However, the development of proper cathode materials that match with Zn anode well remains challenging.…”

Electrochemical Performance of N-Doped Carbon-Based Electrodes for Supercapacitors

“…The morphology of the carbon derivatives has a direct influence on the available active sites for charge accumulation. In graphene, the aggregation due to the van der Waals forces and the π–π interaction between the graphene nanosheets ,, leads to poor contact between the surface of the material and the electrolyte, which affects the transport of ions and electrons. ,,, …”

“…One of the most important strategies to overcome the effects of the reduction in electrode–electrolyte surface area due to aggregation is the introduction of heteroatom dopants, such as nitrogen, in the graphitic structure. This process increases the active sites for charge accumulation by enlarging the interlayer space and, consequently, improving the wettability and opening the path to the electrolyte , The nitrogen doping process has been studied as a promising strategy to enable desirable interactions between the N lone pair electrons and the carbon structure . Because of the similarity of the covalent radius between nitrogen and carbon atoms and the free valence electrons of the N atoms, doping can be easily done by forming C–N stable covalent bonds. , The doping procedure introduces surface functionalization, modulates the catalytic activity, improves the electrical conductivity, and induces a pseudocapacitance behavior. ,, In addition to the nitrogen doping process in carbon derivatives, advances in new carbon substrates have been explored from the codoping with heterostructures such as boron and phosphorus by methods of the anchoring of nanoparticles into N-doped carbon nanotubes, strategies of encapsulation of nickel into N-doped carbon nanotubes, , the synthesis of core–shell structures, nanocomposites , with metal phosphide nanoparticles, and the confinement of cobalt phosphide nanocrystals into N-doped carbon nanostructures …”

“…The morphology of the carbon derivatives has a direct influence on the available active sites for charge accumulation. In graphene, the aggregation due to the van der Waals forces and the π−π interaction between the graphene nanosheets 14,28,29 leads to poor contact between the surface of the material and the electrolyte, which affects the transport of ions and electrons. 10,14,15,29 One of the most important strategies to overcome the effects of the reduction in electrode−electrolyte surface area due to aggregation is the introduction of heteroatom dopants, such as nitrogen, in the graphitic structure.…”

Microphase Separation Engineering toward 3D Porous Carbon Assembled from Nanosheets for Flexible All-Solid-State Supercapacitors

“…The FT-IR spectra shown in Figure b revealed the structural differences between CTP, HCTP, and HCAs. The strong FT-IR peaks at 3100–2800 cm –1 (C–H stretching vibration), 1600 cm –1 (aromatic skeleton CC stretching vibration), 1460 cm –1 (methylene C–H in-plane bending vibration), and 950–670 cm –1 (out-of-plane bending vibration of aromatic C–H) suggest that the nonpolar polycyclic aromatic hydrocarbon with a small amount of alkyl side chains dominates the molecules of CTP − (Figure S2). Compared with CTP, the FT-IR peaks of HCTP are weakened at 3150–2800 cm –1 and 950–670 cm –1 , but enhanced at 3380 cm –1 (O–H), 1730 cm –1 (CO), and 1100 cm –1 (C–O–C), delivering that these oxygen functional groups substitute the alkyl or aromatic hydrogen at the edge of the aromatic nucleus in PAH molecules.…”