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Designing cathode and anode materials that can accommodate capacity and rate performance is a significant challenge in developing lithium-ion capacitors (LICs). Herein, we synthesize a unique N/S dual-doped hierarchical porous carbon (NSC) under the effect of pore distribution modification and heteroatom doping. The nanosheet shape and pore distribution of NSC are highly adjustable, while it demonstrates a reversible capacity that is tens of times more than that of unaltered pristine active carbon. Meanwhile, the prepared glycerol-engineered polyacrylonitrile nanofiber (GPN) form a fast conducting network in the presence of glycerol and carbon nanotubes (CNTs) and exhibit a 300% higher capacity compared to pure polyacrylonitrile nanofibers at 5 A g−1. On this premise, the constructed highly stable LIC (NSC//GPN x @CNTs) can achieve an energy density of 131.48 Wh kg−1 and have an excellent capacity retention rate (93.5%) over 10,000 cycles at a high current density (5 A g−1). This work may lead to new avenues for the preparation of heteroatom-doped porous carbon and redefine the electrode matching of highly stable LICs. [Display omitted] • Highly tunable pore distribution and nanosheet shape of porous carbon. • The cathode nanofibers exhibit high electrical conductivity. • The LIC achieves high energy density and high power density simultaneously. [ABSTRACT FROM AUTHOR]

In this article, vanadium nitride quantum dot/nitrogen-doped microporous carbon nanofibers (VNQD/CNF) is developed by a method of combination of electrostatic spinning and high-temperature calcination under the atmosphere of NH 3 : N 2 = 3: 2 for high performance supercapacitors. VNQD dispersing into CNF, enrichment of N atom doped in carbon bulk, and abundant porous structure not only prevent the growth and aggregation of VN nanoparticles, improve electrical conductivity, wettability, and stability of the electrode materials, but also enhance fast migration of electrolyte ions during the electrochemical process. Thus, VNQD/CNF exhibits a high specific capacitance of 406.5 F g −1 at 0.5 A g −1 and a good rate capability with a capacitance retention of 75.1% at 5.0 A g −1 . Additionally, VNQD/CNF as a negative electrode are combined with Ni(OH) 2 as a positive electrode to fabricate the hybrid supercapacitor of VNQD/CNF//Ni(OH) 2 . Remarkably, at a power density of 774.6 W kg −1 , the supercapacitor device delivers an ultrahigh energy density of 31.2 Wh kg −1 . [ABSTRACT FROM AUTHOR]

Sluggish extracellular electron transfer (EET) at the anode interface is the major obstacle to achieving satisfactory power density in microbial fuel cells (MFCs). To boost the EET efficiency, herein the anode electrocatalysts, nitrogen-doped carbon nanofibers anchoring Fe nanoparticles (Fe/N-x@CNFs, x = 0.5, 1, 3, 5), are rationally designed via electrospinning and calcination process. The morphology and structure characterization indicates that the Fe/N-3@CNFs electrocatalyst presents a porous structure with uniformly distributed Fe nanoparticles on the carbon matrix, which offer a large-accessible surface area for electroactive bacteria habitation along with facilitated EET efficiency. Electrochemical measurements demonstrate that the as-fabricated Fe/N-3@CNFs exhibit excellent electrocatalytic activity for the charge transfer on the anode, endowing the cell with a maximum power density of 1873.8 mW m−2, which is 1.8 and 3.6 times higher than that of Fe@CNFs (1039.2 mW m−2) and carbon cloth (519.8 mW m−2). The outstanding performance of Fe/N-3@CNFs can be attributed to the increased electronic conductivity of carbon matrix with melamine additives, the enriched electroactive bacteria as demonstrated by high-throughput sequencing, and the released positively charged iron mediators to promote EET efficiency. This investigation introduces an effective method of constructing high-efficient anode electrocatalysts for enhancing the output MFCs performance. [Display omitted] • The Fe/N-3@CNFs anode electrocatalysts are fabricated via electrospinning. • The Fe/N-3@CNFs have excellent biocompatibility. • The bacterial loading content and interfacial charge transfer are improved. • The output power is 3.6 folds higher compared to pristine carbon cloth. • The digital watch and LED light can be lightened. [ABSTRACT FROM AUTHOR]

An efficient, robust and low-cost bifunctional electrocatalyst for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is essential to high-performance zinc-air batteries (ZABs). Metal-nitrogen-carbon (M-N-C) systems have attracted considerable attention recently. Herein, a novel Co-N x -enriched electrospun porous carbon nanofibrous bifunctional electrocatalyst (Co-N x /EPCF) is prepared by electrospinning with cobalt nitrate and SiO 2 , followed by carbonization and acid etching. The catalyst displays an outstanding electrocatalytic activity of reversible oxygen overpotential (ΔE = E j = 10 - E 1/2 = 0.87 V), as well as a high stability. The first-principal calculation reveals that the Co–N–C structure has better ORR paths than that of Co cluster. Furthermore, based on the electrocatalyst, the assembled flexible ZABs possess a power density of 81 mW cm−2, a capacity of 807 mAh g zn −1, and 111 stability cycles. The study provides a novel strategy to prepare high-performance bifunctional catalysts for wearable power sources. [Display omitted] • Electrospun porous carbon nanofibers are prepared by hard template method. • Co-N x -enriched catalyst drives energy-efficient ORR/OER kinetics with ΔE = 0.87 V. • Flexible ZABs achieve a power density of 81 mW cm−2 and a cycle time of 37 h. [ABSTRACT FROM AUTHOR]

The demands for new energy storage systems capable of providing power for various wearable electronic devices are generating more research interest. Herein, we develop a universal and effective strategy to integrate Zn ion battery (ZIB) and asymmetric supercapacitor (ASC) into one flexible energy storage device, which can switch between high energy density and high-power density without interfering with each other. The NiCo 2 S 4-x nanosheet arrays with sulfur deficiency grown on carbon cloth substrate are used as efficient cathode for ZIB and ASC. The designed flexible ZIB delivers an energy density of up to 464.2 Wh kg−1, while the assemble flexible ASC provides a maximum power density of 8001.2 W kg−1. Subsequently, a flexible dual-functional three-electrode energy storage device (TEESD) is fabricated by a general stacking strategy. As proof-of-concept demonstrations, two flexible dual-functional TEESDs can switch between ZIB and ASC to power a digital watch and light LED thanks to the common cathode. In addition, the integrated TEESDs exhibits superior electrochemical stability and performance durability, which is beneficial for the practical applications in flexible and wearable devices. The general strategy disclosed herein is expected to shine new light into the development of advanced flexible electronics and wearable energy textiles. [Display omitted] • The sulfur deficient NiCo 2 S 4-x nanosheets were established on flexible CC. • A general strategy was developed to fabricate flexible dual-functional TEESD. • The TEESD can switch between high energy density and high-power density. [ABSTRACT FROM AUTHOR]

Recently, a new class of mixed polyanionic compounds with general formula Na 3 MPO 4 CO 3 (M = Ni, Mn, Fe, Co, Cu), discovered through high-throughput computations have attracted much attention for its secondary battery applications and safety aspects. Here, we combine electrochemical measurements with inductively coupled plasma-optical emission spectrometer (ICP-OES), energy-dispersive X-ray (EDX), field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Raman spectroscopy, x-ray photoelectron spectroscopy (XPS), and an ab-initio DFT approach to unravel the dynamic self-limiting surface restructuring of Na 3 NiCO 3 PO 4 in aqueous 1 M KOH/NaOH electrolyte. The etching of lattice CO 3 2-, PO 4 3- and Na serves as the key to trigger the surface reconstruction. This work establishes a fundamental understanding of the pseudocapacitance mechanism associated with surface self-reconstruction of mixed polyanionic compounds. The reconstruction-derived self-limiting dense Ni(OH) 2 layers at the surface and its oxidation to NiOOH at anodic potentials can be attributed to the observed high-performance pseudocapacitive behavior. The surface reconstructed Na 3 NiCO 3 PO 4 electrode exhibits high specific capacitance (2378.2 F g−1 at 1 A g−1). The assembled symmetric pseudocapacitor delivers a high energy density (57.2 Wh kg−1), power density (1500 W kg−1) at 1 Ag-1 and long cycle life (13000 cycles) with 100% retention. [Display omitted] • The pseudocapacitive behavior of the Na 3 NiCO 3 PO 4 is tested. • The Na 3 NiCO 3 PO 4 undergo surface self-reconstruction. • The etching of lattice CO 3 2-, PO 4 3- and Na lead to the formation of Ni(OH) 2 at the surface. • The electrode exhibits high specific capacitance 2378.2 F g−1 at 1 A g−1 • The assembled device delivers a high energy density, power density and long cycle life. [ABSTRACT FROM AUTHOR]

Sodium-ion hybrid capacitors (SIHCs) are an emerging energy storage device with various potential applications due to their combined merits of batteries and supercapacitors. However, this device still suffers from the slow kinetics of the anode, which severely restricts the rate performance. Herein, we demonstrate that the rate performance of a carbon-nanofiber-based anode can be remarkably enhanced by coating a thin layer of oxygen-vacancy-rich TiO 2. The as-prepared material (TiO 2 @PBC) is used as an anode in a sodium-ion battery, which delivers a reversible capacity of 180.2 mA h g−1 at 10 A g−1 with a capacity retention of 110.7% after 20,000 cycles, outperforming those without TiO 2 coating. Furthermore, the TiO 2 @PBC is assembled into a SIHC with activated carbon as the cathode, which shows an energy density of 91.0 W h kg−1 at a power density of 165 W kg−1 and retaining an energy density of 43.4 W h kg−1 at an ultra-high power density of 13 kW kg−1. The excellent sodium storage performance of TiO 2 @PBC is attributed to the three-dimensionally cross-linked conductive network, the open ion-transportation channels, and more importantly, the TiO 2 coating with high content of oxygen vacancies which expands the lattice and thus enables fast ion transport. [Display omitted] • P-doped carbon nanofiber is coated with TiO 2 by magnetron sputtering. • The TiO 2 coating is rich in oxygen vacancy. • The oxygen vacancy in TiO 2 enhances the sodium storage performance significantly. • The composite enables a power density of 13 kW kg−1 in a sodium ion capacitor. [ABSTRACT FROM AUTHOR]

Developing transition-metal based bifunctional electrocatalysts to efficiently drive oxygen evolution reaction and oxygen reduction reaction is an urgent demand for the implementation of rechargeable Zn-air batteries. Transition-metal sulfides are emerging as alternatives to precious metal-based electrocatalysts, however, their bifunctional activities are usually restricted by inferior electrical conductivities and limited electrochemical active sites. Herein, we highlight a novel metal-organic frameworks derived nitrogen-doped carbon nanofiber coupled FeS 2 –CoS 2 (FeS 2 –CoS 2 /NCFs) by a combination of electrospinning and atomic-layer-deposition approach. Benefiting from the large exposed surface active sites of hierarchical structure and the abundant interfacial vacancies in FeS 2 –CoS 2 heterointerface, the FeS 2 –CoS 2 /NCFs integrated electrocatalyst delivers a high bifunctional activity together with a good durability in alkaline medium. Notably, the liquid Zn-air battery assembled with this FeS 2 –CoS 2 /NCFs electrode displays a considerable peak power density of 257 mW cm−2, a high specific capacity of 814 mA h g−1 and a long cycling life of 250 h, superior to precious metal based Zn-air batteries. Moreover, the flexible solid-state Zn-air battery using such FeS 2 –CoS 2 /NCFs electrode can stably power LED panels even under twisting state, demonstrating practical potentials in wearable and portable electrochemical devices. Image 1 • Hierarchical FeS 2 –CoS 2 /NCFs with core-shell structure was designed. • FeS 2 –CoS 2 /NCFs displayed efficient bifunctional catalytic activities. • The interfacial vacancies and hierarchical structure increased its activities. • FeS 2 –CoS 2 /NCFs-based batteries exhibited excellent power density and cycling durability. [ABSTRACT FROM AUTHOR]

Hybrid Li-ion capacitors (LICs) are a new kind of electrochemical energy storage device with high energy and power densities. In this work, phosphorus-doped TiO 2 /phosphorus-doped carbon nanofibers (PTO/PC NFs) are fabricated through a simple electrospinning method with disodium hydrogen phosphate as a phosphorus source. Differing from the PTO prepared by hydrothermal method, sol-gel method or calcining treatment at phosphorous atmosphere. The P-doping evenly distributed in PTO/PC NFs and PTO nanoparticles are embedded in PC, which improves the conductivity, structure stability and Li+ ions diffusion of TiO 2. As a result, the PTO/PC NFs anode shows high capacities of 329 and 150 mA h g−1 (0.1 and 2 A g−1), long cycle life (201 mA h g−1 after 1000 cycles at 1 A g−1, 69 mA h g−1 after 1000 cycles at 5 A g−1), and superior pseudocapacitance (87%, 2 mV s−1). Furthermore, the LICs assembled with PTO/PC NFs anode and AC cathode show outstanding capacity of 35 F g−1 at a current density of 0.1 A g−1, high energy density of 72 Wh kg−1 at the power density of 250 W kg−1, and cycle stability (54%, 10 000 cycles, 1 A g−1). This suggests that PTO/PC NFs is a potential anode material for high-performance LICs. Image 1 • P-doped TiO 2 /P-doped C nanofibers (PTO/PC NFs) are fabricated by electrospinning. • The PTO/PC NFs exhibited good conductivity, stability and Li+ ions diffusion. • The PTO/PC anode showed high capacity, long cycle life and high pseudocapacitance. • LIC assembled with PTO/PC NFs anode showed a high energy density and power density. [ABSTRACT FROM AUTHOR]

Bimetallic carbides have aroused wide attention for energy-storage applications recently. In this work, one-dimensional Fe 2 MoC/CNFs (Fe 2 MoC/C nanofibers) are successfully synthesized via a facile electrospinning method for the first time. To obtain the most integrated structure between the Fe 2 MoC nanoparticles and carbon nanofibers, we explore the optimal heating rate during the carbonization treatment. Fe 2 MoC/CNFs exhibits an integrated one-dimensional structure under 800 °C with a heating rate of 5 °C/min. As revealed in the experimental results, Fe 2 MoC/CNFs possesses a high specific surface area of 196.9 m2/g, a high specific capacitance of 347.8 F/g at the current density of 1 A/g, an excellent rate capability of 91% capacitance retention from 1 A/g to 40 A/g, and shows superior cycling stability with the capacitance retention of about 85.6% and Coulombic efficiency of about 100% after 5000 cycles. An asymmetric supercapacitor coin-cell device using Fe 2 MoC/CNFs as the positive electrode displays an energy density of 14.5 Wh/kg at a power density of 300 W/kg and an outstanding cycling life of 93% retention after 5000 cycles. The impressive electrochemical performance indicates that the Fe 2 MoC/CNFs composite is a promising material for efficient supercapacitors. Image 1 • Fe 2 MoC nanofibers can be prepared via a facile electrospinning method. • Fe 2 MoC/CNFs-5 exhibits a superior rate capability and cycle stability. • ASC coin-cell device shows a promising energy and power density. [ABSTRACT FROM AUTHOR]

Persuing both high energy and power density in one supercapacitor at low cost is very challenging to date. Here, we report the fabrication of nitorgen and Sulphur co-doped graphene (GN) modified lignin/polyacrylonitrile (PAN)-based carbon nanofiber (ACNFs) from mainly the biomass of lignin following a process of electrospinning, carbonization and activation. GN is used as nitrogen/sulphur immobilization agent to successfully capture HCN, NH 3 and SO 2 released from lignin and PAN during carbonization, and thus the content of heteroatoms of N and S in ACNFs is increased. The resulting ACNF with 0.30 wt% GN content possesses the maximum specific surface area of 2439 m2 g−1. It shows a typical three-dimensional porous network structures with the highest heteroatom doping content and high degree of crystallinity. The assembled supercapacitor exhibits superior electrochemical performance with ultra-high specific capacitance of 267.32 F g−1, low equivalent series resistance of 5.67 Ω, and outstanding cycling stability of 96.7% capacitance retention after 5000 cycles of charge/discharge in a two-electrode system with 6 mol L−1 KOH as electrolyte. Most importantly, the assembled symmetric supercapacitor shows that ACNFs doping with GNs increases the energy density from 4.12 to 9.28 Wh kg−1 and at the same time with barely reduced power density. • Using GNs as an adsorbent to capture HCN, NH 3 , SO 2 released in carbonization. • Proposing the water wetting behaviour to evaluation the supercapacitor performance. • Elucidated the mechanism between heteroatom doping and electrochemical properties. [ABSTRACT FROM AUTHOR]