N-Doped Hollow Carbon Spheres/Sheets Composite for Electrochemical Capacitor

2D Metal Porphyrin-Based MOFs and ZIF-8 Composite-Derived Carbon Materials Containing M-Nx Active Sites as Bifunctional Electrocatalysts for Zinc-Air Batteries

The main impediment to the development of zinc-air batteries is the sluggish kinetics of the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). Transition metal N-doped carbon catalysts offer a promising alternative to noble metal catalysts, with metal-organic framework (MOF)-derived carbon material catalysts being particularly noteworthy. Here, we synthesized MxP-Z-C carbon catalysts by combining two-dimensional (2D) metal porphyrin-based MOFs (MxPMFs, x = Fe, Co, Ni, Mn) and three-dimensional zeolitic imidazole framework-8 (ZIF-8) through electrostatic interaction, followed by carbonization. ZIF-8 was inserted between the layers of MxPMFs to prevent its Π-Π stacking, allowing the active sites to become fully exposed. MxP-Z-C demonstrated an impressive catalytic activity for both the ORR and the OER reactions. Among them, FeP-Z-C showed the best catalytic activity. The half-wave potential for ORR was 0.92 V (vs the reversible hydrogen electrode (RHE)), while the overpotential for the OER was 290 mV. In addition, the zinc-air battery assembled by FeP-Z-C exhibited high power density (133.14 mW cm-2) and significant specific capacity (816 mAh gZn-1), indicating considerable potential as a bifunctional catalyst for electronic devices.

Tuning pyridinic-N and graphitic-N doping with 4,4'-bipyridine in honeycomb-like porous carbon and distinct electrochemical roles in aqueous and ionic liquid gel electrolytes for symmetric supercapacitors

Doping engineering in nanostructured carbon materials is an effective approach to modify heteroatom species and surface electronic structures. Herein, an advanced electrode material based on a honeycomb-like porous carbon matrix with tunable N-doped configurations is prepared via 4,4'-bipyridine (4,4'-bpy)-assisted pyrolysis of SiO₂@ZIF-8 templates and subsequent etching treatment. Interestingly, the amounts of pyridinic-N and graphitic-N can be controlled by rationally varying the content of 4,4'-bpy which acts as the N source in the pyrolysis process. Both experimental results and density functional theory calculations have revealed that synergistically with 3D interconnected porous architecture, pyridinic-N and graphitic-N have different effects on the electrochemical performances in aqueous and ionic liquid gel electrolytes for symmetric supercapacitors. Highly exposed pyridinic-N endows the carbon electrode with a strengthened pseudocapacitance contribution manifested as a high specific capacitance of 436.1 F g^-1 and exceptional stability of almost 100% capacitance retention after 5000 cycles at 10 A g^-1 in the KOH/polyvinyl alcohol (PVA) electrolyte. By contrast, graphitic-N is propitious for reinforced electrical double-layer capacitance contribution, reflected by a maximum energy density of 125.4 Wh kg^-1 in the 1-ethyl-3-methylimidazolium tetrafluoroborate/poly(vinylidene fluoride-co-hexafluoropropylene) (EMIMBF₄/PVDF-HFP) electrolyte. This work offers an in-depth insight into the understanding of the energy storage mechanism of N-rich carbon electrodes in different electrolyte media.

Sandwich-type electrochemical immunosensing of hypopharyngeal carcinoma biomarker carcinoembryonic antigen based on N-doped hollow mesoporous nanocarbon spheres/gold hybrids as sensing platform and gold/ferrocene as signal amplifier

In the present work, a highly sensitive sandwich-type electrochemical immunosensor of carcinoembryonic antigen (CEA) was developed by preparing N-doped hollow mesoporous nanocarbon spheres/gold hybrids (NHMN/Au) hybridsas sensing platformand Au/ferrocene (Au/Fc) as signal amplifiers. The large surface area and high conductivity as well as good biocompatibility of NHMN/Au can increase the loading of primary antibody (Ab₁) and accelerate the electron transport rate of the electrode surface, while Au can carry immobilized secondary antibodies (Ab₂) and Fc derivative (Fc-SH).By using Fc-SH as response probe, the experiments show that the peak current of probe could increase after occurring the specific recognition of Ab₁-CEA-Ab₂, thus a novel sandwich-type immunosensor of CEA was developed. Finally, the proposed method for CEA detection was applied in human serum and the obtained results are satisfactory, indicating the developed method has important clinical applications for CEA determination.

Recycling decoration wastes toward a high-performance porous carbon membrane electrode for supercapacitive energy storage devices

A porous carbon membrane (DWCM) is facilely fabricated by direct carbonization of decoration waste using KOH as an activator and employed as a self-supported electrode for an aqueous supercapacitor (SC) with a superior capacitive performance.

Ionic liquid surfactant-derived carbon micro/nanostructures toward application for supercapacitors

N-doped mesoporous hollow carbon spheres (MHCSs) with different inner structures have attracted increasing attention in energy storage devices due to their low density and high electrical conductivity. Herein, vesicles formed...

Fabrication of highly-conductive porous capacitor electrodes by the insertion of Cu-nanoparticles into N-doped flocculated carbon catalysts

In carbon-based electric double-layer capacitors (EDLC), an ideal electrode should have convenient mass transport, ensuring rich porosity and rapid electron transfer, guaranteeing the electrode bulk's high conductivity. In this study, ultrafine Cu nanoparticles inserted carbon flocculation is formed on carbon cloth using polydopamine and cupric chloride precursors via pyrolysis and electrochemical oxidation reaction. As a result, the obtained electrode has a large surface area of 55.5 m²g^-1 and high conductivity of 48.7 S/mm, which shows excellent charge storage capability with high specific capacitance of 3546 mF cm^-2 at a current density of 1 mA cm^-2. Moreover, when the as-prepared electrode is used as electrodes in symmetric EDLC, it can provide a high energy density of 23 mWh cm^-3 with a power density of 179 mW cm^-3, making it as a promising carbon electrode for practical EDLCs.

Nitrogen, sulfur co-doped hierarchical carbon encapsulated in graphene with "sphere-in-layer" interconnection for high-performance supercapacitor

Rational design of electrode with hierarchical charge-transfer structure and good electronic conductivity is important to achieve high specific capacitance and energy density for supercapacitor, but it still remains a challenge. Herein, a nitrogen, sulfur co-doped pollen-derived carbon/graphene (PCG) composite with interconnected "sphere-in-layer" structure was fabricated, in which hierarchically pollen-derived carbon microspheres can serve as "porous spacers" to prevent the agglomeration of graphene nanosheets. The optimized PCG composite prepared with 0.5 wt% of graphene oxide (PCG-0.5) exhibited high specific capacitance (420Fg^-1 at 1Ag^-1), rate performance (280Fg^-1 at 20Ag^-1), and excellent cycling stability with 94% of capacitance retention after 10,000 cycles. The symmetrical device delivered a remarkable energy density of 31.3Whkg^-1 in neutral medium. Moreover, density functional theory calculation revealed that PCG electrode possessed the accelerated charge transfer and enhanced electronic conductivity, thus ensuring a remarkable electrochemical performance. This work may afford an effective strategy for the development of biomass-derived carbon electrodes with novel charge-transfer structure toward supercapacitor applications.

Preparation of an N-doped mesoporous carbon sphere and sheet composite as a high-performance supercapacitor

Carbon-based materials with multidimensional structures generally exhibit improved properties compared with single-morphology carbon materials for various applications including catalysis, adsorption, and energy storage. Here, an N-doped mesoporous carbon sphere and sheet composite is prepared by a co-assembly strategy using an ionic liquid ([C18Mim]Br) as the structure-directing agent, ethylenediamine as the catalyst, tetraethyl orthosilicate as the pore-forming agent, and resorcinol formaldehyde resin as the carbon precursor. [C18Mim]Br and ethylenediamine not only induce formation of the unique structure but also lead to in situ nitrogen doping on the N-doped mesoporous carbon skeleton. The obtained N-doped mesoporous carbon shows a unique composite structure of thin sheets embedded with carbon spheres, having high a specific surface area and uniform mesopore distribution. When used as an electrode material, the N-doped mesoporous carbon shows a good specific capacity of 273 F g−1 at a current density of 0.5 A g−1 and a good rate capability (82.1% of the capacitance is retained at a high current density of 10 A g−1). Moreover, the N-doped mesoporous carbon exhibited ideal stability behavior (91.6% capacitive retention after 10,000 cycles), indicating a promising role as an electrode material for excellent performance supercapacitors.

Hierarchically Engineered Nanocarbon Florets as Bifunctional Electrode Materials for Adsorptive and Intercalative Energy Storage

Three-dimensional dendritic nanostructured carbon florets (NCFs) with tailored porosity are demonstrated as electrochemically versatile electrodes for both adsorptive and intercalative energy storage pathways. Achieved through a single-step template-driven approach, the NCFs exhibit turbostratic graphitic lamellae in a floral assembly leading to high specific surface area and multi-modal pore distribution (920 m²/g). The synergism in structural and chemical frameworks, along with open-ended morphology, enables bifunctionality of hard carbon NCFs as symmetric adsorptive electrodes for supercapacitors (SCs) and intercalation anodes for hybrid potassium-ion capacitors (KICs). Flexible, all-solid-state SCs through facile integration of NCF with the ionic-liquid-imbibed porous polymeric matrix achieve high-energy density (20 W h/kg) and power density (32.7 kW/kg) without compromising on mechanical flexibility and cyclability (94% after 20k cycles). Furthermore, NCF as an anode in a full-cell hybrid KIC (activated carbon as cathode) delivers excellent electrochemical performance with maximum energy and power densities of 57 W h/kg and 12.5 kW/kg, respectively, when cycled in a potential window of 1.0-4.0 V. The exceptional bifunctional performance of NCF highlights the possibility of utilizing such engineered nanocarbons for high-performance energy storage devices.

Hierarchical porous carbon derived from jujube fruits as sustainable and ultrahigh capacitance material for advanced supercapacitors

Herein, we propose a new highly porous natural carbon material from renewable and inexpensive jujube fruits as a carbon source applied in supercapacitors. The combination of pre-carbonization and chemical activation approaches is employed to product hierarchical porous carbon from natural jujube fruits. The specific surface area of the prepared porous carbon is increased from 85.4 to 1135 m² g^-1 after the completion of NaOH activation at an optimized condition, which is beneficial to enhancing electrochemical performance of supercapacitors. A 3-electrode configuration was utilized to explore the electrochemical ability of porous carbon in 6 M KOH electrolyte. The acquired results demonstrate that porous carbon displays the specific capacitance of 587, 460 and 324 F g^-1 at 0.1, 1 and 100 A g^-1, respectively, which is confirmed by its admirable capacitance and rate behaviors. The porous carbon also shows a wonderful durability with a capacitance retention of 92.2% after 130,000 cycles at 50 A g^-1. Moreover, the assembled symmetrical coin-like supercapacitors with wide potential window of 2.5 V in 1 M Et₄NBF₄/AN organic electrolyte offer a high energy density of 23.7 Wh kg^-1 at 0.629 kW kg^-1 with remaining 94% capacitance over 10,000 cycles at 30 A g^-1, indicating its practical application prospect. As a result, the present study proves the natural jujube fruits is a promising sustainable carbon source for making more economical and efficient electrode material of high performance supercapacitors.

Ionic liquid-induced tunable N-doped mesoporous carbon spheres for supercapacitors

N-Doped mesoporous carbon spheres with tunable structures have been prepared by a feasible co-assembly under the induction of an ionic liquid for supercapacitors.

Hollow Carbon Nanospheres with Developed Porous Structure and Retained N Doping for Facilitated Electrochemical Energy Storage

Development of highly porous carbons with abundant surface functionalities and well-defined nanostructure is of significance for many important electrochemical energy storage systems. However, porous carbons suffer from a compromise between porosity, doped functionality, and nanostructure that have thus far restricted their performances. Here, we report the design of highly porous, nitrogen-enriched hollow carbon nanospheres (PN-HCNs) by an interfacial copolymerization strategy followed by NH₃-assisted carbonization, and further demonstrate their significance and effectiveness in enhancing the electrochemical performances. The PN-HCN simultaneously delivers a large surface area (1237 m² g^-1) and high N functionalities (6.25 atom %) with a remarkable efficiency of the surface area increase to N loss ratio enabled by NH₃ treatment while inheriting the hollow nanospherical structure. Accordingly, owing to the enhanced surface area and retained N doping, the prepared PN-HCN demonstrates outstanding electrochemical performances as a cathode host in lithium-sulfur batteries, including a near-to-theoretical capacity of 1620 mAh g^-1, high rate capability and good cycling stability (789 mAh g^-1 at 0.5C after 200 cycles). These results are superior to those of HCN without NH₃ treatment. Also, PN-HCN exhibits superior capacitances (203 F g^-1) and fast ion transport ability in supercapacitors. Our finding shows the simultaneous achievement of both highly porous structures and sufficient N functionalities for high-performance applications.