Hybrid Graphene Ribbon/Carbon Electrodes for High‐Performance Energy Storage

Abstract

The utility of supercapacitors for both fixed and portable energy storage would be greatly enhanced if their energy density could be increased while maintaining their high power density, fast charging time and low cost. This study describes a simple, solution-phase and scalable modification of carbon materials by a covalently bonded "brush" of hydrogenterminated graphene ribbons (GRs) with layer thicknesses of 2-20 nm, resulting in a 20-100 times increase in the areal capacitance of the unmodified electrode surface. On a flat sp 2 carbon surface modified by GRs, the capacitance exceeds 1200 µF cm -2 in 0.1 M H 2 SO 4 due to a distinct type of pseudocapacitance during constant current charge/discharge cycling, with minor changes in voltammetry after 10,000 cycles between -0.2 and +0.8 V vs. Ag/AgCl. Modification of high surface area carbon black electrodes with GRs yields capacitances of 950-1890 F g -1 , power densities >40 W g -1 , and minimal change in capacitance during 1500 charge/discharge cycles at 20 A g -1 . A capacitance of 1890 F g -1 affords an energy density of 318 Wh kg -1 operating at 1.1 V and 590 Wh kg -1 at 1.5 V. The projected energy density of a hybrid GR/Carbon supercapacitor greatly exceeds the current 10 Wh kg -1 for commercial supercapacitors, and approaches that of lithium ion batteries.

Effect of Transition Metals on the Oxygen Reduction Reaction Activity at Metal‐N3/C Active Sites

“…Upon functionalization of the tpy ligand to the carbon support, we had previously shown that the surface area decreases due to the tpy molecule blocking some of the pores. [27,36,43] This trend is observed for all of the V-tpy-M catalysts as well. The BET surface area decreases when the tpy and the metal are present on the carbon support.…”

“…Specific surface area and pore size distributions were determined from BET analysis for each catalyst and are presented in Figure S1 and Table 1. Upon functionalization of the tpy ligand to the carbon support, we had previously shown that the surface area decreases due to the tpy molecule blocking some of the pores [27,36,43] . This trend is observed for all of the V‐tpy‐M catalysts as well.…”

Heteroatom‐Doped and Oxygen‐Functionalized Nanocarbons for High‐Performance Supercapacitors

“…While the pseudocapacitors already present ten-to-hundred times higher charge storage capacity than the carbon materials, they show low electrical conductivity, insufficient power density, poor mechanical/electrochemical stability, narrow windows of operation voltage, and some other problems, that limit their prospects for technological R&D. [8,13,24,31] In this regard, carbon-based materials represent the obvious choice for supercapacitor technology owing to their unique combination of features such as versatile dimensionality (0D-3D), abundance on Earth, large surface areas, tunable porous architectures, excellent electrical conductivity, easy functionalization, leading to the high EDL capacitance and remarkable electrochemical stability. [12,[32][33][34][35] Carbonbased materials can also be operated over a wide temperature range of −100 to 60 °C, with extremely low failure rates. [36] Since energy storage and release occur by nanoscale charge separation or EDL formation across the electrode-electrolyte interface, carbon-based supercapacitors offer very fast chargedischarge cycles suitable for prolonged operation.…”

Movements of Mobile Ions in Molecular Electronic Devices

“…Not only current but charge‐storage capability was also greatly enhanced by the polar solvent. To date, there are rare examples of charge‐storage solid‐state molecular electronic junction made with organic molecules . Mobile ions present in the molecular junction play dual role; i) decrease the barrier height for resonant charge‐transport, ii) increase charge‐storage capability significantly.…”