Porous N-doped Graphene Research Articles

Composition-Graded Cu–Pd Nanospheres with Ir-Doped Surfaces on N-Doped Porous Graphene for Highly Efficient Ethanol Electro-Oxidation in Alkaline Media

Tuning the compositions and structures of Pd-based nanomaterials and their supports has shown great potentials in facilitating the sluggish ethanol oxidation reaction (EOR) in alkaline direct ethan...

Biomass-derived highly porous nitrogen-doped graphene orderly supported NiMn2O4 nanocrystals as efficient electrode materials for asymmetric supercapacitors

Herein, three-dimensional N-doped porous graphene materials (3DPNG) are successfully synthesized by potassium ferrate (K2FeO4) activation and graphitization using biomass-loofah as carbon source and dicyandiamide as nitrogen source. Furthermore, the mesoporous structure and defects on the surface of 3DPNG can regulate the in-situ growth of NiMn2O4 nanocrystals formation NiMn2O4/3DPNG composite and achieve conductive networks effectively, which not only make electrolyte ions contact with internal NiMn2O4 nanoparticles, but also provide a good electron transport path for electrochemical reaction. Detailed electrochemical characterization indicate that the NiMn2O4/3DPNG electrode exhibits a specific capacitance as high as 1308.2 F g−1 at a current density of 1 A g−1, demonstrates good rate characteristics of 77.9% when current density increased to 15 A g−1. The calculation of contribution rate of pseudocapacitance demonstrate that the behavior of electrode is combining diffusion property and pseudocapacitive property. Besides, a asymmetric supercapacitor (ASC) is assembled using NiMn2O4/3DPNG as positive electrode, 3DPNG as negative electrode, which displays excellent cyclic stability (91.6% retention after 10,000 cycles) and high energy density (45.25 Wh kg−1 at the power density of 11380 W kg−1), implying the great potential application of biomass-derived carbon materials in supercapacitors.

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.

Positive Effect of Induced Hydrophobicity in 3D N-Doped Porous Graphene Towards ORR Activity Under Acidic Condition

The less activity and durability of non-noble transition metal based ORR catalysts are bringing the metal-free catalysts derived from carbon allotropes on high demand. The pristine graphene is an electroneutral material and inactive towards the catalytic ORR reaction however the alteration of its electronic property with heteroatom doping makes it active towards electrocatalysis.[ 1 , 2 ] In addition, nitrogen doping is reported to be the most effective way to enhance the catalytic properties of nitrogen-doped graphene (NGr) which creates ORR active center at a nearby carbon atom. Previously reported experimental and theoretical results prove that the N-doped graphene with 3D morphology and doped pyridinic-N are the primary reason for the higher activity of N-doped graphene.[ 1 , 3 ] Taking into account the importance of nitrogen doping in graphene, here we have prepared the 3D N-doped reduced graphene oxide by using NaCl crystals as a structure directing agent. In addition, the fundamental understanding of the ORR at the catalyst surface is a major confront which is hindering the improvement of catalyst performance under operating conditions of fuel cell.[4] Moreover, the catalyst surface wettability is considered to be the most significant factor, which directly reflects from the O2 storage and activation by the active biological molecules such as hemoglobin, laccase, etc. Here, we introduced the role of catalysts surface hydrophobicity created by induced defects towards the ORR reaction in acidic medium. We control the hydrophobicity of the catalyst surface by using NaCl crystals as a spacer and defect creator during the preparation of 3D N-doped porous graphene. The physical and electrochemical characterizations of the prepared catalysts revealed the role of surface hydrophobicity towards the triggering of ORR reaction at low overpotential by capturing O2 near to the reaction centers. The catalyst with underwater Wenzel-Cassie (UWC) coexistent state of surface hydrophobicity has started ORR at lower overpotential (onset potential 0.85 VRHE) than the catalyst with underwater Wenzel (UW) state (0.57 VRHE) in acidic medium. The adopted method for the synthesis of 3D porous N-doped graphene catalyst involves NaCl crystals acts as a structure directing agent to get 3D NrGO morphology (Fig. 1a). The used NaCl crystals also help in the introduction of localized defects in the graphene framework during the synthesis process. The prepared catalyst NrGO/NaCl shows a low overpotential and high current density compared to the NrGO, mainly due to the induced surface hydrophobicity involved in O2 storage, high concentration of doped pyridinic-N and the 3D graphene morphology. Fig. 1b shows the comparative Tafel analysis of NrGO and NrGO-NaCl samples displaying comparable ORR activity of the sample prepared by using NaCl as a template with the state-of-the-art (Pt/C) catalyst. Furthermore, we are now trying to demonstrate the effect of catalyst surface hydrophobicity of metal-free N-doped graphene in the real time PEMFCs application. It is believed that the induced catalyst surface hydrophobicity will be involved in prevention of water flooding problem faced in the PEMFCs operation.

Self-assembly of 3D MnO2/N-doped graphene hybrid aerogel for catalytic degradation of water pollutants: Structure-dependent activity

A novel hybrid architecture of 3D MnO2 nanosheet/N-doped graphene aerogel (S-MnO2/NGA) was controllably fabricated by a facile hydrothermal process and applied in peroxymonosulfate (PMS) activation for catalytic degradation. The catalytic efficiency of S-MnO2/NGA is notably higher than MnO2 nanotube/NGA (T-MnO2/NGA), NGA and MnO2 samples as well as some other conventional catalysts. The reaction rate constant (k) and activation energy for ibuprofen oxidation on S-MnO2/NGA are 0.149 min−1 and 10.2 kJ/mol, respectively. The intimate interactions between 2D MnO2 nanosheet and 3D porous N-doped graphene aerogel are beneficial for synergistically enhancing the charge transfer and shortening the diffusion pathway of pollutants to promote mass transport, thus exerting an astonishing enhancement in the catalytic activities. Electron paramagnetic resonance (EPR) spectra and quenching tests verified that both hydroxyl (OH) and sulfate radicals (SO4−) were generated, while SO4− is the major reactive species responsible for ibuprofen oxidation. The positively linear correlation between the k values and pore volume of S-MnO2/NGA indicates that the 3D interconnected framework provides shorter pathways and more active sites for pollutant diffusion and oxidation. This approach contributes to a better understanding of the structure-activity relationship of 3D graphene-based aerogels in advanced oxidation processes (AOPs).

A 2D/2D graphitic carbon nitride/N-doped graphene hybrid as an effective polysulfide mediator in lithium–sulfur batteries

A heterostructured host composed of porous g-C3N4 and N-doped graphene was fabricated by a template-free strategy. The hybrid display excellent cyclability and high coulombic efficiency due to the enhanced polysulfide anchoring-conversion capability.

A synergetic strategy for an advanced electrode with Fe3O4 embedded in a 3D N-doped porous graphene framework and a strong adhesive binder for lithium/potassium ion batteries with an ultralong cycle lifespan

The chemical blowing strategy to fabricate novel Fe3O4 nanoparticles decorated 3D N-doped porous graphene for high-performance LIBs and KIBs.

Facile one-pot synthesis of porous N-doped graphene based NiO composite for parabens removal from wastewater and its reusability

Facile one-pot synthesis of porous N-doped graphene based NiO composite for parabens removal from wastewater and its reusability

High-intensity compact ultrasound assisted synthesis of porous N-doped graphene thin microsheets with well-dispersed near-spherical Ni2P nanoflowers for energy storage

Severe restacking of single-atom-thick two-dimensional graphene and too long ion diffusion path in a thick three-dimensional porous graphene film are both main current problems limiting performance maximization of graphene as an energy storage material. Herein, we report an advance toward the design and fabrication of novel hierarchically porous N-doped graphene thin microsheets (PNGTMSs) with a honeycomb-like network structure allowing good dispersion of near-spherical Ni2P nanoflowers (NFs) by high-intensity compact ultrasound assisted technique. New insights into ultrasonic activation inducing a preferential self-assembly in a planar direction are proposed. High porosity and thin thickness of <500 nm allow the whole interior of isolated microsheets to be ion-accessible, which endows PNGTMSs with advantages of both two-dimensional and three-dimensional graphene as well as enhanced electrical conductivity. Combined with Ni2P nanosheet-built NFs and their good dispersion as well as rich exposed interfaces, Ni2P-PNGTMSs exhibits specific capacitance of 1100 F g−1 at 1.0 A g−1. Asymmetric solid-state device delivers an energy density of 39.8 Wh kg−1 (at 450.6 W kg−1) and remarkable cycling stability with 97% capacitance retention after 5000 charge-discharge cycles. This work provides a convenient and scalable strategy for control over graphene nanostructures and their composites for highly enhanced energy storage.

Iron phthalocyanine supported on 3D nitrogen-doped graphene aerogel as an electrocatalyst for non-aqueous Li−O2 batteries

Solid electrocatalysts of iron phthalocyanine (FePc) embedded in 3D porous N-doped graphene aerogel (NGA) are designed and applied as cathode catalysts for non-aqueous lithium-oxygen (Li−O2) batteries. Two composites with different axial bonding types between FePc and NGA, including a coordinate covalent bond (FePc/NGA-c) and non-covalent π−π stacking interaction (FePc/NGA-π), are fabricated by reflux and physical mixing methods, respectively. Systematical characterizations confirmed the FePc/NGA-c composite using axial coordination between FePc and NGA substrate via the FeNC bond exhibited more thermal stability and less stack and aggregation of FePc molecules in the composite. Combining the bifunctional catalytic activity of the FePc molecule with oxygen reduction reaction/oxygen evolution reaction (ORR/OER) processes and a flexible porous 3D structure and N-doping in NGA, the electrochemical test demonstrated both FePc anchored on NGA composites display higher activity as bifunctional catalysts for O2 electrodes in Li−O2 batteries. However, the FePc/NGA-c electrode displays better electrochemical performance than the FePc/NGA-π composite due to the axial covalent connection of the FePc catalyst with NGA substrate, leading to higher electrocatalytic activity and exceptional structural durability during cycling for FePc/NGA-c. This work provides new insight into the steric effect of the coordination bond between FePc and NGA on the electrocatalytic activity of O2 electrodes. These results indicate our unique structural design of FePc/NGA-c using solid FePc axially anchored on NGA via covalent bonding is a promising cathode material for high performance of rechargeable LiO2 batteries.

Nitrogen-doped graphene aerogel with an open structure assisted by in-situ hydrothermal restructuring of ZIF-8 as excellent Pt catalyst support for methanol electro-oxidation

We report an innovative strategy to prepare the porous N-doped graphene aerogel with an open structure and abundant defects by hydrothermal self-assembly of zeolitic imidazolate framework (ZIF)-8 and graphene oxide. The in-situ hydrothermal restructuring of ZIF-8 on graphene sheets plays a key role in the synthesis of the open structure and the uniform N-doping. The dissolution and restructuring of ZIF-8 on graphene oxide obviously suppress the stacking and reunion of graphene sheets to obtain the continuous macroporous structure. Moreover, the introduction of N and Zn creates the abundant N-doped sites and microporous structure. Its unique structure and composition improve the accessible surface area, the mass transfer diffusion, the dispersion and electronic structure of Pt nanoparticles, further resulting in the high catalytic performance of Pt-based catalyst for methanol oxidation reaction (MOR). Its MOR activity is about 1.8 times of commercial Pt/C, and its long cycling durability is improved by about 18.7% compared with commercial Pt/C. This work renders a promising method by utilizing ZIF-8 derivatives to synthesize the excellent N-doped carbon materials for electrochemical applications.

Carbothermal Synthesis of Nitrogen-Doped Graphene Composites for Energy Conversion and Storage Devices.

Metal oxides and carbonaceous composites are both promising materials for electrochemical energy conversion and storage devices, such as secondary rechargeable batteries, fuel cells and electrochemical capacitors. In this study, Fe3O4 nanoparticles wrapped in nitrogen-doped (N-doped) graphene nanosheets (Fe3O4@G) were fabricated by a facile one-step carbothermal reduction method derived from Fe2O3 and liquid-polyacrylonitrile (LPAN). The unique two-dimensional structure of N-doped graphene nanosheets, can not only accommodate the volume changes during lithium intercalation/extraction processes and suppress the particles aggregation but also act as an electronically conductive matrix to improve the electrochemical performance of Fe3O4 anode, especially the rate capability. What's more, by etching Fe3O4@G to remove the iron-based oxide template, porous N-doped graphene composites (NGCs) were prepared and presented abundant pore structure with high specific surface area, delivering a specific capacitance of 172 F·g−1 at 0.5 A·g−1. In this way, Fe2O3 was both template and activator to adjust the pore size of graphene. And the effect of specific surface area and pore size tuned by the Fe2O3 activator were also revealed.

Single Cobalt Atoms Anchored on Porous N-Doped Graphene with Dual Reaction Sites for Efficient Fenton-like Catalysis.

The Fenton-like process presents one of the most promising strategies to generate reactive oxygen-containing radicals to deal with the ever-growing environmental pollution. However, developing improved catalysts with adequate activity and stability is still a long-term goal for practical application. Herein, we demonstrate single cobalt atoms anchored on porous N-doped graphene with dual reaction sites as highly reactive and stable Fenton-like catalysts for efficient catalytic oxidation of recalcitrant organics via activation of peroxymonosulfate (PMS). Our experiments and density functional theory (DFT) calculations show that the CoN4 site with a single Co atom serves as the active site with optimal binding energy for PMS activation, while the adjacent pyrrolic N site adsorbs organic molecules. The dual reaction sites greatly reduce the migration distance of the active singlet oxygen produced from PMS activation and thus improve the Fenton-like catalytic performance.

Hierarchical Porous N-doped Graphene Monoliths for Flexible Solid-State Supercapacitors with Excellent Cycle Stability

N-doped-graphene-assembled (NG-assembled) monoliths with hierarchical porous structure and outstanding electrochemical properties are desired for making high-performance flexible supercapacitors. H...

Free-Standing 3D Porous N-Doped Graphene Aerogel Supported Platinum Nanocluster for Efficient Hydrogen Production from Ammonia Electrolysis

Ammonia oxidation reaction (AOR) is an environmentally friendly electrochemical technology for hydrogen production. Nowadays, exploiting low-costing, high-performance and robust catalysts for AOR is essential to improve the overall efficiency of ammonia electrolysis cell (AEC). Here, we report the synthesis and characterization of a novel free-standing three-dimensional (3D) porous N-doped graphene aerogel (NGA) anchored with Pt nanocluster (Pt/NGA) monolithic material as a high-performance and robust electrocatalyst for hydrogen production from AEC. The NGA substrate was facilely fabricated through a self-assemble process into the randomly arranged 3D porous backbone structure with graphene oxide (GO) and poly(oxypropylene)diamine D400 as precursors in a pure water solvent. Then, the Pt nanocluster-like structures were uniformly dispersed and embedded onto NGA through the simple electrodeposition method. The as-prepared Pt/NGA monolithic materials exhibited a higher ammonia electro-oxidation activity wit...

A high-performance supercapacitor electrode based on N-doped porous graphene

The development of high-performance supercapacitors (SCs) often faces some contradictory and competing requirements such as excellent rate capability, long cycling life, and high energy density. One effective strategy is to explore electrode materials of high capacitance, electrode architectures of fast charge and mass transfer, and electrolytes of wide voltage window. Here we report a facile and readily scalable strategy to produce high-performance N-doped graphene with a high specific capacitance (∼390 F g−1). A symmetric SC device with a wide voltage window of 3.5 V is also successfully fabricated based on the N-doped graphene electrode. More importantly, the as-assembled symmetric SC delivers a high energy density of 55 Wh kg−1 at a power density of 1800 W kg−1 while maintaining superior cycling life (retaining 96.6% of the initial capacitance after 20,000 cycles). Even at a power density as high as 8800 W kg−1, it still retains an energy density of 29 Wh kg−1, higher than those of previously reported graphene-based symmetric SCs.

Construction of porous N-doped graphene layer for efficient oxygen reduction reaction

Graphitic carbon materials have shown great potential for use as high-performance catalysts for electrochemical reactions and devices. In this work, we developed a simple and versatile method for synthesis of porous N-doped graphene layers (NGS) by high-temperature treatment of chitosan film deposited on the graphitic carbon nitride (g-C3N4) nanosheets. In the sandwiched chitosan/g-C3N4/chitosan structure, the g-C3N4 nanosheet served as a substrate for chitosan film. The pyrolysis of this substrate, g-C3N4 nanosheet, prevented the severe agglomeration of as-carbonized chitosan sheets and resulted the porous structure. The BET surface area, micropore volume, nitrogen content and graphitic level of result sample highly depended on the heat-treatment temperature. The NGS synthesized at 1000 °C (NGS-1000) exhibited an ultrahigh specific surface area (1183 m2 g−1) and high nitrogen content (4.12%). Importantly, NGS-1000 exhibited a higher limiting current density (5.8 mA cm−2) and a greater stability than the commercial Pt/C electrocatalyst in alkaline media for oxygen reduction reaction (ORR). Such excellent electrocatalytic performance can be explained by a balanced combination of appropriate nitrogen doping level, the degree of graphitization, porous structure, and high specific surface area.

A Top-Down Strategy toward SnSb In-Plane Nanoconfined 3D N-Doped Porous Graphene Composite Microspheres for High Performance Na-Ion Battery Anode.

Engineering of 3D graphene/metal composites with ultrasmall sized metal and robust metal-graphene interfacial interaction for energy storage application is still a challenge and rarely reported. In this work, a facile top-down strategy is developed for the preparation of SnSb-in-plane nanoconfined 3D N-doped porous graphene networks for sodium ion battery anodes, which are composed of several tens of interconnected empty N-graphene boxes in-plane firmly embedded with ultrasmall SnSb nanocrystals. The all-around encapsulation (plane-to-plane contact) architecture that provides a large interface between N-graphene and SnSb nanocrystal not only effectively enhances the electron conductivity and structural integrity of the overall electrode, but also offers excess interfacial sodium storage, thus leading to much enhanced high-rate sodium storage capacity and stability, which has been proven by both experimental results and first-principles simulations. Moreover, this top-down strategy can enable new paths to the low-cost and high-yield synthesis of 3D graphene/metal composites for applications in energy-related fields and beyond.

Stable silicon/3D porous N-doped graphene composite for lithium-ion battery anodes with self-assembly

We fabricate a novel 3D N-doped graphene/silicon composite for lithium-ion battery anodes, with Si nanoparticles uniformly dispersed and thoroughly embedded in the N-doped graphene matrix. The favorable structure of the composite results in a BET surface area and an average mesopore diameter of 189.2m2g−1 and 3.82nm, respectively. The composite delivers reversible capacities as high as 1132mAhg−1 after 100 cycles under a current of 5Ag−1 and 1017mAhg−1 after 200 cycles at 1Ag−1, and exhibits an improved rate capability. The present approach shows promise for the preparation of other high-performance anode materials for lithium-ion batteries.

Efficient and Durable Oxygen Reduction Electrocatalyst Based on CoMn Alloy Oxide Nanoparticles Supported Over N-Doped Porous Graphene

Transition metal oxide derived materials are very important for various applications, such as electronics, magnetism, catalysis, electrochemical energy conversion, and storage. Development of efficient and durable catalysts for the oxygen reduction reaction (ORR), an important reaction in fuel cells and metal–air batteries, is highly desirable. Moreover, the futuristic catalysts for these applications need to be cost-effective in order to ensure a competitive edge for these devices in the energy market. This article describes the synthesis of a cost-effective and efficient electrocatalyst for ORR. It is based on supporting CoMn alloy oxide nanoparticles on N-doped porous graphene through a simple and scalable microwave irradiation method. Microwave irradiation was found to be very crucial for the fast creation of pores in the graphene framework with a concomitant formation of the CoMn alloy oxide nanoparticles. A series of catalysts have been synthesized by varying the Co:Mn ratio, among which, the one wi...