Free-standing Nitrogen-doped Carbon Research Articles

Encapsulation hierarchical bimetallic oxide with flexible electrospinning carbon nanofibers for efficient capacitive deionization

Water scarcity, an intensifying issue, has spurred extensive research into the development of sophisticated freestanding pseudocapacitive electrode materials. Characterized by their precise morphology, intricate mechanics, and superior desalination capabilities, these materials are revolutionizing water treatment technologies. However, their broad adoption is hampered by complex fabrication processes and the necessity for various unique components. Herein, the paper introduces a streamlined method combining electrospinning and carbonization to produce a freestanding nitrogen-doped carbon nanofiber encapsulating manganese cobalt oxide (MCO) nanoparticles for desalination purposes. The approach significantly enhances interfacial interactions, mitigates volume shifts during sodium ion adsorption and desorption, and strengthens interfacial stability. Benefiting from its structural and compositional merits, the optimal MCO-1.0 electrode showcases exceptional electrochemical attributes. It achieves an impressive desalination efficiency (34.68 mg g−1), swift capacitive deionization rate (0.58 mg g−1 min−1), and superior cyclic durability. The study enhances our understanding of freestanding carbon fibers encapsulated with metal oxide nanoparticles, a key step toward developing robust electrodes for industrial applications.

High-performance free-standing N-doped C/SiOx film anode materials for lithium ion batteries

Silicon-carbon composites are considered as the most promising anode materials for lithium ion batteries. Currently, most silicon-carbon composites were prepared by solid nano‑silicon particles as the silicon source, which suffers from high price and uneven dispersion. Here, we used tetraethyl orthosilicate as the liquid silicon source and polyvinylpyrrolidone as the carbon source. Both were homogeneously mixed in the liquid phase, and then processed through electrospinning, carbonization and nitrogen-doped processes to obtain free-standing nitrogen-doped carbon coated silicon monoxide (N-doped C/SiOx). When served as anode material, N-doped C/SiOx can possess a reversible capacity of 488 mAh g−1 at 0.5 C (0.6 A g−1) and 377 mAh g−1 at a high current density of 2 C (2.4 A g−1). In addition, copper foil is not used as a collector for free-standing electrode structure, and eliminates the coating process of traditional electrodes, which reduces production costs. It is proposed that a facile strategy to fabricate silicon-carbon composites with good electrochemical properties and cost-effective way for lithium ion batteries.

Nitrogen-doped carbon layer on cellulose derived free-standing carbon paper for high-rate supercapacitors

Free-standing porous carbon have risen to prominent electrode materials for high-rate solid-state supercapacitors, yet they are still plagued by uneconomical petrochemical feedstocks, tedious slurry-casting processes, and suboptimal performance. Herein, a dual‐strategy of combining free-standing nitrogen-doped carbon nanowire array coating and pore engineering is designed to boost the performance of cellulose-derived carbon electrodes. Polyformamide-derived carbon nanowire arrays are in-situ synthesized as N-containing carbon coatings for cellulose-based carbon fibers. More intriguingly, H2O2 activation further enhances the hierarchical porous structure. Benefiting from the synergistic effect of free-standing feature, high electrolyte compatibility, interconnected conductive fiber networks, well-developed hierarchical porous structure and stable heteroatom-doped carbon coatings, the designed electrodes possess high accessibility of electrolyte ions and effective ion/electron transport channels. Thus, the specific capacitance reaches 275.6F g−1 at 0.5 A g−1 for aqueous supercapacitor. The solid-state symmetric supercapacitor demonstrates the specific capacitance of 126.5F g−1 at 0.5 A g−1 with the capacitance retention of 64.5% even when the current densities increased by 40-folds. Their promising energy density (17.5 Wh kg−1) and power density (12.3 kW kg−1) closing to the state-of-the-art biomass-derived free-standing solid-state symmetric supercapacitors. This breakthrough symbolizes a step forward in the advancement of biomass as high‐performance electrodes for supercapacitors.

3D Self-Supported Nitrogen-Doped Carbon Nanofiber Electrodes Incorporated Co/CoOx Nanoparticles: Application to Dyes Degradation by Electro-Fenton-Based Process.

We developed free-standing nitrogen-doped carbon nanofiber (CNF) electrodes incorporating Co/CoOx nanoparticles (NPs) as a new cathode material for removing Acid Orange 7 (AO7; a dye for wool) from wastewater by the heterogeneous electro-Fenton reaction. We produced the free-standing N-doped CNF electrodes by electrospinning a polyacrylonitrile (PAN) and cobalt acetate solution followed by thermal carbonation of the cobalt acetate/PAN nanofibers under a nitrogen atmosphere. We then investigated electro-Fenton-based removal of AO7 from wastewater with the free-standing N-doped-CNFs-Co/CoOx electrodes, in the presence or not of Fe2+ ions as a co-catalyst. The electrochemical analysis showed the high stability of the prepared N-doped-CNF-Co/CoOx electrodes in electrochemical oxidation experiments with excellent degradation of AO7 (20 mM) at acidic to near neutral pH values (3 and 6). Electro-Fenton oxidation at 10 mA/cm2 direct current for 40 min using the N-doped-CNF-Co/CoOx electrodes loaded with 25 wt% of Co/CoOx NPs led to complete AO7 solution decolorization with total organic carbon (TOC) removal values of 92.4% at pH 3 and 93.3% at pH 6. The newly developed N-doped-CNF-Co/CoOx electrodes are an effective alternative technique for wastewater pre-treatment before the biological treatment.

A freestanding nitrogen-doped carbon nanofiber/MoS2 nanoflowers with expanded interlayer for long cycle-life lithium-ion batteries

In this work, a 3D flexible freestanding nitrogen-doped carbon nanofiber/MoS2 nanoflowers (NCNFs/MoS2) network with expanded interlayer spacing is fabricated by facile electrospinning and hydrothermal synthesis method, which is employed as flexible free-standing anodes for lithium-ion batteries (LIBs) without any additives. A poly(acrylonitrile-co-β-methylhydrogen itaconate) copolymer is synthesized and uses as a precursor to improve the conductivity and flexibility of NCNFs. The three-dimensional open structure of NCNFs/MoS2 provides a highly conductive pathway for fast transfer of charge and electron, and expanded interlayer spacing of MoS2 nanoflowers can increase available surface active sites for Li-ion and reduce the obstacle of Li-ion migration during lithiation/delithiation process. Moreover, it can relieve large internal stress and accommodates volume change during cycling. The NCNFs/MoS2 composite delivers a high capacity of 1168.6 mA h g−1 at a current density of 5A g−1 and an excellent reversible capacity retention of 94.49% after 1000 cycles (only 0.055‰ decay per cycle), which makes it one of the highest capacities and best cycling stability ever reported to date. It also exhibits a superior rate capacity of 909.5 mA h g−1 at current densities 10A g−1, indicating the 3D flexible freestanding NCNFs/MoS2 composite network has potential application in high-performance lithium-ion batteries.

Nitrogen doped carbon nanofibers loaded with hierarchical vanadium tetrasulfide for the voltammetric detection of the non-steroidal anti-prostate cancer drug nilutamide.

An electrochemical sensor is described for the determination of nilutamide (NLM) in biological fluids. A flexible mat of nitrogen-doped carbon nanofibers (NCNFs) was prepared by electrospinning. This was followed by carbonization and the growth of one-dimensional vanadium tetrasulfide (VS4) nanorods in the circumference of the NCNFs by a solvothermal route. The material was used to modify a glassy carbon electrode (GCE). Cyclic voltammetry and amperometry revealed an excellent electrocatalytic activity of the VS4/NCNF mat towards NLM at a working potential of - 0.57V (vs Ag/AgCl). The modified GCE has a wide linear range (0.001-760μM), a low limit of detection (90 pM), good stability, and fast response. It was used to detect NLM in spiked serum and urine samples. Graphical abstract Schematic presentation of a glassy carbon electrode (GCE) composed of free-standing nitrogen-doped carbon nanofibers decorated with vanadium tetrasulfide (Patronite) nanorods (VS4/NCNF). It was fabricated by electrospinning followed by stabilization and carbonization. The GCE responds to nilutamide (NLM) with excellent selectivity and nanomolar sensitivity.

Directed synthesis of carbon nanotube arrays based on layered double hydroxides toward highly-efficient bifunctional oxygen electrocatalysis

The exploration of highly-efficient, low-cost bifunctional oxygen electrocatalysts for both oxygen reduction reaction (ORR) and oxygen evolution reactions (OER) is critical for renewable energy storage and conversion technologies (e.g., fuel cells and metal–air batteries). Here we report the design and fabrication of free-standing nitrogen-doped carbon nanotube (NCNT) arrays via a directed growth approach as a high-performance bifunctional oxygen electrocatalyst. By virtue of the unique hierarchical nanoarray structure, uniform N-doping and decreased charge-transfer resistance, the as-prepared NCNT array exhibits rather high activity and stability in both ORR and OER, even superior to the mono-functional commercial Pt/C (for ORR) and IrO2 (for OER). A flexible, rechargeable all-solid-state zinc–air battery is successfully fabricated by using this self-supporting NCNT electrode as air-cathode, which gives excellent discharge-charge performance and mechanical stability.

A novel nonenzymatic hydrogen peroxide sensor based on electrospun nitrogen-doped carbon nanoparticles-embedded carbon nanofibers film

A novel nonenzymatic electrochemical sensor for the detection of hydrogen peroxide (H2O2) was developed based on free-standing nitrogen-doped carbon nanoparticles-embedded carbon nanofibers (NCNPFs) film, which were prepared by the carbonization of electrospun polypyrrole nanoparticles/polyacrylonitrile (PPy NPs/PAN) composite nanofibers. A series of NCNPFs-x samples with different mass concentration of PPy NPs to PAN (wt.%) were prepared. When the PPy NPs precursor is 12wt.%, large amount of resulting NCNPs are embedded uniformly in NCNFs substrate without obvious aggregation. The as-obtained NCNPFs-12wt.% has smaller diameter, higher content of pyrrolic-N and more defective sites, which result in high electrocatalytic activity for H2O2 reduction. The NCNPFs-12wt.%-based H2O2 sensor shows a fast amperometric response within 2s, and a wide linear range of 5.0×10−6 to 2.7×10−2M with a high sensitivity of 383.9μAμM−1cm−2. In addition, this nonenzymatic sensor displays good selectivity, high reproducibility and long-term stability. Because of the remarkable analytical performances, the NCNPFs-12wt.%-based electrochemical sensor shows potential applications for the detection of H2O2 in human serum and disinfectant samples with satisfactory results.

Free-standing nitrogen-doped carbon nanotubes at electrospun carbon nanofibers composite as an efficient electrocatalyst for oxygen reduction

Efficient and non-Pt catalysts are highly desirable for many kinds of electrochemical applications. Herein, we have investigated the free-standing nitrogen-doped carbon nanotubes/carbon nanofibers composite (NCNT/CNFs) as an efficient cathode catalyst for the oxygen reduction reaction (ORR). The composite with a hierarchical structure is prepared by the pyrolysis of pyridine over flexible electrospun carbon nanofibers film (CNFs) supported with the nano-Fe catalyst. Scanning electron microscopy and transmission electron microscopy characterizations indicated that the curved NCNTs are sparsely, but tightly distributed on CNF surface. The as-prepared composite displayed good catalytic activity for ORR in an alkaline medium, with a favorable four-electron pathway, better long-term stability (94.6% retention after 10000 s), selectivity and resistance to the methanol crossover compared to the powder-form NCNTs and commercial Pt/C catalyst. The improved electrochemical performance of the NCNT/CNFs can be mainly attributed to the pyridinic-N doping and unique three-dimensional network structure. The results indicate that this novel composite can be used as a promising Pt-free ORR electrocatalyst.

Electrochemical Performance of Electrospun Free-Standing Nitrogen-Doped Carbon Nanofibers and Their Application for Glucose Biosensing

In spite of excellent electrochemical properties, nitrogen-doped carbon nanofibers (NCNFs) have rarely been studied in the field of electroanalysis. In this work, we investigated the electrochemical properties and biosensing performance of NCNFs prepared by a newly proposed approach. The as-obtained NCNFs present a unique free-standing structure with high flexibility which could be convenient for electrode modification. Electrochemical measurements of typical redox species including [Ru(NH3)6]3+/2+, [Fe(CN)6]3-/4-, [Fe(H2O)6]3+/2+, and dopamine indicate that the NCNFs have a larger surface area and faster electron transfer rate compared with carbon nanofibers (CNFs). The presence of high content of pyrrolic-N and abundant defective sites in NCNFs leads to an obvious positive shift of peak potential for oxygen reduction at NCNFs relative to that obtained at CNFs. The unique structure and properties greatly enhance the electrochemical performance of NCNFs. The glucose biosensor based on glucose oxidase/NCNFs shows linear ranges of 0.2-1.2 mM at -0.42 V and 0.05-3 mM at 0.40 V both with high stability. These results suggest that the NCNFs could be a convenient and stable platform for electrochemical biosensors.

Free-standing nitrogen-doped carbon nanofiber films as highly efficient electrocatalysts for oxygen reduction

Free-standing nitrogen-doped carbon nanofiber (NCNF) films based on polyacrylonitrile (PAN) were prepared simply by the combination of electrospinning and thermal treatment. We reused the nitrogen-rich gas generated as the byproduct of PAN at elevated temperature, mainly NH3, for surface etching and nitrogen doping. The as-obtained NCNFs exhibited a rougher surface and smaller diameter than pristine carbon nanofibers. Despite the decreased total N content, a significant increase in the content of pyrrolic-N was observed for the NCNFs. In application to electrochemistry, the free-standing NCNF films showed comparable catalytic activity with a close four-electron pathway to a commercial Pt/C catalyst in alkaline medium toward oxygen reduction reaction (ORR), which can be attributed to the nitrogen doping and high hydrophilicity. More importantly, the ORR current density on the NCNFs only dropped 6.6% after 10,000 s of continuous operation, suggesting an enhanced long-time durability. In addition, the NCNFs also showed better electrocatalytic selectivity than Pt/C. Our work reveals a facile but efficient approach for the synthesis of free-standing NCNF films as a promising alternative to Pt-based electrocatalysts in fuel cells.