Synthesis of in situ N‐, S‐, and B‐doped few‐layer graphene by chemical vapor deposition technique and their superior glucose electrooxidation activity

At present, N‐, S‐, and B‐doped grapheme‐modified indium tin oxide (ITO) electrodes are produced and doping method effect on the glucose electrooxidation is investigated. Firstly, few‐layer graphene is produced by chemical vapor deposition (CVD) method. Then, N, S, and B doping is carried out after graphene produced by CVD to prepare N‐doped, B‐doped, and S‐doped few‐layer graphene. N, S, and B doping is carried out by two different ways as (a) doping after synthesis of few‐layer graphene and (b) in situ doping during few‐layer graphene production. These materials are characterized by X‐ray diffraction, scanning electron microscopy‐energy (SEM), Raman spectroscopy, and X‐ray photoelectron spectroscopy (XPS). One could note that graphene and nitrogen networks are clearly visible from SEM images. Raman spectra show that B, N, and S are doped on few‐layer graphene/ITO successfully. XPS results of graphene, N‐doped graphene, and in situ N‐doped graphene reveal that graphene and nitrogen atoms used in the preparation of the electrodes obtain mainly in their elemental state. Then, these N‐, S‐, B‐doped and in situ N‐, S‐, B‐doped few‐layer graphene materials are coated onto indium tin oxide (ITO) to obtain N‐, S‐, B‐doped and in situ N‐, S‐, B‐doped ITO electrodes for glucose (C₆H₁₂O₆) electrooxidation. C₆H₁₂O₆ electrooxidation measurements are investigated with cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy measurements. As a result, in situ N‐doped few‐layer graphene/ITO electrode displays the best C₆H₁₂O₆ electrooxidation activity with 9.12 mA.cm^?2 current density compared with other N‐, S‐, B‐doped graphene and in situ doped S and B grapheme‐modified ITO electrodes. Furthermore, this current density value for in situ N‐doped few‐layer graphene/ITO is highly above the values reported in the literature. In situ N‐doped few‐layer graphene/ITO electrode is a promising electrode for C₆H₁₂O₆ electrooxidation because it exhibits the best electrocatalytic activity, stability, and resistance compared with other electrodes.     

Doping sp-hybridized B atoms in graphyne supported single cobalt atoms for hydrogen evolution electrocatalysis

Electrochemical water splitting to hydrogen is considered as a promising approach for clean H₂ production. However, developing highly active and inexpensive electrocatalysts is an important part of the hydrogen evolution reaction (HER). Herein, we present a multifaceted atom (sp²-and sp-hybridized boron) doping strategy to directly fine-modify the electronic structures of the active site and the HER performance by the density functional theory calculations. It is found that the binding strength between the Co atom and the B doped graphyne nanosheets can be enhanced by doping B atoms. Meanwhile, the Co@B₁-GY and Co@B₂-GY catalysts exhibit good thermodynamic stability and high HER catalytic activity. Interestingly, the Co@B₂-GY catalyst has an ideal HER performance with the ΔG_H* value of −0.004 eV. Moreover, the d-band center of the Co atoms is upshifted by the sp²-or sp-hybridized B dopants. The concentrations of the sp-hybridized B atoms have a positive effect on the electrons transformation of the Co atoms. The interaction between the H and Co atoms becomes strong with the increase of the concentrations of the sp-hybridized B atoms and thus the corresponding catalysts show sluggish HER kinetics. This investigation could provide useful guidance for the experimental groups to directly and continuously control the catalytic activity towards HER by precisely doping multifaceted atoms.     

Hydrogen adsorption and storage in boron‐substituted and nitrogen‐substituted nano‐carbon materials decorated with alkaline earth metals

Based on ab initio calculations, we have investigated the H₂ adsorption and storage capacity on boron‐substituted and nitrogen‐substituted nano‐carbon materials doped with alkaline earth metal ions (Be²⁺, Mg²⁺, and Ca²⁺) systematically. The calculation results show that the Be²⁺‐decorated, Mg²⁺‐decorated, and Ca²⁺‐decorated carbon‐based materials with B‐substitution and N‐substitution improve the hydrogen storage capacity. H₂ molecules are bound stronger with lighter cations. The adsorption energy of H₂ molecule on the M²⁺‐nano‐carbon complex (M²⁺ = Be²⁺, Mg²⁺, and Ca²⁺) is disproportional to ionic radii of the M²⁺ cations. The interaction between H₂ and M²⁺@nano‐carbon complex is elucidated by Mulliken charge analysis. It is determined that the highest gravimetric density is predicted to be 13.38 and 19.89 wt.% for the B‐substituted and N‐substituted materials, respectively. Copyright © 2015 John Wiley & Sons, Ltd.     

Adsorption of H2S on carbonaceous materials of different dimensionality

The effect of the dimension of carbonaceous systems, from two to zero, on the adsorption strength of H₂S is investigated by density functional theory based methods. To this end, a carbon nanocone (CNC), a (3, 3) carbon nanotube ((3, 3)-CNT), and graphene (G) are chosen as models for zero-, one- and two-dimensional systems, respectively. Pristine G and CNC have low tendency to adsorb H₂S but on the (3, 3)-CNT the molecule adsorbs dissociatively and deforms the surface. The effect of doping the surface of these materials with Ti has also been investigated. The presence of Ti modifies H₂S adsorption capability to the point that it is chemically adsorbed on the three decorated surfaces although H₂S adsorption on Ti decorated graphene appears to be different from two other doped surfaces. Only in this case, the H₂S molecule dissociates and releases hydrogen atoms which form H₂ molecule. The resulting H₂ molecule is physisorbed on the Ti-decorated graphene surface and the S atom adsorbs directly on the Ti atom. The density of states of pristine, Ti decorated and H₂S adsorbed nanostructures demonstrate that the systems change their conductivity and magnetic properties.     

Influence of transition metals Fe,Ni, and Nb on dehydrogenation characteristics of Mg(BH4)2: Electronic structure mechanisms

First principles calculations on Fe, Ni, and Nb doped Mg(BH₄)₂ were carried out to study the influence of dopants on dehydrogenation properties of Mg(BH₄)₂. It was shown that all dopants considered prefer to substitute for Mg with relatively smaller occupation energies comparing to the B substitution and the interstitial occupation. However, the B substitution shows smaller hydrogen dissociation energy than the Mg substitution. Mechanisms that dopants used to improve dehydrogenation properties of Mg(BH₄)₂ are different. For Mg substitution, Fe strongly interacts with one H atoms of the [BH₄] group, distorts its structural stability and therefore lowers the hydrogen dissociation energy, Ni may attract one particular H atom of the [BH₄] group and weakens the interactions between the B and other H atoms reducing the hydrogen dissociation energy, and the Nb however may drive the formation of NbB₂ and improves the dehydrogenation properties as well. In the B substitution, Fe interacts with the one of H atoms and decreases its structure stability, the Ni will attract its neighbor atoms to form a regular group which is almost identical in structure to that of the NiH₄ group in Mg₂NiH₄, and the NbH₂ and MgH₂ are likely to be generated by Nb doping.     

Heteroatom‐doped graphene and its application as a counter electrode in dye‐sensitized solar cells

The most frequently used counter electrode (CE) in dye‐sensitized solar cells (DSSCs) is platinum on fluorine‐doped tin oxide glass. This electrode has excellent electrical conductivity, chemical stability, and high electrocatalytic affinity for the reduction of triiodide. However, the high cost of metallic platinum and the poor electrochemical stability pose a major drawback in the commercial production. This has necessitated a search for a non‐precious metal and metal‐free electrocatalyst that demonstrates better catalytic activity and longer electrochemical stability for practical use in DSSCs. Graphene has been at the centre of attention due to its excellent optoelectronic properties. However, a defect‐free graphene sheet is not suitable as a CE in DSSCs, because of its neutral polarity which often restricts efficient charge transfer at the graphene/liquid interface, irrespective of the high in‐plane charge mobility. Hence, heteroatom‐doped graphene‐based CEs are being developed with the aim to balance electrical conductivity for efficient charge transfer and charge polarization for enhanced reduction activity of redox couples simultaneously. The elements commonly used in chemical doping of graphene are nitrogen, oxygen, boron, sulfur, and phosphorus. Halogens have also recently shown great promise. It has been demonstrated that edge‐selective heteroatom‐doping of graphene imparts both efficient in‐plane charge transfers and polarity, thereby enhancing electrocatalytic activity. Thus, heteroatom‐doped graphene serves as a good material to replace conventional electrodes and enhance power conversion efficiency in DSSCs. The focus is to reduce the cost of DSSCs. This review explores the performance of DSSCs, factors that influence the power conversion efficiency, and various physicochemical properties of graphene. It further outlines current progress on the synthetic approaches for chemical doping (substitutional and surface transfer doping) of graphene and graphene oxide with different heteroatoms in order to fine‐tune the electronic properties. The use of heteroatom‐doped graphene as a CE in DSSCs and how it improves the photovoltaic performance of cells is discussed.     

N‐doped titania powders prepared by different nitrogen sources and their application in quasi‐solid state dye‐sensitized solar cells

Nitrogen‐doped TiO₂ nanocrystalline particles are synthesized by a microwave‐assisted hydrothermal growth method using different amines (Dipropylamine, Diethanolamine and Ammonium hydroxide) as nitrogen sources. Characterization of the nanoparticles was performed with X‐ray diffraction, UV–vis diffuse reflectance spectroscopy, Field Emission Scanning Electron Microscopy and X‐ray Photoelectron Spectroscopy. The prepared N‐doped TiO₂ nanoparticles exhibit pure anatase phase with average diameter of 9 nm and reduced optical energy gap compared to undoped TiO₂. Immobilization of N‐doped and pure TiO₂ nanoparticles on SnO₂:F conductive glass substrates was successfully performed by using doctor‐blade technique and paste of the aforementioned nanoparticles. A series of N‐doped TiO₂ photoelectrodes with varying N dopant source and concentrations were fabricated for quasi‐solid state dye‐sensitized solar cells. The N‐doped solar cells achieve an overall conversion efficiency ranging from 4.0 to 5.7% while undoped TiO₂ showed 3.6%. The basic difference to the electrical performance of the cells is focused to the enhancement in the current density of N‐doped TiO₂‐based cells which was from 11% to 58% compared with undoped TiO₂ cells. Current densities were directly proportional with nitrogen doping level in TiO₂ lattice which differs depending on the amine source nature such as basicity differences, hydrogen bonding abilities and steric inherences. Copyright © 2013 John Wiley & Sons, Ltd.     

Heteroatom (B,N and P) doped porous graphene foams for efficient oxygen reduction reaction electrocatalysis

Heteroatoms (B, N and P) doped porous graphene foams are developed via a hard-templating method. We use boric acid as the precursor of boron source, triphenylphosphine as precursor of phosphorus source, cyanamide as the precursor of nitrogen source and ferrous chloride as the precursor of transition metal to synthesize a series of transition metal iron-modified multi-element doped porous graphene foams catalysts. Our results showed that heteroatoms (B, N and P) doped porous graphene foams exhibited excellent ORR performance. The most efficient one, i.e., PGF-Fe-NBP, received the onset potential of 0.95 V and a half-wave potential of 0.84 V in alkaline medium. Even in acidic medium, PGF-Fe-NBP received the onset potential of 0.85 V and a half-wave potential of 0.68 V. In addition, it also obtained superb electro activities of low H₂O₂% and high electron transfer number in both alkaline and acidic medium. Moreover, we found that iron modification can promote doping amount of heteroatoms and increase the degree of graphitization to form a relatively larger specific surface area for more active sites, thus improving the ORR performance of heteroatoms (B, N and P) doped porous graphene foams. Meanwhile, we systematically compare multi-element doping with that of single-element doping and dual-element doping.     

Photocatalytic hydrogen production from glycerol–water mixture over Pt‐N‐TiO2 nanotube photocatalyst

The effects of several modifications on TiO₂ P25 in producing hydrogen from glycerol–water mixture have been investigated. Prior to further modification, TiO₂ underwent hydrothermal treatment at 130°C for several hours to obtain nanotube shape. TiO₂ nanotubes (TiNT) was then doped with platinum (Pt) and nitrogen (N) by employing photo‐deposition and impregnation method, respectively. SEM and XRD results showed that Pt‐N‐TiNT was successfully obtained as pure anatase crystal structure. The effects of glycerol content to photocatalytic activity of hydrogen production have also been studied, result in 50%v of glycerol as the optimum concentration correspond to the stoichiometric volume ratio of glycerol reforming. The results of photo‐production test showed that TiNT (nanotube) could enhance hydrogen generation by two times compared with unmodified P25 (nanoparticle). Meanwhile, simultaneous modification of TiNT by Pt and N dopants (Pt‐N‐TiNT) lead to activity improvement up to 13 times compared with P25. The output of this study may contribute toward finding an alternative pathway to produce H₂ from renewable resources. Copyright © 2012 John Wiley & Sons, Ltd.     

A first-principle study of calcium-decorated BC2N sheet doped by boron or carbon for high hydrogen storage

Hydrogen adsorption and storage on calcium-decorated BC₂N sheets doped by Boron or Carbon were investigated using the first-principles calculations. Unlike the weak bond between Ca atoms and pristine BC₂N, doping boron or carbon atoms on BC₂N sheet can significantly strengthen the Ca atoms on the BC₂N, especially for BC₂NB_C and BC₂NC_N. It is observed that Ca decorated BC₂NB_C and BC₂NC_N possess strong donation and back-donation of Ca with the sheets, which is responsible for enhanced binding energy to eliminate the clustering problem. Up to four hydrogen molecules can stably attach to a Ca atom with an average adsorption energy of ∼0.3 eV, which is in the range that permits hydrogen recycling at ambient conditions. The Ca decorated BC₂NB_C and BC₂NC_N complexes can work as high-capacity hydrogen storage materials with the practical usable capacities of 8.36 wt% and 8.38 wt%, respectively.     

Preparation of N‐doped graphene‐based electrode via electrochemical method and its application in vanadium redox flow battery

An N‐doped graphene electrode has been prepared by cyclic voltammetric method in 5.0 M of HNO₃ solution on a graphite‐based electrode at room temperature. The modification of the electrode surface with different types of N‐containing groups, such as nitro groups, pyrrolic N, and pyridinic N, has been controlled by changing the scanned potential ranges. The formation of an N‐doped graphene electrode has been confirmed by scanning electron microscopic, atomic force microscopic, X‐ray photoelectron, and Raman spectroscopic methods. The prepared N‐doped graphene‐modified electrodes have been used in positive electrolyte of a vanadium‐based redox flow battery. As positive electrodes, the electrochemically modified electrodes prepared in 5.0 M of HNO₃ solution ?1.0 to (+1.9) and ?0.7 to (+1.9) V had more than 140 and 120 mA/cm² anodic and cathodic peak currents, respectively, in vanadium redox battery. This fast, low‐cost, and environmentally friendly method can be used in many application areas, such as optical devices, (bio)sensors, energy storage materials, and electronic devices.     

Hydrogen dissociation and diffusion on transition metal (= Ti,Zr, V,Fe, Ru,Co, Rh,Ni, Pd,Cu, Ag)-doped Mg(0001) surfaces

The kinetics of hydrogen absorption by magnesium bulk is affected by two main activated processes: the dissociation of the H₂ molecule and the diffusion of atomic H into the bulk. In order to have fast absorption kinetics both activated processed need to have a low barrier. Here we report a systematic ab initio density functional theory investigation of H₂ dissociation and subsequent atomic H diffusion on TM (= Ti, V, Zr, Fe, Ru, Co, Rh, Ni, Pd, Cu, Ag)-doped Mg(0001) surfaces. The calculations show that doping the surface with TMs on the left of the periodic table eliminates the barrier for the dissociation of the molecule, but the H atoms bind very strongly to the TM, therefore hindering diffusion. Conversely, TMs on the right of the periodic table do not bind H, however, they do not reduce the barrier to dissociate H₂ significantly. Our results show that Fe, Ni and Rh, and to some extent Co and Pd, are all exceptions, combining low activation barriers for both processes, with Ni being the best possible choice.     

Influence of the Fe-doping on hydrogen behavior on the ZrCo surface

Ab initio calculations have been carried out to investigate the adsorption, dissociation, and diffusion of atomic and molecular hydrogen on the Fe-doped ZrCo (110) surface. It is found that the adsorption of H₂ on doped surface seems thermodynamically more stable with more negative adsorption energy than that on the pure surface, and the dissociation energy of H₂ on doped surface is much bigger therefore. However, compared with the pure system, there are fewer adsorption sites for spontaneous dissociation. After dissociation, the higher hydrogen adsorption strength sites would promote the H atom diffusion towards them where they can permeate into the bulk further. Furthermore, the ZrCo (110) surface possesses much higher hydrogen permeability and lower hydrogen diffusivity than its corresponding ZrCo bulk. Moreover, further comparison of the present results to analogous calculations for pure surface reveals that the Fe dopant facilitates the H₂ molecule dissociation. Unfortunately, this does not improve the hydrogen storage performance of ZrCo alloy due to the H atom diffusion on the surface and into bulk are prevented with higher reaction energetic barriers by doping Fe. Consequently, ZrCo (110) surface modified with Fe atoms should not be preferred as a result of its terrible hydrogen permeability. A clear and deep comprehending of the inhibiting effect of Fe dopant on the hydrogen storage of ZrCo materials from the perspective of the surface adsorption of hydrogen are obtained from the present results.     

Density functional theory calculations of hydrogen adsorption on Ti-, Zn-, Zr-, Al-, and N-doped and intrinsic graphene sheets

The effect of different doped atoms on the interactions between graphene sheets and hydrogen molecules were investigated by density functional theory calculations. The interactions between graphene sheets and hydrogen molecules can be adjusted by doped atoms. The Ti-doped graphene sheet had the largest interaction energy with the hydrogen molecule (approximately −0.299 eV), followed by the Zn-doped graphene sheet (about −0.294 eV) and then the Al-doped graphene sheet (approximately −0.13 eV). The doped N atom did not improve the interactions between the N-doped graphene sheet and the hydrogen molecule. Our results may serve as a basis for the development of hydrogen storage materials.     

Hydrazine decomposition on nickel-embedded graphene

In this article, the catalytic effect of the Ni-embedded graphene has been investigated for hydrazine (N₂H₄) decomposition reaction through Density Functional Theory (DFT) calculations with Grimme-D2 dispersion correction. Nickel embedded graphene systems are expected to be much cheaper than pristine nickel surfaces in the future because of relatively few numbers of Ni atom usage, experimentally synthesizable, and limit the Ni usage. The transformation of N₂H₄ has been taken into account in two different ways. The first way is sequential N–H and, the second one is the N–N bond cleavage from the gauche conformation which is the most stable conformation in gas phase and sole conformation observed on the Ni site. According to our findings, ·NH₂ formation breaking the N–N bond in hydrazine has lower activation energy than hydrogen abstraction from hydrazine. The difficulty of breaking N–H bonds stems from the spatial accumulation of negative and positive charges, so it causes a mismatch between hydrogen atoms and negatively charges carbon atoms. NH₃ formation pathway through the interaction of N₂H_x (x = 1 → 4) species with co-adsorbed ·NH₂ radicals is accompanied by much lower activation barriers and highly exothermic. Nevertheless, metal-embedded graphene systems are promising materials for hydrazine dehydrogenation and can be tailored to have more efficient charge distribution.     

Cooperatively enhanced catalytic properties of Ti@Al(100) near-surface alloy for aluminum hydrogenation

We have carried out detailed first-principles studies of the catalytic properties of Ti@Al(100) near-surface alloy. The single Ti atom, (0,2) Ti–Ti pair, and [0,2] Ti doping domain have better catalytic performances. These species doped in the top surface can develop back-bonding interaction with H₂ to catalyze the splitting, which however on the other hand hinder the dissociated H atoms to diffuse. Doped in the subsurface, they can also enhance hydrogen interaction on aluminum to catalyze H₂ splitting. The activation energies are 0.80, 0.68, and 0.48 eV for Ti atom, (0,2) pair, and [0,2] doping domain, respectively. Without Ti–H bond, the dissociated H atom could diffuse away with small energy cost. The structural expansion induced by titanium doping, the lower electronegativity of Ti, and the more valence electrons of Ti may cooperatively facilitate the charge transfer from the above Al atoms to H₂ molecule, accounting for the enhanced splitting properties.     

DFT study of boron doped MgH2: Bonding mechanism,hydrogen diffusion and desorption

The impact of boron doping on MgH₂ bonding mechanism, hydrogen diffusion and desorption was calculated using density functional theory (DFT). Atomic interactions in doped and non-doped system and its influence on hydrogen and vacancy diffusion were studied in bulk hydride. Slab calculations were performed to study hydrogen desorption energies from (110) boron doped surface and its dependence on the surface configuration and depth position. To study kinetics of hydrogen diffusion in boron vicinity and hydrogen molecule desorption activation energies from boron doped and non-doped (110) MgH₂ surface Nudged Elastic Band (NEB) method was used. Results showed that boron forms stronger, covalent bonds with hydrogen causing the destabilization in its first and second coordination. This leads to lower hydrogen desorption energies and improved hydrogen diffusion, while the impact on the energy barriers for H₂ desorption from hydride (110) surface is less pronounced.     

Ab initio study of effects of Al and Y co-doping on destabilizing of MgH2

First-principles calculations based on density functional theory (DFT) were performed to study the destabilizing mechanism of co-doped MgH₂ with Al and Y. From the minimization of total electronic energy, the preferential positions of dopants are determined. The calculated formation enthalpy and substitution enthalpy show that incorporation of Al combined with Y atoms into MgH₂ is energetically favorable relative to Al doping alone. Due to strong interaction of the dopant Y with Mg and Al, the hydrogen dissociation energy and the dehydrogenation enthalpy are both reduced, indicating that the synergetic effect of Al and Y on destabilizing the MgH₂ is superior to that of Al doping. The electronic structures show that the breakage of Mg–H bond is much easier in co-doped case, because of the conduction band shift below the Fermi level and the hybridization of dopants with Mg atoms, which effectively decrease the hybridization between Mg and H.     

Electrospun zeolitic imidazolate framework‐derived nitrogen‐doped carbon nanofibers with high performance for lithium‐sulfur batteries

Three‐dimensional (3D) nitrogen‐doped carbon nanofibers (N‐CNFs) which were originating from nitrogen‐containing zeolitic imidazolate framework‐8 (ZIF‐8) were obtained by a combined electrospinning/carbonization technique. The pores uniformly distributed in N‐CNFs result in the improvement of electrical conductivity, increasing of BET surface area (142.82 m² g^?1), and high porosity. The as‐synthesized 3D free‐standing N‐CNFs membrane was applied as the current collector and binder free containing Li₂S₆ catholyte for lithium‐sulfur batteries. As a novel composite cathode, the free‐standing N‐CNFs/Li₂S₆ membrane shows more stable electrochemical behavior than the CNFs/Li₂S₆ membrane, exhibiting a high first‐cycle discharge specific capacity of 1175 mAh g^?1at 0.1 C and keeping discharge specific capacity of 702 mAh g^?1 at higher rate. More importantly, as the sulfur mass in cathodes was increased at 7.11 mg, the N‐CNFs/Li₂S₆ membrane delivered 467 mAh g^?1after 150 cycles at 0.2 C. The excellent electrochemical properties of N‐CNFs/Li₂S₆ membrane can be ascribed to synergistic effects of high porosity and nitrogen‐doping in N‐CNFs from carbonized ZIF‐8, illustrating collective effects of physisorption and chemisorption for lithium polysulfides in discharge‐charge processes.     

Synthesis of nitrogen‐doped graphene catalyst by high‐energy wet ball milling for electrochemical systems

Platinum group metal‐based (PGM) catalysts are widely applied in many electrochemical systems such as fuel cells or metal–air batteries because of their excellent catalytic performance. But the high raw material cost of PGM catalysts has become a significant issue. In recent years, huge efforts have been made to reduce the material cost of electrochemical systems by developing non‐PGM catalysts, and as one of the promising non‐PGM catalysts, nitrogen‐doped graphene (N‐G) has emerged. In this research, nanoscale high‐energy wet ball milling methodology was investigated as an effective synthesis method for N‐G catalysts by using graphene oxide and melamine as raw materials. The main purpose is to study reaction mechanism of the synthesis process and the physical, chemical, and electrochemical properties of N‐G catalysts generated by this mechanochemical approach. The elemental composition, chemical bonding composition, and electron transfer number of the synthesized products were characterized. The results show that the electron transfer number of the N‐G catalyst with 23.2 at% nitrogen doping content, synthesized by the high‐energy wet ball milling method, has attained a value of 3.87, which is close to the number (3.95) of Pt/C catalysts, and the grinding time was found to be a significant factor in the properties of N‐G catalysts in the experiments. The results also show that the high‐energy wet ball milling developed in this research is a promising method to synthesize high‐performance N‐G catalysts with a simple and easy controllable approach. Copyright © 2016 John Wiley & Sons, Ltd.