Three-dimensional Nitrogen-doped Graphene Research Articles

Hierarchical modulation of NiSe2 nanosheets/nanodendrites by phase engineering on N-doped 3D porous graphene as self-supporting anode for superior lithium ion batteries

In order to deal with the shortage of fossil fuel reserves and environmental pollution, lithium-ion batteries (LIBs) have been widely studied as a new type of sustainable green energy device. In the work, the NiSe2 nanosheets/nanodendrites hierarchical material with two phases is deposited on the framework of three-dimensional nitrogen-doped graphene (NPG) through the hydrothermal method to construct a self-supporting anode for LIBs. The NPG has ultralow self-weight as well as excellent electrical conductivity, which inhibits the agglomeration during the growth of active materials. Furthermore, the unique hierarchical NiSe2 active material also relieves its structural damage during the charge and discharge process. As a result, the NiSe2 combined with NPG (NiSe2@NPG) expresses specific capacities of 860 mAh/g and 568 mAh/g at current densities of 0.2 A/g and 3.2 A/g, respectively, making it a promising lithium-ion battery anode material.

N-Doped Carbon-Wrapped Cobalt–Manganese Oxide Nanosheets Loaded into a Three-Dimensional Graphene Nanonetwork as a Free-Standing Anode for Lithium-Ion Storage

A high-quality and centimeter-level three-dimensional (3D) nitrogen-doped graphene (NG) nanonetwork is synthesized via a chemical vapor deposition method to serve as a substrate and a current collector, which directly germinates active metal oxides to act as a free-standing electrode in lithium-ion batteries. By means of facile electrodeposition and annealing processes, the tetragonal spinel cobalt–manganese oxide nanosheets wrapped with polypyrrole pyrolytic carbon are in situ hybridized with a 3D NG nanonetwork. In particular, the introduced carbon protective layer can enhance the Li-ion storage capacity and cycle stability of the composite electrode. The metallic synergistic effect and rational carbonaceous hybridization jointly provide high-performance charge storage and cycle stability. Notably, the surface-controlled capacitive effect stands out contributing to the total charge storage more than ever in nanostructure electrodes.

Three-dimensional nitrogen-doped graphene hydrogel-based flexible all-solid-state supercapacitors

In this paper, a three-dimensional nitrogen-doped graphene nano-gel electrolyte (3DNG-PDMA nano-gel) for the preparation of high-performance all-solid-state supercapacitors was studied. Our research shows that the gel electrolyte has a stable three-dimensional network structure and good ionic conductivity (0.0625 S cm−1), and the all-solid-state supercapacitors (SCs) prepared by this gel electrolyte present good electrochemical performance. The specific capacitance of supercapacitor is 187.5 F g−1 under the current density of 1 A g−1. Even at the high power density of 5 kW kg−1, the energy density of supercapacitor can still reach 38 Wh kg−1. After 2500 cycles, the specific capacitance remains 84.1% of the initial value, indicating that the material has good cycle stability. Besides, the gel has high mechanical flexibility, the strain reaches 2409.4% under the stress of 1805.48 kPa, and it has excellent swelling performance with the swelling rate of 706% in 5 h.

Adopting sulfur-atom sharing strategy to construct CoS2/MoS2 heterostructure on three-dimensional nitrogen-doped graphene aerogels: A novel photocatalyst for wastewater treatment

One of the significant challenges arising from the design of the structure of photocatalytic materials lies in the control over how the photogenerated electrons and hole pairs on semiconductors are re-combined to accelerate the surface catalytic reaction. In this work, the bottom-up approach is applied to design three-dimensional (3D) CoS2/MoS2-nitrogen-doped graphene aerogel (CoS2/MoS2-NGA) photocatalyst, where a large number of small-sized ultra-thin MoS2 nanosheets are connected to CoS2 nanoparticles by means of sulfur-atoms (S-atoms) sharing, and covered on the CoS2 surface uniformly. The chemical bonding between the CoS2 and MoS2 completely restricts the aggregation of nanoscale MoS2 so as to expose more edge active sites. In the meantime, it is demonstrated that CoS2 plays a critical role in accelerating charge separation at the heterojunction interface and in preventing electron-hole recombination. As indicated by the results, CoS2/MoS2-NGA possesses excellent photocatalytic properties and high cycle stability when applied for the photodegradation of organic pollutants, which provides a potential solution to the treatment of wastewater in practice.

Engineering three-dimensional nitrogen-doped carbon black embedding nitrogen-doped graphene anchoring ultrafine surface-clean Pd nanoparticles as efficient ethanol oxidation electrocatalyst

The engineering efficient electrocatalysts with low cost, high activity and robust durability for ethanol oxidation reaction (EOR) is vital for large-scale commercializing direct ethanol fuel cells. Herein, the “surface-clean” Pd nanoparticles anchored on the nitrogen-doped carbon black embedding nitrogen-doped graphene (Pd/NCB@NGS) with unique three-dimensional hierarchical architecture was fabricated through a self-assembly strategy followed by a surfactant-free chemical reduction. The size of Pd nanoparticles on NCB@NGS can be controlled without surfactant. As an electrocatalyst for EOR, the Pd/NCB@NGS displays improved electrocatalytic performance compared with commercial Pd/C and other counterparts, due to the prominent roles of unique three-dimensional hierarchical architecture with abundant nitrogen atoms. Particularly, the electrocatalytic EOR property of Pd/NCB@NGS-2 (the mass ratio of OCB/GO is 1:1) is optimal among the tested-electrocatalysts, owing to it balances the clash between increased nitrogen atoms and decreased electrical conductivity. This study also developed a superior carbon-based material for various electrocatalysts and beyond.

Assessment of three-dimensional nitrogen-doped mesoporous graphene functionalized carbon felt electrodes for high-performance all vanadium redox flow batteries

We demonstrate the synthesis of three-dimensional (3D) nitrogen doped mesoporous graphene-functionalized carbon felt (NMG-CF) via a facile hydrothermal process. These NMG-CF act as electrocatalysts in an all-vanadium redox flow battery (VRFB). NMG-CF exhibits a uniform distribution of nitrogen atoms and spectroscopic studies indicate successful N-doping in the form of pyridinic-N, pyrrolic-N, quaternary-N and oxidic-N configurations. NMG-CFs show superior electrocatalytic activity towards V2+/V3+ and VO2+/VO2+ redox couples than activated-CF (A-CF) and mesoporous graphene-CF (MG-CF). Furthermore, NMG-CF exhibits 14–16% greater energy and voltage efficiencies than A-CF at 150 mA cm−2, with an excellent rate capability and cycling stability at current densities of 50–275 mA cm−2. These enhancements are attributed to improved hydrophilicity, 3D N-doped mesoporous structures, enhanced specific surface area and rapid charge/electron transfer. Moreover, N-doping generates defects acting as active sites and alters the electronic and chemisorption properties of NMG due to the large electronegativity difference between C and N atoms, making NMG-CFs more electrochemically accessible than A-CF and MG-CF. Notably, electrocatalytic activity is dependent not only on N-doping content but also on nitrogen configuration. The above results reveal the great potential of NMG-CFs as advanced electrode materials for VRFB.

Nitrogen-Doped Graphene Foam as a Metal-Free Catalyst for Reduction Reactions under a High Gravity Field

Herein, we report on the effect of a high gravity field on metal-free catalytic reduction, taking the nitrobenzene (NB) reduction and methylene blue (MB) degradation as model reactions in a high-gravity rotating tube reactor packed with three-dimensional (3D) nitrogen-doped graphene foam (NGF) as a metal-free catalyst. The apparent rate constant (kapp) of the metal-free catalytic reduction of NB in the rotating tube reactor under a high gravity level of 6484g (g = 9.81 m·s−2) was six times greater than that in a conventional stirred reactor (STR) under gravity. Computational fluid dynamics (CFD) simulations indicated that the improvement of the catalytic efficiency was attributed to the much higher turbulent kinetic energy and faster surface renewal rate in the high-gravity tube reactor in comparison with those in a conventional STR. The structure of the 3D metal-free catalysts was stable during the reaction process under a high gravity field, as confirmed by X-ray photoelectron spectroscopy (XPS) and Raman spectra. In the other model reaction, the rate of MB degradation also increased as the high gravity level increased gradually, which aligns with the result for the NB catalytic reduction system. These results demonstrate the potential to use a high-gravity rotating packed tube reactor for the process intensification of metal-free catalytic reduction reactions.

Effects of two- and three-dimensional graphene-based nanomaterials on the fatigue behavior of epoxy nanocomposites

Epoxy resins and their derivatives, such as composites and epoxy adhesives, are widely used in various industries. However, epoxy resins have low performance against dynamic loading and crack propagation. Graphene-based nanomaterials can improve the mechanical performance of polymeric composites because of their appropriate mechanical properties and high surface area. This study aimed to investigate the effect of Two-Dimensional Graphene Oxide (2DGO) and Three-Dimensional Nitrogen-Doped Graphene (3D(N)G) nanomaterials on the fatigue behavior of epoxy resin. 2DGO was produced by the modified Hummer’s method and 3D(N)G was synthesised by hydrothermal process, followed by freeze-drying. Nanocomposite specimens were prepared by adding 0.1 wt.% nanomaterials to epoxy resin. Tensile properties were analysed using the static tensile test. The tensile strength of epoxy resins reinforced with 2DGO and 3D(N)G improved by 16% and 19%, respectively. Subsequently, tension–tension cyclic fatigue tests with 0.1 stress ratio were conducted on pure epoxy, 2DGO/epoxy, and 3D(N)G/epoxy nanocomposites. Due to the addition of graphene-based nanomaterials, a significant enhancement in fatigue life of epoxy resin was obtained. For example, at a 35 MPa stress, fatigue life for 2DGO/epoxy and 3D(N)G/epoxy nanocomposites increased by 143% and 236%, respectively, compared to that of pure epoxy. Fractographic analysis revealed that the incorporation of 3D(N)G in the epoxy resin causes the formation of microcracks and resistance to devastating fatigue cracks in the early stages of their formation. Moreover, the high specific surface area and relatively strong bonding of 3D(N)G with the resin are the secondary factors in preventing crack prorogation and higher energy absorption during the fatigue process.

Three-Dimensional Nitrogen-Doped Graphene Aerogel-Supported MnO Nanoparticles as Efficient Electrocatalysts for CO2 Reduction to CO

Electrochemical CO2 reduction reaction (CO2RR) is a promising alternative to deal with CO2 and generate green energy. Carbon monoxide (CO) is one key desired product of the CO2RR. Herein, a Mn-base...

Surface engineering of phosphorus low-doping palladium nanoalloys anchored on the three-dimensional nitrogen-doped graphene for enhancing ethanol electroxidation

The development of superior supporting materials supported surface-engineered metallic nanocrystals is desired and necessary for promoting the electrocatalytic performance of ethanol electroxidation. Additionally, the facile and mild synthetic strategy for advanced electrocatalyst is also urgently needed. Herein, a new catalyst comprising of phosphorus low-doping palladium nanoalloys uniformly anchored on the three-dimensional nitrogen-doped graphene (denoted as Pd-P/3DNGS) is synthesized by a facile one-pot surfactant-free hydrothermal method. Notably, the optimized Pd-P/3DNGS-2 displays an inspiring enhanced electrochemical behavior to ethanol oxidation in terms of catalytic activity, accelerated kinetics, improved long-term stability and boosted anti-poisoning capability, which may be derived from the unique architecture of 3DNGS and the providential electron effect between Pd and P. This work provides a new access for rational design of nano-electrocatalysts.

3D nitrogen-doped porous graphene aerogel as high-performance electrocatalyst for determination of gallic acid

In this work, three-dimensional nitrogen-doped porous graphene aerogel (NPGA) was easily synthesized via one-step hydrothermal reduction by mixing graphene oxide (GO) with p-phenylenediamine (PPD) and ammonia solution and then followed by freeze-dried. The NPGA sample was studied by different techniques such as SEM, TEM, nitrogen adsorption-desorption isotherms, XRD, XPS, and electrochemical measurements. NPGA composite exhibits a microporous with 3D structure, a large specific surface area and exposes edge plane like-sites/defects which lead to high electrical conductivity and facilitate electrons transfer towards the probe. The appropriate experimental conditions such as supporting electrolyte, pH value and scan rate were optimized before applying NPGA electrode to determine gallic acid (GAL) using differential pulse voltammetry (DPV) method. NPGA electrode shows superior electrochemical performance compared to the previous studies with regard to the limit of detection (0.067 μmol/L) and linear range (2.5–1000 μmol/L). The NPGA electrode provides a new way for GAL concentration determination with high selectivity, excellent stability, and good reproducibility. In addition, it is highly suitable for the detection of GAL concentration in real samples with excellent reliability.

Nitrogen-doped graphene oxide aerogel anchored with spinel CoFe2O4 nanoparticles for rapid degradation of tetracycline

Antibiotic-like organic pollutants are harmful for aquatic ecosystems and seriously disrupt the ecological balance. Herein, we design a three-dimensional nitrogen-doped graphene oxide aerogel anchored with CoFe2O4 nanoparticles (3D CoFe2O4/N-rGA) via simple hydrothermal method, which can be used for peroxomonosulfate (PMS) activation toward rapidly and highly efficient degradation of tetracycline (TC). Nitrogen doped into the graphene cellular network can effectively enhance the catalytic activity of the anchored CoFe2O4 by weakening the O-O band, creating new active sites and acting as an excellent electron bridge through synergistic effects. The degradation efficiency of TC is detected to be as high as 85% only within 10 s and the degradation rate can remain above 90% after five cycles under the presence of 3D CoFe2O4/N-rGA and PMS. The catalyst also has a high efficiency for various antibiotic and pharmaceutical wastewater containing multiple antibiotics degradation.

A three-dimensional nitrogen-doped graphene framework decorated with an atomic layer deposited ultrathin V2O5 layer for lithium sulfur batteries with high sulfur loading

Lithium–sulfur batteries with ultra-high theoretical capacity have gradually become candidates to replace existing energy systems.

Three-dimensional nitrogen-doped graphene aerogel toward dendrite-free lithium-metal anode

Lithium metal, with the highest specific capacity (3860 mAh g−1) and the lowest reduction potential (− 3.04 V vs. standard hydrogen electrode), is considered as an ideal anode for the next-generation lithium-metal batteries with high energy density. However, the poor cycling performance and safety problems seriously restrict the commercial application of lithium-metal batteries. Herein, a three-dimensional (3D) porous nitrogen-doped graphene aerogel (NGA) was prepared by a hydrothermal method followed with lyophilization and high-temperature treatment to guide the uniform and dendrite-free Li deposition. On the one hand, the 3D porous structure with a large specific surface area can reduce the effective current density of the electrode, decrease the Li nucleation overpotential, and provide large spaces for Li deposition. On the other hand, the doped nitrogen atoms could provide strong affinity between Li and the NGA substrate for uniform Li deposition. Based on the synergistic effect of the above-mentioned two reasons, the Coulombic efficiency of Li deposition on NGA electrode can remain as high as 99% for over 150 cycles at a constant current density of 0.5 mA cm−2 with a fixed capacity of 1 mAh cm−2. The LiFePO4 (LFP) full cells with Li-NGA anode also exhibit excellent cycling performance and rate performance, indicating NGA has a good application prospect toward high-performance lithium-metal anode.

In situ coupled amorphous cobalt nitride with nitrogen-doped graphene aerogel as a trifunctional electrocatalyst towards Zn-air battery deriven full water splitting

Herein, we report a new type of efficient trifunctional electrocatalyst by in situ coupling amorphous cobalt nitride (CoNx) nanoparticles within three-dimensional (3D) nitrogen-doped graphene aerogel (NGA). The CoNx/NGA nanohybrid with hierarchical porous strucuture guarantees the superior activities toward ORR, OER and HER, due to abundant dual active CoNx and NxC sites. Impressively, it also exhibits a long lifetime and exceptionally high electrochemical performances as a cathode and an anode in a two-electrode overall water splitting electrolyzer, and also as an air-cathode in a rechargeable Zn-air battery. In addition, the CoNx/NGA-based water splitting electrolyzer and two Zn-air batteries can be integrated together to effectively self-drive electrochemical water splitting device with high gas evolution rates of 186 and 372 μmol h−1 for O2 and H2, respectively. This work paves a way for designing advanced non-noble multifunctional catalysts, aiming for the real application of energy storage and conversion devices.

In situ deposition of α-Co nanoparticles on three-dimensional nitrogen-doped porous graphene foams as microwave absorbers

Three-dimensional (3D) porous microstructures in graphene-based composites have been a promising strategy to reinforce their electromagnetic wave absorption performance. Herein, the 3D super-light nitrogen-doped porous graphene foams (GFs) embedded with α-Co nanoparticles (N-MGF@Co) have been constructed through in situ simultaneous deposition of α-Co on graphene sheets. Their crystalline structure, chemical composition, morphology and magnetic properties were characterized by XRD, XPS, SEM/EDS, TEM and VSM. The electromagnetic wave (EMW) absorption properties of N-MGF@Co composites with different α-Co proportions were investigated in detail. Compared with the two-dimensional hierarchical graphene-based hybrids, the obtained 3D super-light N-doped porous magnetic graphene foams exhibited much better EMW absorption properties in terms of both the effective absorption bandwidth (EAB) and minimum reflection loss (RLmin). Interestingly, EMW absorption nanoparticles properties of the as-prepared samples can be tuned by varying proportions of α-Co and the thickness of absorbers layer. The results indicate that the 3D porous magnetic graphene foams could be potential candidates for lightweight and high performance EMW absorption materials.

3D cross-linking N-doped graphene framework for high sulfur nanocrystal storage

Three-dimensional (3D) nitrogen-doped graphene frameworks contributing to high-efficiency and high-stability Li-S batteries have received wide interest in energy storage fields. Herein, a 3D nitrogen-doped graphene composite framework was prepared with spatial dendritic triamines as crosslinking interconnectors, and subsequently employed for Li-S batteries with high efficiency and stability. The nanoscale spatial network of triamine-bonded graphene as molecular spacers can enlarge the interlayer spacing and change surface topography, which allows the nanocomposites to inhibit phase separation and thus capture and homogeneously store well-dispersed sulfur nanocrystals at a high capacity exceeding 70%, even by a solution process. In our work, the composite of S@GO-TAPA as the cathode material delivers the highest initial discharge capacity of 965 mAh g−1. Besides that, an average coulombic efficiency of 91% is achieved after more than 100 cycles and 66.5% of the capacity remains, even after 100 cycles at 0.2 °C. The results suggest that the shuttle effect is remarkably suppressed. Therefore, the design strategy for cathode media is promising for fully solution-processing energy storage devices with printing, coating and spraying techniques.

Three-dimensional Fe3O4/N-graphene sponge as an efficient organosulfide host for high-performance lithium-organosulfur batteries

The rapid capacity decay and unclear mechanism for the capacity fade limit the practical application of lithium-organosulfur batteries. Herein, we employ dimethyl trisulfide (DMTS) as a model compound to investigate the capacity fading mechanism and propose a solution to improve its cycling stability. Our results reveal that both DMTS and its discharge products (e.g., LiSCH3, LiSSCH3) are soluble in the electrolyte, leading to severe active material migration and loss, which becomes the predominant capacity fading mechanism. A three-dimensional nitrogen-doped graphene sponge decorated with Fe3O4 nanoparticles (3DFNG) is designed as a host for DMTS, which effectively confine the active material, enabling a specific capacity of 822 mA h g−1 at C/10 rate and good cycling stability for 500 cycles with a capacity decay of as low as 0.09% per cycle. This work is expected to open up a promising direction to realize highly efficient hosts for lithium-organosulfur batteries.

0D/3D MoS2-NiS2/N-doped graphene foam composite for efficient overall water splitting

Electrochemical water splitting is strongly dependent on mass transport and active sites, however, the difficulty in facilitating mass transport and exposing sufficient active sites is the major bottleneck for both half reactions of the overall water splitting, i.e., hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). To address these two issues, a facile and economical strategy is demonstrated for the preparation of the bimetallic sulfides anchored three-dimensional (3D) nitrogen-doped graphene foam (MoS2-NiS2/NGF) hybrid for efficient overall water splitting. As a result, strong interactions occur between MoS2-NiS2 nanoparticles and NGF with unique 3D interconnected tubular hollow structure, leading to the superior performance towards HER and OER. The overpotential and charge transfer resistance of the hybrid are much lower than those of the bare NGF, MoS2/NGF, NiS2/NGF, and physically mixed MoS2-NiS2 + NGF, which can be attributed to the synergistic effect of NGF and bimetallic sulfides with hetero interfaces, thus endowing MoS2-NiS2/NGF abundant active sites and diversified pathways for highly-efficient transport of mass and electron. This bifunctional catalyst also exhibits excellent overall water splitting capability with a current density of 10 mA cm−2 at 1.64 V, which provides a platform for the synthesis of large-scale and cost-efficient catalysts for water splitting.

Construction of three-dimensional nitrogen-doped graphene aerogel (NGA) supported cobalt catalysts for Fischer-Tropsch synthesis

Abstract Co/NGA catalysts were one-step hydrothermal synthesized during the construction of three-dimensional nitrogen-doped graphene aerogel (NGA). The structure and properties of the catalysts were characterized by TGA, Raman, FTIR, XRD,TEM, SEM, XPS and H2-TPR, and their catalytic performance was tested by Fischer-Tropsch synthesis (FTS) reaction. Characterization and reaction results showed that higher cobalt dispersion was found on the catalyst with higher cobalt loading, and majority of cobalt species in the freeze-dried samples was fcc phase Co°. Excessive cross linking originated by high Co2+ concentration during the construction of 3D NGA led to the restraint of mass transfer of reactants to cobalt active sites, and therefore, lower FTS activity was observed on the catalysts with higher cobalt loadings. The fcc phase Co° in fresh Co/NGA catalysts was transformed in to hcp phase Co° during FTS reaction, and as a result, catalytic activity was increased with increasing time on stream.