N-doped porous carbon capsules with tunable porosity for high-performance supercapacitors

Abstract

A procedure for the fabrication of N-doped hollow carbon spheres with a high rate capability for supercapacitors has been developed. The approach is based on a nanocasting method and the use of a nitrogen-rich compound (pyrrole) as a carbon precursor. The carbon particles thus produced combine a large BET surface area ($1500 m 2 g À1 ) with a porosity made up of mesopores of $4 nm, a high nitrogen content ($6 wt%) and a capsule morphology which entails short ion diffusion paths derived from the shell morphology (thickness $60 nm). The porous properties of these hollow particles can be enhanced by means of an additional activation step with KOH. The activation process does not alter the hollow structure or spherical morphology, but strongly modifies the pore structure from a mesoporous network to a microporous one. The N-doped carbon capsules were tested in aqueous and organic electrolytes. In an aqueous medium (1 M H 2 SO 4 ), the mesoporous carbon capsules offer the best performance due to the pseudocapacitive contribution of the N-groups, exhibiting a specific capacitance of $240 F g À1 at 0.1 A g À1 and a capacitance retention as high as 72% at 80 A g À1 . In contrast, in an organic electrolyte(1 M TEABF 4 /AN), where the charge storage mechanism is based on the formation of the electric double-layer, the microporous capsules perform better due to the larger specific surface area. Thus, the microporous carbon capsules display a specific capacitance of up to 141 F g À1 at 0.1 A g À1 and an outstanding capacitance retention of 93% for an ultra-high discharge current density of 100 A g À1 .

Construction of nitrogen-doped porous carbon buildings using interconnected ultra-small carbon nanosheets for ultra-high rate supercapacitors

“…21,22 However, carbon nanosheets tend to aggregate (self-restacking) during the preparation of the electrode and electrochemical process, resulting in a substantial loss of active surface area that reduces their electrochemical performance. 16,23 In addition, the low packing density (<0.5 g cm -3 ) results in poor volumetric performances, 24,25 which severely limits their future practical applications such as mobile electronics and electric vehicles. By contrast, mesoporous carbons hold an enormous advantage for offering rapid ion transport with improved rate capability.…”

“…Microporous network is beneficial for the enhancement of energy storage, but the long diffusion paths severely limit the ion-transport kinetics, resulting in poor rate performance for supercapacitors. [15][16][17][18][19] To enhance ion-transport kinetics of microporous carbon, the fabrication of ultra-small particles (<200 nm) is another choice. 16,20 However, superabundant interfaces between nanoparticles are going against the formation and maintenance of conductive network of electrode materials during charge and discharge process.…”

Nitrogen-enriched meso-macroporous carbon fiber network as a binder-free flexible electrode for supercapacitors

“…This finding distinguishes from other reported nanostructures, whose double-layer capacitance mixed with pseudocapacitance and one has to rely on ion kinetics analysis to determine each component's contribution [37,38]. Despite its low surface area, our meso-macroporous NCF still exhibits specific capacitance quite comparable to other nitrogen-(and/or oxygen-) enriched porous carbon [21,[39][40][41][42][43]. Moreover, increasing the scan rate up to 100 mV/s results in the maintenance of a rectangular shape CV of NSF-66% SiO 2 , without deviation, which is indicative of pseudocapacitive and fast rate responses (Fig.…”

Controlled Fabrication of Interconnected Porous Carbon Nanosheets for Supercapacitors with a Long Cycle Life

“…Thus, pore properties of APC3‐700 are superior to those of APC0‐700. Based on the morphologies and textural properties before and after activation, it is clearly verified that the KOH activation can efficiently improve the surface area and micropore while only little change in morphology occurs …”