Supramolecular‐mediated ball‐in‐ball porous carbon nanospheres for ultrafast energy storage

Abstract

Hierarchical porous carbons are the most viable electrode material for supercapacitors because of their balanced capacitive performance and chemical stability. Their pore connectivity plays a pivotal role in electrolyte transport, which is quantified by a new parameter, defined in this work as the longest possible pore separation (LPPS). Herein, we report hierarchical porous carbon nanospheres (HPC-NS) with a unique ball-in-ball structure, which is achieved by the pyrolysis of a supramolecular complex of γ-cyclodextrin (γ-CD)/PEO-PPO-PEO (F127). This approach differs from the conventional softtemplating method in that, apart from the assembly of the monomicelles that leads to the host nanospheres (approximately 300 nm), the γ-CD-containing monomicelles themselves are converted to small porous carbon nanospheres (<10 nm), which results in an ultralow LPPS of 10 nm, representing the bestknown pore connectivity of the HPC family. The HPC-NS delivers a high specific capacitance (405 F g À1 at 1 A g À1 and 71% capacitance retention at 200 A g À1 ), wide voltage window (up to 1.6 V), and simultaneously high energy and power densities (24.3 Wh kg À1 at a power density of 151 W kg À1 and 9 Wh kg À1 at 10 5 W kg À1 ) in aqueous electrolytes. This new strategy boosts the development of porous carbon electrodes for aqueous supercapacitors with simultaneously high power and energy densities.

Efficient Activation Engineering from the Inside Out toward Hierarchically Porous Carbon Framework as Electrode Materials for Supercapacitors

“…The enhanced connectivity of pores can provide a faster ion transportation pathway. 18 In comparison, even if numerous micropores are discerned in the PC/K (SI Figure S1a,b), most of them are isolated pores, hindering the ion transport to a certain extent. However, few micropores are located in the PC to confine active ions for energy storage (Figure 1j).…”

“…The good balance of micropores and meso-/ macropores in the case of PC-K can benefit its remarkable electrochemical capacitances particularly at high rates. 18,21 It is especially worthy of pointing out that the distinct differences in morphologies and microstructures of the PC, PC/K, and PC-K should be highly dependent on the specifically applied activation avenues, as schematically illustrated in Figure 3. Specifically, the diagrammatic sketch of PVA hydrogel, the mixture of the PVA and KOH powders, and the PVA-KOH hydrogel are represented in Figure 3a−c, respectively.…”

“…In addition, the variation of the imaginary part capacitance (C″) versus frequency for PC-K, PC/K, and PC (SI Figure S6b) reveals that the relaxation time constant (τ 0 ) of the PC-K in 1 M H 2 SO 4 is ∼7.9 s, which is smaller than that of PC-K (∼15.9 s), PC/K (∼26.3 s), and PC (∼45.5 s) in 6 M KOH, indicating a faster ion transport and charge transfer in 1 M H 2 SO 4 . 18,36 Electrochemical Evaluation of Two-Electrode Symmetrical Devices. The promising applications of our PC-K in an aqueous symmetric supercapacitor were further investigated by constructing the two-electrode symmetrical devices both with the acidic and alkaline electrolytes.…”

“…The reason may be that the O group can be effectively increased because of the activation of uniform KOH in the PVA-KOH hydrogel. Furthermore, the addition of KOH can increase the O−I content in PC-K (2.0 atom %) and PC/ K (1.7 atom %), which are larger than that of PC (0.7 atom %), thus resulting in more capactive contribution from the OC group 11,17,18.…”

Preparation of High-Performance Porous Carbon Materials by Citric Acid-Assisted Hydrothermal Carbonization of Bamboo and Their Application in Electrode Materials

“…At present, a major factor restricting SCs is their relatively low specific energy density, − which is less than 20% of the typical lithium-based energy storage devices . Objectively, the performance of SCs mainly depends on the properties of electrode materials.…”