N-doped Graphene Research Articles

Boosting oxygen reduction catalysis by introducing Fe bridging atoms between Pt nanoparticles and N-doped graphene

Introducing heterometals into Pt/C catalyst to construct multi-metal catalyst for improving the intrinsic activity is a rational strategy which can optimize the over-strong *O adsorption of Pt nanoparticles for oxygen reduction reaction (ORR). However, the practical activity and stability of such carbon supported Pt-based bimetallic catalysts are simultaneously limited by the conductivity degradation and deactivation caused by the weaker interaction between Pt and carbon support. Herein, by taking advantage of the precise control and self-limiting reaction of atomic layer deposition, we construct a novel Pt-Fe-NG structure in which Fe atoms play the bridging role between Pt nanoparticles and the N-doped graphene by multistep deposition. Impressively, the obtained catalyst exhibits an outstanding ORR half-wave potential of 0.948 V, a total four-electron pathway and superior durability over 10,000 cycles. The mass activity of the catalyst at 0.9 V is 15 times higher than that of commercial Pt/C. Moreover, when used as the cathode catalyst of Zn-air battery, the Pt-Fe-NG performs a maximum density power of 230 mW cm-2 and excellent stability after 180 discharge–charge cycles. The experimental results and theoretical calculations indicate that Fe bridging atoms play the role of elevating the d-band center of Pt nanoparticles and enhancing the interaction between Pt nanoparticles and carbon support, which paves a pathway for constructing novel multi-metal catalysts.

Tailoring of Three-Atom Metal Cluster Catalysts for Ammonia Synthesis

Electrocatalytic nitrogen reduction reaction (NRR) can realize the green production of ammonia while developing electrocatalysts with high selectivity and ability is still an ongoing challenge. Two-dimensional (2D) graphitic carbon nitride (CN) frameworks can provide abundant hollow sites for stably anchoring several transition metal (TM) atoms to facilitate single-cluster catalysis, promising to overcome the problems of low activity and poor selectivity in the process of ammonia synthesis. Herein, extensive density functional theory (DFT) calculations were performed to investigate the feasibility of six bimetallic triatomic clusters FexMoy (x = 1, 2; x + y = 3) supported on C6N6, C2N, and N-doped porous graphene (NG) as NRR electrocatalysts. Through a systematic screening strategy, we found that the Fe2Mo–NG possesses the highest activity with a limiting potential of –0.36 V through the enzymatic mechanism and could be the promising catalyst for NH3 synthesis. The Fe2Mo moiety in Fe2Mo–NG moderately regulates the electron transfer between reaction intermediates and NG, which is ascribed to enhanced performance. This work accelerates the rational design of catalysts in the field of NRR and contributes to broadening the understanding of cluster catalysis.

Intriguing physicochemical properties and impact of co-dopants on N-doped graphene oxide based ZnS nanowires for photocatalytic application

Superparamagnetic N-doped graphene oxide (GO)- with ZnS nanowires was synthesized by a one-step hydrothermal method by doping dilute amounts of Ga, Cr, In, and Al ions for water treatment and biomedical applications. In these experiments, to enhance their properties, 2% of Ga3+, In3+, and or Al3+ were codoped along with 2% Cr ions in these ZnS nanowires. The nanocomposite with the composition, In0.02Cr0.02Zn0.96S, has better photocatalytic efficiency than other co-doped nanocomposites. The In (metalloids) and Cr (transition metal ion) are the best combinations to increase the magnetic properties which are beneficial for photocatalytic activity. Synthesized nanocomposite materials were characterized by several techniques such as X-ray diffraction, Field emission-scanning electron microscope (FESEM) with EDAX, vibrating sample magnetometer (VSM), UV–Vis, X-ray photoelectron spectroscopy (XPS), and fluorescence spectroscopy. The correlation of intriguing magnetic properties with their photocatalytic properties is also discussed. XPS was employed for the detection of surface defects, phase transformation, and the nature of chemical components present in the nanocomposites. The Frankel and substitutional defects have a direct impact on photocatalytic activity that was determined from the fluorescence (FL) spectroscopy. FL and XPS reveal that the Cr and In codoped composite has a higher percentage of defects hence its photocatalytic efficiency reaches 94.21%.

Single-atom Cu anchored on N-doped graphene/carbon nitride heterojunction for enhanced photocatalytic H2O2 production

Photocatalytic production of H2O2 by polymeric carbon nitride has been regarded as a promising approach for the conversion of solar energy into valuable chemicals. However, the efficiency of pristine carbon nitride is limited by the rapid charge recombination and the lack of suitable active sites. Herein, we introduce single-atom Cu anchored on N-doped graphene (Cu-NG) as a cocatalyst coupled with carbon nitride via covalent bonding to enhance photocatalytic H2O2 production. The Cu-NG/carbon nitride could broaden the light absorption from UV to near-infrared region, contributing to the photocatalytic process. Moreover, NG containing electron-rich N atoms could serve as anchoring sites for stabilizing single-atom Cu. Importantly, the single-atom Cu acts not only as an electron sink to steer the interfacial charge separation but also as an active site for molecular oxygen adsorption and activation. With the synergistic effect of the enhanced interfacial charge separation and suitable active sites, Cu-NG/carbon nitride exhibits improved photocatalytic performance with an H2O2 generation rate of 2856 µmol g−1 h−1, which is 2.6 times that of pristine carbon nitride. This work provides a protocol for high-performance photocatalytic H2O2 production using a single-atom cocatalyst.

Si-C nanocomposites supported on vertical graphene sheets grown on graphite for fast-charging lithium ion batteries

Silicon/carbon (Si/C) anodes have been successfully used in commercial lithium-ion batteries because of their high capacity and excellent safety. Nevertheless, their cycling stability and fast-charging capability are still unsatisfactory due to large volume expansion and slow charge transport capability under industrial electrode conditions. Here, we fabricate a Si/C anode via homogeneously depositing amorphous SiC nanolayers on graphite armored with N-doped porous flexible vertical graphene sheets (VGSs) (named as Si-C/VGSs/graphite). SiC nanolayers consist of homogeneously dispersed sub-nanometer Si particles in 3D carbon skeleton, which effectively alleviate the volume change of Si, and hugely accelerate electron and Li-ion transport. The N-doped VGSs possess porous structure, good flexibility, numerous exposed edges, and directional ion transport channels, which provide rational space for accommodating volume change of Si, buffer the stress caused by the volume change, increase the electrical contact points between Si-C/VGSs/graphite, and accelerate Li-ion transport, respectively. Consequently, Si-C/VGSs/graphite delivers superior rate capacity and long cycle life under industrial electrode conditions. When matched with the cathode of Li[Ni0.8Co0.1Mn0.1]O2, the full cell demonstrates a predominant fast-charging capability (180.8 Wh kg−1, charging for 8.2 min, 5C) accompanied by long cycle life.

Self-powered triboelectric sensor with N-doped graphene quantum dots decorated polyaniline layer for non-invasive glucose monitoring in human sweat

A novel non-invasive wearable self-powered triboelectric sensor (TES) for simultaneous physiological monitoring had shed the light on its extraordinary performance, which become a promising choice for detecting glucose concentration from human sweat via non-invasive strategy. For realizing the function of wearable TES, the flexible substrate of conducting polymers commonly served as matrix for not only immobilizing the specific enzyme, but also played as the sensing layer by the coupling effect of triboelectrification/enzymatic reaction. To boost up the reliability and sensitivity of conducting polymer-based TES, in this study, a nanocomposite of N-doped graphene quantum dots decorated polyaniline (NGQDs/PANI) is designed as a triboelectric layer for non-invasive glucose detection. The surface electronegativity of PANI was changed by decorating the NGQDs with electron-rich functional groups for increasing the surface charge, which further facilitating the charge transfer between the PANI and intermedia and then enhancing triboelectric outputs. Upon the enhanced electron transfer and surface charge by NGQDs, NGQDs/PANI/GOx based TES offers greater sensitivity (23.52 mM−1) in glucose detection compared to pristine PANI/GOx one (16.44 mM−1). Notably, this study demonstrates the feasibility of wearable TES on human skin and their reliable and sensitive performance with a self-driving system without any external power source.

Relationship between pore structure of N-doped 3D porous graphene and electrocatalytic performance of oxygen reduction in zinc-air battery

Relationship between pore structure of N-doped 3D porous graphene and electrocatalytic performance of oxygen reduction in zinc-air battery

The role of single-boron of N-doped graphene for effective nitrogen reduction

Room-temperature electrocatalytic nitrogen reduction reaction (NRR) is of paramount significance for the fertilizer industry and fundamental catalysis science. However, many NRR catalysts were based on the use of metals. Herein, we focus on exploring boron-based, metal-free, efficient catalysts for NRR by density functional theory calculations with van der Waals corrections (DFT+D3). Our results show that the NRR performance of the boron active site can be improved by tuning the N-coordination environment in a graphene sheet, and the B-N-C structures show excellent stability. By considering the correlation between the Bader charges of the boron dopant over N-decorated graphene and their NRR activities, the rational design principle of a boron-based catalyst for NRR is developed. The boron-site with one pyridinic nitrogen in a double-vacancy structure is found to be a highly active center, with low reaction energy (0.53 eV) and kinetic barrier (0.84 eV) through the distal mechanism. We also found that the charge loss of boron considerably hampers hydrogen adsorption, which in turn promotes the NRR efficiency by hindering the competing hydrogen evolution. This work offers new insights into developing low-cost, highly effective boron-based materials as promising electrocatalysts for green ammonia synthesis.

Separator modification by MoxC/N-doped graphene enabling polysulfide catalytic conversion for high-performance Li–S batteries

The shuttle effect and sluggish electrochemical conversion of polysulfides have been believed to strongly influence the performances of lithium-sulfur (Li–S) batteries. Herein, we propose the synthesis of nanosized MoxC electrocatalysts embedded on N-doped graphene and develop its application for separator modification of Li–S batteries. The N-doped graphene provides a two-dimension conductive barrier layer to chemically adsorb polysulfides and inhibit polysulfides diffusion, while MoxC nanoparticles could serve as the functional electrocatalyst to facilitate the redox kinetics of the multiphase conversion. The Li–S coin cells with MoxC@N-rGO-modified separator can exhibit good long-term cycling stability with a capacity decay of 0.069% per cycle after 400 cycles at 0.5C and excellent rate performance with a discharge capacity of 653 mAh/g at 4C. An area capacity of 4.5 mAh/cm2 is also achieved with a high sulfur loading of 5.2 mg/cm2 and a low electrolyte/sulfur ratio of ∼5 μL/mg.

N, O-diatomic dopants activate catalytic activity of 3D self-standing graphene carbon aerogel for long-cycle and high-efficiency Li-CO2 batteries

Carbon-based metal-free materials are regarded as viable cathode catalysts for Li-CO2 batteries due to their low costs and lightweight. And heteroatom doping (such as N atom) has great potential to improve the catalytic activity of carbon-based catalysts. However, the underlying catalytic mechanism is yet unclear, which hinders the construction of high-efficiency catalysts and further improvements in electrochemical performance. Especially, the role of oxygen-containing groups prevalent in carbon-based catalysts has never been explored. In this work, guided by theoretical simulation, a self-standing N-doped graphene carbon aerogel with certain oxygenic groups was well-designed and synthesized by a straightforward, one-step thermal approach as the cathode catalyst. N dopant can effectively regulate the electronic structure of graphene and thus lower the free energy change of reactants/intermediate species. The intrinsic oxygen-containing functional groups still presented in graphene aerogel can further stabilize CO2-related intermediate species and improve the catalytic activity through a synergistic coupling effect with N dopant. This effect was originally discovered and clarified in the Li-CO2 battery system. Additionally, intriguing 3D hierarchical pores of as-obtained graphene carbon aerogel not only guarantee good conductivity but also offer a vast surface area to expose numerous accessible active sites. The resulting Li-CO2 batteries showed a significantly enhanced initial energy efficiency of approximately 78.46% and remarkable cyclic stability of more than 1500 h at 20 μA cm−2. This fundamental understanding of the structure-performance relationship gives new ideas for creating extremely effective carbon-based metal-free catalysts for Li-CO2 batteries.

The nanocomposites of N-doped graphene oxide decorated with La-doped Zn-Cu-Ni ferrite with lightweight and excellent absorption-dominant electromagnetic interference shielding performance

The nanocomposites of N-doped graphene oxide decorated with La-doped Zn-Cu-Ni ferrite with lightweight and excellent absorption-dominant electromagnetic interference shielding performance

Design of Frustrated Lewis Pairs by Functionalizing N-Doped Graphene Edge with Tunable Activity for H2 Dissociation

While the frustrated Lewis pair (FLP) concept has been successfully extended to heterogeneous catalysis, the underlying factors governing the catalytic performances of FLPs and designing strategies remain elusive. Herein, a theoretical study is performed to design metal-free heterogeneous FLPs with tunable activity for hydrogen dissociation. The designed FLPs constructed by functionalizing the N-doped zigzag graphene edge with eight functional groups −BX2 (X = F, Cl, Br, H, CH3, CF3, CN, NO2) can readily heterolytically dissociate H2 (H2 → Hδ− + Hδ+) with reaction barriers varying from 0.15 to 0.70 eV, showing their comparable activity to homogeneous FLPs. More importantly, FLP acidities of designed FLPs are linearly correlated with the reaction energies of H2 dissociation, suggesting the significant role of FLP acidity in determining their catalytic activity. Further calculations show that the reaction barriers of hydrogenation of CO2 also linearly correlate with the reaction energies of H2 dissociation and accordingly are governed by FLP acidity. Overall, this study provides a route for designing metal-free heterogeneous FLPs on graphene materials and discloses a close relationship between the composition (N···BX2), the electronic structure (FLP acidity), and the functionality (catalytic ability) of the FLPs.

Effectiveness and mechanisms of the adsorption of phenol from wastewater onto N-doped graphene oxide aerogel

Phenol, as a representative toxic substance in coking wastewater, will cause harm to the ecology and human beings. Therefore, advanced treatment of phenol is urgently needed. However, most adsorbents have the problems of low adsorption capacity and difficult recovery in water dephenolization. It is imminent to develop a recyclable and effective adsorbent. Herein three-dimensional (3D) N-doped graphene oxide aerogel (NGOA) was synthesized by using ammonium citrate as reductant and nitrogen source. NGOA exhibits large specific surface area, developed pores, excellent hydrophilicity and mechanical properties. The static and dynamic adsorption properties of NGOA were investigated. NGOA has good adsorption performance and reusability. The static saturated adsorption capacity of NGOA for phenol reached 108.19 mg g−1, which was obviously higher than most adsorbents. Furthermore, the dynamic adsorption capacity of NGOA was 43.69 mg g−1, which illustrates that NGOA has immense potential in the uptake of phenol for industrial application. Importantly, monolithic NGOA could be easily separated and recovered after adsorption saturation. The adsorption behavior conforms to the endothermic physical adsorption process, which is matched with the Pseudo-first-order kinetic model and Langmuir-Freundlich isotherm model. This work has good scientific research value and practical application prospect.

Precursor-mediated in situ growth of hierarchical N-doped graphene nanofibers confining nickel single atoms for CO2 electroreduction

Despite the various strategies for achieving metal-nitrogen-carbon (M-N-C) single-atom catalysts (SACs) with different microenvironments for electrochemical carbon dioxide reduction reaction (CO2RR), the synthesis-structure-performance correlation remains elusive due to the lack of well-controlled synthetic approaches. Here, we employed Ni nanoparticles as starting materials for the direct synthesis of nickel (Ni) SACs in one spot through harvesting the interaction between metallic Ni and N atoms in the precursor during the chemical vapor deposition growth of hierarchical N-doped graphene fibers. By combining with first-principle calculations, we found that the Ni-N configuration is closely correlated to the N contents in the precursor, in which the acetonitrile with a high N/C ratio favors the formation of Ni-N3, while the pyridine with a low N/C ratio is more likely to promote the evolution of Ni-N2. Moreover, we revealed that the presence of N favors the formation of H-terminated edge of sp2 carbon and consequently leads to the formation of graphene fibers consisting of vertically stacked graphene flakes, instead of the traditional growth of carbon nanotubes on Ni nanoparticles. With a high capability in balancing the *COOH formation and *CO desorption, the as-prepared hierarchical N-doped graphene nanofibers with Ni-N3 sites exhibit a superior CO2RR performance compared to that with Ni-N2 and Ni-N4 ones.

Coordinating Interface Polymerization with Micelle Mediated Assembly Towards Two-Dimensional Mesoporous Carbon/CoNi for Advanced Lithium-Sulfur Battery.

Lithium-sulfur battery has attracted significant attention by virtues of their high theoretical energy density, natural abundance, and environmental friendliness. However, the notorious shuttle effect of polysulfides intermediates severely hinders its practical application. Herein, a novel 2D mesoporous N-doped carbon nanosheet with confined bimetallic CoNi nanoparticles sandwiched graphene (mNC-CoNi@rGO) is successfully fabricated through a coordinating interface polymerization and micelle mediated co-assembly strategy. mNC-CoNi@rGO serves as a robust host material that endows lithium-sulfur batteries with a high reversible capacity of 1115 mAh g-1 at 0.2 C after 100 cycles, superior rate capability, and excellent cycling stability with 679.2 mAh g-1 capacity retention over 700 cycles at 1 C. With sulfur contents of up to 5.0mg cm-2 , the area capacity remains to be 5.1 mAh cm-2 after 100 cycles at 0.2 C. The remarkable performance is further resolved via a series of experimental characterizations combined with density functional theory calculations. These results reveal that the ordered mesoporous N-doped carbon-encapsulated graphene framework acts as the ion/electron transport highway with excellent electrical conductivity, while bimetallic CoNi nanoparticles enhance the polysulfides adsorption and catalytic conversion that simultaneously accelerate the multiphase sulfur/polysulfides/sulfides conversion and inhibit the polysulfides shuttle.

Comprehensive Mechanism for CO Electroreduction on Dual-Atom-Catalyst-Anchored N-Doped Graphene.

Carbon neutrality has drawn increasing attention for realizing the carbon cyclization and reducing the greenhouse effect. Although the C1 products, such as CO, can be achieved with a high Faraday efficiency, the targeted production of C2 fuels as well as the mechanism have not been systematically investigated. In this work, we carry out a first-principles study to screen dual-atom catalysts (DACs) for producing C2 fuels through the electrocatalytic carbon monoxide reduction reaction (e-CORR). We find that methanol, ethanol and ethylene can be produced on both DAC-Co and DAC-Cu, while acetate can be achieved on DAC-Cu only. Importantly, methanol and ethylene are preferred on DAC-Co, while acetate and ethylene on DAC-Cu. Furthermore, we show that the explicit solvent can enhance the adsorption and influence the protonation steps, which subsequently affects the protonation and dimerization behavior as well as the performance and selectivity of e-CORR on DACs. We further demonstrate that the C-C coupling is easy to be formed and stabilized if the Integrated Crystal Orbital Hamilton Population (ICOHP) is low because of the low energy barrier. Our findings provide not only guidance on the design of novel catalysts for e-CORR, but an insightful understanding on the reduction mechanism.

High electrochemical stability and low-agglomeration of defective Co3O4 nanoparticles supported on N-doped graphitic carbon nano-spheres for oxygen evolution reaction

The design of hybrid electrocatalysts with abundant active sites and long term stability is crucial for efficient oxygen evolution reaction (OER) application. Cobalt oxide is considered as one of the most promising electrocatalysts to replace noble metal due to its low cost, availability, and electrocatalytic activity towards the oxygen evolution reaction in alkaline media. However, nano-scale cobalt oxide suffers from severe surface self-agglomeration during the OER process, so that leading to poor activity and durability. Herein, ultra-small cobalt oxide nanoparticles are anchored on the surface of nitrogen doped porous 3D graphitic carbon nano-spheres (N-ACS@Co3O4) to increase the amount of exposed active site and avoid the self-agglomeration. The obtained electrocatalyst (N-ACS@Co3O4) is enriched with abundant oxygen vacancies and exhibits a superior OER activity (Overpotential of 237 mV at 10 mA.cm−2) and exceptional stability for at least 30 h in alkaline electrolyte (1 M KOH). The DFT calculations demonstrate that the strong adsorption of Co3O4 on N-doped graphene can prevent its agglomeration, and therefore improves the stability of Co3O4 nanoparticles during OER process in line with the experimental results.

Low temperature selective catalytic reduction of NOx with NH3 with improved SO2 and water resistance by using N-doped graphene dots-CuO–CeO2 nano-heterostructures modified vanadate catalysts

Herein, we report a facile strategy for efficient NH3-SCR catalytic performance of vanadate-based catalysts with superior sulfur and water resistance at low temperature (<200 °C). The catalyst design strategy is based on the selective adsorption of NO2 via the functionalization of N-doped graphene quantum dots (N-GQDs) and fast-SCR via the functionalization of CuO–CeO2 (CuCe) on 4V1W/Ti catalysts. The impregnation of 1 wt% N-GQDs and 2.8 wt% CuCe leads to more surface acid sites and facilitate the strong interaction between Cu-Ce-V oxides, thus improving NOx adsorption and improved redox process in low temperature ranges (180–220 °C). The synthesized CuCe-N-GQD-4V1W/Ti catalyst shows high DeNOx activity over 92 % with excellent N2 selectivity and SO2/H2O resistance at 200 °C. In situ diffuse reflectance Fourier transform analysis confirmed the Eley–Rideal SCR reaction pathway over the CuCe-N-GQDs-4V1W/Ti catalyst.

Electrocatalytic nitrogen reduction on defective graphene modulated from single atom catalyst to aluminium clusters

Density Functional Theory (DFT) investigation on the most earth-abundant Al-based catalysts, has been conducted detailing its electronic properties and catalytic efficacy for nitrogen reduction at ambient condition. The Al-based catalysts have been modulated to perform as par a highly performing, but rare, Ru-single atom catalytic center by varying number of Al atoms, shape, and size. The coalesce of band-center, work function and electronic properties in metal atom catalysts along with N-N bond activation has been demonstrated to be responsible for an efficient nitrogen reduction reaction (NRR) with ΔGmax of 0.78 eV in Al5 supported on N-doped double vacancy graphene (Al5@N4-DVG) catalyst. Electron localization function analysis has shown a weak physisorption of N2 in the Al-based catalysts. Projected Density of States (PDOS) illustrates the enhancement of aluminium electron density in Al5@N4-DVG led to enhanced orbital densities overlap of Alp and Np electrons. The Bader charge analysis and electronic analysis of the intermediates show efficient electron gain on the N atoms, leading to formation of NH3 from the NxHy intermediates in Al5@N4-DVG catalyst.

Iron-doped nickel sulfide nanoparticles grown on N-doped reduced graphene oxide as efficient electrocatalysts for oxygen evolution reaction

Transition metal sulfide electrocatalysts have attracted substantial attention because of their outstanding activity in the oxygen evolution reaction (OER). Herein, the highly efficient iron-doped nickel sulfide catalyst supported on functionalized N-doped reduction graphene oxide (Fe-NiS/NrGO) was successfully prepared via a combination of hydrothermal and vulcanization methods. The doped Fe modifies the electronic structure of NiS, which accelerates the kinetics of OER. The NrGO, with a large specific surface area and high conductivity, facilitates the homogeneous dispersion of Fe-NiS nanoparticles, increasing the active catalytic area and accelerating the charge transfer rate. The Fe-NiS(2)/NrGO exhibits superior OER performance with an overpotential of 344 mV to achieve a current density of 100 mA cm−2 in 1.0 M KOH, and the Tafel slope is as low as 47 mV dec−1. The OER performance of Fe-NiS(2)/NrGO is better than that of commercial RuO2. This work will eventually help to rationally design efficient transition-metal catalysts in future technologies for OER.