Yunling Xu

N-doped carbon foam based three-dimensional electrode architectures and asymmetric supercapacitors

Improving the electrochemical performance of supercapacitors mainly depends on the electrode design and system construction. A new kind of additive-free asymmetric supercapacitors (ASCs) has been successfully fabricated using a self-supported carbon foam/ordered mesoporous carbon (CF-OMC) film as the negative electrode and free-standing CF-NiCo2O4 nanosheets (NSs) as the positive electrode, respectively. The highly conductive three-dimensional (3D) CF framework could facilitate electron transfer while the porous thin film of OMC and ultrathin NiCo2O4 nanosheets could shorten the ion diffusion path and facilitate the rapid migration of electrolyte ions. The optimized asymmetric supercapacitors could work with an operational voltage of 1.6 V, delivering a high energy density (∼47.8 W h kg−1), high power density (∼9800 W kg−1 at 17.7 W h kg−1) and outstanding cycle stability (∼10000 times). This research may pave the way for fabricating lightweight, low-cost, and high-performance electrodes for energy storage applications.

Crumpled Nitrogen-Doped Graphene for Supercapacitors with High Gravimetric and Volumetric Performances

Graphene is considered a promising electrochemical capacitors electrode material due to its high surface area and high electrical conductivity. However, restacking interactions between graphene nanosheets significantly decrease the ion-accessible surface area and impede electronic and ionic transfer. This would, in turn, severely hinder the realization of high energy density. Herein, we report a strategy for preparation of few-layer graphene material with abundant crumples and high-level nitrogen doping. The two-dimensional graphene nanosheets (CNG) feature high ion-available surface area, excellent electronic and ion transfer properties, and high packing density, permitting the CNG electrode to exhibit excellent electrochemical performance. In ionic liquid electrolyte, the CNG electrode exhibits gravimetric and volumetric capacitances of 128 F g(-1) and 98 F cm(-3), respectively, achieving gravimetric and volumetric energy densities of 56 Wh kg(-1) and 43 Wh L(-1). The preparation strategy described here provides a new approach for developing a graphene-based supercapacitor with high gravimetric and volumetric energy densities.

Hollow NiCo2S4 nanotube arrays grown on carbon textile as a self-supported electrode for asymmetric supercapacitors

Although supercapacitors possess a fast charge/discharge capability, the practical application of supercapacitors is still hindered largely by their low energy density. Improving the electrochemical performance of supercapacitors depends largely on the development of novel electrode materials and hybrid systems. In this work, hollow NiCo2S4 nanotube arrays are successfully grown on carbon textile (CT) with robust adhesion through a two-step synthesis, involving the growth of a solid nanowire precursor and subsequent conversion into NiCo2S4 nanotubes using a sulfidation process. Using CT-supported NiCo2S4 nanotube arrays as the positive electrode and activated carbon as the negative electrode, a high-performance asymmetric supercapacitor with a maximum voltage of 1.6 V has been fabricated, which manifests high energy density (∼40.1 W h kg−1 at 451 W kg−1), high power density (∼4725 W kg−1 at 21 W h kg−1) and excellent cyclability.

Lamellar-structured biomass-derived phosphorus- and nitrogen-co-doped porous carbon for high-performance supercapacitors

As electrical energy storage and delivery devices, carbon-based supercapacitors have attracted much attention for advancing the energy-efficient economy. It is important to develop a facile, low-cost and environmentally friendly method of producing novel carbon materials. In this study, we report a scalable synthesis of phosphorus- and nitrogen-co-doped porous carbons using lamellar-structured fish scale. The special lamellar structure of fish scale allows the production of porous carbons with large specific surface areas (up to 1300 m2 g−1) and a high level of mesoporosity. Their inherent organic composition could be adapted with abundant N and P functional groups on the final carbons. Their high levels of porosity and rich surface functionality permit the carbons to exhibit excellent electrochemical performance as electrode materials for supercapacitors. The energy densities of supercapacitors approach 11.7 and 33.1 W h kg−1 in aqueous and IL electrolytes, respectively.

Nanospace-confined synthesis of oriented porous carbon nanosheets for high-performance electrical double layer capacitors

Two-dimensional (2D) carbon nanosheets have emerged as an attractive candidate for electrical double layer capacitors (EDLCs) due to their large specific surface area, good electrical conductivity and high charge mobility. However, the easy aggregation nature of nanosheets hinders rapid transport of electrolyte ions, reducing the ion-accessible area and restricting the ion transportation. Herein, we propose a template strategy for preparing three-dimensional (3D) porous carbon nanosheets (PCNs) with an oriented and interconnected nanostructure. Zinc layered hydroxide nitrate is used as a layered template and provides a nanospace to confine the carbonization process of the organic carbon precursor (gallic acid). The unique nanostructure and large surface area of chemically activated PCNs (aPCNs) significantly shorten the ion transport length in low dimensions and improve the electrolyte wettability and ion accessible surface area for charge storage. The aPCNs exhibit excellent performance as demonstrated by their large specific capacitance (327 F g−1 at a current density of 0.5 A g−1), superior rate capability (retaining 60.2% at 20 A g−1) and stable cyclability. In particular, the assembled symmetric device based on aPCNs delivers an energy density as high as 10.2 W h kg−1 at a power density of 301 W kg−1.

Confined Self‐Assembly in Two‐Dimensional Interlayer Space: Monolayered Mesoporous Carbon Nanosheets with In‐Plane Orderly Arranged Mesopores and a Highly Graphitized Framework

Although two-dimensional (2D) carbon materials are widely investigated, a well-defined 2D carbon nanosheet with an ordered mesostructure has rarely been realized. Monolayer-ordered mesoporous carbon nanosheets (OMCNS) were prepared through confinement assembly of resol and F127 in the interlayer of montmorillonite (MONT). The nanoscale distance of the interlayer space of MONT only allow the assembly of resol and F127 in the same plane, leading to ordered mesopores perpendicular to carbon nanosheets, and favor the formation of sp2 carbon, resulting in a high degree of graphitization. The mesopores on the carbon nanosheets provide efficient ion diffusion, and the high degree of graphitization provides a fast electron-transport route, enabling OMCNS as excellent electrode materials for electric double layer capacitors.

Facile Synthesis of Nitrogen-Containing Mesoporous Carbon for High-Performance Energy Storage Applications.

Porous carbon with high specific surface area (SSA), a reasonable pore size distribution, and modified surface chemistry is highly desirable for application in energy storage devices. Herein, we report the synthesis of nitrogen-containing mesoporous carbon with high SSA (1390 m(2) g(-1)), a suitable pore size distribution (1.5-8.1 nm), and a nitrogen content of 4.7 wt % through a facile one-step self-assembly process. Owing to its unique physical characteristics and nitrogen doping, this material demonstrates great promise for application in both supercapacitors and encapsulating sulfur as a superior cathode material for lithium-sulfur batteries. When deployed as a supercapacitor electrode, it exhibited a high specific capacitance of 238.4 F g(-1) at 1 A g(-1) and an excellent rate capability (180 F g(-1), 10 A g(-1)). Furthermore, when an NMC/S electrode was evaluated as the cathode material for lithium-sulfur batteries, it showed a high initial discharge capacity of 1143.6 mA h g(-1) at 837.5 mA g(-1) and an extraordinary cycling stability with 70.3% capacity retention after 100 cycles.

Heteroatom-Doped Porous Carbon Nanosheets: General Preparation and Enhanced Capacitive Properties.

High-performance electrical double-layer capacitors (EDLCs) require carbon electrode materials with high specific surface area, short ion-diffusion pathways, and outstanding electrical conductivity. Herein, a general approach combing the molten-salt method and chemical activation to prepare N-doped carbon nanosheets with high surface area (654 m2  g-1 ) and adjustable porous structure is presented. Owing to their structural features, the N-doped carbon nanosheets exhibited superior capacitive performance, demonstrated by a maximum capacitance of 243 F g-1 (area-normalized capacitance up to 37 μF cm-2 ) at a current density of 0.5 A g-1 in aqueous electrolyte, high rate capability (179 F g-1 at 20 A g-1 ), and excellent cycle stability. This method provides a new route to prepare porous and heteroatom-doped carbon nanosheets for high-performance EDLCs, which could also be extended to other polymer precursors and even waste biomass.