Nitrogen-doped Porous Carbon Nanofibers Research Articles

Elucidating the efficacious capacitive deionization defluorination behaviors of heteroatom-doped hierarchical porous carbon nanofibers membrane

Heteroatom-doped porous carbons, particularly those incorporating nitrogen functionalities, demonstrate exceptional electrochemical properties advantageous for capacitive deionization (CDI) defluorination. Nevertheless, the underlying mechanism of fluoride removal remains inadequately understood, warranting comprehensive investigation to facilitate the practical implementation of CDI technology. Herein, a novel nitrogen-doped hierarchical porous carbon nanofiber membrane (HPCNM) derived from a hydrochloric acid etched FeNi3@CNFs (FeNi3 alloy encapsulated within carbon nanofibers) network was reasonably designed and synthesized for CDI defluorination. The HPCNM electrode exhibited superior defluorination capabilities, attributed to its distinctive hierarchical porosity and compositional architecture. The novel material achieves remarkable performance metrics, including a defluorination capacity of 58.38 mg g−1, rapid ion removal kinetics (0.97 mg g−1 min−1), and maintained efficiency throughout 20 operational cycles. Density functional theory (DFT) calculations indicate that nitrogen-doped carbon (NC) preferentially adsorbs fluoride, exhibiting the lowest adsorption energy. Fluoride interacts with NC through a combination of weak covalent bonds and van der Waals forces. Its inherent electronegativity, hardness, and high electrophilicity index, contrasted with low softness and nucleophilicity, facilitate the selective adsorption. Furthermore, an optimized NC electrode, operating at 1.2 V in simulated industrial wastewater, achieved fluoride removal compliant with national standards, demonstrating its practical applicability for treating contaminated effluent. These findings advance the understanding of selective fluoride removal, contributing to the development of targeted electrodes for industrial applications.

Constructing interconnected hierarchical porous structures and nitrogen-doped carbon nanofibers for superior capacitive deionization

Capacitive Deionization (CDI) has emerged as a sustainable and efficient method for desalinating low-salinity water sources. However, CDI materials are often limited by insufficient surface area, slow electron/ion transport, and suboptimal electrolyte wettability, which restrict desalination capacity and rate. Herein, we simultaneously construct interconnected hierarchical porous structures and nitrogen-doping in carbon nanofibers by pyrolyzing polymer nanofiber precursors embedded with Zeolite Imidazolate Framework-8 (ZIF-8) nanoparticles. ZIF-8 nanoparticles serve not only as precise pore-forming templates but also act as a rich source of nitrogen for doping the carbon nanofibers. We optimize the pore structure and nitrogen content of the carbon nanofibers by tuning the diameter of ZIF-8 nanoparticles within the polymer nanofiber precursor, thereby achieving superior CDI performance. This unique structure not only substantially increases the specific surface area and significantly enhances mass transfer processes, but also introduces abundant nitrogen into the porous carbon fibers. This improves their hydrophilicity, adjusts their electronic structure, increases active sites, and greatly boosts the electrodes’ adsorption capacity and desalination efficiency. An electrode constructed from the optimized porous nanofibers with a larger specific surface area (LPCNF) achieves a peak desalination capacity of 68.11 mg/g. Furthermore, the electrode maintains a high salt adsorption capacity (SAC) retention of 93.4 % after 50 cycles, significantly outperforming conventional materials such as activated carbon, graphene, and carbon nanotubes. Overall, the developed method optimizes both the pore structure and enhances the nitrogen content, providing a novel strategy for developing high-performance CDI electrode materials.

A two-pronged strategy to boost the capacitive deionization performance of nitrogen-doped porous carbon nanofiber membranes

Carbon-based capacitive deionization (CDI) systems are universally subject to the limited desalination capacity, due to the electrosorption characteristics and undesirable pore structures. Herein, a two-pronged strategy is proposed to boost the desalination performance of the electrospun carbon nanofibers (CNFs), where silicalite-1 nanoparticles as the internal porogen create mesopores and macropores, and layered zeolitic imidazolate framework (ZIF-L) leaves as the external carbon source provide micropores and mesopores. This combination results in the large surface area, well-developed graded pore structure, and increased nitrogen content of the core-shell polyacrylonitrile/silicalite-1@ZIF-L-derived CNFs (defined as PCNFs-SZ) electrode, which delivers a superior specific capacitance of 145.4 F g−1 in a neutral electrolyte. The symmetric CDI cell assembled by the self-supporting PCNFs-SZ membrane electrodes holds a prominent desalination capacity of 37.09 mg g−1 and a rapid salt removal rate of 10.36 mg g−1 min−1 at 1.2 V (initial NaCl concentration: 500 mg L−1), and demonstrates significant potential for real-world applications in the desalination and purification of reclaimed water. Furthermore, theory calculations confirm the enhanced Na+-capture capability of PCNFs-SZ. The present work highlights an effective and viable approach to enhance the desalination performance of carbon-based CDI cells.

Integrating Cu+/Cu0 sites on porous nitrogen-doped carbon nanofibers for stable and efficient CO2 electroreduction to multicarbon products

The Cu+/Cu0 sites of copper-based catalysts are crucial for enhancing the production of multicarbon (C2+) products from electrochemical CO2 reduction reaction (eCO2RR). However, the unstable Cu+ and insufficient Cu+/Cu0 active sites lead to their limited selectivity and stability for C2+ production. Herein, we embedded copper oxide (CuOx) particles into porous nitrogen-doped carbon nanofibers (CuOx@PCNF) by pyrolysis of the electrospun fiber film containing ZIF-8 and Cu2O particles. The porous nitrogen-doped carbon nanofibers protected and dispersed Cu+ species, and its microporous structure enhanced the interaction between CuOx and reactants during eCO2RR. The obtained CuOx@PCNF created more effective and stable Cu+/Cu0 active sites. It showed a high Faradaic efficiency of 62.5% for C2+ products in H-cell, which was 2 times higher than that of bare CuOx (∼31.1%). Furthermore, it achieved a maximum Faradaic efficiency of 80.7% for C2+ products in flow cell. In situ characterization and density functional theory (DFT) calculation confirmed that the N-doped carbon layer protected Cu+ from electrochemical reduction and lowered the energy barrier for the dimerization of *CO. Stable and exposed Cu+/Cu0 active sites enhanced the enrichment of *CO and promoted the C–C coupling reaction on the catalyst surface, which facilitated the formation of C2+ products.

Synergistic Engineering of CoO/MnO Heterostructures Integrated with Nitrogen-Doped Carbon Nanofibers for Lithium-Ion Batteries.

The integration of heterostructures within electrode materials is pivotal for enhancing electron and Li-ion diffusion kinetics. In this study, we synthesized CoO/MnO heterostructures to enhance the electrochemical performance of MnO using a straightforward electrostatic spinning technique followed by a meticulously controlled carbonization process, which results in embedding heterostructured CoO/MnO nanoparticles within porous nitrogen-doped carbon nanofibers (CoO/MnO/NC). As confirmed by density functional theory calculations and experimental results, CoO/MnO heterostructures play a significant role in promoting Li+ ion and charge transfer, improving electronic conductivity, and reducing the adsorption energy. The accelerated electron and Li-ion diffusion kinetics, coupled with the porous nitrogen-doped carbon nanofiber structure, contribute to the exceptional electrochemical performance of the CoO/MnO/NC electrode. Specifically, the as-prepared CoO/MnO/NC exhibits a high reversible specific capacity of 936 mA h g-1 at 0.1 A g-1 after 200 cycles and an excellent high-rate capacity of 560 mA h g-1 at 5 A g-1, positioning it as a competitive anode material for lithium-ion batteries. This study underscores the critical role of electronic and Li-ion regulation facilitated by heterostructures, offering a promising pathway for designing transition metal oxide-based anode materials with high performances for lithium-ion batteries.

Accelerating lithium-sulfur battery reaction kinetics and inducing 3D deposition of Li2S using interactions between Fe3Se4 and lithium polysulfides

Although lithium-sulfur batteries (LSBs) exhibit high theoretical energy density, their practical application is hindered by poor conductivity of the sulfur cathode, the shuttle effect, and the irreversible deposition of Li2S. To address these issues, a novel composite, using electrospinning technology, consisting of Fe3Se4 and porous nitrogen-doped carbon nanofibers was designed for the interlayer of LSBs. The porous carbon nanofiber structure facilitates the transport of ions and electrons, while the Fe3Se4 material adsorbs lithium polysulfides (LiPSs) and accelerates its catalytic conversion process. Furthermore, the Fe3Se4 material interacts with soluble LiPSs to generate a new polysulfide intermediate, LixFeSy complex, which changes the electrochemical reaction pathway and facilitates the three-dimensional deposition of Li2S, enhancing the reversibility of LSBs. The designed LSB demonstrates a high specific capacity of 1529.6 mA h g−1 in the first cycle at 0.2 C. The rate performance is also excellent, maintaining an ultra-high specific capacity of 779.7 mA h g−1 at a high rate of 8 C. This investigation explores the mechanism of the interaction between the interlayer and LiPSs, and provides a new strategy to regulate the reaction kinetics and Li2S deposition in LSBs.

Dendritic boron and nitrogen doped high-entropy alloy porous carbon fibers for high-efficiency hydrogen evolution reaction

Among various electrocatalysts, high-entropy alloys (HEAs) have gained significant attention for their unique properties and excellent catalytic activity in the hydrogen evolution reaction (HER). However, the precise synthesis of HEA catalysts in small sizes remains challenging, which limits further improvement in their catalytic performance. In this study, boron- and nitrogen-doped HEA porous carbon nanofibers (HE-BN/PCNF) with an in situ-grown dendritic structure were successfully prepared, inspired by the germination and growth of tree branches. Furthermore, the dendritic fibers constrained the growth of HEA particles, leading to the synthesis of quantum dot-sized (1.67nm) HEA particles, which also provide a pathway for designing HEA quantum dots in the future. This work provides design ideas and guiding suggestions for the preparation of borated HEA fibers with different elemental combinations and for the application of dendritic nanofibers in various fields.

Unveiling the Synergy of Architecture and Anion Vacancy on Bi2Te3-x@NPCNFs for Fast and Stable Potassium Ion Storage.

Large volume strain and slow kinetics are the main obstacles to the application of high-specific-capacity alloy-type metal tellurides in potassium-ion storage systems. Herein, Bi2Te3-x nanocrystals with abundant Te-vacancies embedded in nitrogen-doped porous carbon nanofibers (Bi2Te3-x@NPCNFs) are proposed to address these challenges. In particular, a hierarchical porous fiber structure can be achieved by the polyvinylpyrrolidone-etching method and is conducive to increasing the Te-vacancy concentration. The unique porous structure together with defect engineering modulates the potassium storage mechanism of Bi2Te3, suppresses structural distortion, and accelerates K+ diffusion capacity. The meticulously designed Bi2Te3-x@NPCNFs electrode exhibits ultrastable cycling stability (over 3500 stable cycles at 1.0 A g-1 with a capacity degradation of only 0.01% per cycle) and outstanding rate capability (109.5 mAh g-1 at 2.0 A g-1). Furthermore, the systematic ex situ characterization confirms that the Bi2Te3-x@NPCNFs electrode undergoes an "intercalation-conversion-step alloying" mechanism for potassium storage. Kinetic analysis and density functional theory calculations reveal the excellent pseudocapacitive performance, attractive K+ adsorption, and fast K+ diffusion ability of the Bi2Te3-x@NPCNFs electrode, which is essential for fast potassium-ion storage. Impressively, the assembled Bi2Te3-x@NPCNFs//activated-carbon potassium-ion hybrid capacitors achieve considerable energy/power density (energy density up to 112 Wh kg-1 at a power density of 1000 W kg-1) and excellent cycling stability (1600 cycles at 10.0 A g-1), indicating their potential practical applications.

Silver Metal-Organic Framework Derived N-Doped Carbon Nanofibers for CO2 Conversion into β-Oxopropylcarbamates.

Developing efficient heterogeneous catalysts for chemical fixation of CO2 to produce high-value-added chemicals under mild conditions is highly desired but still challenging. Herein, we first reported an approach to prepare a novel catalyst (Ag@NCNFs), featuring Ag nanoparticles (NPs) embedded within porous nitrogen-doped carbon nanofibers (NCNFs), via growing a Ag metal-organic framework on one-dimensional electrospun nanofibers followed by pyrolysis. Benefiting from the abundant nitrogen species and porous structure, Ag NPs is well dispersed in the obtained Ag@NCNFs. Catalytic studies indicated that Ag@NCNFs exhibited excellent catalytic activity for the three-component coupling reaction of CO2, secondary amines, and propargylic alcohols to generate β-oxopropylcarbamates under mild conditions with a turnover number (TON) of 16.2, and it can be recycled and reused at least 5 times without an obvious decline in catalytic activity. The reaction mechanism was clearly clarified by FTIR, NMR, 13C isotope labeling, control experiments, and density functional theory calculations. The results suggest that Ag@NCNFs and 1,8-diazabicyclo[5.4.0]undec-7-ene can synergistically activate propargylic alcohol to react with CO2, and then the generated α-alkylidene cyclic carbonate was invaded by secondary amine to produce β-oxopropylcarbamate. Importantly, to the best of our knowledge, this is the first experimental and theoretical investigation on this reaction.

Red phosphorus encapsulated in 3D N-doped porous carbon nanofibers: an enhanced sodium-ion battery anode material.

We report a sodium-ion battery anode design using red phosphorus encapsulated in nitrogen-doped porous carbon nanofibers that mitigates volume expansion and poor conductivity issues, enhancing battery performance. Density functional theory calculations suggest nitrogen doping promotes robust phosphorus interactions, and finite element analysis indicates the design controls volume expansion.

A Freestanding Multifunctional Interlayer Based on Fe/Zn Single Atoms Implanted on a Carbon Nanofiber Membrane for High-Performance Li-S Batteries

By virtue of the high theoretical energy density and low cost, Lithium–sulfur (Li-S) batteries have drawn widespread attention. However, their electrochemical performances are seriously plagued by the shuttling of intermediate polysulfides and the slow reaction kinetics during practical implementation. Herein, we designed a freestanding flexible membrane composed of nitrogen-doped porous carbon nanofibers anchoring iron and zinc single atoms (FeZn-PCNF), to serve as the polysulfide barrier and the reaction promotor. The flexible porous networks formed by the interwoven carbon nanofibers not only offer fast channels for the transport of electrons/ions, but also guarantee the structural stability of the all-in-one multifunctional interlayer during cycling. Highly dispersed Fe and Zn atoms in the carbon scaffold synergistically immobilize sulfur species and expedite their reversible conversion. Therefore, employing FeZn-PCNF as the freestanding interlayer between the cathode and separator, the Li-S battery delivers a superior initial reversible discharge capacity of 1140 mA h g−1 at a current density of 0.5 C and retains a high capacity of 618 mA h g−1 after 600 cycles at a high current density of 1 C.

HKUST-1 derived one-dimensional Cu/N-doped carbon nanofibers for simultaneous detection of acetaminophen and sulfanilamide

The design of novel signal amplification elements was key to improving the sensing and analysis performance of electrochemical sensors. In this work, porous one-dimensional copper nitrogen-doped carbon nanofibers (Cu-NCNFs) were successfully prepared via the coupled process of electrospinning technology and high-temperature pyrolysis. This coupling of multiple processes and the introduction of heteroatoms pyrolyzed the HKUST-1 particles to generate three-dimensional Cu-doped carbon octahedra and mosaic them inside the one-dimensional carbon nitride channels, obtaining small-sized Cu particles while introducing a large number of N species, and constructing a three-dimensional MOFs-derived metal-carbon hybrid one-dimensional multistage carbon nitride structure. The resulting Cu-NCNFs sensor could simultaneously determine acetaminophen and sulfanilamide and exhibit superior electroanalytical performance, reproducibility, stability, and selectivity. This strategy provides a new approach to preparing novel signal amplification elements for the efficient monitoring of micropollutants.

PtZn nanoparticles supported on porous nitrogen-doped carbon nanofibers as highly stable electrocatalysts for oxygen reduction reaction

The oxygen reduction reaction (ORR) electrocatalytic activity of Pt-based catalysts can be significantly improved by supporting Pt and its alloy nanoparticles (NPs) on a porous carbon support with large surface area. However, such catalysts are often obtained by constructing porous carbon support followed by depositing Pt and its alloy NPs inside the pores, in which the migration and agglomeration of Pt NPs are inevitable under harsh operating conditions owing to the relatively weak interaction between NPs and carbon support. Here we develop a facile electrospinning strategy to in-situ prepare small-sized PtZn NPs supported on porous nitrogen-doped carbon nanofibers. Electrochemical results demonstrate that the as-prepared PtZn alloy catalyst exhibits excellent initial ORR activity with a half-wave potential (E1/2) of 0.911 ​V versus reversible hydrogen electrode (vs. RHE) and enhanced durability with only decreasing 11 ​mV after 30,000 potential cycles, compared to a more significant drop of 24 ​mV in E1/2 of Pt/C catalysts (after 10,000 potential cycling). Such a desirable performance is ascribed to the created triple-phase reaction boundary assisted by the evaporation of Zn and strengthened interaction between nanoparticles and the carbon support, inhibiting the migration and aggregation of NPs during the ORR.

Nitrogen-doped porous carbon nanofibers embedded with Cu/Cu3P heterostructures as multifunctional current collectors for stabilizing lithium anodes in lithium-sulfur batteries

Among the various beyond-lithium-ion battery systems, lithium-sulfur batteries (Li-S) have been widely considered as one of the most promising technologies owing to their high theoretical energy density. However, the irregular Li plating/stripping and infinite volume change associated with low Coulombic efficiency and safety concerns of host-less lithium anode hinder the practical application of Li-S batteries. Herein, Cu/Cu3P heterostructure-embedded in carbon nanofibers (Cu/Cu3P-N-CNFs) are developed as multifunctional current collectors for regular lithium deposition. The 3D porous interconnected carbon skeleton endows effectively reduced local current density and volume expansion, meanwhile the Cu/Cu3P particles function as nucleation sites for uniform lithium plating. Consequently, the developed ion/electron-conducting skeleton delivers remarkable electrochemical performances in terms of high Coulombic efficiency for 500 cycles at 1 mA cm−2, and the accordingly symmetric cell exhibits long-term cyclic duration over 1500 h with a low voltage hysteresis of ∼ 80 mV at 1 mA cm−2. Moreover, Li-S full cells paired with the developed anode and S@CNTs cathode also show superior rate capability (568 mAh/g at 2C) and excellent stability of >500 cycles at 0.2C, further demonstrating the great potential of Cu/Cu3P-N-CNFs as promising current collectors for advanced lithium-metal batteries.

Engineering the electronic structure of platinum single-atom sites via tailored porous carbon nanofibers for large-scale hydrogen production

Pt single-atom catalysts are promising for efficient hydrogen evolution reactions (HER) due to their ultra-high catalytic activity and atomic utilization. However, developing a scalable preparation method of binder-free Pt single-atom catalysts with optimal electronic structures for large-scale hydrogen production is still a serious challenge. In this work, we fabricated tailored nitrogen-doped porous carbon nanofibers as a support for engineering the electronic structure of Pt single-atom sites via initial micropore trapping and subsequent optimized nitrogen/carbon anchoring. The as-prepared Pt single-atom catalysts exhibited impressively enhanced HER activity and satisfactory stability, superior to the state-of-the-art single-atom catalysts. X-ray absorption structure analysis combined with theoretical simulation demonstrated the mechanisms for HER performance improvement. In particular, the free-standing Pt single-atom catalysts for a binder-free electrode showed a low overpotential of 64 mV even at 500 mA cm−2, indicating promising application for the large-scale hydrogen production.

Hierarchical porous carbon nanofibers with facilely accessible iron-based active sites for efficient oxygen reduction in alkaline and acidic media

Reasonable design of hierarchically porous structures with mass transport maximization and highly accessible active sites still remains a great challenge. Herein, we successfully fabricated Fe3O4 nanoparticles embedded in the nitrogen-doped hierarchical porous carbon nanofibers as efficient and durable electrocatalysts for oxygen reduction reaction (ORR), which was synthesized by a stepwise electrospinning-pyrolysis strategy. The unique hierarchically porous carbon nanofibers could not only improve the dispersion and exposure of metal active sites, but also maximize the mass transport, thereby enhancing the accessibility of active sites and chemical reaction rate with efficient transport channels for reactants and products. Remarkably, the optimized sample (Fe3O4@Fe–N/HPCNF) displayed outstanding ORR activity with an onset potential of 0.99 V and a half-wave potential of 0.88 V in alkaline media, even comparable to that of commercial Pt/C. Additionally, Fe3O4@Fe–N/HPCNF catalyst also revealed excellent ORR performance with a half-wave potential of 0.75 V in acidic solution. More importantly, the optimal power density of Fe3O4@Fe–N/HPCNF assembled Zn-air battery can achieve 116 mW cm−2. The excellent electrocatalytic performance is benefited from the synergistic coupling between unique hierarchically porous carbon nanofibers and highly accessible Fe-based active sites.

Rational synthesis of chitin-derived nitrogen-doped porous carbon nanofibers for efficient polysulfide confinement

Rational synthesis of chitin-derived nitrogen-doped porous carbon nanofibers for efficient polysulfide confinement

Geometric and Electronic Structural Engineering of Isolated Ni Single Atoms for a Highly Efficient CO2 Electroreduction.

Tuning the coordination environment and geometric structures of single atom catalysts is an effective approach for regulating the reaction mechanism and maximize the catalytic efficiency of single-atom centers. Here, a template-based synthesis strategy is proposed for the synthesis of high-density NiNx sites anchored on the surface of hierarchically porous nitrogen-doped carbon nanofibers (Ni-HPNCFs) with different coordination environments. First-principles calculations and advanced characterization techniques demonstrate that the single Ni atom is strongly coordinated with both pyrrolic and pyridinic N dopants, and that the predominant sites are stabilized by NiN3 sites. This dual engineering strategy increases the number of active sites and utilization efficiency of each single atom as well as boosts the intrinsic activity of each active site on a single-atom scale. Notably, the Ni-HPNCF catalyst achieves a high CO Faradaic efficiency (FECO ) of 97% at a potential of -0.7V, a high CO partial current density (jCO ) of 49.6mA cm-2 (-1.0V), and a remarkable turnover frequency of 24900 h-1 (-1.0V) for CO2 reduction reactions (CO2 RR). Density functional theory calculations show that compared to pyridinic-type NiNx , the pyrrolic-type NiN3 moieties display a superior CO2 RR activity over hydrogen evolution reactions, resulting in their superior catalytic activity and selectivity.

Metal-free nitrogen-doped porous carbon nanofiber catalyst for solar-Fenton-like system: Efficient, reusable and active catalyst over a wide range of pH

Water pollution is a growing environmental crisis caused by industrialization. In-situ production of reactive oxygen species (ROS) is one of the most promising strategies to challenge this problem. However, developing a robust and efficient catalyst that can operate in harsh conditions without generating secondary pollution and tackle the recycling difficulties of powder catalysts remains a challenge. In this study, a graphitized N-doped carbon nanofiber (CNF) catalyst was synthesized in a direct synthesis approach, which is more efficient in time and cost and suitable for industrial applications, by means of electrospinning and carbonization process. Zinc acetate and iron nitrate functioned as a template for porous structure generation and carbon graphitizing catalysts. The as-synthesized catalyst was used in the wide pH range. This was mainly due to: i) the high surface area (∼ 652 m2 g−1) and the micro-mesoporous structure, which have reduced the inner diffusion resistance and facilitated mass transport radically during the reaction. ii) The enhanced electron transfer kinetics through the long 1D CNF revealed by the cyclic voltammetry analysis. iii) The abundance of oxygen-containing function groups, graphitic-C pyridinic-N and graphitic-N active sites that facilitated the activation of H2O2 and the generation of the ROS responsible for the degradation of the organic pollutants. The catalysts’ 1D structure and lightweight enabled the catalyst recovery and reuse.

MOF-derived nitrogen-doped porous carbon nanofibers with interconnected channels for high-stability Li+/Na+ battery anodes.

Heteroatom-doped porous carbon materials have been widely used as anode materials for Li-ion and Na-ion batteries, however, improving the specific capacity and long-term cycling stability of ion batteries remains a major challenge. Here, we report a facile based metal-organic framework (MOFs) strategy to synthesize nitrogen-doped porous carbon nanofibers (NCNFs) with a large number of interconnected channels that can increase the contact area between the material and the electrolyte, shorten the diffusion distance between Li+/Na+ and the electrolyte, and relieve the volume expansion of the electrode material during cycling; the doping of nitrogen atoms can improve the conductivity and increase the active sites of the carbon material, can also affect the microstructure and electron distribution of the electrode material, thereby improving the electrochemical performance of the material. As expected, the obtained NCNFs-800 exhibited excellent electrochemical performance with high reversible capacity (for Li+ battery anodes: 1237 mA h g-1 at 100 mA g-1 after 200 cycles, for Na+ battery anodes: 323 mA h g-1 at 100 mA g-1 after 150 cycles) and long-term cycling stability (for Li+ battery anodes: 635 mA h g-1 at 2 A g-1 after 5000 cycles, for Na+ battery anodes: 194 mA h g-1 at 2 A g-1 after 5000 cycles).