N-doped Graphene Foam Research Articles

Graphyne Nanotubes as Promising Sodium-Ion Battery Anodes

Sodium-ion batteries (SIBs) are promising candidates for the replacement of lithium-ion batteries (LIBs) because of sodium’s abundant reserves and the lower cost of sodium compared to lithium. This is a topic of interest for developing novel anodes with high storage capacity. Owing to their low cost, high stability, and conductivity, carbon-based materials have been studied extensively. However, sp2-C based carbon materials have low-rate capacities. Intensive density functional theory calculations have been implemented to explore the applicability of α, β, and γ graphyne nanotubes (αGyNTs, βGyNTs, and γGyNTs, respectively) as SIB anodes. Results suggest that (3, 0)-αGyNT, (2, 2)-βGyNT, and (4, 0)-γGyNT have, respectively, maximum Na storage capacities of 1535, 1302, and 1001 mAh/g, which exceeds the largest reported value of carbon materials (N-doped graphene foams with 852.6 mAh/g capacity). It was determined that αGyNTs have the largest storage capacity of the three types because they possess the largest specific surface area. Moreover, the larger pores of αGyNTs and βGyNTs allow easier diffusion and penetration of Na atoms compared to those of γGyNTs, which could result in better rate capacity.

Compressible Neuron-like 3D Few-Layered MoS2/N-Doped Graphene Foam as Freestanding and Binder-Free Electrodes for High-Performance Lithium-Ion Batteries

Compressible Neuron-like 3D Few-Layered MoS₂/N-Doped Graphene Foam as Freestanding and Binder-Free Electrodes for High-Performance Lithium-Ion Batteries

Complementary performance improved crystalline N-doped carbon encapsulated CoFe/mesoporous N-doped graphene foam as bifunctional catalyst

Future energy conversion that will replace fossil energy can be expected from oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) among high-performance bi-functional electrocatalysts. Herein, a hybrid material, CoFe@N-C/MNGF containing an N-doped carbon shell on the surface of CoFe alloy nanoparticles and three-dimensional (3D) mesoporous N-doped graphene foam with exposed active sites as an electron transfer substrate has been successfully synthesized to replace noble-metal catalysts. The electrocatalytic performance of CoFe@N-C/MNGF demonstrates better OER activity in 0.1 M KOH alkaline electrolyte with a remarkably low overpotential of 330 mV and low Tafel plot 130.6 mV⋅dec-1 at a current density of 10 mA⋅cm−2. And CoFe@N-C/MNGF has considerable ORR performance in terms of catalyst activity, electron transfer number and stability, which suggests its usefulness as a suitable replacement for ORR catalysts based on noble-metal used for cathode electrode of alkaline fuel cells. In particular, it showed a potential of 0.87 V in 0.1 M KOH alkaline electrolyte and low Tafel plot 71.7 mV⋅dec-1 at 5 mA⋅cm−2 and the number of electrons (n) transferred was estimated to be 2.1–3.61 at 0.15 to 0.35 V. Based on these results, this study provides new insights into a cost-efficient non-noble metal bi-functional electrocatalyst.

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.

NiSe2-anchored N, S-doped graphene/Ni foam as a free-standing bifunctional electrocatalyst for efficient water splitting.

It is still challenging to develop non-precious free-standing bifunctional electrocatalysts with high efficiency for hydrogen and oxygen evolution reactions. Herein, for the first time, we present a novel hybrid electrocatalyst synthesized via a facile hydrothermal reaction, which is constructed from ultrafine NiSe2 nanoparticles/nanosheets homogeneously anchored on 3D graphene/nickel foam (NiSe2/3DSNG/NF). This hybrid delivers superior catalytic performances for hydrogen/oxygen evolution reactions and overall water splitting: it shows an ultra-small Tafel slope of 28.56 mV dec-1 for hydrogen evolution in acid, and a small Tafel slope of 42.77 mV dec-1 for the oxygen evolution reaction; particularly, in a two-electrode setup for water splitting, it requires an ultra-small potential of 1.59 V to obtain 10 mA cm-2 with nearly 100% faradaic efficiencies for H2 and O2. This study presents a new approach of catalyst design and fabrication to achieve highly efficient and low-cost water electrolysis.

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.

Synthesis of lightweight N-doped graphene foams with open reticular structure for high-efficiency electromagnetic wave absorption

Chemical doping of graphene with heteroatoms is expected to be a promising strategy to enhance the electromagnetic wave attenuation capability, however, the intrinsic mechanism is not investigated in-depth. In this manuscript, ultra-lightweight N-doped graphene foams (ρ ≈ 10.5–16.6 mg/cm3) with high porosity and open reticular structures are prepared via a self-assembled hydrothermal reaction and a freeze-drying process. Compared with pure graphene foams, the presence of N heteroatoms helps to build open reticular walls and tailors the electrical properties, leading to strong electromagnetic wave absorption capacity and broad absorption bandwidth simultaneously, and meanwhile, the investigation of N bonding configurations illustrates that the presence of pyrrolic/pyridinic N are mainly essential for the dipolar relaxation loss whereas graphitic N is beneficial to the conduction loss. When the bulk density is 11.6 mg/cm3, the maximum reflection loss of the absorber is −53.9 dB at 3.5 mm with a low filler loading of only 5 wt%, and the absorption bandwidth exceeding −10 dB is 4.56 GHz with a thickness of 2 mm, the highly efficient electromagnetic wave absorption performance strongly originates from the enhanced dipolar/interfacial polarizations, the multiple scatterings, the microscale circular conductive structures as well as the balanced impedance match. Furthermore, this monocomponent absorber can be an optimal candidate for ultra-lightweight and high-efficiency electromagnetic wave absorber without decorating other nanomaterials.

Powder metallurgy template growth of 3D N-doped graphene foam as binder-free cathode for high-performance lithium/sulfur battery

Here, we present a facile technique to design self-supported 3D N-doped graphene foam (NGF) via simply annealing in chemical vapor deposition furnace which used powder metallurgy nickel template and melamine as both carbon and nitrogen source. The NGF possesses highly conductive and interconnected mesoporous network. Particularly nitrogen-doping provided strong polysulfide immobilization ability, significantly suppressing the shuttle effect. The NGF was directly used as binder-free electrode which delivered a high initial discharge capacity of 987 mA h g−1 and maintains at 819 mA h g−1 after 200 cycles at 0.2 C, corresponding to 82.9% capacity retention. Specifically, even at high current density of 2 C, it still possesses a good long life cycle performance (from 633.8 mA h g−1 to 440.3 mA h g−1 after 500 cycles, with ultralow capacity fading rate of 0.061% per cycle). 7Li nuclear magnetic resonance (7Li NMR) suggested strong interaction between NGF and polysulfide. Moreover, X-ray photoelectron spectroscopy and density function theory calculation further revealed the strong interaction mostly ascribed to chemisorption and physisorption of polysulfide by pyridinic and pyrrolic nitrogen, respectively. As we know this method-based NGF as binder free electrode was first reported, which provided an effective strategy for developing high-performance Li/S batteries.

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.

Highly Compressible and Conductive N-Doped Graphene Foam for Lithium Batteries

Over almost five years, 3-dimensional graphene and graphene-based nanostructured foams have been widely progressed. These materials have potential for use in next-generation energy-related technology for energy storage and generation as well as use in sensors and actuators. Among graphene-based materials, graphene oxides (GOs) can be described as rising material candidates because they show multiple advantage of ultra-light, strong, flexible, elastic, and porous. In addition, they have excellent properties such as high surface area, robust mechanical strength, resistive chemical behavior, and scaffolds with high conducivity. In this presentation, we describe the simple synthesis of ultralow-density 3-dimensional reduced graphene oxide (rGO) foams that show high electrical conductivity and excellent compressibility for the applicaion of lithium batteries. The rGO foams are synthesized using the combination of hydrothermal and thermal annealing method in which hexamethylenetetramine is employed. We confirm that the N-binding configurations of rGO foams increase as evidenced by the change in pyridinic-N/quaternary-N ratio. The conductivity of this graphene foam is almost 12 S/m at 0 strain, whereas the conductivity is ≈704 S/m at the compressive strain (≈80%), which is comparable to previous reported any 3D sponge-like low-density carbon materials. The foam also has excellent hydrophobicity (contact angle on water surface: ≈137°) and shows selective absorption for organic solvents and oils. The compressive modulus of the rGO foam is higher than that of other carbon-based foams. This graphene foam is the simplified, light-weight architecture allowing for large mass loading of guest materials. Our graphen foam has unique electrical and mechanical properties due to the presence of N-doped monolithic graphene, and can be suitable for the use in electrodes for lithium batteries, fuel cells, energy absorption, energy storage, and sensing applications. * K.-Y. Chun & J. Oh are equally contributed as corresponding authors in this study .

Hierarchical porous N-doped graphene foams with superior oxygen reduction reactivity for polymer electrolyte membrane fuel cells

Oxygen reduction reaction (ORR) is one of the most important processes in energy conversion and conservation such as in fuel cells, metal–air batteries and water-splitting devices. In this work, hierarchical porous N-doped graphene foams (HPGFs) functioned by a transition metal were successfully prepared using silica nanoparticles as a template. The introduction of a silica template and a transition metal provided HPGFs with a large specific surface area (918.7m2/g) and abundant active sites. By selecting proper nitrogen precursors (cyanamide, melamine and urea), HPGFs exhibit excellent ORR catalytic activity in 0.1M KOH with a high onset potential of 1.03V and a limiting current of ∼9mAcm−2, even better than that of commercial Pt/C catalysts at the same loading. Surprisingly, they show superior catalytic activity in an acidic medium with an onset potential of 0.81V and a limiting current reaching ∼10mAcm−2. Furthermore, the catalysts deliver good methanol tolerance and excellent long term durability after 5000 cycles of accelerated durability tests in both acidic and alkaline solutions, much better than that of a commercial Pt/C catalyst. Very inspiring cell performance was observed with HPGF-1 catalyst upon integration into a zinc–air battery. Our study presents an experimental realization of rationally designing a highly efficient ORR electrocatalyst for electrochemical energy conversion systems particular to fuel cells and metal–air batteries.

Ultrafast Synthesis of Multifunctional N-Doped Graphene Foam in an Ethanol Flame.

A hard template method to prepare N-doped graphene foams (NGF) with superfast template removal was developed through a pyrolyzing commercial polyurethane (PU) sponge coated with graphene oxide (GO) sheets in an ethanol flame. The removal of the template was fast and facile, and could be completed in less than 60 s in an open environment. The synthesized graphene foams consisted of a unique structure of 3D interconnected hollow struts with highly wrinkled surfaces, and the morphology of the hollow struts could be tuned by controlling the GO dispersion concentration. The foams showed high hydrophobicity and were used as absorbents for a variety of organic solvents and oils. The unique NGF structure afforded a high absorption rate and capacity, and a remarkable 98.7% pore volume of the foam could be utilized for absorption of hexane, exhibiting one of the highest capacity values among existing absorptive counterparts. The N-doping brought higher capacitive performance than conventional graphene foams prepared by chemical vapor deposition on nickel foam templates. The NGFs also displayed high elasticity and could recover completely after 50% compressive strain. Owing to easy availability and reduction environment of the flame, complete thermal decomposition of the PU sponge and highly porous open-cell structure, and flame resistance of the graphene foam, the present flame method was demonstrated to be a simple, effective, and ultrafast approach to fabricate ultra-low-density NGFs with good electromechanical response, excellent organic liquid absorption, and high-energy dissipation capabilities.

Tuning Surface Wettability and Adhesivity of a Nitrogen‐Doped Graphene Foam after Water Vapor Treatment for Efficient Oil Removal

An environment‐friendly water vapor treatment for realizing a highly hydrophobic (contact angle ≈147.5°) and oleophilic N‐doped graphene foam (NGF) for efficiently removing oil from oil/water emulsions is presented. 3D porous networks of NGF with high N content are prepared by subjecting a mixture of graphene oxide and 5 vol% pyrrole to a hydrothermal process; the mixture is then freeze‐dried and annealed under a N2 atmosphere. The surface wettability and adhesivity are tuned through water vapor treatment by forming a low‐surface‐energy hydrocarbon layer, with no chemical modification. The effectiveness of the hydrophobic/oleophilic NGF in removing oil from an oil/water emulsion is demonstrated.

High-performance sodium ion batteries based on a 3D anode from nitrogen-doped graphene foams.

A 3D N-doped graphene foam with a 6.8 at% nitrogen content is prepared by annealing a freeze-dried graphene oxide foam in ammonia. It is used as an anode in sodium ion batteries to deliver a high initial reversible capacity of 852.6 mA h g(-1) at 1 C between 0.02 and 3 V with a long-term retention of 69.7% after 150 cycles.

Facile preparation of N-doped mesocellular graphene foam from sludge flocs for highly efficient oxygen reduction reaction

Sludge flocs (SF) from environmental waste were used to prepare high-quality N-doped mesocellular graphene foam (SF-NMGF)viaa simple one-step pyrolysis method. The SF-NMGF had a high electrocatalytic activity, operational stability and methanol-tolerance in the ORR.

3-Dimensional porous N-doped graphene foam as a non-precious catalyst for the oxygen reduction reaction

Nitrogen-doped graphene materials have been demonstrated as promising alternative catalysts for the oxygen reduction reaction (ORR) in fuel cells and metal–air batteries due to their relatively high activity and good stability in alkaline solutions.

Filling the voids of graphene foam with graphene "eggshell" for improved lithium-ion storage.

Highly porous, N-doped graphene foam is synthesized by chemical vapor deposition process on nickel foam. The voids of the graphene foam can be filled with curved graphene sheets by impregnating the nickel foam template with micrometer-sized nickel powder. Subsequent etching of nickel produces a graphene "eggshells"-in-graphene foam structure. The reversible capacity of such graphene foam when used as anode in lithium ion battery is improved by the presence of graphene "eggshells", as compared to the unfilled foam. The improvement is attributed to the higher rate of lithium diffusion, better buffering of strain associated with lithiation/delithiation and higher volumetric energy density of the unique eggshell-in-graphene foam structure.

Dually functional, N-doped porous graphene foams as counter electrodes for dye-sensitized solar cells.

A series of nitrogen-doped porous graphene foams (NPGFs) have been prepared by hydrothermally treating a mixed solution of graphite oxide (GO) and ammonia. The NPGFs are used as the counter electrode (CE) material for dye-sensitized solar cells (DSCs) in conjunction with the conventional iodide-based electrolyte and the recently developed sulfide-based electrolyte. Tafel-polarization tests and electrochemical impedance spectroscopic (EIS) measurements confirmed that the NPGFs work efficiently in both electrolyte systems, and under air mass (AM) 1.5G 100 mW cm(-2) light illumination, optimal efficiencies of 4.5% and 2.1% were obtained for the iodide-based electrolyte and sulfide-based electrolyte, respectively. To the best of our knowledge, this is the first study on N-doped graphene CEs in conjunction with sulfide-based electrolytes and therefore, the current results are deemed to provide new insights into developing novel low-cost and metal-free CEs for DSCs.