Heteroatom-doped Carbon Research Articles

Nitrogen-doped hierarchically ellipsoidal porous carbon derived from Al-based metal-organic framework with enhanced specific capacitance and rate capability for high performance supercapacitors

Nitrogen-doped porous carbon is prepared by the fusion and carbonization processes of Al-based metal-organic frameworks and melamine, and following removal of thermal decomposed Al2O3 via dissolving in NaOH solution. The hierarchically porous carbon has a large surface area of 1452 m2 g−1 with mesopores of suitable size (4.64 nm). It exhibits an enhanced specific capacitance and rate capability of 318.7 F g−1(1 A g−1) and 210.5 F g−1 (100 A g−1), respectively. The cycling life tests indicate the material offers superior stability with 96.4% retention at ultra-high current density of 100 A g−1 during 50, 000 cycles. The improved electrochemical properties of this carbon can be attributed to the exogenous nitrogen-doping, special ellipsoid shape and hierarchically porous structure. This method is a new potential strategy to configure unique structure and particular heteroatom-doped porous carbon material for power supercapacitors via the fusion of metal-organic frameworks and heteroatom-containing polymer.

Electrode Materials for Rechargeable Zinc-Ion and Zinc-Air Batteries: Current Status and Future Perspectives

Advanced energy storage systems hold critical significance in satisfying the ever-increasing global demand for energy. And as a viable and effective alternative to lithium-ion batteries that dominate the current energy market, Zn-based batteries [i.e. Zn-ion batteries (ZIBs) and Zn-air batteries (ZABs)] have attracted extensive research efforts. Zn metal possesses many advantages because of its high theoretical capacity, its inexpensiveness and its good safety characteristic, and in recent years, tremendous efforts have been carried out to accelerate the development of ZIBs and ZABs with various electrode materials and electrocatalysts being proposed and investigated. In addition, with advances in characterization techniques, the underlying reaction mechanisms of these materials are also being elucidated. Therefore, this review will provide a comprehensive summary of the latest progress in various electrode materials adopted in the current ZIBs and ZABs along with corresponding mechanisms. Specifically, Mn- and V-containing cathode materials for ZIBs and associated reaction mechanisms will be thoroughly discussed, and emerging cathodes such as Prussian blue analogues, NASICON-type nanostructures and organic compounds will be presented. In terms of ZABs, this review will discuss three major types of electrocatalysts, including noble metals, heteroatom-doped carbons and transition metal oxides/sulphides/phosphides/nitrides. In addition, as a critical factor in the performance of Zn-based batteries, challenges encountered by the current Zn anodes and strategies developed to tackle these issues will be discussed as well. Finally, a short summary including the current progress and future perspectives of ZIBs and ZABs will be provided.

Efficient hydrogen evolution from ammonia borane hydrolysis with Rh decorated on phosphorus-doped carbon

Development of supported ligand-free ultrafine Rh nanocatalysts for efficient catalytic hydrogen evolution from ammonia borane (AB) is of importance but remains a tremendous challenge. Here, ultrafine and ligand-free Rh nanoparticles (NPs) (2.19 nm in diameter) were in-situ decorated on porous phosphorus-functionalized carbon (PPC) prepared by pyrolyzing hyper-cross-linked networks of triphenylphosphine and benzene. The resultant Rh/PPC showed excellent hydrogen production activity from AB hydrolysis (Turnover frequency: 806 min−1). Kinetic investigations indicated that AB hydrolysis using Rh/PPC exhibited first-order and zero-order reactions with Rh and AB concentrations, respectively. Activation energy (Ea) toward hydrogen generation from AB with Rh/PPC is as low as 22.7 kJ/mol. The Rh/PPC catalyst was recyclable and reusable for at least four times. The oxygen- and phosphorus-functional groups are beneficial for the affinity of Rh complex on the PPC surface, resulting in ultrafine and ligand-free Rh NPs with high dispersity and ability to supply abundant surface accessibility to catalytically active sites for AB hydrolysis. This study proposes a feasible approach for the synthesis of ultrafine and ligand-free metal NPs supported on heteroatom-doped carbon by using hyper-cross-linked networks.

Heteroatom-doped porous carbon with tunable pore structure and high specific surface area for high performance supercapacitors

Biomass-derived porous carbons with very high specific surface area (SSA) and heteroatom-doping are important for obtaining high performance supercapacitor. In this study, we report a simple and straightforward strategy, which involves the efficient and exothermic pyrolysis of Mg/K/Mg·K-nitrate-urea-cellulose mixture with subsequent high temperature carbonization and washing treatment, to produce N-doped porous carbon with tunable pore structure. The vigorous exothermic pyrolysis of Mg/K/Mg·K-nitrate-urea-cellulose induces the formation of large macropores. The subsequent high temperature carbonization and washing treatments remove Mg,K compounds and facilitate the creation of numerous micro and mesopores. The pore size distribution of the obtained carbon is quite dependent on the Mg·K ratio in the precursors. In this manner, the three-dimensional hierarchical porous carbon with SSA larger than 2700 m2 g−1 is obtained. The obtained porous carbon as the electrodes for supercapacitor in two-electrode measurement shows high specific capacitance (279 F g−1 at 1 A g−1 in a 6 M KOH electrolyte), excellent cycling stability (larger than 89% capacitance retention after 10,000 cycles at 2 A g−1) and good rate capability (235 F g−1 at even 30 A g−1). These results indicate that biomass cellulose-derived heteroatom-doped hierarchical porous carbon is a promising material for supercapacitor.

Selective Activation of S or N-Containing Carbon Segments by Alkalic or Acidic Activators

To date, the activation reactions of heteroatom-containing carbon segments have not been systematically studied. Here, activation of S,N dual-doped petroleum coke (SNC) by acidic (CO2), alkalic (KOH and NH3), and neutral (H2O) activators is investigated. The reactions between activators and S/N-containing segments are similar to the typical acid–base reactions. SNC exhibits higher activation reactivity as compared to the undoped carbon, thus leading to a high SSA even at low activation temperature. S-Containing groups exhibit higher reactivity to alkalic activators, and N-containing groups show higher reactivity to acidic activators. Compared to the activation by KOH, activation by CO2 and NH3 can lead to a high retention of S and N content, thus resulting in higher area-normalized capacitance in a three-electrode supercapacitor. Our results give better understanding of the activation mechanism of heteroatom-doped carbons and provide an easy method to selectively remove or keep heteroatoms during activation.

Nitrogen-Doped Mesoporous Carbon Layer with Embedded Co/CoOx Nanoparticles Coated on CNTs for Oxygen Reduction Reaction in Zn–Air Battery

One-dimension (1D) heteroatom-doped mesoporous carbon is a promising alternative catalyst for oxygen reduction reaction (ORR). This work reported a hybrid ORR electrocatalyst composed of Co/CoOx nanoparticles embedded in N-doped mesoporous carbon layer coated on carbon nanotubes (CNTs@Co–N–C). Owing to the 1D mesoporous architecture with abundant active sites, CNTs@Co–N–C hybrid showed superior ORR activity, high selectivity, and long-term durability. Moreover, as cathode catalyst for primary Zn–air battery, CNTs@Co–N–C also showed excellent performance comparable to Pt/C. Thus, this study can offer a good idea for preparing noble-metal-free electrocatalysts for energy applications.

(Invited) Electrochemical Oxygen Reduction Catalyzed at Pt–Ni Nanostructured Electrocatalysts Immobilized on Nitrogen-Doped Carbon Supports

Oxygen reduction reaction (ORR) is the key reaction in future energy generation devices such as polymer electrolyte fuel cells (PEFCs) and metal–air batteries. To drive the ORR in state-of-the-art PEFCs, carbon-supported Pt–M alloys (M = Ni and Co) are used. Since platinum is rare and expensive, there is a need to develop ORR electrocatalysts with not only high catalytic activity but also high durability. Under electrocatalytic conditions, catalyst degradation mechanisms are known to involve many processes including particle detachment, agglomeration and metal dissolution.[1] These phenomena can be suppressed by increase metal/support interactions. Carbon black is typically used as the catalyst support and can be chemically modified by heteroatom-doping. Heteroatom-doped carbon supports can show strong metal/support interactions with Pt nanoparticles.[2] Herein, we report the enhancement of electrocatalytic ORR activity and durability of Pt–Ni alloy nanoframes by immobilization on nitrogen-doped carbon supports. Strong metal/support interactions between the nanoframe and the support caused the downshift of the d-band center position of the surface Pt, proved by X-ray photoelectron spectroscopy and surface-enhanced infrared absorption spectroscopy.[3] In situ X-ray absorption spectroscopy also revealed that the Pt surface oxide formation was suppressed by the immobilization on nitrogen-doped carbon supports. Our findings demonstrate that tuning the electronic structure of nanostructured Pt alloy electrocatalysts via strong metal/support interactions will allow the development of highly active and robust electrocatalysts for the ORR.

Graphitic Carbon Nitride (g-C3 N4 )-Derived N-Rich Graphene with Tuneable Interlayer Distance as a High-Rate Anode for Sodium-Ion Batteries.

Heteroatom-doped carbon materials with expanded interlayer distance have been widely studied as anodes for sodium-ion batteries (SIBs). However, it remains unexplored to further enlarge the interlayer spacing and reveal the influence of heteroatom doping on carbon nanostructures for developing more efficient SIB anode materials. Here, a series of N-rich few-layer graphene (N-FLG) with tuneable interlayer distance ranging from 0.45 to 0.51 nm is successfully synthesized by annealing graphitic carbon nitride (g-C3 N4 ) under zinc catalysis and selected temperature (T = 700, 800, and 900 °C). More significantly, the correlation between N dopants and interlayer distance of resultant N-FLG-T highlights the effect of pyrrolic N on the enlargement of graphene interlayer spacing, due to its stronger electrostatic repulsion. As a consequence, N-FLG-800 achieves the optimal properties in terms of interlayer spacing, nitrogen configuration and electronic conductivity. When used as an anode for SIBs, N-FLG-800 shows remarkable Na+ storage performance with ultrahigh rate capability (56.6 mAh g-1 at 40 A g-1 ) and excellent long-term stability (211.3 mAh g-1 at 0.5 A g-1 after 2000 cycles), demonstrating the effectiveness of material design.

Effect of two-step doping pathway on the morphology, structure, composition, and electrochemical performance of three-dimensional N,S-codoped graphene framework

Abstract

Hierarchical nitrogen-doped porous carbon/carbon nanotube composites for high-performance supercapacitor

Abstract Heteroatom-doped hierarchical porous carbon materials have aroused widespread concern in the field of supercapacitors due to their effective ion-accessible surface, abundant porosity and low manufacturing cost. However, their relatively poor electric conductivity might not completely meet the requirements of comprehensive application of supercapacitor. Herein, to further promote conductivity of porous carbon, an all carbon nanocomposite was successfully fabricated by implanting carbon nanotubes (CNTs) into the surface and edge of hierarchical porous carbon (HPC). The sp2 CNTs endows the composites with high conductivity and connect porous carbons to each other, which renders rapid ion transfer and store during charge/discharge process. Benefiting from strong bonding effects due to plentiful heteroatom functional groups, the nitrogen-doped hierarchical porous carbon/CNT hybrid exhibits considerable charge transport ability, superior specific capacitance of 293.1 F g−1 at current density of 1 A g−1 and high rate capability of 207.0 F g−1 at 30 A g−1. Furthermore, the assembled symmetric supercapacitor displays a high energy density of 27.46 Wh kg−1 at the power density of 874.98 W kg−1. The unique hierarchical three-dimensional hybrid structure provides a novel way to develop conductive carbon electrode materials for advanced supercapacitors.

Synthesis and electrochemical properties of benzoxazine-based heteroatom-doped carbon materials

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Intrinsic Carbon-Defect-Driven Electrocatalytic Reduction of Carbon Dioxide.

Heteroatom-doped carbon catalysts are currently attracting enormous attention due to their excellent performance for the electrocatalytic carbon dioxide reduction reaction (ECRR). However, the origin of the high catalytic activities of doped-carbon materials remains obscure with the role of intrinsic carbon defects in promoting the ECRR receiving little attention despite the abundance of carbon defects in all carbon-based catalytic materials. Herein, a positive correlation is reported between the ECRR performance of carbon-based catalysts and the content of intrinsic carbon defects contained within these catalysts. Further, it is demonstrated that defective porous carbon catalysts containing no active heteroatom dopants also show excellent catalytic performance for ECRR. C K-edge near edge X-ray absorption fine structure measurements and density functional theory calculations reveal that sp2 defects (octagonal and pentagonal) rather than edge defects are key to the excellent ECRR activity of the defective porous carbon catalysts. This work thus makes an important contribution to the understanding of the origin of the ECRR activity of carbon-based catalysts, with heteroatom doping perhaps being less important than previously envisaged for achieving a high ECRR performance.

Controllable Sulfur, Nitrogen Co-doped Porous Carbon for Ethylbenzene Oxidation: The Role of Nano-CaCO3.

Heteroatom-doped porous carbon materials have exhibited promising applications in various fields. In this work, sulfur, nitrogen co-doped carbon materials (SNCs) with abundant pore structure were prepared by pyrolysis of sulfur, nitrogen-containing porous organic polymers (POPs) mixed with nano-CaCO3 at high temperature. Among the resultant materials, SNC-Ca-850 possesses a relatively high level of doped heteroatoms and exhibits an excellent catalytic performance for the selective oxidation of benzylic C-H bonds. It is noteworthy that nano-CaCO3 increases the doped sulfur content in the synthesized carbon materials to a large extent and impacts the existence modes of sulfur. In addition, it enhances the porous structure and specific surface area of the resultant SNCs significantly. This work provides a viable strategy to promote the doping of sulfur into carbon materials during the pyrolysis process.

Atomically dispersed nickel\u2013nitrogen\u2013sulfur species anchored on porous carbon nanosheets for efficient water oxidation

Developing low-cost electrocatalysts to replace precious Ir-based materials is key for oxygen evolution reaction (OER). Here, we report atomically dispersed nickel coordinated with nitrogen and sulfur species in porous carbon nanosheets as an electrocatalyst exhibiting excellent activity and durability for OER with a low overpotential of 1.51 V at 10 mA cm−2 and a small Tafel slope of 45 mV dec−1 in alkaline media. Such electrocatalyst represents the best among all reported transition metal- and/or heteroatom-doped carbon electrocatalysts and is even superior to benchmark Ir/C. Theoretical and experimental results demonstrate that the well-dispersed molecular S|NiNx species act as active sites for catalyzing OER. The atomic structure of S|NiNx centers in the carbon matrix is clearly disclosed by aberration-corrected scanning transmission electron microscopy and synchrotron radiation X-ray absorption spectroscopy together with computational simulations. An integrated photoanode of nanocarbon on a Fe2O3 nanosheet array enables highly active solar-driven oxygen production.

Functionalized Carbon Dots on Graphene as Outstanding Non-Metal Bifunctional Oxygen Electrocatalyst.

Carbon-based bifunctional electrocatalysts for both oxygen reduction and evolution reactions are potentially cost-effective to replace noble metals in energy devices such as fuel cells, metal-air batteries, and photoelectrochemical converters, but enrichment of active sites holds the key to efficiency. Here, graphene frameworks with heteroatom-doped carbon dots (CDs) are developed via a hydrothermal route followed by pyrolysis. The CDs are rationally prepared with careful selection of heteroatoms, embedded on the substrate to provide enriched active sites. Structural characterizations (e.g., transmission electron microscopy and X-ray photoelectron spectroscopy) reveal the successful addition of CDs with nitrogen and sulfur species. Especially, a heat-treated N,S codoped sample, NS-CD@gf_a900, exhibits the optimum oxygen electrocatalysis, even closer to noble-metal counterparts, as a result of the effect of active sites of the CDs and the synergistic behavior of N and S. Considering the importance of size and dopants of the material, this approach not only suggests a straightforward preparation route of nanocarbons, but also appoints the utilization of a new class of non-metal species as efficient oxygen electrocatalysts.

Molten-salt strategy for fabrication of hierarchical porous N-doped carbon nanosheets towards high-performance supercapacitors

Abstract The efficient conversion of renewable biomass to advanced carbons with high porosity and heteroatoms doping is of huge significance towards energy-related applications. However, most of the resultant carbon materials are always bulk materials with low aspect ratio and unsatisfactory electronic properties owing to the severe activation process. In this work, the KNO3 modified molten-salt (KCl/LiCl) strategy is explored to fabricate two dimensional nitrogen-doped carbon nanosheets (NCNs) by using agaric as the precursor. Benefiting from its large surface area (1376 m2 g−1), high-ratio micro-porosity (72%), high-content N doping (4 at.%) and high graphitization, the optimized NCNs sample is endowed with exceptional electrochemical capacitances both in aqueous electrolyte (6 M KOH) and organic electrolyte (1 M tetraethylammonium tetrafluoroborate/acetonitrile), when evaluated as a competitive electrode for supercapacitors. It is strongly envisioned that the method developed here holds great potential for advanced porous heteroatom-doped carbons from natural biomass for next-generation supercapacitors.

Fabrication of nitrogen-doped hollow carbon nanospheres with variable nitrogen contents using mixed polymer brushes as precursors

Design and synthesis of heteroatoms-doped porous carbon model materials with controllable nitrogen contents and similar pore structure are of great importance for fundamental understanding of the correlation between their intrinsic properties and applications. Herein, we report a synthetic strategy for synthesis of nitrogen-doped hollow carbon nanospheres with variable nitrogen contents, similar pore structure and morphology by pyrolysis of mixed polymer brushes formed through surface-initiated atom transfer radical polymerization of monomer mixtures of styrene and 4-vinylpyridine. With increasing 4-vinylpyridine fractions in the monomer mixture, nitrogen contents in the final carbon products increase up to about 5.5 wt%. As example applications, electrocatalytic performance for oxygen reduction reactions in both basic and acidic media and carbon dioxide adsorption properties of the thus-formed materials are investigated to evaluate the synthetic approach. The results reveal that the higher nitrogen contents doped in carbon do not guarantee the better performance for either electrocatalysis or carbon dioxide adsorption. It is the fraction of pyridinic nitrogen that dominates the electrocatalytic activity and carbon dioxide adsorption capacity. The findings demonstrate that mixed polymer brushes are promising precursors for the formation of heteroatoms-doped carbon materials, particularly as model materials for fundamental understanding their structure–properties correlations.

Nanoporous Heteroatom-Doped Carbons Derived from Cotton Waste: Efficient Hydrazine Oxidation Electrocatalysts

In this work, cotton-based denim waste is successfully used as a precursor to synthesize nanoporous P- and N-co-doped carbon materials that can serve as efficient electrocatalysts for the hydrazine oxidation reaction (HzOR). In the synthesis, the cotton denim waste is mixed with H3PO4 in two different denim/H3PO4 (wt/vol) ratios, namely, 1:1 and 1:3, wherein H3PO4 serves as both an activating agent and a source of P dopant atoms while the indigo carmine dye present in denim serves as a source of N dopant atoms to the carbon materials. The resulting P- and N-co-doped carbon materials, named PNC1 and PNC3, respectively, are characterized by various analytical techniques. The XPS spectra show that PNC1 has ca. 2.17 atomic % P and 1.95 atomic % N whereas PNC3 has 2.54 atomic % P and 0.71 atomic % N. Pore analyses by N2 porosimetry indicate that PNC1 has a higher surface area (1582 m2 g–1) than PNC3 (486 m2 g–1), although the former has a lower mesopore volume (0.39 cm3 g–1) than the latter (0.58 cm3 g–1). The...

High-performance voltammetric sensor for dichlorophenol based on β-cyclodextrin functionalized boron-doped graphene composite aerogels

2, 2-methylenebis (4-chlorophenol) (dichlorophenol, Dcp) is a priority pollutant that poses a serious health threat to the public. Thus, the sensitive analysis of Dcp is of great significance. Heteroatom-doped carbon nanomaterials modified electrodes have been proven to be good electrocatalysts for electrochemical sensing application. β-cyclodextrin (β-CD) as a signal amplifier has also been utilized in biosensors. Inspired by these, in this study, a new composite of β-CD and three-dimensional (3D) boron-doped graphene aerogels (BGAs/β-CD) has been designed as a high-performance electrochemical sensing platform for Dcp determination. Graphene aerogels possess high specific surface area, large pore volume and good conductivity, which ensure rapid mass transfer and accelerated electron transfer. Besides, boron doping causes uneven charge distribution on the graphene lattice surface, producing a large amount of flowing π electrons, which provide abundant active sites for the catalytic oxidation reaction of Dcp. In addition, Dcp molecules could be captured into β-CD through host-guest recognition, which can effectively amplify the detection signal. Combining the merits of BGAs and β-CD, the BGAs/β-CD based sensor achieved sensitive detection of Dcp. Under optimized experimental conditions, the oxidation currents and the concentration of Dcp had a good linear relationship within 1.0 nM ∼ 21 μM. The detection limit was estimated as 0.33 nM (S/N = 3). This study might provide a new basis for the fabrication of 3D BG-based aerogel architectural material and its application in Dcp detection.

Outstanding long-term cycling stability of a sulfur-doped graphene electrode for supercapacitors obtained by post-tailoring the chemical states of doped-sulfur

For further enhancing the supercapacitive performances of carbon materials, heteroatoms-doping has proved to be one of the most promising approaches. Up to now, most of the researches focus on the effects of the dopant type and the doping amount. However, it is presently not understood how affects the capacitive performances if the chemical states of the heteroatom doped in carbon materials are further tailored. In this paper, we report for the first time the effect of post-tailoring the chemical states of doped‑sulfur on the supercapacitive performances of a sulfur-doped graphene. In our post-tailoring strategy, the S-doping is firstly realized by thermally treating the H2SO4-GIC compound, and then the chemical states of doped-S are post-tailored by the subsequent Hummers' oxidation. Our work has demonstrated that a unique oxidized-S species (CS(O)xC), which is transformed from the thiophene-S species by the Hummers' oxidation, has superior contribution to the supercapacitive performances (e.g., specific capacitance, rate performance and long-term cycling stability). Interestingly, the S-doped graphene sample, which contains the highest content of the unique oxidized-S species, exhibits an outstanding long-term cycling stability, its capacitance retention being up to 100.8% after 10,000 consecutive cycling test, far higher than those previously report for the heteroatom-doped carbon materials. The present work suggests that post-tailoring the chemical states of the doped-heteroatoms can be considered as an effective strategy to obtain the optimal electrochemical performances for the heteroatoms-doped carbon materials.