Ultramicroporous Carbons Puzzled by Graphene Quantum Dots: Integrated High Gravimetric, Volumetric, and Areal Capacitances for Supercapacitors

Abstract

Porous carbons integrated with high gravimetric/volumetric/areal capacitances, especially at high mass loadings (>10 mg cm−2), are important for practical applications in supercapacitors. Here, a strategy is developed for the synthesis of ultramicroporous carbons puzzled by graphene quantum dots as the building units through chemical welding and in situ activation. The resulted carbon has unique ultramicroporous structure (≈0.5 nm) with both high surface area (1730 m2 g−1) and packing density (0.97 g cm−3), providing high gravimetric and volumetric capacitances of 270 F g−1 and 262 F cm−3 at 1 A g−1, respectively. More importantly, such carbon achieves an ultrahigh areal capacitance of 5.70 F cm−2 with a high mass loading of 25 mg cm−2 at 1 A g−1, which is one of the best among the previously reported porous carbons. Furthermore, a two‐electrode supercapacitor exhibits an ultrahigh areal capacitance of 3 F cm−2 at 0.5 A g−1, rapid charge–discharge ability, and long lifespan. This work paves an avenue for developing advanced porous carbons with integrated capacitive performances for supercapacitors.

A General Route to Prepare Low‐Ruthenium‐Content Bimetallic Electrocatalysts for pH‐Universal Hydrogen Evolution Reaction by Using Carbon Quantum Dots

“…Ther esulting products were designated as RuNi/CQDs-T,where T is the annealing temperature.D uring the pyrolysis, Ru and Ni atoms joined to form bimetallic Ni-doped RuNi NPs,w hereas the CQDs self-crosslinked to form aN -rich graphene skin surface because of hydrogen bonding between their van der Waals bonding and surface functional groups (e.g., hydroxyl (-OH), carboxyl (-COOH), and amino (-NH 2 ) groups) induced between adjacent CQDs. [36][37][38] The transmission electron microscopy (TEM) image in Figure 1b clearly show that RuNi NPs were uniformly dispersed on the surface of the CQDs.T he mean diameter of the RuNi NPs of RuNi/CQDs-600 was 8.63 nm, as indicated by the particle size distribution in the inset of Figure 1b.T he atomic-resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image in Figure 1c displays well-defined lattice fringes with lattice spacings of 1.99 and 2.26 ,c orresponding closely to the (101) and (100) planes of RuNi alloy.The lattice fringe spacings of 2.05 at the edge position is attributed to the (101) plane of hexagonal Ru. Atomic-resolution energy-dispersive X-ray (EDX) line scanning and EDX mapping were performed in Figure 1d,i ndicating that Ru and Ni elements were homogeneously distributed throughout the structure.…”

Tin Nanodots Derived From Sn2+/Graphene Quantum Dot Complex as Pillars into Graphene Blocks for Ultrafast and Ultrastable Sodium‐Ion Storage

“…Graphene quantum dots (GQDs) with “octopus” structure were synthesized through acid oxidation method using coal as the precursor. [ 32 ] Scanning electron microscope (SEM) and transmission electron microscopy (TEM) images exhibit that the GQDs with sizes of about ≈2 nm are uniformly distributed in the fields ( Figure a; Figure S1, Supporting Information). The survey of X‐ray photoelectron spectroscopy (XPS) reveals that the predominant elements of GQDs skeleton are C, N (5.0%), and O (32.1%), and the main oxygen doping is ascribed to the carboxyl groups (COOH, 288.2 eV in C1s and 531.1 in O 1s spectra, Figure 1b; Figure S2, Table S1, Supporting Information), which is also supported by FTIR spectra with the characteristic peaks of CO stretching vibration at 1720 cm −1 and OH stretching vibration at 1650 cm −1 (Figure 1c).…”

“…The GQDs were prepared through a chemical oxidation method in an HNO 3 and H 2 SO 4 system based on the precursor of bituminous coal (Heishan, Xinjiang, China) according to the authors’ previous work. [ 32 ]…”

High‐efficiency utilization of carbon materials for supercapacitors

“…[18] Recently, we prepared an ultra-microporous carbon by KOH activation using graphene quantum dots as the precursor. [53] Due to the unique small-sized structure and K + coordinated on the edge-enriched carboxylic groups, a small amount of KOH was uniformly distributed inside the compressed precursor, leading to the formation of interconnected ultra-microporous structure (∼0.52 nm).…”