N-doped Reduced Graphene Oxide Aerogel Research Articles

Mechanism of high-quality N-doped reduced graphene oxide aerogel synthesis for dye-sensitized solar cells

Mechanism of high-quality N-doped reduced graphene oxide aerogel synthesis for dye-sensitized solar cells

Customized design of nZVI supported on an N-doped reduced graphene oxide aerogel for microwave-assisted superefficient degradation of imidacloprid in wastewater

High-performance and energy-saving microwave (MW)-assisted catalysts are of great significance for MW-assisted treatments of wastewater. Herein, a novel nitrogen-doped reduced graphene oxide aerogel with supported nanoscale zero-valent iron (nZVI@N-rGOA) was successfully synthesized and used in the MW-assisted removal of imidacloprid (IMI) from wastewater. The resulting nZVI@N-rGOA had an open pomegranate-like multicompartment structure consisting of wrinkled flaky reticular N-rGOA walls and embedded nZVI particles, and the nZVI@N-rGOA/MW system rapidly eliminated nearly 100% of the IMI in a 10 mg/L solution within 2 min. The highly efficient MW-assisted catalytic degradation of IMI resulted from synergistic effects, including the nZVI active centres, pyridinic N sites and open pomegranate-like multicompartment structures, which facilitated MW harvesting, mass transfer of the reactants and generation of heat, electrons, holes and •OH radicals. Accordingly, the localized surface plasmon resonance and electron transfer processes enabled catalytic oxidations/reductions, respectively. This work provides a novel paradigm for designing MW-assisted catalysts for wastewater treatment.

NiO/NiFe2O4@N-doped reduced graphene oxide aerogel towards the wideband electromagnetic wave absorption: Experimental and theoretical study

Constructing the ferromagnetic N-doped reduced graphene oxide aerogel (N-rGA) with broadband and low filler loading is essential for absorbing electromagnetic waves (EMWs). In this work, an unique hierarchical structure of NiO/NiFe2O4 (NFO) with specific porous derived from NiFe layered double hydroxide (LDH) and N-rGA composite is successfully prepared through a facile hydrothermal method and freeze-drying technique. The NiO/NFO embedded into N-rGA (NNGA) possesses a hierarchical porous structure, abundant defects, and multiple interfaces, which can significantly enhance the EMW absorption capability of the composite. Here, when the mass ratio of NiO/NFO to N-rGA is 1:2.5, NNGA-2 exhibits excellent EMW absorption property, and its minimum reflection loss (RLmin) can reach −57.7 dB with an effective absorption bandwidth (EAB) of 6.58 GHz (10.34–16.92 GHz), appearing at 1.93 mm. Besides, NNGA-3 manifests a suitable EMW absorption property in a low-frequency band. To ulteriorly expose the inner EMW absorption mechanism of composites, the N-doped reduced graphene oxide (N-rGO) layer is constructed following the Lerf–Klinowski model, which uses a 2 × 2 unit cell of graphene to simulate the effects of polarization of N-rGA in our experiment. The combination of experimental and theoretical research clarified the mechanism of NNGA composites, indicating that NNGA composites can develop a novel route to build a 3D hierarchical porous structure to promote EMW absorption abilities.

Achieving super-broad effective absorption bandwidth with low filler loading for graphene aerogels/raspberry-like CoFe2O4 clusters by N doping

A unique three-dimension (3D) porous network structure where N-doped reduced graphene oxide aerogels (N-rGA) are decorated by raspberry-like CoFe2O4 (CFO) clusters. Super-broad effective microwave absorption bandwidth (7.28 GHz) of the CFO/N-rGA composite is obtained at 2.53 mm by changing N contents. Here, the dipolar relaxation loss and conduction loss are highly sensitive to the presence of pyridinic, pyrrolic and graphitic N in the CFO/N-rGA composites. A minimum reflection loss of the CFO/N-rGA composites reaches up to −55.43 dB at 15.36 GHz with a matching thickness (2.3 mm) and low filler loading (10 wt%). Its effective absorption bandwidth completely covers X-band from 7.76 to 12.72 GHz at 3.3 mm. The high-efficiency microwave absorption of the composites mainly results from the enhanced polarization relaxation, the specific design of conductive network and the superior impedance matching. This study offers a promising technical route to explore new N-doped magnetic/dielectric composites as ideal microwave absorbers.

Carbon fibers assisted 3D N-doped graphene aerogel on excellent adsorption capacity and mechanical property

In order to improve structural stability of aerogel, supported N-doped reduced graphene oxide aerogels are prepared by introducing fiber materials (biomass cellulose and carbon fibers) via self-assembly method. Thereinto, N-doped carbon fibers/reduced graphene oxide aerogel exhibits ultra-light density (7.19 mg/cm3), high specific surface area (329.6 m2/g), excellent superhydrophobicity, high adsorption capacity (206.38 g/g), which is superior to most reported cellulose aerogels. Moreover, regardless of multiple heating or squeezing cycles, adsorption capacity of this aerogel is also more than 90 %. In addition, N-doped carbon fibers/reduced graphene oxide aerogel shows good mechanical compressive property and thermal stability, which contributes to high-valued utilization in practice.

CoFe2O4/N-doped reduced graphene oxide aerogels for high-performance microwave absorption

Nowadays, to solve electromagnetic radiation issues, an urgent demand is to develop high-performance microwave wave absorption materials with lightweight, broad bandwidth and strong absorbing capacity. In this work, by embedding CoFe2O4 (CFO) nanoparticle into N-doped reduced graphene oxide (N-rGO) aerogels, a unique CFO/N-rGO aerogel microwave wave absorber with a 3D porous architecture is synthesized via a facile solvothermal method and lyophilization technique. Impressively, the as-synthesized N-rGO aerogels exhibit typical ferromagnetic behavior. The electromagnetic parameters of CFO/N-rGO aerogels can be immensely improved by tuning the additive amount of CoFe2O4 nanoparticle. An optimal microwave absorption performance is achieved when the mass ratio of graphene oxide (GO) to CoFe2O4 is 1:2. Here, a strong reflection loss (RL) reaches −60.4 dB at 14.4 GHz with a thickness of 2.1 mm and a low filler loading ratio of 20 wt%. Further, the effective absorption bandwidth (RL < −10 dB) can be up to 6.48 GHz (11.44–17.92 GHz) with a thickness of 2.2 mm. Notably, at only 3 mm, its effective absorption bandwidth can completely cover X-band. The superior microwave wave absorption performance of as-synthesized CFO/N-rGO aerogels is attributed to the specific surface morphology and porous structures, leading to the multiple scattering and reflecting, interfacial polarization and optimal impedance matching. This work not only provides a deep insight on tuning microwave absorption performance of ferrite/N-rGO aerogels, but also offers a new route to design high-performance magnetic/dielectric absorbers.

N-doped reduced graphene oxide aerogels containing pod-like N-doped carbon nanotubes and FeNi nanoparticles for electromagnetic wave absorption

Lightweight and low filler loading of electromagnetic wave absorption materials remain a huge challenge under the premise of strong absorption and broad absorption band. Here, we offer a facile strategy to prepare the ultralight self-supported N-doped reduced graphene oxide aerogels containing pod-like N-doped carbon nanotubes and FeNi@N-doped graphene layer core-shell nanoparticles for high-performance electromagnetic wave absorbing materials. The mass density of the ultralight aerogels is 0.0131 g cm−3, greatly lower than those of activated carbons. With a filling loading of only 10 wt% and the matching thickness of 2.0 mm, the minimal reflection loss of aerogels reaches −39.39 dB at 13.28 GHz. When the matching thickness is smaller than 2.0 mm (1.6–2.0 mm), the minimal reflection loss values of the optimized aerogels can still exceed −20 dB superior to most of reported electromagnetic wave absorption counterparts. Moreover, its maximum effective absorption bandwidth is up to 4.7 GHz at the matching thickness of merely 1.8 mm. The excellent performance of the ultralight bimetal-based aerogels mainly derives from increased dielectric loss, better matching impedance and larger specific surface area. It could be believed our designed ultralight self-supported aerogels can be promising candidates for lightweight absorbers with strong attenuation abilities.

Ru supported on N-doped reduced graphene oxide aerogels with different N-type for alcohol selective oxidation

Reduced graphene oxide aerogels doped with nitrogen have been prepared via two different strategies, namely, direct doping of rGO nanosheets with NH3 (GANH3) and coating the rGO nanosheets with an N-containing amorphous carbon derived from polydopamine (GADA). Both methods lead to comparable N/C ratios (3.4–4.7 %) but the relative contribution of quaternary nitrogen is 30 % for GADA while only 15 % for GANH3. Moreover, the N is incorporated within graphene lattice for GANH3 while it is within an amorphous carbon layer on top of graphene nanosheets for GADA. The Ru catalyst supported on the aerogels exhibited very distinct performance in the selective oxidation of benzyl alcohol depending on the support material despite having similar Ru particle size. The best performance for 5 wt% Ru on GADA can be explained by the larger reduction extent of Ru and the more hydrophobic surface. The open macroporosity of the aerogel makes it an excellent platform for using as structured catalyst in a continuous flow process.

Insight into the Effect of Cationsin Ionic Liquidelectrolytes on Charge Storage Capacity of High-Performance Supercapacitors of N-Doped Graphene Aerogels

Even though room temperature ionic liquids (RTILs) have been widely used as electrolytes in electrochemical applications including supercapacitors and batteries, the behavior of RTILs at charged interfaces is still not well understood. The cations are expected to have a significant effect on physical properties (i.e., electrolyte viscosity and conductivity) as well as the electrochemical performance.1, 2 For a fully understanding of the cation-effect, herein, we provide a systematic study of the influence of the physical properties of RTIL electrolytes with different structures of cations on the electrochemical performance of carbon-based supercapacitors along with a molecular dynamics (MD) simulation. N-doped reduced graphene oxide aerogel (N-rGO) supercapacitors are incorporated with RTIL electrolytes consisting of cyclic nitrogen-based cations i.e., imidazolium, which are connected with a variable length of alkyl chains (i.e., ethyl, butyl and hexyl). Changing these cations do not widen the potential window of the ionic liquid; however, they do affect the electrochemical performance in term of specific capacitances and specific energies of the supercapacitor. We found that the heterocycles of RTILs affect ionic conductivity while the alkyl chain plays a role in ion diffusion. In this perspective, we hope that this fundamental study may pave the way to design the structure of RTIL electrolyte for high energy storage performance.

Addition of Redox Additive to Ionic Liquid Electrolyte for High-Performance Electrochemical Capacitors of N-Doped Graphene Aerogel

To enhance the specific energy of electrochemical capacitors, several methods have been introduced including complex electrode modification as well as asymmetric cell development. Herein, an alternative approach to enhance both specific energy and power of N-doped reduced graphene oxide aerogel electrochemical capacitor via the introduction of hybrid redox electrolyte is proposed. The electrochemical properties of the hybrid electrolyte composing of 1-butyl-1-methylpyrrolidinium dicyanamide ionic liquid with 100 mM ferrocene methanol redox additive were studied via cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy. The combination between a unique nanostructure of N-doped reduced graphene oxide aerogel and novel hybrid electrolyte results in an excellent specific capacitance and specific energy of 112.1 F g−1 and 34.2 Wh kg−1, respectively, as compared to 76.7 F g−1 and 23.5 Wh kg−1 of the neat 1-butyl-1-methylpyrrolidinium dicyanamide electrolyte. The remarkable improvements can be explained by the emerging of the Faradaic-redox activity of the ferrocene methanol at the electrode-electrolyte interface. This simple approach could demonstrate another feasible route to improve the performance of ionic liquid-based electrochemical capacitors.

Thin-Film Photoelectrode of p-Type Ni-Doped Co3O4 Nanosheets for a Single Hybrid Energy Conversion and Storage Cell

A thin-film Ni0.07Co2.93O4 p-type semiconductor finely tuned with better electronic conductivity and electrochemical activity than NiO and Co3O4 is proposed as a new photoelectrode of single asymmetric hybrid energy conversion and storage cell (HECS). Photoactive Ni0.07Co2.93O4 and N-doped reduced graphene oxide aerogel (N-rGOAE) were used as positive and negative electrodes of the HECS. Under light illumination, the Ni0.07Co2.93O4 can generate a hole (photogenerated carrier, Ni0.07Co2.93O4+) at the valence band (VB) and a photoelectron at the conduction band (CB) via the photoelectric effect. During charging, the active hole (Ni0.07Co2.93O4+) of the positive electrode can chemically react with OH− and H2O forming CoO(OH) and NiO(OH). This process can enhance the redox mechanism leading to the charge storage performance of the Ni0.07Co2.93O4 electrode since OH− can easily react with the active Ni0.07Co2.93O4+ hole having the lower energy level of the VB when compared with the electrode under the dark condition. The changes in the oxidation state of Ni and Co in Ni0.07Co2.93O4 were fundamentally investigated by an in situ electrochemical X-ray absorption spectroscopy. The electrochemical performance of Ni0.07Co2.93O4//N-rGOAE HECS can be enhanced under light illumination about 1.9-fold higher than that under dark condition. The HECS device may be useful for renewable energy applications.

Asymmetric hybrid energy conversion and storage cell of thin Co3O4 and N-doped reduced graphene oxide aerogel films

Although batteries and supercapacitors can store electrical energy, they cannot convert energy like solar cells. Here, we introduce a new asymmetric hybrid energy conversion and storage (HECS) cell consisting of thin photoactive cobalt oxide (Co3O4) film with a thickness of 1 μm coated on the fluorine-doped tin oxide (FTO) glass as the positive electrode and thin N-doped reduced graphene oxide aerogel (N-rGOAE) film with a thickness of 10 μm coated on the FTO glass as the negative electrode. The HECS cell can convert light to electricity, which is subsequently stored within its electrode materials. The as-fabricated asymmetric HECS cell of Co3O4//N-rGOAE thin films exhibits 140% higher specific capacitance under red LED light illumination than that under dark condition and provides a specific energy and a specific power of ca. 3.5 Wh kg−1 and ca. 7000 W kg−1, respectively. The Co3O4 can absorb all visible light spectrum and excite its valence electron to the conduction band via its indirect band gap (1.45 eV) so-called the photovoltaic effect. Whilst, the N-rGOAE can balance all charges generated at the Co3O4 positive electrode via the electrochemical double-layer capacitance. The asymmetric HECS of Co3O4//N-rGOAE may be an ideal solution for future renewable and sustainable energy.

A Single Energy Conversion and Storage Device of Cobalt Oxide Nanosheets and N-Doped Reduced Graphene Oxide Aerogel

The hybridization between energy conversion and energy storage materials in a single cell (HECS) is proposed in this work. The HECS cell consists of photoactive cobalt oxide (Co3O4) positive electrode as the energy conversion material and N-doped reduced graphene oxide aerogel (N-rGOAE) as the energy storage material. The photoactive Co3O4 nanosheets were prepared by using various calcination temperatures for which the in situ electrochemical XAS suggests that the Co3O4 nanosheets calcined at 300oC exhibit the highest change in oxidation state compared to other conditions. The HECS cell using photoactive Co3O4 film calcined at 300oC and N-rGOAE exhibits 1.7-fold higher specific capacitance under LED light illumination than that of the dark condition. Under white LED light illumination, the photovoltaic effect can be generated in the Co3O4 electrode with electron-hole pairs, while the N-rGOAE can balance all the charges generated from the Co3O4 via both electrochemical double-layer and pseudocapacitive behaviours.

Graphene-Based Materials with Different Morphologies and Structures as Interlayers for High-Performance Lithium-Sulfur Batteries

Lithium-sulfur batteries have recently attracted great attention as the promising candidates for next-generation energy storage devices due to its high theoretical capacity (~1675 mAh g-1), environmentally friendly, and natural abundance. However, the practical application of LSBs is still hindered by the shuttle of soluble lithium polysulfides (LPSs) and low conductivity of sulfur itself causing the poor electrochemical performance and poor cycling stability. In this work, graphene-based interlayers with different morphologies and structures were introduced to trap LPSs and reduce the shuttle effect. The LSB using 3D N-doped reduced graphene oxide aerogel interlayer exhibits the highest specific capacities of 1236.0, 1037.5, 979.7, 835.0, and 345.4 mAh g-1 at the applied current densities of 0.1, 0.2, 0.5, 1.0, and 2.0C, respectively which is higher than other graphene-related interlayers. The synergistic effect between N-doping and 3D frameworks can suppress the LPSs via both chemical adsorption interaction and physical confinement as well as increase the electrical conductivity of the entire electrode.

Addition of Redox Additive to Ionic Liquid Electrolyte for High-Performance Supercapacitors of N-Doped Graphene Aerogel

Even though the electrochemical capacitors could exhibit an impressive specific power as compared to other energy storage systems, their specific energies still limit their superiority in term of battery replacement. Apart from conventional method to improve the specific energy via complex electrode development, here an alternative route to enhance the performance of the N-doped graphene oxide aerogel supercapacitor using a redox active electrolyte was introduced. The effect of ferrocene methanol in 1-butyl-1-methylpyrrolidinium dicyanamide ionic liquid electrolyte as a redox active electrolyte was investigated. The coupling of this new hybrid electrolyte and a unique nanostructure of the N-doped reduced graphene oxide aerogel could exhibit an excellent specific capacitance and specific energy of 112.1 F g-1 and 34.2 Wh kg-1, respectively as compared to 76.7 F g-1 and 23.5 Wh kg-1 of the conventional 1-butyl-1-methylpyrrolidinium dicyanamide ionic liquid electrolyte. These significant improvements are attributed to the enablement of the Faradaic charge transfer contribution within the redox active electrolyte itself. This redox electrolyte could be used in any high-energy supercapacitors.

Graphene-based materials with different morphologies and structures as interlayers for high-performance lithium-sulfur batteries

Lithium-sulfur batteries have attracted much attention for energy storage. However, the shuttle effect causes the poor cycling performance. In this study, we applied a carbon-based interlayer to trap polysulfide to reduce shuttle effect. The carbon-based materials including 3D reduced graphene oxide aerogel, 3D N-doped reduced graphene oxide aerogel, and 2D reduced graphene oxide. The materials were coated on one side of carboxylate-modified carbon fiber paper. The effect of the assemble direction of the coated materials facing in and out of the cathode were investigated. The results showed that the interlayer with 3D N-doped reduced graphene oxide aerogel exhibits superior performance and stability. In addition, the coated material placed face-to-face the cathode can improve the battery performance as compared to another direction.

A Single Energy Conversion and Storage Device of Cobalt Oxide Nanosheets and N-Doped Reduced Graphene Oxide Aerogel

A single hybrid energy conversion and storage (HECS) cell of asymmetric Cobalt oxide (Co3O4)//N-doped reduced graphene oxide aerogel (N-rGOAE) in 6 M KOH is proposed in this work. The Co3O4 serves as a photo-positive electrode material having an energy bang gap of 2.45 eV which can absorb all visible light region. Whilst, the N-rGOAE as a negative electrode material can balance all the charges and excited electrons from the Co3O4 positive electrode due to its interconnected three-dimensional structure with nitrogen doping. Under red LED light source (627 nm = 1.98 eV), the current densities and specific capacitances of the as-fabricated asymmetric Co3O4//N-rGOAE HECS cell are 1.4-fold higher than that under dark condition due to the photovoltaic effect. In addition, the charge storage mechanism and photo-charging behaviour of the Co3O4 electrode were also investigated by in situ electrochemical X-ray absorption spectroscopy and I-V characterization, respectively.

N-doped reduced graphene oxide aerogel for the selective adsorption of oil pollutants from water: Isotherm and kinetic study

N-doped graphene aerogel with a 3D inter-connected network was synthesized using graphene oxide and pyrrole in an aqueous medium with ammonia. Hydrothermal and thermal annealing methods were employed to do it so. The structure and surface properties of the synthesized aerogel were characterized using Fourier Transform Infrared (FTIR) spectroscopy, X-ray Diffraction (XRD), Raman spectroscopy, Field Emission Scanning Electron Microscopy (FE-SEM), XPS, and nitrogen adsorption/desorption measurements. The prepared n-doped aerogel exhibited elevated specific surface area (340m2/g), hydrophobic nature, and excellent adsorption capacity (210g/g for crude oil removal). Adsorbent recyclability was also investigated; it is worth noting that after ten subsequent cycles, only just a negligible decrement in adsorption capacity was observed. Furthermore, the effect of salts and temperature on adsorption capacity was studied. Isotherm and kinetic studies were last examined. The conformity of various adsorption models, including Freundlich, Langmuir, Temkin, and Dubinin–Radushkevich (D–R) to the equilibrium data was evaluated among which Langmuir isotherm model gave the best fitting result. The sorption kinetics data were well described by the pseudo-second-order kinetic model. As a consequence, oil spills adsorption using n-doped graphene aerogel is a relatively cost-effective method which can be scaled up, and it could be a promising material for removal of organic contaminants from water.

Synergic mechanism of adsorption and metal-free catalysis for phenol degradation by N-doped graphene aerogel

3D porous N-doped reduced graphene oxide (N-rGO) aerogels were synthesized by a hydrothermal reduction of graphene oxide (GO) with urea and following freeze-drying process. N-rGO aerogels have a high BET surface of 499.70 m2/g and a high N doping content (5.93–7.46 at%) including three kinds of N (graphitic, pyridinic and pyrrolic). Their high catalytic performance for phenol oxidation in aqueous solution was investigated by catalytic activation of persulfate (PS). We have demonstrated that N-rGO aerogels are promising metal-free catalysts for phenol removal. Kinetics studies indicate that phenol degradation follows first-order reaction kinetics with the reaction rate constant of 0.16799 min−1 for N-rGO-A(1:30). Interestingly, the comparison of direct catalytic oxidation with adsorption-catalytic oxidation experiments indicates that adsorption plays an important role in the catalytic oxidation of phenol by decreasing the phenol degradation time. Spin density and adsorption modeling demonstrates that graphitic N in N-rGO plays the most important role for the catalytic performance by inducing high positive charge densities to adjacent carbon atoms and facilitating phenol adsorption on these carbon sites. Furthermore, the activation mechanism of persulfate (PS) on N-rGO was first investigated by DFT method and PS can be activated to generate strongly oxidative radical (SO4·-) by transferring electrons to N-rGO.

Hybrid Energy Storage of Ni(OH)2-coated N-doped Graphene Aerogel//N-doped Graphene Aerogel for the Replacement of NiCd and NiMH Batteries

Although Nickel–Cadmium (NiCd) and Nickel–metal hydride (NiMH) batteries have been widely used, their drawbacks including toxic Cd and expensive La alloy at the negative electrodes, low energy density (40–60 Wh/kg for NiCd and 140–300 Wh/L for NiMH), low power density (150 W/kg for NiCd and 1000 W/kg for NiMH), and low working potential (1.2 V) limit their applications. In this work, Cd and La alloy were replaced with N-doped reduced graphene oxide aerogel (N-rGOae) providing a hybrid energy storage (HES) having the battery and supercapacitor effects. The HES of Ni(OH)2-coated N-rGOae//N-rGOae provides 1.5 V, a specific energy of 146 Wh/kg, a maximum specific power of 7705 W/kg, and high capacity retention over 84.6% after 5000 cycles. The mass change at the positive electrode during charging/discharging is 8.5 µg cm−2 owing to the insertion/desertion of solvated OH− into the α-Ni(OH)2-coated N-rGOae. At the negative electrode, the mass change of the solvated K+, physically adsorbed/desorbed to the N-rGOae, is 7.5 μg cm−2. In situ X-ray absorption spectroscopy (XAS) shows highly reversible redox reaction of α-Ni(OH)2. The as-fabricated device without using toxic Cd and expensive La alloy has a potential as a candidate of NiCd and NiMH.