N-doped Graphene Nanosheets Research Articles

Ultrafine Mo2N Quantum Dots Embedded in N-Doped Graphene Sheets Enable Efficient Adsorption-Catalytic Transformation of Polysulfides.

Because of the high theoretical energy density of 2600 Wh kg-1, lithium-sulfur batteries (LSBs) are anticipated to be among the next generation of high-energy-density storage technologies. However, the practical application of LSBs has been severely hampered by the significant shuttle effect and slow redox kinetics of polysulfides (LiPSs). To address the above problems, in this paper, the concept of quantum dots (QDs) was introduced to design and synthesize Mo2N QD-modified N-doped graphene nanosheets (marked as Mo2N-QDs@NG), which were used as separator modification materials for LSBs. The experimental results demonstrated that the introduction of Mo2N QDs avoids stacking of graphene sheets and provides more active sites for the conversion of LiPSs. Moreover, Mo2N enhances the chemical fixation and catalyzes the liquid-solid conversion of soluble LiPSs by forming Mo-S and Li-N bonds with LiPSs. Additionally, establishing Mo-C bonds with Mo2N, N-doped graphene sheets can facilitate the transport of electrons and ions and physically prevent the diffusion of LiPSs, thus creating a highly conducting carbon structure to support electrochemical reactions. Benefiting from the synergistic effect of chemical immobilization and catalysis of Mo2N QDs with the physical confinement of NG, Mo2N-QDs@NG-PP batteries exhibit enhanced electrochemical performance.

Asymmetric Coordination of Bimetallic Fe-Co Single-Atom Pairs toward Enhanced Bifunctional Activity for Rechargeable Zinc-Air Batteries.

The advancement of rechargeable zinc-air batteries (RZABs) faces challenges from the pronounced polarization and sluggish kinetics of oxygen reduction and evolution reactions (ORR and OER). Single-atom catalysts offer an effective solution, yet their insufficient or singular catalytic activity hinders their development. In this work, a dual single-atom catalyst, FeCo-SAs, was fabricated, featuring atomically dispersed N3-Fe-Co-N4 sites on N-doped graphene nanosheets for bifunctional activity. Introducing Co into Fe single-atoms and secondary pyrolysis altered Fe coordination with N, creating an asymmetric environment that promoted charge transfer and increased the density of states near the Fermi level. This catalyst achieved a narrow potential gap of 0.616 V, with a half-wave potential of 0.884 V for ORR (vs the reversible hydrogen electrode) and a low OER overpotential of 270 mV at 10 mA cm-2. Owing to the superior activity of FeCo-SAs, RZABs exhibited a peak power density of 203.36 mW cm-2 and an extended cycle life of over 550 h, exceeding the commercial Pt/C + IrO2 catalyst. Furthermore, flexible RZABs with FeCo-SAs demonstrated the promising future of bimetallic pairs in wearable energy storage devices.

Synergetic effect of trimetallic double hydroxide nanospikes embraced N-doped graphene nanosheets as electrode material for supercapacitors

In the energy storage sector, layered double hydroxides (LDHs) are coming to the forefront as a promising option for electrode materials. However, LDHs suffer from insufficient intrinsic conductivity and agglomeration during formation which restrict their wide applications. In this context, a two-step hydrothermal technique is employed to synthesize NiCoMn hydroxide (NCM)/N-doped graphene (NG). Initially, NG is produced through hydrothermal treatment utilizing urea to serve as both a reduction and doping source. Subsequently, a straightforward hydrothermal technique is utilized to cultivate NCM onto the surface of NG nanosheets. The electrochemical properties of NCM-NG composite with different compositions of NG have been analyzed, resulting in capacitance increment on account of increased conductivity and large number of active sites upon incorporation of NG as compared to pristine NCM. Moreover, NG nanosheets inhibit the agglomeration of NCM nanospikes. Amongst different compositions, NCM-NG-2 nanohybrid secured the highest specific capacitance (Cs) of 783.5 F/g at 0.25 A/g. The Asymmetric supercapacitor device assembled with NCM-NG-2 (anode) and activated carbon (AC) (cathode) exhibits the Cs of 114.5 F/g at 0.5 A/g. The optimized specific energy (Es) of 31.8 Wh/kg and specific power (Ps) of 473.4 W/kg with remarkable retention of 101.9 % up to 15,000 continuous cycles, indicating a higher potential of the NCM-NG-2 electrode in energy storage applications. These findings open new avenues for developing highly productive multi-material electrodes for utilization in energy storage systems.

CoN nanorods anchored on N-doped reduced graphene oxides for high-efficient microwave absorption performance

Nowadays, to solve the related electromagnetic radiation and pollution issues, it is urgent to exploit and design high-efficient microwave absorption materials, which owns the advantages of broad bandwidth, lightweight, thin matching thickness, and strong absorbing capacity. In this work, by anchoring CoN nanorods on the N-doped graphene nanosheets, a high-performance CoN/N-rGO hybrids microwave absorption absorber was fabricated with a two-step hydrothermal-nitridation method. Impressively, compared with the pure CoN nanorods, CoN/N-rGO hybrids present boosting microwave absorption properties which can be modulated by component of graphene. The strongest reflection loss (RL) value of CoN/N-rGO (40) hybrids absorber can reach −67.3 dB at 12.4 GHz with a thin matching thickness of 1.97 mm and the effective absorption bandwidth (RL ≤ −10 dB) of 5 GHz (10.4–15.4 GHz) can be gained at only 1.79 mm. This enhancement of microwave absorption is mainly attributed to the polarization, interface interaction, synergistic effect and optimal impedance matching between N-rGO nanosheets and CoN nanorods. This work provides not only a deep insight into adjusting the microwave absorption property of CoN/N-rGO hybrids, but a new route to design high-efficient nitride-based absorbers.

Boosting the catalytic activity toward oxygen reduction via a heterostructure of porous iron oxide-decorated 2D NiO/NG nanosheets

As a noble metal substitute, two-dimensional (2D) hierarchical nano-frame structures have attracted great interest as candidate catalysts due to their remarkable advantages – high intrinsic activity, high electron mobility, and straightforward surface functionalization. Therefore, they may replace Pt-based catalysts in oxygen reduction reaction (ORR) applications. Herein, a simple method is developed to design hierarchical nano-frame structures assembled via 2D NiO and N-doped graphene (NG) nanosheets. This procedure can yield nanostructures that satisfy the criteria correlated with improved electrocatalytic performance, such as large surface area, numerous undercoordinated atoms, and high defect densities. Further, porous NG nanosheet architectures, featuring NiO nanosheets densely coordinated with accessible holey Fe2O3 moieties, can enhance mesoporosity and balance hydrophilicity. Such improvements can facilitate charge transport and expose formerly inaccessible reaction sites, maximizing active site density utilization. Density functional theory (DFT) calculations reveal favored O2 adsorption and dissociation on Fe2O3 hybrid structures when supported by 2D NiO and NG nanomaterials, given 2D materials donated charge to Fe2O3 active sites. Our systematic studies reveal that synergistic contributions are responsible for enriching the catalytic activity of Fe2O3@NiO/NG in alkaline media – encompassing internal voids and pores, unique hierarchical support structures, and concentrated N-dopant and bimetallic atomic interactions. Ultimately, this work expands the toolbox for designing and synthesizing highly efficient 2D/2D shelled functional nanomaterials with transition metals, endeavoring to benefit energy conversion and related ORR applications.

Ecologically Sustainable N-doped Graphene Nanosheets as High-Performance Electrodes for Zinc–Air Batteries and Zinc-Ion Supercapacitors

Ecologically Sustainable N-doped Graphene Nanosheets as High-Performance Electrodes for Zinc–Air Batteries and Zinc-Ion Supercapacitors

Anchoring FeRu Bimetallic Nanoparticles on N-Doped Graphene Nanosheets for Efficient Overall Water Splitting

Anchoring FeRu Bimetallic Nanoparticles on N-Doped Graphene Nanosheets for Efficient Overall Water Splitting

A Comparative DFT Investigation on the Structural, Electric, Thermodynamic, and Optical Properties of the Pristine and Various Metals and Nonmetals (Li, Be, B, N, O, and F) Doped Graphene and Silicene Nanosheets

In recent times 2D nanosheets have come to the fore of the attention of researchers due to their unique properties. In this work, the comparative studies between graphene and silicene nanosheets before and after doping with different metals and nonmetals doping have been performed using a quantum mechanical approach, density functional theory (DFT) employing B3LYP functional along with the LanL2DZ. For Li, Be, B, N, O, and F dopants, periodic changes have been observed for both graphene and silicene nanosheets. Li doping causes increasing surface area and higher reactivity which suggests its feasibility in sensor development. On the other hand, N causes higher structural, and thermodynamical stability along with favorable electric properties. So, based on purposes, both Li and N-doped graphene and silicene nanosheets are suitable for real-life applications, especially in emerging technologies including supercapacitors, optoelectronic sensing devices, energy storage devices, and so on.

Single-atom Fe nanozymes with excellent oxidase-like and laccase-like activity for colorimetric detection of ascorbic acid and hydroquinone.

Although traditional Fe-based nanozymes have shown great potential, generally only a small proportion of the Fe atoms on the catalyst's surface are used. Herein, we synthesized single-atom Fe on N-doped graphene nanosheets (Fe-CNG) with high atom utilization efficiency and a unique coordination structure. Active oxygen species including superoxide radicals (O2•-) and singlet oxygen (1O2) were efficiently generated from the interaction of the Fe-CNG with dissolved oxygen in acidic conditions. The Fe-CNG nanozymes were found to display enhanced oxidase-like and laccase-like activity, with Vmax of 2.07 × 10-7M∙S-1 and 4.54 × 10-8M∙S-1 and Km of 0.324mM and 0.082mM, respectively, which is mainly due to Fe active centers coordinating with O and N atoms simultaneously. The oxidase-like performance of the Fe-CNG can be effectively inhibited by ascorbic acid (AA) or hydroquinone (HQ), which can directly obstruct the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB). Therefore, a direct and sensitive colorimetric method for the detection of AA and HQ activity was established, which exhibited good linear detection and limit of detection (LOD) of 0.048μM and 0.025μM, respectively. Moreover, a colorimetric method based on the Fe-CNG catalyst was fabricated for detecting the concentration of AA in vitamin C. Therefore, this work offers a new method for preparing a single-atom catalyst (SAC) nanozyme and a promising strategy for detecting AA and HQ.

Asymmetric Electrode Design for High-Area Capacity and High-Energy Efficiency Hybrid Zn Batteries.

Compared to Zn-air batteries, by integrating Zn-transition metal compound reactions and oxygen redox reactions at the cell level, hybrid Zn batteries are proposed to achieve higher energy density and energy efficiency. However, attaining relatively higher energy efficiency relies on controlling the discharge capacity. At high area capacities, the proportion of the high voltage section can be neglected, resulting in a lower energy efficiency similar to that of Zn-air batteries. Here, a high-loading integrated electrode with an asymmetric structure and asymmetric wettability is fabricated, which consists of a thick nickel hydroxide (Ni(OH)2) electrode layer with vertical array channels achieving high capacity and high utilization, and a thin NiCo2O4 nanopartical-decorated N-doped graphene nanosheets (NiCo2O4/N-G)catalyst layer with superior oxygen catalytic activity. The asymmetric wettability satisfies the wettability requirements for both Zn-Ni and Zn-air reactions. The hybrid Zn battery with the integrated electrode exhibits a remarkable peak power density of 141.9mWcm-2, superior rate performance with an energy efficiency of 71.4% even at 20mAcm-2, and exceptional cycling stability maintaining a stable energy efficiency of ≈84% at 2mAcm-2 over 100 cycles (400 h).

Surfactant-assisted Fe-anchored and N-doped ultrathin graphene nanosheets for enhanced electrocatalytic oxygen reduction

Exploration of tremendous electrocatalysts for oxygen reduction reaction (ORR) as promising alternatives is urgent in various electrochemical applications. As a result, one catalyst of homogeneously dispersed Fe, N sites anchored on two-dimensional (2D) ultrathin graphene nanosheets (Fe-N@C) is rationally designed and synthesized via a surfactant-assisted pyrolysis approach. Water-soluble F127 surfactant facilitates the uniform dispersion of Fe and restrains the aggregation of Fe-based particles during pyrolysis treatment, which promotes the formation of plentiful FeNx species. The 2D ultrathin structure is beneficial to expose more FeNx and make the most use of these active sites. Therefore, the developed Fe-N@C catalyst demonstrates enhanced catalytic properties in alkaline media with an approximate 4e− pathway and more positive half-wave potential (E1/2, 0.85 V), which is plus 0.04 V than commercial 20 % Pt/C catalyst. Besides, the target catalyst also exhibits superb poison resistance and long-term stability. This work presents a practical direction for the fabrication of other high-efficient catalysts and a new insight into ORR.

Coconut waste to green nanomaterial: Large scale synthesis of N-doped graphene nano sheets

In this paper, a breakthrough was achieved in large-scale production of N-doped Graphene Nano Sheets (N-GNS) using coconut fruits. The main objectives were to produce N-GNS on a large scale and assess its electrical conductivity. The process involved two key steps: first, producing GNS from coconut fruits through pyrolysis, and then generating N-GNS by doping with nitrogen using ammonia solution at room temperature. Various analytical techniques were used to characterize the produced N-GNS, including X-ray Diffraction (XRD), Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM-EDS), Transmission Electron Microscopy (TEM), X-ray Photoelectron Spectroscopy (XPS), Raman spectroscopy, and electrochemical cyclic voltammetry and electrochemical impedance spectroscopy. The XRD data indicated that the C (002) peak of N-GNS shifted to a higher 2θ value (2θ = 24.72°) compared to GNS (2θ = 23.86°), suggesting an incorporation of nitrogen into carbon structure in N-GNS. This was further supported by XPS data, which identified N-pyridine (BE = 402.0 eV) and C-N (BE = 286.8 eV) in N-GNS. TEM images showed that N-GNS had a flat surface, and the distance between graphene layers slightly expanded (0.36 nm) compared to graphene layers (0.34 nm). SEM images and EDX data validated the morphology, resembling honeycomb lattices, with a significant content of N atoms. Raman data successfully identified the D-band and G-band in N-GNS, further validating its production. Most importantly, N-GNS exhibited electrical conductivity, making it a promising candidate for conductive and supporting materials in various applications. The significance of this research extends beyond N-GNS production, opening up new avenues for the sustainable synthesis of valuable nanomaterials from coconut fruit waste, contributing to both graphene technology and environmental conservation.

Lamellar α-Zirconium Phosphate Nanoparticles Supported on N-Doped Graphene Nanosheets as Electrocatalysts for the Detection of Levofloxacin

Lamellar α-Zirconium Phosphate Nanoparticles Supported on N-Doped Graphene Nanosheets as Electrocatalysts for the Detection of Levofloxacin

Sonoelectrochemical nitrided graphene nanosheets with vacancies and their applications for catalysis and sensing of uric acid oxidation

A sonoelectrochemical method for preparing N-doped defective graphene nanosheets (N/O-dGNs) with point defects and 5-9 or 5-8-5 vacancies and oxygen-containing groups was successfully demonstrated. In this one-pot approach, the N-bonding configuration and N content of N/O-dGNs were finely tuned by the ultrasonic power (192, 320, and 640 W). The N content in atomic percentage (at%) for N/O-dGN (N/O-dGN320W) with point defects and 5-8-5 vacancy prepared at 320 W power was 5.6 at%, greater than 3.0 at% and 2.6 at% for N/O-dGN with point defects and 5-9 vacancies at 192 W and 640 W power (N/O-dGN192W and N/O-dGN640W), respectively. N-bonding sites on N/O-dGN320W were dominantly amine N (2.1 at%) and pyrrolic N (2.4 at%). Additionally, the electrocatalytic activity of N/O-dGN192W, N/O-dGN320W, and N/O-dGN640W was successfully demonstrated for the sequential uric acid (UA) oxidation reaction (UOR), in which N/O-dGN320W displayed a significant mass activity (2.51 A/g). As in the transient catalysis of UOR, N/O-dGN320W with amine N showed 400.8 μA mM−1 cm−2 in sensitivity within a wide linear analysis range (1.5 × 10–2–6 mM) for amperometrically sensing UA. The results of real sample experiments using serum samples further demonstrated the potential of N/O-dGN320W as a non-enzymatic UA sensor.

Activating the PdN4 single-atom sites for 4 electron oxygen reduction reaction via axial oxygen ligand modification

The absence of Pd ensemble sites and weak affinity for O-intermediates in tetracoordinate planar PdN4 sites inhibit O-O bond dissociation and restrict 4e- oxygen reduction reaction (ORR) pathway. Optimizing the adsorption energy between O-intermediates and PdN4 sites is a rational approach for selectively promoting 4e- ORR electrocatalysis. Herein, we propose a molten-salt strategy for introducing axial oxygen ligand into the PdN4 sites to manipulate the electronic structure and create catalytic O-PdN4 sites (one subsurface axial Pd-O configuration on PdN4 plane) on N-doped graphene nanosheets (O-PdN4-NGS). Density functional theory calculations revealed that the axial Pd-O coordination can induce charge redistribution, downshift the d-band center of Pd and enhance the adsorption affinity of PdN4 site for O-intermediates, thereby leading to superior electrocatalysis activity and selectivity for 4e- ORR process compared to conventional PdN4 sites in 0.1 M KOH (with a positive half-wave potential E1/2 of 0.90 V vs RHE). Moreover, zinc-air battery featuring with O-PdN4 sites delivers a peak power density of 178 mW cm−2 at 227.5 mA cm−2 and stable long-term cycling performance, effectively showcasing the advantages of the axial O ligand modification in practical application. This work provides a constructive strategy to activate the reaction activity and specificity of PdN4 single-atom sites by precisely-tuning the local coordination environment of Pd.

Dual-atom Co-Fe catalysts for oxygen reduction reaction

Controlled synthesis of dual-atom catalysts (DACs) for heterogeneous catalytic reactions is vital but still demanding. Herein, we construct a novel dual-atom catalyst containing FeN3-CoN3 sites on N-doped graphene nanosheets (CoFe-NG), which exhibits remarkable catalytic performance with a half-wave potential of 0.952 V for oxygen reduction reaction (ORR) and shows higher endurance to methanol/carbon monoxide poisoning and better durability than commercial Pt/C. The assembled Zn-air battery with CoFe-NG as the air electrode delivers a peak power density of 230 mW cm–2 and exhibits negligible change in output voltage at 5 mA cm–2 for 250 h. Theoretical calculations reveal that FeN3-CoN3 sites on N-doped graphene exhibit lower ORR barrier than FeN4 and CoN4 sites, and the rate-limiting step on the former is the transformation of *OH intermediate to H2O, different from the transformation of *O to *OH on the FeN4 site and the transformation of O2 to *OOH on the CoN4 site.

Fused heteroaromatic benzothiazoles functionalized nitrogen-doped graphene by non-covalent bonds for high-performance supercapacitors

Benzothiazole (Bz) molecules with excellent electrochemical stability and activity are favor of enhancing the capacitance performance of N-doped graphene (NG) by non-covalent functionalization. Herein, Bz molecules with different substituent groups (-ketone, -methoxy, -ketone and-methoxy) are used to functionalize NG nanosheets by a hydrothermal method and freeze-drying procedure. The surface chemistry and structure of as-prepared functionalized NG nanosheets are investigated through UV − vis, FTIR, SEM, AFM, XPS, TGA, XRD, Raman and BET. The electrochemical results of four functionalized NG nanosheets show that the substituent groups on Bz molecules have a great influence on their capacitive properties, among which the NG modified by the 6-methoxy benzothiazol-2-ketone (1-MhzNG) demonstrates the highest specific capacitance (420 F g−1 at 1 A g−1) and excellent cycle stability of 95.7 % after 10,000 cycles. In addition, the assembled supercapacitor based on the 1-MhzNG electrode delivers the highest energy density of 22.5 Wh kg−1 at 809 W kg−1. Our work provides a new idea to modify graphene with novel organic small molecules for high-performance SCs.

Nonenzymatic Sweat Wearable Uric Acid Sensor Based on N-Doped Reduced Graphene Oxide/Au Dual Aerogels.

Sweat wearable sensors enable noninvasive and real-time metabolite monitoring in human health management but lack accuracy and wearable applicability. The rational design of sensing electrode materials will be critical yet challenging. Herein, we report a dual aerogel-based nonenzymatic wearable sensor for the sensitive and selective detection of uric acid (UA) in human sweat. The three-dimensional porous dual-structural aerogels composed of Au nanowires and N-doped graphene nanosheets (noted as N-rGO/Au DAs) provide a large active surface, abundant access to the target, rapid electron transfer pathways, and a high intrinsic activity. Thus, a direct UA electro-oxidation is demonstrated at the N-rGO/Au DAs with a much higher activity than those at the individual gels (i.e., Au and N-rGO). Moreover, the resulting sensing chip displays high performance with a good anti-interfering ability, long-term stability, and excellent flexibility toward the UA detection. With the assistance of a wireless circuit, a wearable sensor is successfully applied in the real-time UA monitoring on human skin. The obtained result is comparable to that evaluated by high-performance liquid chromatography. This dual aerogel-based nonenzymatic biosensing platform not only holds considerable promise for the reliable sweat metabolite monitoring but also opens an avenue for metal-based aerogels as flexible electrodes in wearable sensing.

Ultrafine Core@Shell Cu1Au1@Cu1Pd3 Nanodots Synergized with 3D Porous N-Doped Graphene Nanosheets as a High-Performance Multifunctional Electrocatalyst

Rationally combining designed supports and metal-based nanomaterials is effective to synergize their respective physicochemical and electrochemical properties for developing highly active and stable/durable electrocatalysts. Accordingly, in this work, sub-5 nm and monodispersed nanodots (NDs) with the special nanostructure of an ultrafine Cu1Au1 core and a 2-3-atomic-layer Cu1Pd3 shell are synthesized by a facile solvothermal method, which are further evenly and firmly anchored onto 3D porous N-doped graphene nanosheets (NGS) via a simple annealing (A) process. The as-obtained Cu1Au1@Cu1Pd3 NDs/NGS-A exhibits exceptional electrocatalytic activity and noble-metal utilization toward the alkaline oxygen reduction, methanol oxidation, and ethanol oxidation reactions, showing dozens-fold enhancements compared with commercial Pd/C and Pt/C. Besides, it also has excellent long-term electrochemical stability and electrocatalytic durability. Advanced and comprehensive experimental and theoretical analyses unveil the synthetic mechanism of the special core@shell nanostructure and further reveal the origins of the significantly enhanced electrocatalytic performance: (1) the prominent structural properties of NGS, (2) the ultrasmall and monodispersed size as well as the highly uniform morphology of the NDs-A, (3) the special Cu-Au-Pd alloy nanostructure with an ultrafine core and a subnanometer shell, and (4) the strong metal-support interaction. This work not only develops a facile method for fabricating the special metal-based ultrafine-core@ultrathin-shell nanostructure but also proposes an effective and practical design paradigm of comprehensively and rationally considering both supports and metal-based nanomaterials for realizing high-performance multifunctional electrocatalysts, which can be further expanded to other supports and metal-based nanomaterials for other energy-conversion or environmental (electro)catalytic applications.

N-doped graphene nanosheets-based optical nano switch for the selective detection of guanine and Pb2+

N-doped graphene nanosheets synthesised from biomass are used as a PL probe for the on-off-on detection of Pb2+ and guanine.