Graphitic Carbon Matrix Research Articles

Tailoring Coral-Like Fe7Se8@C for Superior Low-Temperature Li/Na-Ion Half/Full Batteries: Synthesis, Structure, and DFT Studies.

The intrinsic charge-transfer property bears the primary responsibility for the sluggish redox kinetics of the common electrode materials, especially operated at low temperatures. Herein, we report the crafting of homogeneously confined Fe7Se8 nanoparticles with a well-defined graphitic carbon matrix that demonstrate a highly efficient charge-transfer system in a designed natural coral-like structure (cl-Fe7Se8@C). Notably, the intricate architecture as well as highly conductive peculiarity of C concurrently satisfy the demands of achieving fast ionic/electrical conductivities for both Li/Na-ion batteries in a wide temperature range. For example, when cl-Fe7Se8@C is employed as the anode material to assemble full batteries with the cathode of Na3V2(PO4)2O2F (NVPOF), decent capacities of 323.1 and 175.9 mA h g-1 can be acquired at temperatures of 25 and -25 °C, respectively. This work is significant for further developing potential anode materials for advanced energy storage and conversion under low-temperature conditions.

Selectively anchored vanadate host for self-boosting catalytic synthesis of ultra-fine vanadium nitride/nitrogen-doped hierarchical carbon hybrids as superior electrode materials

Hierarchically nanostructured carbon hybrids with highly exposed active sites and specific surface area have been widely researched in high-performed electrochemical capacitors. Inspired from the synergistic effect of uniformly distributed active components and stable carbon substrate, combining with green solvent extraction process, we explored a facile strategy to prepare vanadium nitride quantum dots/nitrogen-doped hierarchical carbon nanocomposites (VNQD/NDHCs) from vanadium aqueous solution, which can provide large pseudocapacitance and excellent electrochemical stability. Vanadate is selective recovered from aqueous solution in form of vanadium-organic compounds (VAORCs) as precursor. Primary amines favor not only the selective metal-polymer coordination, but also the formation of cross-linked carbon matrix. Then, during chemical molecules vapor deposition (CMVD), the vanadate is in-situ nitrided along with the formation of hierarchical carbon. The prepared VNQD/NDHCs-800 exhibits exceptional capacitance (318.3 F g−1 at 1 A g−1) and retains 89.7% of the initial capacities after 12000 cycles. SEM and TEM images confirm that a large amount of quantum dots are well embedded in a graphitic carbon matrix, which provides abundant electroactive sites and fast ion diffusion for capacitive storage. This work indicates that it is feasible to directly recovery valuable metals from aqueous solutions to prepare high-performance electrode materials.

Simple Preparation of Hierarchically Porous Ce/TiO2/Graphitic Carbon Microspheres for the Reduction of CO2 with H2O under Simulated Solar Irradiation.

Hierarchically porous Ce/TiO2/graphitic carbon microsphere composites (xCe/TiO2/GCM, where x = 0.2, 1.0, 2.0, 5.0 mmol·L–1) were prepared for the first time by using a simple colloidal crystal template and characterized by X-ray diffraction, nitrogen adsorption and desorption, scanning electron microscopy, and ultraviolet–visible diffuse reflectance spectra. In addition, the photocatalytic activity of CO2 reduction by H2O under simulated solar irradiation was studied. The results showed that the Ce/TiO2/GCM composite material was characterized by large porosity, high concentration of metal compounds and graphitized carbon matrix, and the content of acetone solvent having a great impact on its form. In terms of the photocatalytic CO2 reaction, the CH4 and CO productions were 4.587 and 357.851 μmol·g–1, respectively. The 2Ce/TiO2/GCM photocatalyst gave the highest production rate for three products. Under simulated solar irradiation, the Ce/TiO2/GCM has excellent photocatalytic activity in the photoreduction of CO2 from H2O, which was related to the special composition and the Ce/TiO2/GCM structure.

Mixed-metal MOF-derived Co-doped Ni3C/Ni NPs embedded in carbon matrix as an efficient electrocatalyst for oxygen evolution reaction

The exploration of electrocatalysts with high oxygen evolution reaction (OER) activity is highly desirable and remains a significant challenge. Transition metal carbides (TMCs) have been investigated as remarkable hydrogen evolution reaction (HER) electrocatalysts but few used as oxygen evolution reaction (OER) electrocatalysts. Herein, a Co doped Ni3C/Ni uniformly dispersed in a graphitic carbon matrix was prepared by pyrolysis of a metal organic framework (Co/Ni-MOF) under a flow of Ar/H2 at 350 °C, and Ni3C/Ni@C was also prepared for comparison. The various characterization techniques confirmed the successful preparation of the heteroatom doped TMCs-based catalysts by pyrolysis of MOFs. Co doped Ni3C/Ni@C exhibited superior electrocatalytic properties for OER. For example, Co–Ni3C/Ni@C depicts a lower overpotential and smaller Tafel slope than Ni3C/Ni@C and IrO2 during the OER in 1 M KOH solution, additionally, it shows a higher active surface area than Ni3C/Ni@C. The outstanding electrocatalytic performance of Co-doped Ni3C/Ni@C in the OER was mainly ascribed to the synergistic effect of the Co and Ni3C/Ni active sites.

A New Hybrid Material: Monolithic Biomorphic Carbon/Nickel Nanoparticles for Energy Storage Devices

A simple, inexpensive, and ecologically safe method has been used to obtain a new hybrid material—biomorphic carbon/nickel nanoparticles (bioC/NiNPs) composite—comprising a highly porous, partly graphitized carbon matrix (bioC) containing uniformly distributed nickel nanoparticles (NiNPs) with 5–70 nm dimensions. Transmission electron microscopy investigation showed that the bioC matrix consists predominantly of onion-like carbon with hollow capsules/pores about 5 nm in size and also contains graphite globules with dimensions up to 200 nm. The obtained bioC/NiNPs composite demonstrates high electrochemical capacitance stable up to about 1000 charge/discharge cycles and can be considered as promising material for monolithic electrodes of supercapacitors.

Bimetallic cerium and ferric oxides nanoparticles embedded within mesoporous carbon matrix: Electrochemical immunosensor for sensitive detection of carbohydrate antigen 19-9

A label-free electrochemical immunosensor was successfully developed for sensitively detecting carbohydrate antigen 19–9 (CA19-9) as a cancer marker. To achieve this, a series of bimetallic cerium and ferric oxide nanoparticles embedded within the mesoporous carbon matrix (represented by CeO2/FeOx@mC) was obtained from the bimetallic CeFe-based metal organic framework (CeFe-MOF) by calcination at different high temperatures. The formed CeO2 or FeOx nanoparticles were uniformly distributed within the highly graphitized mesoporous carbon matrix at the calcination temperature of 500 °C (represented by CeO2/FeOx@mC500). However, the obtained nanoparticles were aggregated into large size when calcined at the temperatures of 700 and 900 °C. The CA 19–9 antibody can be anchored to the CeO2/FeOx@mC network through chemical absorption between carboxylic groups of antibody and CeO2 or FeOx by ester-like bridging. The CeO2/FeOx@mC500-based immunosensor displayed superior sensing performance to the pristine CeFe-MOF, CeO2/FeOx@mC700- and CeO2/FeOx@mC900-based ones. Electrochemical impedance spectroscopy results showed that the developed immunosensor exhibited an extremely low detection limit of 10 μU·mL−1 (S/N = 3) within a wide range from 0.1 mU·mL−1 to 10 U·mL−1 toward CA 19–9. It also illustrated excellent specificity, good reproducibility and stability, and acceptable application analysis in the human serum solution which was diluted 100-fold with 0.01 M PBS solution (pH 7.4) and spiked with different amounts of CA19-9. Consequently, the proposed electrochemical immunosensor is capable enough of determining CA 19–9 in clinical diagnostics.

Molecular-level design of Fe-N-C catalysts derived from Fe-dual pyridine coordination complexes for highly efficient oxygen reduction

Iron-nitrogen-carbon (Fe-N-C) materials as the most promising non-precious metal catalysts for oxygen reduction reaction (ORR) to replace Pt-based catalysts are in high demand for large scale application of fuel cells. However, their activity and durability are still critical issues. Development of Fe/N/C-containing precursors is a straightforward strategy for obtaining advanced Fe-N-C ORR catalysts to address these issues. Herein, we report an advanced Fe-N-C catalyst with a hybrid structure of single Fe atom sites (Fe-Nx moieties) and exposed Fe carbides/nitrides nanodots with diameters <2 nm embedded onto highly graphitic N-doped carbon matrix. The catalyst is synthesized by pyrolysis of a new kind of Fe-dual pyridine coordinated complex as the precursor. This facile chemical route results in a non-conventional Fe-N-C catalyst with encapsulated Fe-metallic phase nanoparticles or Fe-Nx moieties. The catalyst exhibits excellent ORR activity and remarkable durability in both acidic and alkaline media. Its onset and half-wave potentials are 1.08 V and 0.88 V vs. (RHE) in 0.1 M KOH, respectively, and 0.95 V and 0.81 V vs. RHE, respectively, in 0.5 M H2SO4. Furthermore, a single proton exchange membrane (PEM) fuel cell fabricated by our catalyst generates the output power of 0.65 W cm−2, which indicates great potential of our hybrid structured Fe-N-C catalyst for the practical application in fuel cells.

Metal-organic-framework-derived formation of Co–N-doped carbon materials for efficient oxygen reduction reaction

Abstract Non-precious metal nitrogen-doped carbonaceous materials have attracted tremendous attention in the field of electrochemical energy storage and conversion. Herein, we report the designed synthesis of a novel series of Co-N-C nanocomposites and their evaluation of electrochemical properties. Novel yolk-shell structured Co nanoparticles@polymer materials are fabricated from the facile coating polymer strategy on the surface of ZIF-67. After calcination in nitrogen atmosphere, the Co–N–C nanocomposites in which cobalt metal nanoparticles are embedded in the highly porous and graphitic carbon matrix are successfully achieved. The cobalt nanoparticles containing cobalt metal crystallites with an oxidized shell and/or smaller (or amorphous) cobalt-oxide deposits appear on the surface of graphitic carbons. The prepared Co–N–C nanoparticles showed favorable electrocatalytic activity for oxygen reduction reactions, which is attributed to its high graphitic degree, large surface area and the large amount existence of Co–N active sites.

Tuning the Properties of Iron-Doped Porous Graphitic Carbon Synthesized by Hydrothermal Carbonization of Cellulose and Subsequent Pyrolysis.

The applied pyrolysis temperature was found to strongly affect composition, structure, and oxidation behavior of pure and iron oxide nanoparticle (NP)-loaded carbon materials originating from hydrothermal carbonization (HTC) of cellulose. A strong loss of functional groups during pyrolysis at temperatures beyond 300 °C of the HTC-derived hydrochars was observed, resulting in an increase of the carbon content up to 95 wt% for the carbon materials pyrolyzed at 800 °C and an increase of the specific surface area with a maximum of 520 m2 g–1 at a pyrolysis temperature of 600 °C. Devolatilization mainly took place in the range from 300 to 500 °C, releasing light pyrolysis gases such as CO, CO2, H2O and larger oxygen-containing molecules up to C11. The presence of iron oxide NPs lowered the specific surface areas by about 200 m2 g–1 and resulted in the formation of mesopores. For the iron oxide-containing composites pyrolyzed up to 500 °C, the oxidation temperature was decreased by about 100 °C, indicating tight contact between the iron oxide NPs and the carbon matrix. For higher pyrolysis temperatures, this catalytic effect of iron oxide on carbon oxidation vanished due to carbothermal reduction to iron and iron carbide, which, however, catalyzed the graphitization of the carbon matrix. Thus, the well-controlled two-step synthesis based on a biomass-derived precursor yielded stably embedded iron NPs in a corrosion-resistant graphitic carbon matrix.

Fe3O4 quantum dots embedded in porous carbon microspheres for long-life lithium-ion batteries

We report here Fe3O4 quantum dots embedded Fe3O4@C electrode materials via a facile micelle-colloid template method for pushing forward the Li-ion battery technology. To improve uniform dispersion of Fe3O4 quantum dots (5–10 nm) and create macropores in the carbon matrix, ferric micelle colloids of CTA+X−1 Fe3+ with chelate adsorption of ferric colloids on CTAB micelle corona by electrostatic attraction has been developed in a resin layer. Thus, nanocrystalline Fe3O4 and graphitic carbon matrix are mutually formed from the same texture during the pyrolysis process, resulting in a tightly tangled carbon-Fe3O4 hybrids. The conformable embedment of Fe3O4 quantum dots in carbon matrix can effectively prevent its loss and alleviate local tension stress for volume variation during change-discharge process. The well structure-designed Fe3O4@C electrode materials deliver a stable capacity of 601 mA h g−1 at 2 A g−1 even after 800 cycles. This work provides a new strategy for design of transition-metal-oxide based electrode materials for long-life lithium-ion batteries.

Integrating carbonyl iron with sponge to enable lightweight and dual-frequency absorption

In this work, sponge impregnated with iron pentacarbonyl was utilized to obtain a novel composite in which the carbonyl iron (CI) was embedded in a graphitized carbon matrix (CI-C). The CI that results from the thermal pyrolysis of iron pentacarbonyl can homogeneously disperse into the pore structures of the sponge skeleton, which not only improves the stability of the CI, but also modifies the impedance matching character. Moreover, the sponge bulk turns into graphitized carbon during the heat treatment (graphitized catalysis of magnetic metal on carbon at high temperature). Due to the respective strong dissipation ability of CI and the graphitized carbon matrix, the as-prepared CI-C sample exhibits a good microwave absorption performance, including expanding the effective absorption bandwidth and reduced weight, compared to pure CI. Moreover, the sample with 30 wt% paraffin loading not only shows strong reflection loss absorbing ability, but also possesses continuous dual-absorption peaks (9.96 GHz, −38.7 dB, and 13.8 GHz is −37.6 dB). This work not only extends the application of carbonyl iron as a lightweight microwave absorber with dual-absorption peaks but also initiates a new approach for artificially designed carbon-based composites via a simple sponge-impregnation method.

The Challenge of Achieving a High Density of Fe-Based Active Sites in a Highly Graphitic Carbon Matrix

As one of the most promising platinum group metal-free (PGM-free) catalysts for oxygen reduction reaction (ORR), Fe–N–C catalysts with a high density of FeNx moieties integrated in a highly graphitic carbon matrix with a proper porous structure have attracted extensive attention to combine the high activity, high stability and high accessibility of active sites. Herein, we investigated a ZnCl2/NaCl eutectic salts-assisted ionothermal carbonization method (ICM) to synthesize Fe–N–C catalysts with tailored porous structure, high specific surface area and a high degree of graphitization. However, it was found to be challenging to anchor a high density of FeNx sites onto highly graphitized carbon. Iron precursors with preexisting Fe–N coordination were required to form FeNx sites in the nitrogen-doped carbon with a high degree of graphitization, while individual Fe and N precursors led to a Fe–N–C catalyst with poor-ORR activity. This provides valuable insights into the synthesis-structure relationship. Moreover, the FeNx moieties were identified as the major active sites in acidic conditions, while both FeNx sites and Fe2O3 were found to be active in alkaline medium.

Onion-like graphitic carbon covering metallic nanocrystals derived from brown coal as a stable and efficient counter electrode for dye-sensitized solar cells

A graphitic carbon matrix decorated with highly dispersed metallic nanocrystals and ash components is fabricated via a facile self-sacrificed template strategy derived from brown coal. The variation of the morphology and structure, as well as the influence of annealing temperature and acid treatment of coal-derived catalysts on the electrocatalytic activity are investigated. The as-made Coal-800 counter electrode with robust structural stability shows remarkable photovoltaic and electrocatalytic performance, achieves a high power conversion efficiency of 9.03%, which is superior to that of Pt counter electrode (8.24%). The synergistic effect of the heteroatom-doped Coal-800 catalyst containing the ash components and Ca nanocrystals endows this graphitic carbon covering structure with outstanding catalytic performance, which may be the active species for the triiodide reduction reaction. This work not only demonstrates that brown coal-derived composite is a strong candidate to solve the issues related with the Pt counter electrode for dye-sensitized solar cells but also sheds light on the exploration of low-cost and highly efficient electrocatalysts that can be applied to energy-related applications.

Cohesive Porous Co3O4/C Composite Derived from Zeolitic Imidazole Framework-67 (ZIF-67) Single-Source Precursor as Supercapacitor Electrode

Composite materials containing metal oxide and carbon with optimized structures have shown potential advantages in improving the supercapacitor performance. Herein, the cohesive porous Co3O4/C composites are synthesized via a two-step calcination of zeolitic imidazole framework-67 (ZIF-67) single-source precursor. The results indicate that Co3O4 nanopaticles are in situ incorporated with partial graphitized carbon. As supercapacitor electrode material, the Co3O4/C composite exhibit higher specific capacitance (875.6 F g−1 at 1 A g−1) and better cycling stability (capacitance retention of 87.8% after 1000 cycles at 6 A g−1) compared to pure Co3O4 (245.3 F g−1 and 78.4% at the same condition). In addition, it shows good cycling stability with capacitance retention of 82% after 1000 cycles at 6 A g−1 in the symmetric supercapacitor device. The better electrochemical performance can be attributed to the improvement of the conductivity, larger surface area for more active sites, and the ameliorative volume expansion of Co3O4 by the stable structure of Co3O4 nanopaticles well embedded in partial graphitized carbon matrix during long cycling process.

A Multi‐Doped Electrocatalyst for Efficient Hydrazine Oxidation

AbstractWe report an efficient electrocatalyst for the oxidation of hydrazine, a promising fuel for fuel cells and an important analyte for health and environmental monitoring. To design this material, we emulated natural nitrogen‐cycle enzymes, focusing on designing a cooperative, multi‐doped active site. The catalytic oxidation occurs on Fe2MoC nanoparticles and on edge‐positioned nitrogen dopants, all well‐dispersed on a hierarchically porous, graphitic carbon matrix that provides active site exposure to mass‐transfer and charge flow. The new catalyst is the first carbide with HzOR activity. It operates at the most negative onset potentials reported for carbon‐based HzOR catalysts at pH 14 (0.28 V vs. RHE), and has good‐to‐excellent activity at pH values down to 0. It shows high faradaic efficiency for oxidation to N2 (3.6 e−/N2H4), and is perfectly stable for at least 2000 cycles.

A Multi-Doped Electrocatalyst for Efficient Hydrazine Oxidation.

We report an efficient electrocatalyst for the oxidation of hydrazine, a promising fuel for fuel cells and an important analyte for health and environmental monitoring. To design this material, we emulated natural nitrogen-cycle enzymes, focusing on designing a cooperative, multi-doped active site. The catalytic oxidation occurs on Fe2 MoC nanoparticles and on edge-positioned nitrogen dopants, all well-dispersed on a hierarchically porous, graphitic carbon matrix that provides active site exposure to mass-transfer and charge flow. The new catalyst is the first carbide with HzOR activity. It operates at the most negative onset potentials reported for carbon-based HzOR catalysts at pH 14 (0.28 V vs. RHE), and has good-to-excellent activity at pH values down to 0. It shows high faradaic efficiency for oxidation to N2 (3.6 e- /N2 H4 ), and is perfectly stable for at least 2000 cycles.

Embedding ZnSe nanoparticles in a porous nitrogen-doped carbon framework for efficient sodium storage

Sodium-ion batteries (SIBs) have drawn great attentions due to the abundance of sodium and their similar electrochemical principles to that of lithium-ion batteries. However, larger ionic radius of Na+ greatly retards Na+ transport and causes severe volume expansion. Therefore, delicate design of anodes for SIBs that can reversibly accommodate sodium ions is a crucial, but challenging task. In this paper, we rationally engineer a hybrid composite featured with ZnSe nanoparticles uniformly wrapped in three-dimensional (3D) porous nitrogen-doped carbon matrix (ZnSe NP@p-NC). The synthesis is achieved through the domination of the self-template-induced reaction between Zn-based zeolitic imidazolate framework (ZIF-8) nanododecahedra and Se powder at an elevated temperature. Due to the structural and compositional merits, including a 3D porous structure, the uniform distribution of the small-size ZnSe nanoparticles, and graphitic carbon matrix, these unique ZnSe NP@p-NC popcorn balls display a high sodium-storage performance, including cycling stability (181.7 mAh g−1 after 2000 cycles at 10 A g−1), rate capability, and initial Coulombic efficiency.

Cobalt nanoparticles confined in carbon matrix for probing the size dependence in Fischer-Tropsch synthesis

The size effect of the metallic Co (Co0) over supported catalysts for Fischer-Tropsch synthesis (FTS) has imposed great importance for developing a high-performance catalyst. However, the lack of well-structured catalysts makes the clarification of the intrinsic size-dependence of Co0 still a challenge. In this work, the Co/C catalysts with Co0 particles from 8.4 ± 1.9 to 74.8 ± 11.6 nm were synthesized by well-controlled pyrolysis of ZIF-67. Based on different characterizations, Co/C catalysts via pyrolyzing ZIF-67 above 450 °C were confirmed as Co0 entrapped in partially graphitized carbon matrix polished by a certain amount of pyridinic and graphitic N and a small portion of adsorbed oxygen. Without the limitation of high-temperature reduction and the dispersion-reducibility dependence, the intrinsic size effect of Co0 on the activity and product selectivity of FTS was rigorously revealed, and the critical size was determined to be 10.5 ± 1.9 nm.

Bi-functional iron embedded carbon nanostructures from collagen waste for photocatalysis and Li-ion battery applications: A waste to wealth approach

Creation of functional materials, displaying diverse properties simultaneously, from bio-wastes is in great demand in various industries. Herein, we report the synthesis of bi-functional iron encapsulated carbon (Fe@C) nanoparticles from collagen bio-waste for energy and environmental remediation applications. A simple high-temperature treatment transformed highly insulating and paramagnetic collagen-FeCl3 scaffolds into perfectly conducting and ferromagnetic bi-functional Fe@C nanoparticles. The structural and morphological analysis reveals that different phases of Fe nanoparticles are embedded in the graphitized carbon matrix forming a core-shell type of nanostructures. The mesoporous nanoparticles showed an exceptional photocatalytic activity towards 100% degradation of methylene blue within 80 min of sunlight irradiation. We also demonstrate that the presence of Fe nanoparticles in graphitic carbon lattice enabled an outstanding Li+ storage property with large reversible specific capacity (∼384 mAh/g) after 75 cycles. Our results provide a cost-effective, scalable and sustainable approach for the synthesis of functional nanomaterials from industrial bio-waste for applications in energy and environmental remediation.

NiTe2/N-doped graphitic carbon nanosheets derived from Ni-hexamine coordination frameworks for Na-ion storage

Metal-organic-frameworks (MOFs) have recently been an emerging self-templated precursor to derive various nanomaterials for Na-ion storage. However, synthesis of MOF-derived two-dimensional nanomaterials has been rarely explored. Here, Ni(NO3)2/hexamine coordination-frameworks are employed as a precursor to prepare NiTe2/nitrogen-doped graphitic carbon nanosheets (NiTe2@NCNs) via pyrolysis and subsequent tellurization. Layered NiTe2 nanoparticles are uniformly anchored on the carbon nanosheets. As anode materials, NiTe2@NCNs exhibit ultrafast and long-life Na-ion storage performance. NiTe2@NCNs can deliver a reversible capacity of 289.5 mA h g−1 at 0.1 A g−1 and exhibit a negligible capacity fading with the increasing of current density from 0.1 to 10 A g−1. Even at 10 and 20 (ca. 70 C) A g−1, reversible capacities remain at 267.7 and 189.0 mA h g−1, respectively, and cyclic life can be up to 5000 cycles. Besides, NiTe2@NCNs exhibit minimal increasing of polarization from 0.1 to 5 A g−1. The superior electrochemical performance of NiTe2@NCNs should be attributed to the two-dimensional structure, N-doped graphitic carbon matrix and lager interlayer spacing of NiTe2, which contribute to enhance kinetics of electron and Na-ion transfer so as to result in a capacitive-controlled Na-ion storage process. Therefore, NiTe2@NCNs have a promising potential as anode materials for practical Na-ion storage applications.