Bamboo-shaped Carbon Nanotubes Research Articles

Fluorinated carbon tubes as carriers for MgH2 with enhanced hydrogen storage performances

Heterogeneous elements doping in carbon materials has been an effective strategy to promote their chemical properties. In this work, fluorine atoms with strong electronegativity are doped on the surfaces of bamboo-shaped carbon nanotubes (FBCNTs) which serve as carriers for MgH2 nanoparticles (MgH2@FBCNTs) to improve the reversible hydrogen storage properties. Detailed experiments indicate that MgH2@FBCNTs begin to release hydrogen at 197.8 °C, and can release 5.36 wt% H2 at 275 °C within 30 min, and quickly absorb 3.48 wt% H2 at 100 °C under hydrogen pressure of 80 bar. In addition, cycling performance is significantly enhanced in the case of fluorinated Mg-based system. The mechanism of fluorine catalysis is mainly ascribed to the formation of C-F bonds, accelerating the dissociation or combination of hydrogen atoms, offering more active sites for the de/hydrogenation and preventing the growth and agglomeration during cycling. It is also important that fraction of F is consumed and form new phases MgF2/MgF2-xHx, which offers another pathway for H atoms.

Product Selection Toward High-Value Hydrogen and Bamboo-Shaped Carbon Nanotubes from Plastic Waste by Catalytic Microwave Processing.

The escalating levels of plastic waste and energy crises underscore the urgent need for effective waste-to-energy strategies. This study focused on converting polypropylene wastes into high-value products employing various iron-based catalysts and microwave radiative thermal processing. The Al-Fe catalysts exhibited exceptional performance, achieving a hydrogen utilization efficiency of 97.65% and a yield of 44.07 mmol/g PP. The gas yields increased from 19.99 to 94.21 wt % compared to noncatalytic experiments. Furthermore, this catalytic system produced high-value bamboo-shaped carbon nanotubes that were absent in other catalysts. The mechanism analysis on catalytic properties and product yields highlighted the significance of oxygen vacancies in selecting high-value products through two adsorption pathways. Moreover, the investigation examined the variations in product distribution mechanisms between conventional and microwave pyrolysis, in which microwave conditions resulted in 4 times higher hydrogen yields. The technoeconomic assessment and Monte Carlo risk analysis further compared the disparity. The microwave technique had a remarkable internal rate of return (IRR) of 39%, leading to an income of $577/t of plastic with a short payback period of 2.5 years. This research offered sustainable solutions for the plastic crisis, validating the potential applicability of commercializing the research outcomes in real-world scenarios.

Catalytic Decomposition of CH4 to Hydrogen and Carbon Nanotubes Using the Pt(1)-Fe(30)/MCM-41 Catalyst

The catalytic decomposition of CH4 to H2 and carbon nanotubes (CNTs) was investigated regarding Pt(1)-Fe(30)/MCM-41 and Fe(30)/MCM-41 using a fixed-bed flow reactor under an atmosphere. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscope (TEM), and Raman spectroscopy were used to characterize the behavior of Pt(1)-Fe(30)/MCM-41 and Fe(30)/MCM-41. The hydrogen yield of Pt(1)-Fe(30)/MCM-41 was 3.2 times higher than that of Fe(30)/MCM-41. When 1 wt% of Pt was added to Fe(30)/MCM-41(Mobil Composition of Matter No. 41), the atomic percentage of Fe2p increased from 13.39% to 16.14% and the core Fe2p1/2 electron levels of Fe0 and Fe2+ chemically shifted to lower energies (0.2 eV and 0.1 eV, respectively) than those of Fe(30)/MCM-41. The Fe, Pt, Si, and O nanoparticles were uniformly distributed on the catalyst surface, and the average iron particle sizes of the Pt(1)-Fe(30)/MCM-41 and Fe(30)/MCM-41 were about 33.4 nm and 58.5 nm, respectively. This is attributed to the uniform distribution of the nano-sized iron particles on the MCM-41 surface, which was due to the suitable metal-carrier interaction (SMCI) between Fe, Pt, and MCM-41 and the high reduction degree of Fe due to the spillover effect of H2 from Pt to Fe. Pt(1)-Fe(30)/MCM-41 produced multiwalled CNTs and bamboo-shaped CNTs with high crystallinity and graphitization degree using the tip-growth mechanism, with an ID/IG ratio of 0.93 and a C(101)/C(002) ratio of 0.64.

Bamboo-shaped N-doped carbon nanotubes encapsulated with Co nanoparticles for improved microwave absorption properties

High reflection loss and wide absorption bandwidth materials are in great demand to prevent electromagnetic pollution and military applications. The composites prepared by combining different components with good dielectric and magnetic losses are expected to achieve ideal absorbing performance. In this study, a composite of cobalt nanoparticles enveloped in nitrogen-doped bamboo-like carbon nanotubes (Co@N-CNTs) was prepared by one-step annealing the mixture of melamine and cobalt nitrate at 800 °C in a mixed atmosphere of hydrogen and argon. Co nanoparticles derived from the reaction between H2 and cobalt nitrate during the sintering process were used as catalysts to prompt the carbonization of melamine and the formation of the bamboo-shaped N-doped carbon nanotubes, thus forming the composite structure of bamboo-shaped N-doped carbon nanotubes encapsulated with Co nanoparticles. This Co@N-CNTs composite not only had an excellent dielectric loss and magnetic loss but also greatly improved its impedance matching, thus having good electromagnetic wave absorption performance. The coating made from the Co@N-CNTs composite had a maximum reflection loss (RL) of −35.89 dB at only 1.8 mm thickness at 14.1 GHz and possessed an effective absorption bandwidth of up to 4.91 GHz (12.35–17.26 GHz), suggesting it a high-performance and wide-absorption bandwidth composite material.

Synergistic Catalysis of Cobalt Tetroxide and Bamboo-Shaped Carbon Nanotubes Doped with Nitrogen for Oxygen Reduction in Zn-Air Batteries.

Zinc-air batteries (ZABs) have been considered as one of the most emerging systems for energy conversion and storage. However, the preparation of highly efficient oxygen reduction reaction (ORR) catalysts on an air cathode is still faced with significant challenges. Herein, we report a secondary nitrogen source strategy for fine-tuning the active center, which provides a carbon-based hierarchical porous catalyst (termed Co3O4@N/CNT-1000) for highly efficient ORR activity (E1/2 = 0.87 V, JL = 5.32 mA cm-2, and Eonset = 1.021 V) and excellent stability. Controlled experiments demonstrate that such high activity derives from the synergistic effect of cobalt tetroxide and bamboo-shaped carbon nanotubes doped with nitrogen, prepared by the pyrolysis of a two-dimensional metal-organic framework nanosheet (termed NTU-70) and melamine. Furthermore, the ZAB assembled with Co3O4@N/CNT-1000 displays high specific capacity (854 mA h g-1Zn) and power density (179 mW cm-2), excellent long-term cycling (330 h), and durable charging/discharging ability.

N-doped graphene leaves on carbon nanotubes and NiMn2O4-graphene hybrid nanocomposites with ionogel film for flexible symmetric and asymmetric supercapacitors

The efficient fusion of the various components into hybrid nanostructures in a hierarchical three-dimensional fashion is found to be one of the significant strategies to obtain potential electrode materials for supercapacitors. In addressing this, two diverse kinds of 3D graphene-based hybrid nanomaterials are synthesized using facile and scalable approaches, and then their microstructural properties are studied. The developed 3D nitrogen doped-graphene leaves on bamboo shaped carbon nanotubes (N-glbNT-850) exhibit a high specific capacitance of 528 F/g at a 2 A/g current density. 3D blooming flower structured NiMn2O4-graphene electrode exhibit a high specific capacity and rate capability of 1632 C/g, and 88.1%, respectively. Further, a new ionogel electrolyte film is developed by incorporating a high concentration (96 wt%) of ionic liquid into a 4 wt% polymer host. A flexible symmetric supercapacitor fabricated by using this solid-state ionogel electrolyte film and a flexible asymmetric supercapacitor fashioned of N-glbNT//NiMn2O4-graphene could exhibit a wide working voltage range (3.4 V and 1.6 V, respectively), excellent energy density (96.3 and 156.8 Wh/kg, respectively), outstanding power density (3.39 and 2.34 kW/kg, respectively), and good rate performance with high cycle stability and remarkable flexibility. Thus, the development of inexpensive and efficient electrode materials based on graphene and effective solid-state ionogel electrolytes and the application of these technologies for efficient energy storage devices have all been made possible by the new and effective strategic process, which can be beneficial for commercial applications of energy storage, conversion, and environmental systems.

Synergistic effect of carbon nanotubes and carbon black as nanofillers of silicone rubber pressure sensors

Pressure sensors based on nitrogen-doped bamboo-shaped carbon nanotubes (N-BCNT) and carbon black (CB) as nanofillers, polyurethane foam (PU) as supporting substrate, and silicone rubber (SR) as a matrix were prepared. Dip coating was used to coat PU with 0.44 wt% nanofiller, including different mixing ratios of N-BCNT and CB (5:5; 6:4; 7:3; 8:2; 9:1). Then, the coated PU is impregnated in SR to fill the pores. Due to the higher aspect ratio of the N-BCNT, it contributes more to improving the electrical conductivity in the composites, while the CB fills the smaller gaps. The prepared sensors were tested in various applications, and it was found that the optimal mixing ratio of nanofillers was 7:3 N-BCNT:CB. Thus, a multifunctional pressure sensor has been developed successfully with excellent flexibility and good resilience, suitable for motion detection and finger touch applications. The pressure sensor showed high sensitivity, and the ability to detect a wide range of pressures. The sensor exhibited success in a range of applications, paving the way for its potential use in various fields in the future, such as wearable devices, prosthetics, robotic devices, and medical devices.

The Effect of Pore Volume on the Behavior of Polyurethane-Foam-Based Pressure Sensors.

In this work, three different polyurethane (PU) foams were prepared by mixing commonly used isocyanate and polyol with different isocyanate indices (1.0:0.8, 1.0:1.0, 1.0:1.1). Then, the prepared polyurethane foam samples were coated by dip-coating with a fixed ratio of nitrogen-doped, bamboo-shaped carbon nanotubes (N-BCNTs) to obtain pressure sensor systems. The effect of the isocyanate index on the initial resistance, pressure sensitivity, gauge factor (GF), and repeatability of the N-BCNT/PU pressure sensor systems was studied. The pore volume was crucial in finetuning the PU-foam-based sensors ability to detect large strain. Furthermore, large pore volume provides suitable spatial pores for elastic deformation. Sensors with large pore volume can detect pressure of less than 3 kPa, which could be related to their sensitivity in the high range. Moreover, by increasing the pore volume, the electrical percolation threshold can be achieved with a minimal addition of nanofillers. On the other hand, PU with a smaller pore volume is more suitable to detect pressure above 3 kPa. The developed sensors have been successfully applied in many applications, such as motion monitoring and vibration detection.

In-situ growth of bamboo-shaped carbon nanotubes and helical carbon nanofibers on Ti3C2Tx MXene at ultra-low temperature for enhanced electromagnetic wave absorption properties

The potential of two-dimensional layered MXenes in electromagnetic wave (EMW) absorption needs further development. Herein, we carried out the in situ growth of carbon nanotubes (CNTs) on the surface of Ti3C2Tx MXene at ultra-low temperature via chemical vapor deposition. The obtained CNTs exhibited a bamboo-like structure and were accompanied by helical carbon nanofibers. The ultra-low temperature solved the problem that the high temperature required in the traditional CNT growth process would destroy the structural integrity of MXene. The lush CNT forest cross-linked the MXene layers, transforming the two-dimensional layered structure into a three-dimensional conductive network, providing abundant conductive channels for carriers, optimizing the impedance matching of the CNT/MXene hybrid, and resulting in a significant dielectric loss. The as-prepared CNT/MXene hybrid exhibited a minimal reflection loss of −52.56 dB (99.9994% EMW absorption) in the X-band. This work proposes a new idea to enhance the EMW absorption properties of Ti3C2Tx MXene and fabricate high-performance MXene-based EMW absorbers.

Ultralight Coral-like hierarchical Fe/CNTs/Porous carbon composite derived from biomass with tunable microwave absorption performance

In order to widen the application field of microwave absorption (MA) materials, it is still challenging to obtain high-performance MA materials with wide frequency bandwidth, lightweight, thin thickness, and strong absorption by an economical and sustainable method. Herein, the novel coral-like hierarchical structure with zero-dimensional Fe nanocrystals, one-dimensional N-doped carbon nanotubes (CNTs) and three-dimensional porous carbon (PC) matrix is rationally constructed to enhance MA performance. Based on renewable biomass residues, the composite consisted of PC as matrix, bamboo-shaped CNTs with magnetic nanoparticles at the top grow on the surface of PC. By controlling the growth conditions of carbon nanotube, the microstructure and dielectric loss capacity of composite can be manipulated to optimize the impedance matching, reflection loss (RL), and effective absorption bandwidth (EAB, the bandwidth of RL < -10 dB). Benefitting from the unique architecture and hierarchical composite, the composite exhibited a minimum RL of −70 dB at thin thickness of 1.9 mm under low filler content of 12.5 wt%. Even with the thickness of 1.5 mm, the RL could reach −51.8 dB with a broadcast EBA of 5.0 GHz. This work provides an insight for designing advanced microwave absorbers with lightweight, thin thickness, strong RL, and wide EAB.

Preparation of Bamboo-Like Carbon Nanotube Loaded Piezoresistive Polyurethane-Silicone Rubber Composite.

In this study, a novel technology is reported to prepare a piezoresistive polyurethane-silicone rubber nanocomposite. Polyurethane (PU) foam was loaded with a nitrogen-doped bamboo-shaped carbon nanotube (N-BCNT) by using dip-coating, and then, impregnated with silicone rubber. PU was used as a supporting substrate for N-BCNT, while silicone rubber was applied to fill the pores of the foam to improve recoverability, compressive strength, and durability. The composite displays good electrical conductivity, short response time, and excellent repeatability. The resistance was reduced when the amount of N-BCNT (0.43 wt %) was increased due to the expanded conductive path for electron transport. The piezoresistive composite has been successfully tested in many applications, such as human monitoring and finger touch detection.

Nickel nanoparticles encapsulated by nitrogen-doped bamboo-shaped carbon nanotubes with a high-level doping: A boosting electrocatalyst for alkaline hydrogen evolution

The development of highly active and stable alkaline hydrogen evolution electrocatalysts is highly desired in the field of clean energy. Herein, we chose urea and nickel chloride as precursors, and synthesized metallic Ni nanoparticles encapsulated by nitrogen-doped bamboo-shaped carbon nanotubes through one-pot calcination at low temperature (550 °C). Along with the increase in the amount of Ni salt, the electrocatalyst support has undergone a transformation from polymeric carbon nitride to nitrogen-doped carbon, and the charge transport ability and electrochemical active surface area of the electrocatalysts have been significantly improved. For the optimized Ni/NC-0.35 electrocatalyst with 13.42 wt% nitrogen-doping level, the overpotential at cathodic current density of 10 mA cm−2 is 133 mV (vs. RHE) in alkaline electrolyte, the corresponding Tafel slope is 109 mV dec-1, and there is no significant decrease in hydrogen evolution activity after 16 h. The boosting activity can be attributed to the synergistic effect of the mixed phase Ni nanoparticles, the high nitrogen-doping level and the bamboo-shaped carbon nanotube structure towards the alkaline hydrogen evolution reaction. This work provides a new way for the design of high-activity alkaline hydrogen evolution electrocatalysts and the facile synthesis of high nitrogen-doping carbon-coated metal nanoparticle catalysts.

Synthesis of single-walled, bamboo-shaped and Y-junction carbon nanotubes using microwave plasma CVD on low-temperature and chemically processed catalysts

The low temperature nucleation and high yield growth of CNTs with their diverse range of layered structures and shapes is of significant interest to the research community in view of obtaining distinctive properties necessary for specific applications. In this regard, several strategies have been employed to control the growth characteristics of CNTs. In the present investigation, the low temperature growth of CNTs has been enabled using CO2 as a suitable oxidizing gas. CNTs have been grown via an optimum etching process conducted under diffuse plasma generated using a specially designed shadow mask assembly that shields the growth surface from direct plasma bombardment, and subsequent abrasive etching by the reactive plasma species. Furthermore, CO2 as a component in the plasma facilitates the elimination of amorphous carbonaceous components from the surface of the CNTs. The growth of narrow CNTs has been achieved via the formation of a low diameter (~20 nm) catalyst comprised of Fe nano-particles grown in a low temperature (10 °C) chemical process under an inert atmosphere via simultaneous aerial oxidation and neutralization in a single step. Further plasma optimization by controlling the MW power has facilitated the growth of CNTs with controlled diameters, wall numbers and different morphologies (e.g., Y-junction and bamboo-shaped MWCNTs, and very low diameter (~1.5 nm) SWCNTs). The tip growth mechanism for CNT nucleation has been established using HR-TEM, in which the Fe catalyst nanoparticles are detected within the top shell of the growing CNTs.

Direct curvature measurement of the compartments in bamboo-shaped multi-walled carbon nanotubes via scanning probe microscopy

Bamboo-shaped multi-walled carbon nanotubes (BS-MWCNTs) have compartmented structures inherently obtained during their catalytic growth, and the curvature of the compartmented structure is known to be determined by the morphology of the metal catalysts. In this study, the inside curvature of the BS-MWCNTs was directly measured through scanning probe microscopy (SPM). The surface of the compartment structures of BS-MWCNTs has discontinuous graphene layers and different frictional force levels depending on the curvature direction. That of the inside curvature can be directly observed through tribological analysis by adding and subtracting the lateral force microscopy images obtained on opposite sides along the axial direction of the BS-MWCNT (diameter of 500 nm). This tells us the direction of the inside curvature of the BS-MWCNT, which was also confirmed by identifying the growth direction of the BS-MWCNTs via scanning electron microscopy. Our demonstration implies that SPM can give the same insight into the structural characterization of nanomaterials that is relatively inexpensive and more user-friendly than currently used methods.

Hydrogenation of benzophenone by carbon-supported Pd catalysts

Catalytic activity of palladium catalysts with two different types of carbon support, Norit (an activated carbon), and bamboo-shaped carbon nanotubes (BCNT) have been tested for benzophenone hydrogenation. The selectivity toward the two possible reaction products (benzhydrol and diphenylmethane) can be directed by the catalyst support. It has been found that the Norit support preferred the over-hydrogenation of benzhydrol to diphenylmethane. The BCNT support proved to be much more selective and resulted as much as 99.3% benzhydrol selectivity at 96.3% benzophenone conversion. The high benzhydrol selectivity might be explained by the presence of covalently bonded nitrogen atoms in the catalyst (BCNT: 6.19 w/w%, Norit 0.54 w/w%) that can inhibit the over-hydrogenation process, thereby BCNTs are better catalyst supports for benzhydrol production than the commonly used activated carbon–supported catalysts.

Nickel-assisted synthesis of magnetic bamboo-shaped N-doped carbon nanostructure for excellent microwaves absorption

The development of carbon materials with unique nanostructure and appropriate magnetism is of great importance in design of high-performance microwaves absorption materials. In this work, we provide a convenient strategy for one-step synthesis of a bamboo-shaped magnetic N-doped carbon nanotube (BMN-CNT) via a nickel (Ni)-assisted pyrolysis process. During synthetic process, Ni nanoparticles form and play as a catalyst for the catalytic calcination of melamine. The BMN-CNT exhibits excellent microwaves absorption performance, where the maximal reaches − 19 dB. A model referring to multi-polarization, internal reflection, and magnetic loss is used to explain the dissipation mechanism of BMN-CNT on microwaves. This research opens up the exploration of novel magnetic carbon nanostructures for MA applications.

Tin dioxide decorated on Ni-encapsulated nitrogen-doped carbon nanotubes for anodic electrolysis and persulfate activation to degrade cephalexin: Mineralization and degradation pathway

In this study, bamboo-shaped carbon nanotubes exhibiting high nitrogen content and Ni encapsulation (Ni@NCNT) were effectively synthesized by a simple pyrolysis method. The catalytic peroxydisulfate activation for cephalexin (CPX) degradation was investigated using the prepared material. SnO2 was further decorated and fabricated on the anode material (SnO2/Ni@NCNT) for electrochemical degradation of CPX in an aqueous solution. Transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy indicated that the SnO2 nanoparticles were uniformly distributed on the surface of Ni@NCNT. Electrochemical characterization employing cyclic voltammetry and linear sweep voltammetry demonstrated that SnO2/Ni@NCNT displayed higher oxygen evolution potential and electrocatalytic activity than Ni@NCNT. Mineralization of CPX in wastewater was performed using electrolysis coupled with persulfate oxidation. The analysis revealed a synergistic strengthening effect. The electropersulfate oxidation resulted in higher total organic carbon (TOC) removal (70.3%) than the sum of electrooxidation (48.1%) and persulfate oxidation (9.2%) toward CPX. This phenomenon might result from the regeneration of sulfate radicals (SO4•−) on the anode and complementary oxidation by SO4•− and OH. Persulfate oxidation alone was shown to result in low TOC removal, although CPX was mostly degraded. Additionally, the CPX degradation pathway involving electropersulfate oxidation was proposed and it is indicated that CPX molecules were completed decomposed by the examination of short chain acids, mineralized ions, and ecotoxicity evolution indicated that the antibiotic was completely degraded. This study provides a new approach for the design and preparation of novel electrode materials and electrochemical degradation facilities for the removal of pollutants via persulfate activation.

A facile synthesis of nitrogen-doped bamboo-shaped carbon nanotubes by catalytic decomposition of 2-aminopyrimidine over Fe@MgO catalyst through chemical vapor deposition method

In this work, nitrogen-doped bamboo-shaped carbon nanotube (nitrogen-doped CNT) was prepared using the Chemical Vapor Deposition Method (CVD). For the first time, 2-aminopyrimidine (a carbon and nitrogen resources) was used as a precursor over Fe@MgO catalyst and employed in CVD. The prepared CNT was characterized via elemental analysis, Fourier Transform Infrared Spectroscopy (FT-IR), Energy Dispersive X-ray Spectroscopy (EDX), Transmission Electron Microscopy (TEM), X-ray Diffraction (XRD), Raman Spectroscopy and Scanning Electron Microscope (SEM). The amount of nitrogen in the prepared CNT was about 5.8%. The FT-IR spectrum reveals the presence of C–N and C = N bonds in the prepared CNT structure. The prepared CNT has bamboo-like structure with a diameter of less than 100 nm.

Bamboo-Shaped Carbon Nanotubes on Coal Fly Ash Cenospheres for Pb(II) Adsorption.

The structural defects of bamboo-shaped carbon nanotubes (B-CNTs) provide abundant active sites for ion adsorption during wastewater treatment. However, a suitable supporting material for the growth of B-CNTs growth is less reported. In this paper, the catalytic growth of B-CNTs on the cenospheres (CSs) of coal fly ash was studied. The results showed that all CSs were covered by a layer of B-CNTs during the chemical vapor deposition (CVD) process, regardless of the fluctuation of the iron distribution from 0.52 to 2.09 wt%. B-CNTs with a diameter of 30-40 nm shared a similar morphology of compartment structures, which were uniformly scattered on the surfaces of the CSs and formed a 3D network structure. A high level of structural defects was present on the B-CNTs, which was denoted by an ID/IG value of 1.77 via Raman spectrum analysis. Adsorption experiments of the as-prepared CSs@B-CNTs revealed an excellent adsorption capacity for lead ions of 37.32 mg/g (pH 7, initial concentration of 70 mg/L). By excluding the function of CSs, the adsorption capacity of the pure B-CNTs was estimated to be as high as 275.19 mg/g, which has not been previously reported.

Hemoglobin-derived Fe-Nx-S species supported by bamboo-shaped carbon nanotubes as efficient electrocatalysts for the oxygen evolution reaction

Herein, we report a facile route to synthesize isolated single iron atoms on nitrogen-sulfur-codoped carbon matrix via a direct pyrolysis process in which hemoglobin, a by-product of the meat industry, was utilized as a precursor for iron, nitrogen and sulfur while bamboo-shaped carbon nanotubes served as a support owing to their excellent conductivity and numerous defects. The resulting metal-nitrogen complexed carbon showed outstanding catalytic performance for the oxygen evolution reaction (OER) in alkaline solutions. At an overpotential of 380 mV, the optimal sample yielded a current density of 83.6 mA cm−2, which is 2.5 times that of benchmark IrO2 (32.8 mA cm−2), rendering it as one of the best OER catalysts reported so far. It also showed negligible activity decay in alkaline solutions during long-term durability tests. Control experiments and X-ray absorption fine structure analyses revealed that Fe-Nx species in the samples are the active sites for OER. Further density functional theory calculations indicated that the presence of sulfur in the carbon matrix modified the electronic structures of active species, thereby leading to the superior activity of the sample.