Nitrogen Co-doped Carbon Nanofibers Research Articles

Synergistic Electrocatalysis and Spatial Nanoconfinement to Accelerate Sulfur Conversion Kinetics in Aqueous Zn-S Battery.

Aqueous zinc batteries based on the conversion-type sulfur cathodes are promising in energy storage system due to the high theoretical energy density, low cost, and good safety. However, the multi-electron solid-state intermediate conversion reaction of sulfur cathodes generally possess sluggish kinetics, which leads to lower discharge voltage and inefficient sulfur utilization, thus suppressing the practical energy density. Herein, sulfur nanoparticles derived from metal-organic frameworks confined in situ within electrospun fibers derived sulfur and nitrogen co-doped carbon nanofibers (S@S,N-CNF) composite, which possesses yolk-shell S@C nanostructure, is fabricated through successive sulfidation, pyrolysis, and sulfide oxidation processes, and served as a high-performance cathode material for Zn-S battery. The S and N dopants on carbon can collectively catalyse sulfur reduction reaction (SRR) by lowering energy barrier and accelerating kinetics to increase discharge voltage and specific capacity. Meanwhile, the yolk-shell S@C structure with spatially confined S nanoparticle yolks is beneficial to improve charge transfer and lower activation energy, thus further expediting SRR kinetics. Furthermore, extensive density functional theory (DFT) calculations reveal that S and N dual-doping can thermodynamically and dynamically reduce the energy barrier of rate-determining step (i.e., the transformation of *ZnS4 into *ZnS2) for the overall SRR, thereby significantly accelerating SRR kinetics.

NiFeP nanosheet arrays supported on nickel nitrogen codoped carbon nanofiber as an efficient bifunctional catalyst for overall water splitting

Transition metal phosphides have emerged as effective electrocatalysts for water splitting. In this study, novel NiFeP nanosheet arrays supported on nickel nitrogen codoped carbon nanofiber (NiFeP@Ni-NCNF) was synthesized through a combination of electrospun, template-directed growth, and phosphorization strategy. The utilization of Ni-NCNF as a substrate for constructing the nanoarrays structure with superhydrophilic and superaerophobic properties significantly enhances the electrochemical active specific surface area of the electrocatalytic material. The synergistic effect of Ni2P and Fe2P and the excellent conductivity of the Ni-NCNF substrate promote NiFeP@Ni-NCNF to exhibit excellent HER/OER electrocatalytic properties. The NiFeP@Ni-NCNF exhibits low overpotentials of 131 mV and 204 mV for HER and OER at 10 mA cm−2, respectively. Additionally, using NiFeP@Ni-NCNF as the anode and cathode of the electrolytic water device displays a voltage of 1.61 V at 10 mA cm−2, and the Faraday efficiency of the two electrodes is near 100 %. This research presents an extensible and cost-effective strategy for synthesizing phosphide-based catalysts with unique nanostructures and desirable water splitting catalytic properties.

Sulfur & nitrogen co-doped electrospun carbon nanofibers as freestanding electrodes for membrane capacitive deionization

Capacitive deionization (CDI), especially membrane capacitive deionization (MCDI) technology, is an energy-efficient and environmentally friendly water desalination technology. Tremendous efforts have been devoted to designing and preparing high-performance and applicable electrode materials for CDI and MCDI. In this work, sulfur and nitrogen co-doped carbon nanofibers (SCNFs) are prepared by a facile co-electrospinning strategy coupled with subsequent high-temperature heat treatment, and directly used as monolithic and binder-free electrodes for MCDI. Benefiting from the integrated structural and compositional merits, i.e. 3D network composed of disorderly stacked 1D nanofibers and uniform distribution of nitrogen and sulfur atoms, the as-obtained SCNFs exhibit superior electrosorption ability and excellent cycling stability, with the salt adsorption capacity up to 29.50 mg g−1 and the current efficiency higher than 80% when desalting 500 mg L−1 NaCl solution at the voltage of 1.4 V. The doped nitrogen and sulfur atoms in SCNFs not only effectively improve their electrical conductivity and wettability but also tailor the pore structure, thus providing more active sites for ions adsorption. The heteroatom doping strategy could shed new light on the design of high-performance carbon-based electrodes for the electrochemical MCDI application.

Plasma-Assisted Synthesis of Defect-Rich O and N Codoped Carbon Nanofibers Loaded with Manganese Oxides as an Efficient Oxygen Reduction Electrocatalyst for Aluminum-Air Batteries.

The oxygen reduction reaction (ORR) with sluggish kinetics on the cathode of aluminum-air (Al-air) batteries greatly limits their further development. Here, a new strategy is proposed to synthesize oxygen and nitrogen codoped carbon nanofibers loaded with manganese oxides (MnO/Mn2O3/ONCNF-n) as an efficient electrocatalyst for ORR by using oxygen plasma surface etching. The MnO/Mn2O3/ONCNF-3 exhibit superior ORR performance in an alkaline electrolyte, which is attributed to various active sites including N and O heteroatoms, vacancies, and manganese oxides. Additionally, the fabricated homemade Al-air battery (AAB) with MnO/Mn2O3/ONCNF-3 exhibits a maximum power density of 129.7 mW cm-2, demonstrating comparable performance to AABs based on the commercial Pt/C catalyst. This work provides a new approach of using O2 plasma for enhancing the ORR catalytic activities of carbon materials.

Hybrid TiO-TiO2 nanoparticle/B-N co-doped CNFs interlayer for advanced Li S batteries

Herein, a novel composite nanofiber, which consists of TiO-TiO2 heterostructure nanoparticles and boron, nitrogen co-doped carbon nanofibers (BNCNF), has been successfully prepared through a facile electrospinning method. Remarkably, as interlayer for LiS batteries, the TiO-TiO2 heterostructure not only enhances the adsorbability of the interlayer to lithium polysulfides (LiPSs) via the Lewis acid-base interactions, but also accelerates the redox reaction kinetics of the LiS batteries dramatically. Moreover, the BNCNF as a flexible framework can remit the volumetric change of the sulfur cathode, physically retard the migration of LiPSs and chemically adsorb to the LiPSs. Attributing to the synergistic effect of TiO-TiO2 nanoparticle and BNCNF membrane, the LiS batteries with the novel composite interlayer (named as TiO-TiO2/BNCNF) exhibit outstanding cycling stability and high discharge capacity, especially at high current density. With the sulfur loading of 2.5 mg cm−2, the cell with the TiO-TiO2/BNCNF interlayer delivers a high initial discharge capacity of 1014.7 mA h g−1 with a decay rate of 0.092% over 400 cycles at 0.5C, and also possesses excellent initial discharge capacity of 650.0 mA h g−1 with a decay rate of 0.068% over 120 cycles even at 2.0C.

Cobalt and Nitrogen Co-Doped Electrospun Carbon Nanofibers as a Bifunctional Oxygen Electrocatalyst

Nowadays, it is urgent to prepare a bifunctional electrocatalyst with effectively improve catalytic properties towards ORR and OER, replacing precious metals and commercial catalysts. Cobalt nitrogen co-doped carbon nanofibers (Co-N/CNFs) are successfully synthesized via solvothermal, pyrolysis of electrospun nanofibers containing cobalt phthalocyanine and melamine. The electrochemical characterization of Co-N/CNFs-800 is carried out using cyclic voltammetry, and Tafel studies compared with Pt/C and RuO2. The Co-N/CNFs-800 exhibits the higher ORR catalytic activity with half-wave potential (0.77 V) and the lower OER overpotential (370 mV). Furthermore, the activity parameter of Co-N/CNFs-800 (0.83 V) is much lower than that of Pt/C (0.95 V), and closer to RuO2 (0.82 V). This research opens an effective method to synthesize an excellent bifunctional electrocatalyst for ORR/OER.

An innovative synthetic approach for core-shell multiscale hierarchically porous boron and nitrogen codoped carbon nanofibers for the oxygen reduction reaction

In this work, polyacrylonitrile (PAN) and metal-organic framework (MOF)-derived 3D B and N codoped core-shell carbon nanofibers (CNFs) with multiscale carbon layers derived from continuous zeolitic imidazolate frameworks (ZIF-8 and ZIF-67) are synthesized via dual-functional ZnO and Co3O4 nanostructures. Here, ZnO and Co3O4 act as a metal-ion source for the MOF formation and as pore creating agents. Further, dual-function NaBH4 reduces metallic ions into respective metals as well as providing three-dimensionality to the conventional two dimensional CNF mat. Additionally, B and N doping can be achieved by treatment with a single dopant, NH4HB4O7·3H2O. The resulting core-shell multiscale-3D CNFs with hierarchical pores (ZIF-8@BN-CNF) deliver exceptional onset (0.94 V vs RHE) and half wave potential (0.86 V vs RHE)) with excellent cyclic stability toward the oxygen reduction reaction (ORR). Moreover, the electrode maintained a remarkably high current retention of 97.2%, even after 25 000 s, which is better than that of a commercial Pt/C catalyst (89.6%). The superior catalytic activity and stability of the CNF-based catalyst are attributed to the synergistic effect of the structure and codoping of B and N with highly porous 3D hierarchical core-shell nanoarchitecture.

Synergy of interlayer expansion and capacitive contribution promoting sodium ion storage in S, N-Doped mesoporous carbon nanofiber

Heteroatoms doping is proved to be an effective strategy to improve the electrochemical performance of carbon materials by adjusting its physical and chemical properties. In this work, sulfur, nitrogen co-doped carbon nanofiber (SNCNF) is prepared by electrospinning technique with the following heat and hydrothermal treatment route. Benefiting from the S, N co-doping, SNCNF demonstrates perfect pseudocapacitance characteristic improving rate performance (N-doping) and large interlayer distances promoting reversible insertion/extraction of Na+ (S-doping). SCNNF displays high charge-discharge specific capacity (290.3 mA h g−1 at 0.1 A g−1), superior cycling stability (247.4 mA h g−1 and 98.2% retention at 0.5 A g−1 over 600 cycles) and ultra-long circulation characteristics at high current rate (160.2 mA h g−1 at 10.0 A g−1 after 10,000 cycles), which can be served as a very promising material as anode for sodium ion batteries.

3D Sulfur and Nitrogen Codoped Carbon Nanofiber Aerogels with Optimized Electronic Structure and Enlarged Interlayer Spacing Boost Potassium-Ion Storage.

Carbonaceous materials are promising anodes for potassium-ion batteries (PIBs). However, it is hard for large K ions (1.38 Å) to achieve long-distance diffusion in pristine carbonaceous materials. In this work, the following are synthesized: S/N codoped carbon nanofiber aerogels (S/N-CNFAs) with optimized electronic structure by S/N codoping, enhanced interlayer spacing by S doping, and a 3D interconnected porous structure of aerogel, through a pyrolysis sustainable seaweed (Fe-alginate) aerogel strategy. Specifically, the S/N-CNFAs electrode delivers high reversible capacities of 356 and 112 mA h g-1 at 100 and 5000 mA g-1 , respectively. The capacity reaches 168 mA h g-1 at 2000 mA g-1 after 1000 cycles. A full cell with a S/N-CNFAs anode and potassium prussian blue cathode displays a specific capacity of 198 mA h g-1 at 200 mA g-1 . Density functional theory calculations indicate that S/N codoping is beneficial to synergistically improve K ions storage of S/N-CNFAs by enhancing the adsorption of K ions and reducing the diffusion barrier of K ions. This work offers a facile heteroatom doping paradigm for designing new carbonaceous anodes for high-performance PIBs.

Self-assembled and well separated B and N co-doped hierarchical carbon structures as high-capacity, ultra-stable, LIB anode materials

Self-assembled porous hierarchical networks of boron and nitrogen co-doped carbon nanofibers (BN-CNN) or graphene sheets (BN-GSN) exhibit high reversible capacities and ultra-stable cycle performances as LIB anode materials.

A polysulfide-trapping interlayer constructed by boron and nitrogen co-doped carbon nanofibers for long-life lithium sulfur batteries

The shuttle effect of soluble lithium polysulfides (LiPSs) and their insoluble reduction products (Li2S/Li2S2) depositing on the surface of lithium anode are the major drawbacks for the practical application of lithium sulfur (Li-S) batteries. In this work, a thin and light interlayer constructed by boron and nitrogen co-doped carbon nanofibers (BNCNF) has been produced by a facile electrospinning method with following thermal treatment. Through introducing BNCNF film between cathode and separator, the charge transfer resistance decreases largely and the shuttle effect remits to a great extent. The BNCNF exhibits excellent absorption ability for polysulfides under the role of the B⋯S and N⋯Li chemical interaction, and especially the formation of N=B/N-B structure in the carbon nanofiber framework reinforces the electropositive interaction between B atoms and Sx2− and the electronegative interaction between N atoms and Li+ cation, simultaneously. The capacity and cycling life of Li-S batteries are improved significantly due to the BNCNF interlayer. The cell with BNCNF interlayer delivered an initial capacity of 1054.7mAhg−1 at 1.0C over 1000cycles with a decay rate of 0.058%. And even at high current density of 5.0C, it had an initial capacity of 612.2mAhg−1 over 600cycles with a decay rate of 0.085%. The BNCNF interlayer developed here provides a promising methodology to enhance the performance of Li-S batteries.

Facile preparation of efficient electrocatalysts for oxygen reduction reaction: One-dimensional meso/macroporous cobalt and nitrogen Co-doped carbon nanofibers

Efficient electrocatalyst for oxygen reduction reaction (ORR) is an essential component for stable operation of various sustainable energy conversion and storage systems such as fuel cells and metal-air batteries. Herein, we report a facile preparation of meso/macroporous Co and N co-doped carbon nanofibers (Co-Nx@CNFs) as a high performance and cost-effective electrocatalyst toward ORR. Co-Nx@CNFs are simply obtained from electrospinning of Co precursor and bicomponent polymers (PVP/PAN) followed by temperature controlled carbonization and further activation step. The prepared Co-Nx@CNF catalyst carbonized at 700 °C (Co-Nx@CNF700) shows outstanding ORR performance, i.e., a low onset potential (0.941 V) and half wave potential (0.814 V) with almost four-electron transfer pathways (n= 3.9). In addition, Co-Nx@CNF700 exhibits a superior methanol tolerance and higher stability (>70 h) in Zn-air battery in comparison with Pt/C catalyst (∼30 h). The outstanding performance of Co-Nx@CNF700 catalysts is attributed to i) enlarged surface area with bimodal porosity achieved by leaching of inactive species, ii) increase of exposed ORR active Co-Nx moieties and graphitic edge sites, and iii) enhanced electrical conductivity and corrosion resistance due to the existence of numerous graphitic flakes in carbon matrix.

Porous Iron-Nitrogen-Carbon Nanofiber As Efficient Oxygen Reduction Reaction Catalyst and Durable Support for Platinum

Polymer electrolyte membrane fuel cells (PEMFCs) have been considered as one of the most promising energy conversion devices for future due to their high efficiency, and environmental friendly system. However, large-scale applications of PEMFCs have still faced some challenges in terms of cost and durability. Catalyst plays a great role in determining cost and durability of PEMFCs. Conventional catalyst for PEMFCs is a state-of-the-art carbon supported platinum nanoparticles (Pt/C). Pt/C has an outstanding catalytic activity for both hydrogen oxidation reaction (HOR) at anode and oxygen reduction reaction (ORR) at cathode. But, high price of Pt is a major contributory factor in increasing PEMFCs cost. And, conventional carbon support is vulnerable to corrosion under oxidative potential, which leads to serious degradation of cell performance. Therefore, it has been one of the major issue in PEMFCs to develop low-priced and durable catalysts without sacrificing catalytic performance. Recent studies proposed that co-doping of transition metal (Fe, Co, Mn..) and nitrogen into graphene-like carbon structure can draw remarkable ORR activity under PEMFCs operating conditions. In addition, this graphene-like carbonaceous materials also can have higher corrosion resistance than conventional carbon support with amorphous structure. Herein, we synthesized iron (Fe) and nitrogen co-doped carbon nanofiber (Fe-N-CNF) with highly porous structure as efficient oxygen reduction reaction catalyst and durable support for platinum catalyst. We could successfully synthesize porous CNF by using silica nanoparticles (SiO2 NPs) as sacrificing materials. After leaching of SiO2 NPs, BET surface area and electrochemical surface area (ECSA) were 3-times and 6-times enhanced, respectively. So, porous Fe-N-CNF has excellent ORR activity and durability in acidic media. Fig. 1. TEM images of Fe-N-CNF and porous Fe-N-CNF Figure 1

Synthesis of boron and nitrogen co-doped carbon nanofiber as efficient metal-free electrocatalyst for the VO2+/VO2+ Redox Reaction

Boron or nitrogen mono-doped carbon nanofiber (CNF), and boron, nitrogen co-doped CNF are intentionally prepared as positive electrodes in a vanadium redox flow battery (VRFB). The structures and electrochemical properties of the materials are investigated by Scanning electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, cyclic voltammetry and electrochemical impendence spectroscopy. The experimental results indicate that either B or N mono-doped CNF shown better electrochemical performance than untreated one. Interestingly, for the B and N co-doped CNF, the separated case exhibited an outstanding electrochemical activity better than either B or N mono-doped case, while the bonded case leading to a sharp drop in conductivity and shown poor electrochemical performances. These results demonstrated that not the total amount of incorporated B and N but how the B and N are incorporated into carbon nanostructures determines the catalytic activity toward VO2+/VO2+ reaction. Moreover, the individual mechanism of the nitrogen and boron containing functional groups act as active sites have been analyzed.