Four-Fold Increase in the Intrinsic Capacitance of Graphene through Functionalization and Lattice Disorder

Abstract

Graphene has been heralded as a promising electrode material for high energy and power density electrochemical supercapacitors. This is in spite of recent work confirming the low double-layer capacitance (C DL ) of the graphene/electrolyte interface limited by graphene's low quantum capacitance (C Q ), an effect known for the basal-plane of graphite for over four decades. Consistent with this limit, much of the supercapacitor research implies the use of pristine graphene but, in contrast, uses a functionalized and defective graphene formed through the reduction of graphene oxide, without clarifying why reduced graphene oxide is needed to achieve high capacitance. Herein, we show that an optimal level of functionalization and lattice disorder in reduced graphene oxide yields a four-fold increase in C DL over that of pristine graphene, suggesting graphene-based materials can indeed be tailored to engineer electrodes with significantly higher gravimetric capacitance limits exceeding 450 F/g than what has been achieved (~ 274 F/g) thus far, even in non-aqueous electrolytes capable of high voltage operation. TOC GRAPHICS

Nitrogen Codoped Unique Carbon with 0.4 nm Ultra‐Micropores for Ultrahigh Areal Capacitance Supercapacitors

“…These effects can considerably enhance the capacitance of carbon electrodes by contributing an additional pseudocapacitance in the form of surface Faradaic reactions . In recent years, nitrogen‐doped carbon materials have emerged as the most promising candidates for alternative electrode materials for EDLC applications owing to their excellent performance . Recently, Lin et al developed a nitrogen‐doped ordered mesoporous few‐layer carbon with a high specific surface area (1580 m 2 g −1 ) and a very high nitrogen doping concentration (12 at% nitrogen doping), which displayed a record gravimetric capacitance of 855 F g −1 in aqueous electrolytes.…”

The critical role of bulk density of graphene oxide in tuning its defect concentration through microwave-driven annealing

“…However, it is only active in the presence of defects such as functional groups and lattice defects [22,32,33,36,37] . The D' band is also associated with the presence of defects, and typically observed for GO-derived materials [18] . On the other hand, the G-band arises from any sp 2 carbon pairs.…”

“…Abundance of surface oxygen functional groups in GO enables its high dispersion in polar solutions [2] , enabling liquid-phase processes to prepare thin membrane [7] , catalytic materials [8][9][10][11] , energy storage materials [12,13] , energy conversion materials [14] , conducting films [2] , and light monolithic adsorbents [15,16] . In addition, chemical or thermal reduction of GO forms graphene-like materials [1][2][3][17][18][19] . However, even after reduction, GO contains residual oxygen atoms [1,3,20,21] with a high concentration of structural defects [4,21] as often characterized by a strong D-band in Raman spectroscopy data [22] .…”

“…Thus, it is desirable to be able to tune the density of defects ( n D ) as well as in-plane crystallite size ( L a ) that are suitable for specific applications. Although high-temperature thermal reduction of GO using a graphite furnace may be used to achieve such goals, it re-quires treatment exceeding 1500 °C [18,26] and limits energy efficiency.…”

Topological Design of Graphene

“…Topological defects and the resulting 3D curvatures have also been shown to contribute to the performance of electrochemical supercapacitors [172] made of graphene. DFT calculations [173] have predicted that topological defects such as 5-7-5-7 rings, 5-8-5 rings could substantially enhance the quantum capacitance of graphene by inducing quasi-localized states near the Fermi level, achieving a nearly 4-fold increase [174] in double-layer capacitance after combining with functionalization ( Fig 15d). Note that in the studies discussed above, topological defects and 3D curvature serve as a new platform to couple mechanical deformation, chemical reaction and electronic structures of graphene in enhancing specific targeted properties via topological design.…”