首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 31 毫秒
1.
Nanoporous carbons (NPCs) with engineered specific pore sizes and sufficiently high porosities (both specific surface area and pore volume) are necessary for storing energy in the form of electric charges and molecules. Herein, NPCs, derived from biomass pine‐cones, coffee‐grounds, graphene‐oxide and metal‐organic frameworks, with systematically increased pore width (<1.0 nm to a few nm), micropore volume (0.2–0.9 cm3 g?1) and specific surface area (800–2800 m2 g?1) are presented. Superior CO2, H2, and H2O uptakes of 35.0 wt% (≈7.9 mmol g?1 at 273 K), 3.0 wt% (at 77 K) and 85.0 wt% (at 298 K), respectively at 1 bar, are achieved. At controlled microporosity, supercapacitors deliver impressive performance with a capacity of 320 and 230 F g?1 at 500 mA g?1, in aqueous and organic electrolytes, respectively. Excellent areal capacitance and energy density (>50 Wh kg?1 at high power density, 1000 W kg?1) are achieved to form the highest reported values among the range of carbons in the literature. The noteworthy energy storage performance of the NPCs for all five cases (CO2, H2, H2O, and capacitance in aqueous and organic electrolytes) is highlighted by direct comparison to numerous existing porous solids. A further analysis on the specific pore type governed physisorption capacities is presented.  相似文献   

2.
Zeolite‐templated, high‐surface‐area, microporous, N‐doped carbons exhibit the highest CO2 uptake capacity recorded to date for any carbon material and one of the highest for any inorganic or organic porous material of up to 6.9 mmol g?1 at 273 K and ambient pressure and 4.4 mmol g?1 at ambient temperature and pressure, along with an initial CO2 adsorption energy of 36 kJ mol?1 at lower coverage and 20 kJ mol?1 at higher CO2 coverage. Combined with their ease of preparation, excellent recyclability and regeneration stability, and high selectivity for CO2, the N‐doped zeolite‐templated carbons are amongst the most promising solid‐state absorbents reported so far for CO2 capture and storage.  相似文献   

3.
A series of experiments is presented that establishes for the first time the role of some of the key design parameters of porous carbons including surface area, pore volume, and pore size on battery performance. A series of hierarchical porous carbons is used as a model system with an open, 3D, interconnected porous framework and highly controlled porosity. Specifically, carbons with surface areas ranging from ≈500–2800 m2 g?1, pore volume from ≈0.6–5 cm3 g?1, and pore size from micropores (≈1 nm) to large mesopores (≈30 nm) are synthesized and tested. At high sulfur loadings (≈80 wt% S), pore volume is more important than surface area with respect to sulfur utilization. Mesopore size, in the range tested, does not affect the sulfur utilization. No relationship between porosity and long‐term cycle life is observed. All systems fail after 200–300 cycles, which is likely due to the consumption of the LiNO3 additive over cycling. Moreover, cryo‐scanning transmission electron microscopy imaging of these carbon–sulfur composites combined with X‐ray diffraction (XRD) provides further insights into the effect of initial sulfur distribution on sulfur utilization while also revealing the inadequacy of the indirect characterization techniques alone in reliably predicting distribution of sulfur within porous carbon matrices.  相似文献   

4.
Crumpled nitrogen‐doped MXene nanosheets with strong physical and chemical coadsorption of polysulfides are synthesized by a novel one‐step approach and then utilized as a new sulfur host for lithium–sulfur batteries. The nitrogen‐doping strategy enables introduction of heteroatoms into MXene nanosheets and simultaneously induces a well‐defined porous structure, high surface area, and large pore volume. The as‐prepared nitrogen‐doped MXene nanosheets have a strong capability of physical and chemical dual‐adsorption for polysulfides and achieve a high areal sulfur loading of 5.1 mg cm–2. Lithium–sulfur batteries, based on crumpled nitrogen‐doped MXene nanosheets/sulfur composites, demonstrate outstanding electrochemical performances, including a high reversible capacity (1144 mA h g–1 at 0.2C rate) and an extended cycling stability (610 mA h g–1 at 2C after 1000 cycles).  相似文献   

5.
Natural gas is the cleanest fossil fuel source. However, natural gas wells typically contain considerable amounts of CO2, with on‐site CO2 capture necessary. Solid sorbents are advantageous over traditional amine scrubbing due to their relatively low regeneration energies and non‐corrosive nature. However, it remains a challenge to improve the sorbent's CO2 capacity at elevated pressures relevant to natural gas purification. Here, the synthesis of porous carbons derived from a 3D hierarchical nanostructured polymer hydrogel, with simple and effective tunability over the pore size distribution is reported. The optimized surface area reaches 4196 m2 g?1, which is among the highest of carbon‐based materials, with abundant micro‐ and narrow mesopores (2.03 cm3 g?1 with d < 4 nm). This carbon exhibits a record‐high CO2 capacity among reported carbons at elevated pressure (i.e., 28.3 mmol g?1 total adsorption at 25 °C and 30 bar). This carbon also shows good CO2/CH4 selectivity and excellent cyclability. Molecular simulations suggest increased CO2 density in micro‐ and narrow mesopores at high pressures. This is consistent with the observation that these pores are mainly responsible for the material's high‐pressure CO2 capacity. This work provides insights into material design and further development for CO2 capture from natural gas.  相似文献   

6.
Lithium–sulfur batteries (LSBs) are a class of new‐generation rechargeable high‐energy‐density batteries. However, the persisting issue of lithium polysulfides (LiPs) dissolution and the shuttling effect that impedes the efficiency of LSBs are challenging to resolve. Herein a general synthesis of highly dispersed pyrrhotite Fe1?xS nanoparticles embedded in hierarchically porous nitrogen‐doped carbon spheres (Fe1?xS‐NC) is proposed. Fe1?xS‐NC has a high specific surface area (627 m2 g?1), large pore volume (0.41 cm3 g?1), and enhanced adsorption and electrocatalytic transition toward LiPs. Furthermore, in situ generated large mesoporous pores within carbon spheres can accommodate high sulfur loading of up to 75%, and sustain volume variations during charge/discharge cycles as well as improve ionic/mass transfer. The exceptional adsorption properties of Fe1?xS‐NC for LiPs are predicted theoretically and confirmed experimentally. Subsequently, the electrocatalytic activity of Fe1?xS‐NC is thoroughly verified. The results confirm Fe1?xS‐NC is a highly efficient nanoreactor for sulfur loading. Consequently, the Fe1?xS‐NC nanoreactor performs extremely well as a cathodic material for LSBs, exhibiting a high initial capacity of 1070 mAh g?1 with nearly no capacity loss after 200 cycles at 0.5 C. Furthermore, the resulting LSBs display remarkably enhanced rate capability and cyclability even at a high sulfur loading of 8.14 mg cm?2.  相似文献   

7.
Iron‐ or cobalt‐coordinated heteroatom doped carbons are promising alternatives for Pt‐based cathode catalysts in polymer‐electrolyte fuel cells. Currently, these catalysts are obtained at high temperatures. The reaction conditions complicate the selective and concentrated formation of metal–nitrogen active sites. Herein a mild procedure is introduced, which is conservative toward the carbon support and leads to active‐site formation at low temperatures in a wet‐chemical metal‐coordination step. Active‐site imprinted nitrogen doped carbons are synthesized via ionothermal carbonization employing Lewis‐acidic Mg2+ salt. The obtained carbons with large tubular porosity and imprinted N4 sites lead to very active catalysts with a half‐wave potential (E1/2) of up to 0.76 V versus RHE in acidic electrolyte after coordination with iron. The catalyst shows 4e? selectivity and exceptional stability with a half‐wave potential shift of only 5 mV after 1000 cycles. The X‐ray absorption fine structure as well as the X‐ray absorption near edge structure profiles of the most active catalyst closely match that of iron(II)phthalocyanine, proving the formation of active and stable FeN4 sites at 80 °C. Metal‐coordination with other transition metals reveals that Zn–Nx sites are inactive, while cobalt gives rise to a strong performance increase even at very low concentrations.  相似文献   

8.
Rational design and preparation of SnO2‐based materials with superior electrochemical performance for lithium‐ion batteries are highly desirable. In this work, the synthesis of SnO2/nitrogen‐doped carbon (SnO2/NC) submicroboxes with excellent lithium storage properties is reported. The as‐synthesized SnO2/NC submicroboxes are highly porous with a high specific surface area of 125 m2 g?1, well‐defined hollow structure (around 400 nm in size) with a shell thickness of 40 nm, and ultrasmall SnO2 nanoparticles uniformly coated with nitrogen‐doped carbon layer. As a result, the SnO2/NC submicroboxes show outstanding electrochemical performance as an anode material for lithium‐ion batteries. A high reversible capacity of 491 mAh g?1 can be retained after 100 cycles at a current density of 0.5 A g?1.  相似文献   

9.
Active carbons have unique physicochemical properties, but their conductivities and surface to weight ratios are much poorer than graphene. A unique and facile method is innovated to chemically process biomass by “drilling” holes with H2O2 and exfoliating into graphene‐like nanosheets with HAc, followed by carbonization at a high temperature for highly graphitized activated carbon with greatly enhanced porosity, unique pore structure, high conductivity, and large surface area. This graphene‐like carbon exhibits extremely high specific capacitance (340 F g?1 at 0.5 A g?1) and high specific energy density (23.33 to 16.67 W h kg?1) with excellent rate capability and long cycling stability (remains 98% after 10 000 cycles), which is much superior to all reported carbons including graphene. Synthesis mechanism for deriving biomass into porous graphene‐like carbons is discussed in detail. The enhancement mechanism for the porous graphene‐like carbon electrode reveals that rationally designed meso‐ and macropores are very critical in porous electrode performance, which can network micropores for diffusion freeways, high conductivity, and high utilization. This work has universal significance in producing highly porous and conductive carbons from biomass including biowastes for various energy storage/conversion applications.  相似文献   

10.
Hierarchically porous nitrogen‐doped carbon (HPC)/polyaniline (PANI) nanowire arrays nanocomposites are synthesized by a facile in situ polymerization. 3D interconnected honeycomb‐like HPC was prepared by a cost‐effective route via one‐step carbonization using urea and alkali‐treated wheat flour as carbon precursor with a high specific surface area (1294 m2 g?1). The specific capacitances of HPC and HPC/PANI (with a surface area of 923 m2 g?1) electrode are 383 and 1080 F g?1 in 1 m H2SO4, respectively. Furthermore, an asymmetric supercapacitor based on HPC/PANI as positive electrode and HPC as negative electrode is successfully assembled with a voltage window of 0–1.8 V in 1 m Na2SO4 aqueous electrolyte, exhibiting high specific capacitance (134 F g?1), high energy density (60.3 Wh kg?1) and power density (18 kW kg?1), and excellent cycling stability (91.6% capacitance retention after 5000 cycles).  相似文献   

11.
Novel mechanochemical activation generates biomass‐derived carbons with unprecedented CO2 storage capacity due to higher porosity than analogous conventionally activated carbons but similar pore size. The mechanochemical activation, or so‐called compactivation, process involves compression, at 740 MPa, of mixtures of activating agent (KOH) and biomass hydrochar into pellets/disks prior to thermal activation. Despite the increase in surface area and pore volume of between 25% and 75% compared to conventionally activated carbons, virtually all of the porosity of the biomass (sawdust and lignin) derived mechanochemically activated carbons is from small micropores (5.8–6.5 Å), which results in a dramatic increase in CO2 storage capacity at 25 °C and low pressure (≤1 bar). The ambient temperature CO2 uptake for a carbon derived from sawdust at 600 °C and a KOH/carbon ratio of 2, rises from 1.3 to 2.0 mmol g?1 at 0.15 bar, and from 4.3 to 5.8 mmol g?1 at 1 bar, which is the highest ever reported for carbonaceous materials. The mechanochemically activated carbons have a superior CO2 working capacity for pressure swing adsorption and vacuum swing adsorption processes and, due to a high packing density, they exhibit excellent volumetric CO2 uptake that is higher than for any material reported to date.  相似文献   

12.
A facile approach to synthesize porous disordered carbon layers as energy storage units coating on graphene sheets to form interconnected frameworks by one‐step pyrolysis of the mixture of graphene oxide/polyaniline and KOH is presented. As effective energy storage units, these porous carbon layers play an important role in enhancing the electrochemical performances. The obtained porous carbon material exhibits a high specific surface area (2927 m2 g?1), hierarchical interconnected pores, moderate pore volume (1.78 cm3 g?1), short ion diffusion paths, and a high nitrogen level (6 at%). It displays both unparalleled gravimetric (481 F g?1) and outstanding volumetric capacitance (212 F cm?3) in an aqueous electrolyte. More importantly, the assembled symmetrical supercapacitor delivers not only high gravimetric (25.7 Wh kg?1 based on total mass of electroactive materials) but also high volumetric energy densities (11.3 Wh L?1) in an aqueous electrolyte. Furthermore, the assembled asymmetric supercapacitor yields a maximum energy density up to 88 Wh kg?1, which is, to the best of our knowledge, the highest value so far reported for carbon//MnO2 asymmetric supercapacitors in aqueous electrolytes. Therefore, this novel carbon material holds great promise for potential applications in energy‐related technological fields.  相似文献   

13.
Aqueous asymmetric supercapacitors (ASCs) may offer comparable or higher energy density than electric double‐layer capacitors (EDLCs) based on organic electrolytes. As such, ASCs may be more suitable for integration into smart textiles, where the use of flammable organic solvents is not acceptable. However, reported ASC devices typically suffer from poor rate capability and low areal loadings. This study demonstrates the development of nitrogen‐doped carbon (N‐C) nanowire/metal oxide (Fe2O3 and MnO2) nanocomposite electrodes directly produced on the internal surface of a conductive fabric for use as high‐rate electrodes for solid‐state ASCs. The N‐C nanowires provide fast and efficient pathways for electrons, while short diffusion paths within nanosized metal oxides enable fast ion transport, leading to greatly enhanced performance at high rates. The porous structure of the fabric enables high areal capacitance loading in each electrode (≈150 mF cm?2). Both electrodes show high specific capacitance of ≈180 F g?1 (Fe2O3) and ≈250 F g?1 (MnO2) and excellent rate capability. Solid‐state ASCs assembled by using an aqueous gel electrolyte operate at 1.6 V and deliver over 60 mF cm?2 during ≈50 s charging/discharging time and over 30 mF cm?2 for ≈5 s discharge.  相似文献   

14.
Herein, the authors explicitly reveal the dual‐functions of N dopants in molybdenum disulfide (MoS2) catalyst through a combined experimental and first‐principles approach. The authors achieve an economical, ecofriendly, and most efficient MoS2‐based hydrogen evolution reaction (HER) catalyst of N‐doped MoS2 nanosheets, exhibiting an onset overpotential of 35 mV, an overpotential of 121 mV at 100 mA cm?2 and a Tafel slope of 41 mV dec?1. The dual‐functions of N dopants are (1) activating the HER catalytic activity of MoS2 S‐edge and (2) enhancing the conductivity of MoS2 basal plane to promote rapid charge transfer. Comprehensive electrochemical measurements prove that both the amount of active HER sites and the conductivity of N‐doped MoS2 increase as a result of doping N. Systematic first‐principles calculations identify the active HER sites in N‐doped MoS2 edges and also illustrate the conducting charges spreading over N‐doped basal plane induced by strong Mo 3d –S 2p –N 2p hybridizations at Fermi level. The experimental and theoretical research on the efficient HER catalysis of N‐doped MoS2 nanosheets possesses great potential for future sustainable hydrogen production via water electrolysis and will stimulate further development on nonmetal‐doped MoS2 systems to bring about novel high‐performance HER catalysts.  相似文献   

15.
Yolk‐like TiO2 are prepared through an asymmetric Ostwald ripening, which is simultaneously doped by nitrogen and wrapped by carbon from core to shell. It presents a high specific surface area (144.9 m2 g?1), well‐defined yolk‐like structure (600–700 nm), covered with interweaved nanosheets (3–5 nm) and tailored porosity (5–10 nm) configuration. When first utilized as anode material for sodium‐ion batteries (SIBs), it delivers a high reversible specific capacity of 242.7 mA h g?1 at 0.5 C and maintains a considerable capacity of 115.9 mA h g?1 especially at rate 20 C. Moreover, the reversible capacity can still reach 200.7 mA h g?1 after 550 cycles with full capacity retention at 1 C. Even cycled at extremely high rate 25 C, the capacity retention of 95.5% after 3000 cycles is acquired. Notably, an ultrahigh initial coulombic efficiency of 59.1% is achieved. The incorporation of nitrogen with narrowing the band gap accompanied with carbon uniformly coating from core to shell make the NC TiO2‐Y favor a bulk type conductor, resulting in fast electron transfer, which is beneficial to long‐term cycling stability and remarkable rate capability. It is of great significance to improve the energy‐storage properties through development of the bulk type conductor as anode materials in SIBs.  相似文献   

16.
This study reports an improved method for activating asphalt to produce ultra‐high surface area porous carbons. Pretreatment of asphalt (untreated Gilsonite, uGil ) at 400 °C for 3 h removes the more volatile organic compounds to form pretreated asphalt ( uGil‐P ) material with a larger fraction of higher molecular weight π‐conjugated asphaltenes. Subsequent activation of uGil‐P at 900 °C gives an ultra‐high surface area (4200 m2 g?1) porous carbon material ( uGil‐900 ) with a mixed micro and mesoporous structure. uGil‐900 shows enhanced room temperature CO2 uptake capacity at 54 bar of 154 wt% (35 mmol g?1). The CH4 uptake capacity is 37.5 wt% (24 mmol g?1) at 300 bar. These are relevant pressures in natural gas production. The room temperature working CO2 uptake capacity for uGil‐900 is 19.1 mmol g?1 (84 wt%) at 20 bar and 32.6 mmol g?1 (143 wt%) at 50 bar. In order to further assess the reliability of uGil‐900 for CO2 capture at elevated pressures, the authors study competitive sorption of CO2 and CH4 on uGil‐900 at pressures from 1 to 20 bar at 25 °C. CO2/CH4 displacement constants are measured at 2 to 40 bar, and found to increase significantly with pressure and surface area.  相似文献   

17.
Bifunctional oxygen catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) with high activities and low‐cost are of prime importance and challenging in the development of fuel cells and rechargeable metal–air batteries. This study reports a porous carbon nanomaterial loaded with cobalt nanoparticles (Co@NC‐x/y) derived from pyrolysis of a Co/Zn bimetallic zeolitic imidazolite framework, which exhibits incredibly high activity as bifunctional oxygen catalysts. For instance, the optimal catalyst of Co@NC‐3/1 has the interconnected framework structure between porous carbon and embedded carbon nanotubes, which shows the superb ORR activity with onset potential of ≈1.15 V and half‐wave potential of ≈0.93 V. Moreover, it presents high OER activity that can be further enhanced to over commercial RuO2 by P‐doped with overpotentials of 1.57 V versus reversible hydrogen electrode at 10 mA cm?2 and long‐term stability for 2000 circles and a Tafel slope of 85 mV dec?1. Significantly, the nanomaterial demonstrates better catalytic performance and durability than Pt/C for ORR and commercial RuO2 and IrO2 for OER. These findings suggest the importance of a synergistic effect of graphitic carbon, nanotubes, exposed Co–Nx active sites, and interconnected framework structure of various carbons for bifunctional oxygen electrocatalysts.  相似文献   

18.
Lithium metal is the most promising anode material for high‐energy‐density batteries due to its high specific capacity of 3860 mAh g?1 and low reduction potential of ?3.04 V versus standard hydrogen electrode. However, huge volume change, safety concerns, and low efficiency impede the practical applications of Li metal anodes. Herein, it is shown that the nitrogen‐doped graphene modified 3D porous Cu (3DCu@NG) current collector can mitigate the above problems. The N‐doped graphene, coating on the surface of 3D current collector, not only contributes to a uniform Li+ flux, but also leads to a scattered distribution of electrons throughout the surface, finally contributing to a uniform Li deposition and the improved electrochemical performance. In addition, the continuously porous structure of 3DCu@NG provides a space for the metallic Li deposition and could effectually accommodate the volume expansion during cycling. As a result, the Li‐3DCu@NG anode exhibits a high areal capacity of 4 mAh cm?2, a high Li utilization of ≈98%, and an ultralow voltage hysteresis of ≈19 mV. The multifunctional N‐doped graphene modified 3D porous current collector promisingly provides a strategy for safe and high‐energy lithium metal anodes.  相似文献   

19.
A step‐by‐step strategy is reported for improving capacitance of supercapacitor electrodes by synthesizing nitrogen‐doped 2D Ti2CTx induced by polymeric carbon nitride (p‐C3N4), which simultaneously acts as a nitrogen source and intercalant. The NH2CN (cyanamide) can form p‐C3N4 on the surface of Ti2CTx nanosheets by a condensation reaction at 500–700 °C. The p‐C3N4 and Ti2CTx complexes are then heat‐treated to obtain nitrogen‐doped Ti2CTx nanosheets. The triazine‐based p‐C3N4 decomposes above 700 °C; thus, the nitrogen species can be surely doped into the internal carbon layer and/or defect site of Ti2CTx nanosheets at 900 °C. The extended interlayer distance and c‐lattice parameters (c‐LPs of 28.66 Å) of Ti2CTx prove that the p‐C3N4 grown between layers delaminate the nanosheets of Ti2CTx during the doping process. Moreover, 15.48% nitrogen doping in Ti2CTx improves the electrochemical performance and energy storage ability. Due to the synergetic effect of delaminated structures and heteroatom compositions, N‐doped Ti2CTx shows excellent characteristics as an electrochemical capacitor electrode, such as perfectly rectangular cyclic voltammetry results (CVs, R2 = 0.9999), high capacitance (327 F g?1 at 1 A g?1, increased by ≈140% over pristine‐Ti2CTx), and stable long cyclic performance (96.2% capacitance retention after 5000 cycles) at high current density (5 A g?1).  相似文献   

20.
Alongside rare‐earth metals, Ni, Fe, Co, Cu are some of the critical materials that will be in huge demand thanks to growth in clean‐energy sector. Herein scrap stainless steel wires (SSW) from worn‐out tires are employed as a support material for catalyst integration in the hydrogen evolution reaction (HER). In addition, SSW by corrosion engineering is exercised as an in situ formed freestanding robust electrode for the oxygen evolution reaction (OER). By superficial corrosion of SSW, inherent active species are unmasked in the form of Ni/FeOOH nanocrystallites displaying efficient water oxidation by reaching 500 mA cm?2 at low overpotential (η500) of 287 mV in 1 m KOH. Similarly, cathode scrap SSW with active (alloy) coatings of MoNi4 catalyzes the HER at η‐200 = 77 mV, with a low activation energy (Ea = 16.338 kJ mol?1) and high durability of 150 h. Promisingly, when used in industrial conditions, 5 m KOH, 343 K, these electrodes demonstrate abnormal activity by yielding high anodic and cathodic current density of 1000 mA cm?2 at η = 233 mV and η = 161 mV, respectively. This work may inspire researchers to explore and reutilize high‐demand metals from scrap for addressing critical material shortfalls in clean‐energy technologies.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号