Co-doped Carbon Nanosheets Research Articles

B, N co-doped carbon nanosheets derived from graphene quantum dots: Improving the pseudocapacitive performance by efficient trapping nitrogen

Doping heteroatoms especially nitrogen is widely applied for improving the capacitive energy storage performance of carbon materials. However, preserving nitrogen in carbon skeleton is still challenging because nitrogen species are unstable at high temperature. Herein, we develop a simple boric acid-assisted method for trapping nitrogen into carbon skeleton. Using the graphene quantum dots with an initial nitrogen content of 5.0 at.% as precursors, the B, N co-doped carbon nanosheets with an increased nitrogen content of 7.2 at.%, a boron content of 4.4 at.%, and a surface area of 817 m2 g−1 are prepared. Benefiting from the high heteroatom content, the nanosheets show a significantly improved capacitance of 257 F g−1 at 1 A g−1 and a good rate performance of 150 F g−1 at 50 A g−1. The pseudocapacitance contribution at 10 mV s−1 is as high as 48%. The assembled symmetric capacitor shows a superior cycle stability with no obvious fading after 10,000 cycles at 10 A g−1. Our work can help to understand the synergistic effect of heteroatoms for co-doping of carbon and broaden the avenue for designing functional carbon materials.

Green synthesis of nitrogen, sulfur-co-doped worm-like hierarchical porous carbon derived from ginger for outstanding supercapacitor performance

Herein, we report a low cost, green synthesis of unique hierarchical worm-like porous co-doped thin carbon nanosheets from ginger as biomass source using non-toxic NaCl/KCl salt mixture as activation media (unlike conventional toxic activation agents like KOH) for high performance supercapacitor application. The optimized synthesis of Nitrogen, Sulfur-doped activated ginger carbon (DAGC) exhibits micro-meso-macro porous structure, facilitating efficient electrolyte diffusion, appropriate graphitization degree, enhanced surface wettability, and synergistic effects between co-doped heteroatoms for rapid ion transfer. Transmission electron microscope (TEM) and Raman spectroscopy studies reveal the partially graphitized walls of carbon and graphitization degree respectively. The DAGC electrode exhibits an excellent specific capacitance of 456 F g−1 at 0.3 A g−1 in three-electrode cell. The assembled symmetric DAGC//DAGC supercapacitor delivers an outstanding specific energy of 48.3 Wh Kg−1 at 400 W kg−1 in comparison to other reported porous carbon with traditional activation method. Moreover, the DAGC supercapacitor device works in high potential region (0–1.4 V) with 1 M Na2SO4 as supporting electrolyte, exhibiting an excellent rate capability and high cyclic stability of 95% after 10000 cycles. All these features of DAGC electrode material make it environment friendly and a competitive entrant for electroactive materials in wide range of applications.

A novel strategy to prepare COFs based BN co-doped carbon nanosheet for enhancing mechanical performance and fire safety to PVA nanocomposite

N doped carbon nanosheet and B N co-doped carbon (BNC) nanosheet are first prepared through exfoliation of carbon of Schiff based covalent organic frameworks (COFs) under ultrasound using sodium lignin sulfonate as the intercalation agent and modifier. Then poly (vinyl alcohol) (PVA)/BNC nanocomposite with enhanced thermal oxidation stability, good mechanical performances and enhanced flame retardancy has been prepared through solution blending. The temperature at 5 wt% weight loss and peak heat release rate of PVA loaded with 4 wt% of BNC nanosheet increase by 31.9 °C and 57.3% compared with that of untreated PVA, respectively. A new fire hazard evaluation system based on analytic hierarchy process (AHP) is raised to comprehensively estimate fire risk of prepared sample. It is deduced from AHP that PVA loaded with 4 wt% BNC nanosheet shows the lowest fire risk (77.9 score). The effect of BNC nanosheet on pyrolysis mode of PVA in gaseous and condensed phase has also been investigated to figure out the reason for low fire risk of treated PVA.

3D honeycombed cobalt, nitrogen co-doped carbon nanosheets via hypersaline-protected pyrolysis towards efficient oxygen reduction

The broad application of metal-air batteries and fuel cells have been greatly limited due to their slow kinetics of oxygen electrodes involving the oxygen reduction reaction (ORR), and therefore the development of high-efficient, low-cost and high-reserve ORR electrocatalysts is of great significance. Herein, a hypersaline-protected pyrolysis strategy is presented for preparing 3D honeycombed cobalt, nitrogen co-doped carbon nanosheets (Co/N-CNS) by using eco-friendly biomass as a carbon and nitrogen source. During the hypersaline-protected pyrolysis, the pyridinic nitrogen-rich biomass facilitates the formation of highly active Co/N active sites among the resultant Co/N-CNS, while the templating-washing-drying cyclic utilization of salts creates honeycombed pore structures among the Co/N-CNS. Due to the structural features of honeycombed pores and uniform distributed active sites, the Co/N-CNS catalyst offers excellent ORR activity, high durability and methanol-tolerant performance in an alkaline electrolyte. As a demonstration, a primary Zn-air battery using the Co/N-CNS cathode delivers a high power density and excellent operating stability beyond that of commercial Pt/C cathode.

TiN nanoparticles hybridized with Fe, N co-doped carbon nanosheets composites as highly efficient electrocatalyst for oxygen reduction reaction

Titanium nitride (TiN) nanoparticles hybridized with Fe and N co-doped carbon nanosheets (Fe-N-CNS) composite is constructed by a facile in-situ self-template strategy. During the low-temperature pyrolysis process, uniformly TiO2 nanoparticles were formed and anchored into Fe-doped carbon nitride nanosheets. After further high-temperature pyrolysis, Fe-doped carbon nitride nanosheets as self-template could decompose to form Fe-N co-doped carbon nanosheets and TiO2 nanoparticles were transferred into TiN nanoparticles during the high-temperature nitriding treatment. As a result, TiN nanoparticles hybridized with Fe-N-CNS composites (TiN/Fe-N-CNS) exhibit excellent ORR activity with more positive half-wave potential (0.87 V) and large limiting current density (4.43 mA cm−2) as well as high selectivity (electron transfer number around 4) for ORR in alkaline media. Moreover, it also shows higher stability and better methanol tolerance than those of commercial Pt/C catalyst in both alkaline and acidic media. This excellent ORR performance is attributed to the enhanced specific surface area and synergistically promotion effect of uniformly dispersed TiN on Fe-N-CNS.

Nitrogen and oxygen co-doped broccoli-like porous carbon nanosheets derived from sericin for high-performance supercapacitors

Broccoli-like porous carbon nanosheets with high levels of heteroatoms doping was successfully synthesized from the wasted sericin via an environmental friendliness and cost-effective strategy. The hierarchical porous carbon nanosheets was formed from chemical expansion and activation by Mg2(OH)2CO3·xH2O simultaneously. Benefiting from the elaborate structure of NPCN-4, the prepared material shows the satisfactory energy storage ability in electrical double-layer capacitors (EDLCs) area with an outstanding specific capacitance of 214.5 F g−1 at 0.5 A g−1 in an alkaline solution and high capacitance retention of 87% at 10 A g−1 after 10000 cycles.

Biomass-Derived P/N-Co-Doped Carbon Nanosheets Encapsulate Cu3P Nanoparticles as High-Performance Anode Materials for Sodium-Ion Batteries.

Biomass-derived approaches have been accepted as a practical way for the design of transitional metal phosphides confined by carbon matrix (TMPs@C) as energy storage materials. Herein, we successfully synthesize P/N-co-doped carbon nanosheets encapsulating Cu3P nanoparticles (Cu3P@P/N-C) by a feasible aqueous reaction followed by a phosphorization procedure using sodium alginate as the biomass carbon source. Cu-alginate hydrogel balls can be squeezed into two-dimensional (2D) nanosheets through a freeze–drying process. Then, Cu3P@P/N-C was obtained after the phosphorization procedure. This rationally designed structure not only improved the kinetics of ion/electron transportation but also buffered the volume expansion of Cu3P nanoparticles during the continuous charge and discharge processes. In addition, the 2D P/N co-doped carbon nanosheets can also serve as a conductive matrix, which can enhance the electronic conductivity of the whole electrode as well as provide rapid channels for electron/ion diffusion. Thus, when applied as anode materials for sodium-ion batteries, it exhibited remarkable cycling stability and rate performance. Prominently, Cu3P@P/N-C demonstrated an outstanding reversible capacity of 209.3 mAh g−1 at 1 A g−1 after 1,000 cycles. Besides, it still maintained a superior specific capacity of 118.2 mAh g−1 after 2,000 cycles, even at a high current density of 5 A g−1.

Optimized Enhancement Effect of Sulfur in Fe-N-S Codoped Carbon Nanosheets for Efficient Oxygen Reduction Reaction.

The study on the design and preparation of oxygen reduction reaction (ORR) electrocatalysts with high efficiency is currently attracting great concern. Among different types of catalysts, heteroatom-doped carbon-based catalysts have exhibited promising potential, and the exploration of optimized matching of the doping elements is crucial to the design and fabrication of this category of catalysts. Herein, by annealing commercially available and cost-effective precursors, Fe-N-S codoped graphene-like carbon nanosheet catalysts were prepared. The atomically dispersed Fe atoms coordinated with the N atoms to form FeN4 sites as proved by X-ray absorption spectroscopy. By facile modulation of the relative amount of the precursors, the contents of thiophene-S (Th-S) and Fe-N4 sites could be tuned and a series of catalysts with different Th-S/Fe ratios were prepared. The doped sulfur exhibited an enhancement effect on ORR performance, and strikingly, the enhancement efficiency could be optimized by fine modulation of the Th-S/Fe ratio in the catalysts. Furthermore, it was found that when the Th-S/Fe ratio reached an optimal value of 1.8, the ORR performance was significantly boosted, especially in acidic media. The experimental data were supported by density functional theory calculation results, which indicated that the ORR overpotential of the S2(FeN4) configuration model (corresponding to the Th-S/Fe ratio of 2) was lower than that of S3(FeN4) and S1(FeN4). The optimized catalyst (denoted as FeN/SNC-900-3) displayed highly efficient ORR activity in both alkaline and acidic media. In alkaline media, the half-wave potential was 49 mV more positive than that of the commercial Pt/C catalyst, and in acidic media, the half-wave potential was close to that of Pt/C. Moreover, the stability of FeN/SNC-900-3 was outstanding, and the relative current density showed only a slight decay in both alkaline and acidic media after 40,000 s. A primary Zn-air battery with FeN/SNC-900-3 as the cathode catalyst exhibited a high peak power density of up to 153 mW cm-2 and superior cycling stability over 200 cycles.

Indiscrete metal/metal-N-C synergic active sites for efficient and durable oxygen electrocatalysis toward advanced Zn-air batteries

Carbon has been deemed promising electrocatalyst for oxygen reduction/evolution reaction (ORR/OER). However, most carbon materials are not stable in highly oxidative OER environments. Herein, nitrogen (N) and transition metal (TM) co-doped carbon nanosheets hybridizing with transition metal (TM/TM-N-C, TM = Fe, Co, Ni) are developed from biomass lysine by employing a NaCl template and molten-salt-promoted graphitization process. Among the as-synthesized TM/TM-N-C, the Ni/Ni-N-C with Ni nanocubes embedded in carbon demonstrates an excellent ORR-OER stability during the potential of 0.06–1.96 V. The rechargeable Zn-air battery with the fabricated Ni/Ni-N-C as the cathode catalyst produces a low voltage gap of 0.773 V, which is only slightly increased by 5 % after 150 cycles testing. Combined experimental and theoretical studies reveal that the exceptional activity and ORR-OER wide potential durability of Ni/Ni-N-C can be ascribed to highly active Ni-N4-C configuration, synergistic effect between Ni and Ni-N4-C, carbon nanosheets structure and formation of stable Ni3+-N for protecting carbon from oxidation.

Ultra-low cobalt loading on N-doped carbon nanosheets by polymer pyrolysis strategy for efficient electrocatalytic hydrogen evolution

Electrocatalytic hydrogen evolution reaction (HER) is a promising way to obtain H2, which has been deemed an ideal alternative for fossil fuel because of its renewable and environmental-friendly benefits. Developing a simple and flexible strategy to synthesize non-noble metal HER catalysts to provide high performance is needed for commercial applications. Here, a cobalt, nitrogen co-doped carbon nanosheet catalyst (Co-N-C-Mel) is reported. The catalyst was obtained via pyrolysis of a coordination polymer, amidoxime polyacrylonitrile (aoPAN), coordinated by Co ions. Benefiting from the ultra-low Co loading (0.47 at%), the catalyst provides effective catalytic activity for HER. The overpotential is only 138 mV in 0.5 M sulfuric acid and 196 mV in 1 M potassium hydroxide at the current density of 10 mA/cm−2 (j = 10 mA cm−2). In addition, the Co-N-C-Mel catalyst is efficient and stable for 10000 s without obvious recession.

Preparation of molybdenum phosphide nanoparticles/nitrogen-phosphorus co-doped carbon nanosheet composites for efficient hydrogen evolution reaction

The molybdenum phosphide (MoP) nanoparticles supported by phosphorus and nitrogen co-doped carbon nanosheet (N, P–C) have been prepared through simple one-step calcination method. The composition and morphology of the prepared hybrids were further characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and so on. The characterization results prove that the annealing temperature plays an essential role in the fabrication of nanosheets morphology. All characterization results prove that the MoP nanoparticles were uniformly loaded on N,P–C nanosheets. As excepted, the unique nanosheet structure not only contributes to mass transfer and electron transfer, but also increases electrochemical surface area. The obtained MoP/N,P–C-900 composites exhibit excellent HER activity and long-time stability (η ​= ​129 ​mV for reaching 10 ​mA ​cm−2 and 10 ​h for successive testing), which is superior than many other non-precious metal electrocatalysts. The present work affords a promising strategy for designing novel HER electrocatalysts, which may be applied in storage systems and diverse energy conversion.

Constructing an interface synergistic effect from a SnS/MoS2 heterojunction decorating N, S co-doped carbon nanosheets with enhanced sodium ion storage performance

Bimetallic sulfide SnS/MoS2 heterostructures decorating N, S co-doped carbon nanosheets have been synthesized, and evaluated as high performance anode materials for SIBs.

Template-free synthesis of graphene-like carbons as efficient carbocatalysts for selective oxidation of alkanes

The N-doped and N/S codoped carbon nanosheets were fabricated by metal-free carbonization of nucleobase, which can be used as efficient carbocatalysts for selective oxidation of alkanes.

Cobalt/nitrogen codoped carbon nanosheets derived from catkins as a high performance non-noble metal electrocatalyst for oxygen reduction reaction and hydrogen evolution reaction

Novel energy devices which are capable of alleviating and/or solving the energy dilemma such as overall water splitting and fuel cells require the development of highly efficient catalysts, especially cheap high performance non-precious metal (NPM) catalysts. Here, we prepare highly efficient NPM catalysts of cobalt and nitrogen codoped carbon nanosheets (Co/N–CNSs) for oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) using harmful environment-polluting waste of biomass catkins as carbon precursors via a mild mechanical exfoliation and chemical process which is facile, low-cost, environmentally friendly and up-scalable. Compared with a commercial platinum-based catalyst (commercial 20% Pt/C), the Co/N–CNS electrocatalysts show outstanding ORR activity, acceptable HER activity and long term stability with an onset potential of 0.92 V versus the reversible hydrogen electrode (vs. RHE) and a half-wave potential of 0.83 V vs. the RHE in alkaline electrolytes. The excellent performance is closely related to the presence of abundant CoNx active sites. This work offers a novel and effective approach for preparing highly efficient ORR and HER NPM electrocatalysts from waste biomass materials.

Thin metal organic layer derived Co/Co9S8/N,S co-doped carbon nanosheets synthesized by the space confinement effect of montmorillonite for oxygen electrocatalysis

Co/Co9S8 anchored to N,S co-doped carbon nanosheets resulting T-CCSNC electrocatalysts show excellent ORR and OER catalytic activity and stability.

In situ self-activation synthesis of binary-heteroatom co-doped 3D coralline-like microporous carbon nanosheets for high-efficiency energy storage in flexible all-solid-state symmetrical supercapacitors

Binary-heteroatom co-doped microporous carbon nanosheets were prepared by a facile, one-step, in situ self-activation strategy.

Three-dimensional nitrogen-sulfur codoped layered porous carbon nanosheets with sulfur-regulated nitrogen content as a high-performance anode material for potassium-ion batteries.

Three-dimensional nitrogen-sulfur codoped layered porous carbon nanosheets (3D-NSCNs) with sulfur-regulated nitrogen content are constructed as a high-performance anode material for potassium-ion batteries (KIBs) through a gel and nitrogen-sulfur codoping process. Compared with the sample without sulfur doping, the 3D-NSCNs reveal enhanced electrical conductivity, specific surface area, and pyrrolic (N-5) and pyridinic (N-6) nitrogen contents, all of which are beneficial for increased electrochemical performances. After 200 cycles at a current density of 100 mA g-1, the 3D-NSCNs anode exhibits a specific capacity of 254.9 mA h g-1. After 2900 cycles at a higher charge-discharge current density of 1 A g-1, the specific capacity is still 171.1 mA g-1, and the capacity retention is 78.9%, indicating the application potential of the as-synthesized 3D-NSCNs as an anode material for KIBs. Domination by a surface-driven mechanism is proposed to explain the excellent rate and cycle performances and can also be validated by galvanostatic intermittent titration results, which show that the K+ diffusion coefficient in the 3D-NSCNs is improved after nitrogen-sulfur doping. This work demonstrates a new strategy to improve the electrochemical properties of carbon-based K-storage materials by increasing the N-5 and N-6 contents through sulfur doping while also producing micropores to increase the number of active sites.

Boosting bifunctional electrocatalytic activity in S and N co-doped carbon nanosheets for high-efficiency Zn–air batteries

The synergistic effect of N and S endows S and N-codoped carbon nanosheets excellent bifunctional catalytic activity in Zn–air batteries.

Nucleobase derived boron and nitrogen co-doped carbon nanosheets as efficient catalysts for selective oxidation and reduction reactions.

The search for active, stable and cost-efficient carbocatalysts for selective oxidation and reduction reactions could make a substantial impact on the catalytic technologies that do not rely on conventional metal based catalysts. Here we report a facile strategy for the synthesis of boron (B) and nitrogen (N) co-doped carbon nanosheets (BNC) by using biomolecule guanine as a carbon (C) and N source and boric acid as the B precursor. The whole synthesis process which leads to the formation of a two dimensional (2D) structure and mesoporosity with high surface areas is simple, metal-free and template-free. The as-synthesized carbon nanosheets possess a series of merits, such as relatively high specific surface area, satisfactory pore structure, enough structural defects, abundant B and N dopants as well as oxygen functional groups. The catalytic assessments demonstrate that the presented carbon catalyst is highly active and selective for the liquid phase oxidation of ethyl lactate to ethyl pyruvate and the reduction of nitrobenzene to aniline and outperforms other equivalent benchmarks. Control experiments confirm the importance of the B and N co-doping as well as the carbon matrix which benefit the electron transfer. The carbonyl group masking test indicates that carbonyl groups play an important role in both the selective oxidation and reductions. Given the diversity in the structure of the nucleobase moiety, they represent ideal building blocks for the catalyst-free and metal-free formation of 2D carbon architectures, only induced by hydrogen bonds. This B and N co-doped synthesis strategy provides guidance for the design of carbon-based catalysts for selective oxidation and reductions.

MnS nanoparticles embedded in N,S co-doped carbon nanosheets for superior lithium ion storage

Manganese sulfide has been explored as anode for LIBs owing to its impressive theoretical capacity. However, inferior electronic/ionic conductivity and severe volume expansion occurring during the electrochemical cycle usually result in poor electrochemical performance. In this report, a novel composite, MnS nanoparticles integrating N,S co-doped carbon nanosheets (N,S-C) grown on flexible carbon fiber cloth (MnS@N,S-C/CFC), is fabricated as anode material for LIBs. The N,S co-doped carbon nanosheets protect MnS particles from aggregation so as to facilitate nanosized structure formation, significantly accelerating Li+ diffusivity and accommodating stress/strain caused by volume changes. Nanosheets are also connected by CFC substrate to provide the transmission pathway of the electrons and promote fast electron transfer. Morever, compared to the MnS/CFC particles, the remarkably boosted integration between MnS@N,S-C and CFC substrate ensures superior conductivity and improved mechanical stability. Consequently, the MnS@N,S-C/CFC electrode delivers superior specific capacity of 800 mAh g−1 at 0.05 A g−1 as well as excellent rate-capability (535 mAh g−1 up to 2 A g−1), and improved durability (maintaining 52.7% after 500 cycles at 2 A g−1), presenting a simple strategy to boost the electrochemical performance of LIBs anodes by encapsulation of conductive carbon and heteroatom doping.