Nitrogen-doped Graphene Foam Research Articles

Molecularly imprinted polymers-coated magnetic covalent organic frameworks for efficient solid-phase extraction of sulfonamides in fish

In this study, covalent organic frameworks (COFs) were grown in situ on magnetic nitrogen-doped graphene foam (MNGF), and the resulting composite of COFs-modified MNGF (MNC) was wrapped by molecularly imprinted polymers (MNC@MIPs) for specifically capturing SAs. A magnetic solid phase extraction (MSPE) method for SAs was established using MNC@MIPs with good magnetic responsiveness. The adsorption performance of MNC@MIPs was superior to that of non-molecularly imprinted polymers (MNC@NIPs), with shorter adsorption/desorption time and higher imprinting factors. A high-efficiency SAs analytical method was developed by fusing HPLC and MNC@MIPs-based MSPE. This approach provides excellent precision, a low detection limit, and wide linearity. By analyzing fish samples, the feasibility of the approach was confirmed, with SAs recoveries and relative standard deviations in spiked samples in the ranges of 77.2–112.7 % and 2.0–7.2 %, respectively. This study demonstrated the potential use of MNC@MIPs-based MSPE for efficient extraction and quantitation of trace hazards in food.

A WS2/Co9S8 heterostructure with a carbon layer anchored in nitrogen-doped graphene foam as an anode for boosting lithium storage

A self-supporting electrode with a WS2/Co9S8 heterogeneous structure accelerates electron transportation and demonstrates remarkable electrochemical performance for Li+ storage.

FeCoS2/Co4S3/N-doped graphene composite as efficient electrocatalysts for overall water splitting

Transition metal sulfide is a kind of electrocatalyst with appropriate cost, high efficiency, and stability. However, introducing additional metal atoms into transition metal complexes to form ternary compounds can more effectively optimize the electronic structure and improve its catalytic performance. In this work, FeCoS2/Co4S3 nanoparticles were groundbreakingly synthesized and loaded on nitrogen-doped graphene foam (NGF) with a 3D network structure by facile hydrothermal synthesis and simple chemical vapor deposition (CVD) process. The transition metal sulfide nanoparticles were uniformly distributed on the surface of NGF substrates. The transition metal sulfide nanostructures can provide a larger surface area, enhance the interaction with the medium, and improve the electrocatalytic performance. The synthesized FeCoS2/Co4S3/NGF catalyst exhibits enhanced HER and OER catalytic performance in 1 M KOH, with overpotentials of 172 mV for the HER and 276 mV for the OER at a current density of 10 mA·cm−2. The performance of the FeCoS2/Co4S3/NGF hybrid catalyst could match the best Fe-Co-S bifunctional electrocatalysts reported in the literature. Strong evidence supports that the FeOOH/CoOOH species in situ formed on the surface of FeCoS2/Co4S3/NGF catalyst was the actual catalytic active substance towards OER. In addition, the Tafel slope, TOF, EIS, and stability test results collaboratively support that Fe-Co-S/NGF shows great potential to be used as a bifunctional electrocatalyst for large-scale overall water electrolysis.

Surface and interface engineering of MoNi alloy nanograins bound to Mo-doped NiO nanosheets on 3D graphene foam for high-efficiency water splitting catalysis

Designing high-efficiency and durable non-noble metal catalysts is essential for the large-scale application of electrocatalytic water splitting. Herein, MoNi alloy nanograins are embedded in Mo-doped NiO nanosheets by partial reduction treatment, which vertically grow on three-dimensional (3D) nitrogen-doped graphene foam substrate (MoNi@Mo-NiO@NGF). The hybrid composite demonstrates superb bifunctional electrocatalytic activity towards hydrogen/oxygen evolution reactions. Especially, it possesses the ultra-low hydrogen evolution overpotential of 56 mV at the current density of 10 mA cm−2 in alkaline condition. The excellent catalytic activity and remarkable stability can be attributed to the optimized surface electronic structure of MoNi alloy by Mo doping, the synergy interface interaction between MoNi nanograins and Mo-NiO substrate, and the high conductivity and corrosion resistance of NGF support. Thus, this work provides a new strategy for the high-performance catalyst towards overall water splitting by the dual regulation of surface and interface.

Evaluation of electrochemical hydrogen storage capability of three-dimensional nano-structured nitrogen-doped graphene

In this work, nitrogen-doped graphene foam was synthesized by using hydrothermal routes. In the first step, graphene was synthesized by utilizing a modified Hummer's method and nitrogen-doped graphene foam was then synthesized at 180 °C by using an ammonia and graphene solution for 12 h. X-ray photon spectroscopy (XPS) was applied to determine the extent of doping by nitrogen on the graphene foam; three N-peaks were observed at 398.25, 399.69, and 401.46 eV, and XPS also showed that 6 at% of the synthesized graphene foam consisted of nitrogen atoms. The capability of this foam to absorb hydrogen was evaluated in a 6 M KOH solution through electrochemical impedance spectroscopy (EIS), galvanostatic charge/discharge, and cyclic voltammetry (CV) analysis. The hydrogen storage capacity of the achieved N-doped GF, showing the value of 1916.5 mAh.g−1 significantly improved in comparison to that of pure graphene in previous work, due to the increasing electronegative sites at the surface of the graphene foam.

The effect of nitrogen species on the catalytic properties of N-doped graphene

The production of effective catalysts in the oxygen reduction reaction (ORR) continues to be a great challenge for scientists. A constant increase in demand for energy storage materials is followed by a proportionate increase in the number of reports on electrocatalyst synthesis. The scientific world focuses on environmentally friendly materials synthesized in accordance with the safest possible. In this work, we developed a facile method of obtaining heavy-metal-free electrode materials that are effective in ORR. Graphene-based catalysts were doped using azodicarbonamide (ADC) as the source of nitrogen, then carbonized at high temperatures in the range of 700–900 °C under inert gas flow. The produced materials were tested as catalysts for ORR, which is the most important reaction for Zn–air batteries and fuel cells. All obtained nitrogen-doped graphene foams showed increased catalytic activity in ORR owing to active sites created by nitrogen functional groups on the graphene surface. This paper shows that carbonization temperature has a significant impact on nitrogen content and that a small percentage of nitrogen may have a positive effect on the catalytic activity of the obtained materials. The number of transferred electrons in ORR was found to range from three to the maximal theoretical value, i.e., four.

Co1-xS/N-doped graphene foam composite as efficient bifunctional electrocatalysts for the evolution reaction of oxygen and hydrogen

As an environment-friendly and sustainable energy conversion technology, water electrolysis is strongly dependent on the efficiency and cost of the electrocatalysts. Herein, nanosheet-constructed cobalt sulfide microspheres incorporated with nitrogen-doped graphene foam (Co1-xS/NGF), a highly efficient bifunctional electrocatalyst for overall water splitting, was obtained by controlled two-step synthesis. The nitrogen-doped graphene foam (NGF) underlying the Co1-xS microspheres provides an electrically conducting support for the catalysts, contributes small size and homogeneous distribution of the in-situ grown Co1-xS microspheres, and affords abundant active sites for fast and sufficient transport of mass and electrons and, therefore, highly enhanced catalytic activity through the strong synergistic effect of Co1-xS microspheres and the NGF substrate. In 1 M KOH, the Co1-xS/NGF hybrid catalyst exhibits remarkable OER and HER catalytic performance, with overpotentials of 233.6 mV for the OER and 163.7 mV for the HER at 10 mA cm−2, and the corresponding Tafel slopes of 138 and 95 mV dec−1, respectively. The hybrid material of Co1-xS/NGF even exhibits a lower overpotential (η20) to reach 20 mA cm−2 towards OER than that of RuO2, and its performance matches the best cobalt sulfide bifunctional electrocatalysts reported to date. Besides, the Co1-xS/NGF is highly stable for long-term water electrolysis in the 1 M KOH. These findings support that the current Co1-xS/NGF is a competitive candidate of transition metal-based catalysts for cost-efficient and large-scale overall water electrolysis in the alkaline environment.

N-doped graphene foam obtained by microwave-assisted exfoliation of graphite

The synthesis of metal-free but electrochemically active electrode materials, which could be an important contributor to environmental protection, is the key motivation for this research approach. The progress of graphene material science in recent decades has contributed to the further development of nanotechnology and material engineering. Due to the unique properties of graphene materials, they have found many practical applications: among others, as catalysts in metal-air batteries, supercapacitors, or fuel cells. In order to create an economical and efficient material for energy production and storage applications, researchers focused on the introduction of additional heteroatoms to the graphene structure. As solutions for functionalizing pristine graphene structures are very difficult to implement, this article presents a facile method of preparing nitrogen-doped graphene foam in a microwave reactor. The influence of solvent type and microwave reactor holding time was investigated. To characterize the elemental content and structural properties of the obtained N-doped graphene materials, methods such as elemental analysis, high-resolution transmission electron microscopy, scanning electron microscopy, and Raman spectroscopy were used. Electrochemical activity in ORR of the obtained materials was tested using cyclic voltamperometry (CV) and linear sweep voltamperometry (LSV). The tests proved the materials’ high activity towards ORR, with the number of electrons reaching 3.46 for tested non-Pt materials, while the analogous value for the C-Pt (20 wt% loading) reference was 4.

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.

N-doped porous carbon-graphene cables synthesized for self-standing cathode and anode hosts of Li–S batteries

Lithium-sulfur batteries have high theoretical energy density, but still suffer from polysulfide shuttle effect and lithium dendritic growth. Here, we present a rollable and swellable 3D cable-like carbon material consisting of porous fibrous carbon coated with nitrogen-doped graphene foam as self-standing host for both sulfur cathode and lithium anode. A cathode exhibits high areal energy density (10.2 mWh cm−2) and power density (5.1 mW cm−2) with 92.2% retention for 200 cycles at 0.5 C, and a full cell delivers 525 mAh g−1 (1.8 mAh cm−2) after 100 cycles at 0.5 C with a fade rate of 0.14% per cycle. We found dense urea molecules can assist graphene foam formation, cellulose fibers activation and high-level nitrogen (7.58 atom% N) doping, and the resulting cable-like carbon can improve electrocatalytic polysulfide redox kinetics and lithium dendrite inhibition. This work provides a strategy and understanding of modifying commercial cloth with graphene for dual electrode of Li–S battery.

Near-infrared absorbing 2D/3D ZnIn2S4/N-doped graphene photocatalyst for highly efficient CO2 capture and photocatalytic reduction

Hierarchical heterostructure photocatalysts with broad spectrum solar light utilization, particularly in the near-infrared (NIR) region, are emerging classes of advanced photocatalytic materials for solar-driven CO2 conversion into value-added chemical feedstocks. Herein, a novel two-demensional/three-demensional (2D/3D) hierarchical composite is hydrothermally synthesized by assembling vertically-aligned ZnIn2S4 (ZIS) nanowall arrays on nitrogen-doped graphene foams (NGF). The prepared ZIS/NGF composite shows enhancement in photothermal conversion ability and selective CO2 capture as well as solar-driven CO2 photoreduction. At 273 K and 1 atm , the ZIS/NGF composite with 1.0 wt% NGF achieves a comparably high CO2-to-N2 selectivity of 30.1, with an isosteric heat of CO2 adsorption of 48.2 kJ mol−1 . And in the absence of cocatalysts and sacrificial agents, the ZIS/NGF composite with cyclability converts CO2 into CH4, CO and CH3OH under simulated solar light illumination, with the respective evolution rates about 9.1, 3.5, and 5.9 times higher than that of the pristine ZIS. In-depth analysis using in-situ irradiated X-ray photoelectron spectroscopy (ISI-XPS) in conjunction with Kelvin probe measurements reveals the underlying charge transfer pathway and process from ZIS to NGF.

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.

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.

Direct Observation of Structural Evolution of Metal Chalcogenide in Electrocatalytic Water Oxidation.

As one of the most remarkable oxygen evolution reaction (OER) electrocatalysts, metal chalcogenides have been intensively reported during the past few decades because of their high OER activities. It has been reported that electron-chemical conversion of metal chalcogenides into oxides/hydroxides would take place after the OER. However, the transition mechanism of such unstable structures, as well as the real active sites and catalytic activity during the OER for these electrocatalysts, has not been understood yet; therefore a direct observation for the electrocatalytic water oxidation process, especially at nano or even angstrom scale, is urgently needed. In this research, by employing advanced Cs-corrected transmission electron microscopy (TEM), a step by step oxidational evolution of amorphous electrocatalyst CoS x into crystallized CoOOH in the OER has been in situ captured: irreversible conversion of CoS x to crystallized CoOOH is initiated on the surface of the electrocatalysts with a morphology change via Co(OH)2 intermediate during the OER measurement, where CoOOH is confirmed as the real active species. Besides, this transition process has also been confirmed by multiple applications of X-ray photoelectron spectroscopy (XPS), in situ Fourier-transform infrared spectroscopy (FTIR), and other ex situ technologies. Moreover, on the basis of this discovery, a high-efficiency electrocatalyst of a nitrogen-doped graphene foam (NGF) coated by CoS x has been explored through a thorough structure transformation of CoOOH. We believe this in situ and in-depth observation of structural evolution in the OER measurement can provide insights into the fundamental understanding of the mechanism for the OER catalysts, thus enabling the more rational design of low-cost and high-efficient electrocatalysts for water splitting.

3D cellular CoS1.097/nitrogen doped graphene foam: a durable and self-supported bifunctional electrode for overall water splitting

3D cellular N-doped graphene foam supported CoS1.097 nanoparticles as highly active and stable bifunctional catalysts for overall water splitting.

A collaborative strategy for stable lithium metal anodes by using three-dimensional nitrogen-doped graphene foams.

A collaborative strategy is developed for constructing stable lithium metal anodes by using self-supporting three-dimensional nitrogen-doped graphene foams as the multifunctional host matrix. The resultant electrode shows impressive electrochemical performances, attributable to the three-dimensional porous architecture and nitrogen-doping nature of such a unique host matrix.

Scalable Self-Supported Graphene Foam for High-Performance Electrocatalytic Oxygen Evolution.

Developing efficient electrocatalysts consisting of earth-abundant elements for oxygen evolution reaction (OER) is crucial for energy devices and technologies. Herein, we report self-supported highly porous nitrogen-doped graphene foam synthesized through the electrochemical expansion of carbon-fiber paper and subsequent nitrogen plasma treatment. A thorough characterization, such as electron microscopy and synchrotron-based near-edge X-ray absorption fine structure, indicates the well-developed porous structures featuring homogeneously doped nitrogen heteroatoms. These merits ensure enriched active sites, an enlarged active surface area, and improved mass/electron transport within the continuous graphene framework, thus leading to an outstanding capability toward electrocatalyzing OER in alkaline media, even competitive with the state-of-the-art noble-/transition-metal and nonmetal electrocatalysts reported to date, from the perspectives of the sharp onset potential, a small Tafel slope, and remarkable durability. Furthermore, a rechargeable Zn-air battery with this self-supported electrocatalyst directly used as the air cathode renders a low charge/discharge overpotential and considerable life span. The finding herein suggests that a rational methodology to synthesize graphene-based materials can significantly enhance the oxygen electrocatalysis, thereby promoting the overall performance of the energy-related system.

3D nitrogen-doped graphene decorated CoNi2S4@polypyrrole electrode for pseudocapacitor with ultrahigh electrochemical performance

In this article, we report a novel hybrid electrode with hierarchical architecture were synthesized via a high-throughput hydrothermal approach under low temperature. The unique hierarchical nanostructured CoNi2S4@PPY/N-3DG (CoNi2S4@PPY hierarchical core/shell network on Nitrogen-doped graphene foam) exhibits significantly promoted electrochemical performance in pseudocapacitor. This hybrid electrode takes advantages of the electrochemical activity of CoNi2S4 and polypyrrole (PPY), hierarchical structure of CoNi2S4@PPY/N-3DG, and synergistic effect originated from CoNi2S4, PPY and N-doped 3DG. These design merits lead to the good ion transportation and electron conductivity, excellent long-cycling galvanostatic charging/discharging stability, and durable high-rate-capacitance of ca. 730Fg−1 at 10Ag−1. Moreover, the flexible, aqueous and solid-state asymmetric supercapacitor (ASC) was successfully fabricated with the CoNi2S4@PPY/N-3DG on Ni foam as cathode and activated carbon (AC) as anode. The electrochemical performance of the ASC device shows the high-energy density of 37.4Whkg−1 at 1.6kWkg−1 and the high-power density of 7.2kWkg−1 at 15.1Whkg−1, together with an excellent capacitance retention of ca. 82% after 5000 cycles.

Three-dimensional nitrogen-doped graphene foam as metal-free catalyst for the hydrogenation reduction of p-nitrophenol

Developing metal-free catalysts for various applications has been the focus of high interest over the past decade, especially aiming to replace the expensive noble metal-based catalysts. Herein, a well-defined three-dimensional nitrogen-doped graphene foam (3D-NGF) is synthesized and employed as a metal-free catalyst for the hydrogenation reduction of p-Nitrophenol to p-Aminophenol. The apparent activation energy is calculated, and the reaction mechanism with 3D-NGF as the catalyst for the hydrogenation reduction of p-Nitrophenol is proposed. Importantly, the 3D-NGF demonstrates high catalytic activity and robust stability. The high activity can be ascribed to the synergistic effect between the nitrogen-doping induced change in electronic property and the 3D foam-like structure.

Nitrogen‐Doped Graphene Nanoscroll Foam with High Diffusion Rate and Binding Affinity for Removal of Organic Pollutants

A nitrogen-doped 3D graphene foam assembled with nanoscroll structure is constructed via a facile mild-heating methodology using a polar molecule of formamide as the driving regent. The as-prepared graphene nanoscroll foam exhibits promising performance in organic pollutant removal with improved adsorption rate and high binding affinity, and is thought to be a novel adsorption material.