Photoelectrocatalytic nitrogen fixation with Vo-BiOBr/TiO2 heterostructured photoelectrode as photocatalyst

Photocatalytic or photoelectrocatalytic nitrogen fixation is considered as a very promising way to reduce energy requirements. Here, V_o-BiOBr/TiO₂ nanocomposite photoelectrode was constructed by modifying TiO₂ nanotube arrays with BiOBr nanosheets with oxygen vacancies (V_o) for photoelectrocatalytic nitrogen fixation. The oxygen vacancy promotes the adsorption and activation of N₂ on the catalyst surface. The Lewis basicity of nitrogen is enhanced by transferring the photogenerated electrons on the conduction band of BiOBr to the π anti-bonding orbit of N₂, which is more beneficial for the addition of protons. On the other hand, the heterojunction between TiO₂ and V_o-BiOBr facilitates the separation of photogenerated carriers. The photogenerated holes on the valence band of TiO₂ travelled to the counter electrode to produce oxygen at a negative potential, avoiding the further oxidation of NH₃. V_o-BiOBr/TiO₂ displays a high NH₃ production rate of 25.08 μg h^?1 cm^?2 at ?0.2 V which is 3.3 times higher than that of BiOBr/TiO₂. The synergistic effect between TiO₂ and V_o-BiOBr results in enhanced light absorption and higher photoelectrocatalytic efficiency for the N₂ reduction reaction.     

Controlling hydrogenation pathway by metal hydride enable efficient electrocatalytic N2 fixation

Electrocatalytic nitrogen fixation under ambient conditions represents an energy-saving sustainable alternative strategy to the energy-consuming traditional Haber–Bosch process toward ammonia synthesis. However, the traditional electrocatalysts for nitrogen reduction reaction (NRR) often suffer low selectivity and low activity. From quantum-mechanical calculations, we obtain a benefit clue that the Ni atom adsorbed by the first hydrogen ion in the catalyst exhibits selectivity for the adsorption of N₂ and other H atoms, and it preferentially adsorbs N₂ molecules. Thus, we propose an interfacial engineering strategy to simultaneously accelerate selectivity and activity using metal/metal hydroxide. The remarkable activity of metal/metal hydroxide originates from its synergized water dissociation and unique hydrogenation pathway of metal hydride. The priority absorption of the N₂ suppresses the competitive hydrogen evolution reaction and accelerates the kinetics to generate 1N₂H: 1H + N₂ → 1N₂H, which a is rate-limiting step for NH₃ synthesis. Using Ni/NiFe–OH as prototypes, here we show that selectivity and catalytic activity are simultaneously enhanced, surprisingly, in simple inorganic hybrid and confers exceptionally Faradaic efficiency of 23.34% and NH₃ yield 19.74 μg h^?1 cm^?2 at ?0.15 V versus reversible hydrogen electrode (RHE) in 0.5 M KOH electrolyte under ambient conditions. The long-term durability is also excellent. This work provides a possibility for the rational design of efficient electrocatalysts for N₂ electrochemical reduction with a large-scale production.     

Mo2C embedded on nitrogen-doped carbon toward electrocatalytic nitrogen reduction to ammonia under ambient conditions

Electrochemical nitrogen reduction reaction (e-NRR) is an attractive prospect for ammonia production under mild conditions using renewable energy. However, developing efficient and stable electrocatalysts for driving e-NRR remains a great challenge. Herein, inspired by the biological nitrogen fixation via active Mo-nitrogenase, molybdenum carbide on N-doped porous carbon (Mo₂C/NC) derived from Mo/Zn-ZIFs was developed for the first time, as an efficient e-NRR electrocatalyst under ambient conditions. In 0.1 M Na₂SO₄ electrolyte, the Mo₂C/NC catalyst achieved a maximum NH₃ yield rate of 70.6 μmol h^?1 g_cat.^?1 and a faradaic efficiency of 12.3% at ?0.2 V vs. RHE. Additionally, Mo₂C/NC displayed favorable electrochemical selectivity and durability during the longtime electrolysis, attributed to the structural and electrochemical stability of Mo₂C and ZIFs-derived carbon framework. This work provides new perspectives upon metal carbides and their compounds as catalysts for efficient e-NRR.     

Ambient electrosynthesis of NH3 from N2 using Bi-doped CeO2 cube as electrocatalyst

The synthesis of ammonia (NH₃) from electrochemical nitrogen reduction reaction (NRR) under environmental conditions is a promising technology. Compared with the traditional artificial nitrogen fixation process by the Haber-Bosch process, electrochemical nitrogen reduction reaction (NRR) requires no harsh reaction conditions. In this work, we report that Bi-doped CeO₂ nanocubes show high NRR activity as electrocatalysts. The NH₃ yield of 17.83 μgh⁻¹ mg⁻¹_cat. and the Faradaic Efficiency (FE) of 1.61% at −0.9 V are achieved in 0.1 M Na₂SO₄. The performance is much higher than that for the traditional CeO₂ nanoparticles. The detailed analysis indicates that both the Bi doping and the cube morphology are critical for this encouraging NRR performance. The mechanism for improving NRR is further explored with first-principle calculations, demonstrating the importance of Bi-doping for performance enhancement.     

Perovskite ceramic oxide as an efficient electrocatalyst for nitrogen fixation

The electrochemical conversion of N₂ to NH₃ is an interesting research topic as it provided an alternative and energy-saving method compared with the traditional way of NH₃ production. Although different materials have been proposed for N₂ reduction, the use of defects in oxides was only reported recently and the relevant working mechanism was not fully revealed. In this study, Sr was used as the dopant for LaFeO₃ to create oxygen vacancies, forming the Sr-doped LFO (La_0.5Sr_0.5FeO_3-δ) perovskite oxide. The La_0.5Sr_0.5FeO_3-δ ceramic oxide used as a catalyst achieves an NH₃ yield of 11.51 μgh^?1 mg^?1 and the desirable faradic efficiency (F.E.) of 0.54% at ?0.6 V vs reversible hydrogen electrode (RHE), which surpassed that of LaFeO₃ nanoparticles. The ¹⁵N isotope labeling method was employed to prove the La_0.5Sr_0.5FeO_3-δ catalyst had the function of converting N₂ into NH₃ under the electrolysis condition. The first principle calculations were used to investigate the mechanism at the atomistic level, revealing that the free energy barriers changed significantly with the introduction of oxygen vacancies that accelerated the overall nitrogen reduction reaction (NRR) procedure.     

Catalyst support effect on ammonia decomposition over Ni/MgAl2O4 towards hydrogen production

Ammonia is a prospective fuel for hydrogen storage and production, but its application is limited by the high cost of the catalysts (Ru, etc.) to decompose NH₃. Decomposing ammonia using non-precious Ni as catalysts can therefore improve its prospects to produce hydrogen. This work proposes several Ni/MgAl₂O₄ with the support properties tuned and investigates the support effect on the catalytic performance. Ni/MgAl₂O₄-LDH shows high NH₃ conversion (～88.7%) and H₂ production rate (～1782.6 mmol g^?1 h^?1) at 30,000 L. kg^?1 h^?1 and 600 °C, which is 1.68 times as large as that of Ni/MgAl₂O₄-MM. The performance remains stable over 30 h. The characterizations manifest that the high specific surface area of Ni/MgAl₂O₄-LDH can introduce highly dispersed Ni on the surface. Kinetics analysis implies promoted NH₃ decomposition reaction and alleviated H₂ poisoning for Ni/MgAl₂O₄-LDH. A roughly linear relationship is obtained by fitting the curves of dispersed Ni on the surface vs the reaction orders regarding H₂ and NH₃. This indicates that enhanced NH₃ decomposition performance can be ascribed to the strengthened NH₃ decomposition reaction and weakened H₂ poisoning by the highly dispersed Ni on the MgAl₂O₄-LDH surface. This work provides an opportunity to develop highly active and cost-effective catalysts to produce hydrogen via NH₃ decomposition.     

Amino functionalized carbon nanotubes supported CoNi@CoO–NiO core/shell nanoparticles as highly efficient bifunctional catalyst for rechargeable Zn-air batteries

Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are the core reaction processes of rechargeable Zn-air battery (ZAB) cathode. Therefore, exploring a bifunctional catalyst with excellent electrochemical performance, high durability, and low cost is essential for rechargeable ZAB. In this work, amino functionalized carbon nanotubes supported core/shell nanoparticles composed of CoNi alloy core and CoO–NiO shell (CoNi@CoO–NiO/NH₂-CNTs-1) is synthesized through a simple and efficient hydrothermal reaction and calcination method, which shows higher ORR/OER bifunctional catalytic performance than the single metal-based catalyst, such as Ni@NiO/NH₂-CNTs and Co@CoO/NH₂-CNTs. The fabricated bimetallic alloy based catalyst CoNi@CoO–NiO/NH₂-CNTs-3 with the optimized loading content of CoNi@CoO–NiO core/shell nanoparticles, presents the best bifunctional catalytic performance for ORR/OER. Experimental studies reveal that CoNi@CoO–NiO/NH₂-CNTs-3 exhibits the onset potential of 0.956 V and 1.423 V vs. RHE for ORR and OER, respectively. It also exhibits a low overpotential of 377 mV to achieve a 10 mA cm^?2 current density for OER, and positive half-wave potentials of 0.794 V for ORR. And the potential difference between half-wave potential of ORR (E_1/2) and the potential at 10 mA cm^?2 for OER (E_j10) is 0.813 V. In addition, when CoNi@CoO–NiO/NH₂-CNTs-3 is used as an air electrode catalyst of rechargeable ZAB, its maximum power density and open circuit voltage (OCV) can reach 128.7 mW cm^?2 and 1.458 V (The commercially available catalyst of Pt/C–RuO₂ is 88.1 mW cm^?2), which strongly demonstrates that the fabricated catalyst CoNi@CoO–NiO/NH₂-CNTs-3 can be used as a highly efficient bifunctional catalyst for ZABs, and is expected to replace those expensive precious metal electrocatalysts to meet the growing demand for new energy devices.     

Combination of two H-enriched B–N based hydrides towards improved dehydrogenation properties

A new hydrogen storage system NaZn(BH₄)₃?2NH₃-nNH₃BH₃ (n = 1–5) was synthesized via a simple ball milling of NaZn(BH₄)₃?2NH₃ and NH₃BH₃ (AB) with a molar ratio from 1 to 5. Dehydrogenation results revealed that NaZn(BH₄)₃?2NH₃-nAB (n = 1–5) showed a mutual dehydrogenation improvement in terms of significant decrease in the dehydrogenation temperature and preferable suppression of the simultaneous evolution of by-products (i.e. NH₃, B₂H₆ and borazine) compared to the unitary compounds (NaZn(BH₄)₃?2NH₃ and AB). Specially, the NaZn(BH₄)₃?2NH₃-4AB sample is shown to reach the maximum hydrogen purity (99.1 mol %) and favorable dehydrogenation properties rapidly releasing 11.6 wt. % of hydrogen with a peak maximum temperature of 85 °C upon heating to 250 °C. Isothermal dehydrogenation results revealed that 9.6 wt. % hydrogen was liberated from NaZn(BH₄)₃?2NH₃-4AB within 80 min at 90 °C. High-resolution in-situ XRD and Fourier transform infrared (FT-IR) measurements indicated that the significant improvements on the dehydrogenation properties in NaZn(BH₄)₃?2NH₃-4AB can be attributed to the interaction between the NH₃ group from NaZn(BH₄)₃?2NH₃ and AB in the mixture, resulting a more activated H^δ+···^−δH combination. The research on the reversibility of the spent fuels of NaZn(BH₄)₃?2NH₃-4AB showed that regeneration could be partly achieved by reacting them with hydrazine in liquid ammonia. These aforementioned favorable dehydrogenation properties demonstrate the potential of the combined systems to be used as solid hydrogen storage material.     

Fe(III) grafted MoO3 nanorods for effective electrocatalytic fixation of atmospheric N2 to NH3

Electrocatalytic nitrogen reduction reaction (ENRR) offers a carbon-neutral process to fix nitrogen into ammonia, but its feasibility depends on the development of highly efficient electrocatalysts. Herein, we report that Fe ion grafted on MoO₃ nanorods synthesized by an impregnation technique can efficiently enhance the electron harvesting ability and the selectivity of H⁺ during the NRR process in neutral electrolyte. In 0.1 M Na₂SO₄ solution, the electrocatalyst exhibited a remarkable NRR activity with an NH₃ yield of 9.66 μg h^?1 mg^?1_cat and a Faradaic efficiency (FE) of 13.1%, far outperforming the ungrafted MnO₃. Density functional theory calculations revealed that the Fe sites are major activation centers along the alternating pathway.     

Facile electrochemical fabrication of magnetic Fe3O4 for electrocatalytic synthesis of ammonia used for hydrogen storage application

Ammonia (NH₃) offers extensive applications in industrial production; moreover, it is a potential carrier for hydrogen energy and an eco-friendly fuel. Electrocatalytic synthesis of NH₃ has drawn increasing research attention, wherein an excellent electrocatalyst plays a vital role. Iron (Fe) oxide nanomaterials with their high activity and cost effectiveness of its raw material Fe, have received significant attention in electrocatalytic N₂ reduction reaction (NRR) to synthesize NH₃. This study reports a rapid and cost-effective electrochemical method for synthesizing magnetic Fe₃O₄ nanoparticles, achieving gram-level production under ambient conditions. The synthesized magnetic Fe₃O₄ nanoparticles as electrocatalyst for NRR, achieved excellent faradaic efficiency of 16.9% and an optimal NH₃ yield of 12.09 μg h^?1 mg^?1_cat. at ?0.15 V (versus the reversible hydrogen electrode (RHE)) in 0.1 M Na₂SO₄. Besides, density functional theory (DFT) calculations indicate that the N≡N bond was fully activated, and the NRR proceeds mainly along the alternating hydrogenation pathway.     

One-pot synthesis of supported Ni@Al2O3 catalysts with uniform small-sized Ni for hydrogen generation via ammonia decomposition

Nickel based materials are the most potential catalysts for CO_x-free hydrogen production from ammonia decomposition. However, the facile synthesis of supported Ni-based catalysts with small size Ni particles, high porosity and good structural stability is still of great demand. In this work, uniform small-sized Ni particles supported into porous alumina matrix (Ni@Al₂O₃) are synthesized by a simple one-pot method and used for ammonia decomposition. The Ni content is controlled from 5 at.% to 25 at.%. Especailly, the 25Ni@Al₂O₃ catalyst shows the best catalytic performance. With a GHSV of 24,000 cm³g_cat^?1h^?1, 93.9% NH₃ conversion is achieved at 600 °C and nearly full conversion of NH₃ is realized at 650 °C. The hydrogen formation rate of 25NiAl catalyst reaches 3.6 mmol g_cat^?1min^?1 at 400 °C and 7.8 mmol g_cat^?1min^?1 at 450 °C. The enhanced activity observed on 25Ni@Al₂O₃ catalyst can be attributed to the structural characteristic that large amounts of uniform-sized small (7.2 ± 0.9 nm) Ni particles are highly dispersed into porous alumina matrix. The aggregation of active metallic Ni particles during the high temperature reaction can be effectively prevented by the porous alumina matrix due to the strong interaction between them, thus ensuring a good catalytic performance.     

Hydrogen derived from ammonia: Small-scale costs

A systems study was made to assess the economic prospects for using purchased industrial ammonia as a hydrogen distribution and storage medium for users requiring 0.93–9.34 million std m³ y^?1 of hydrogen (33–330 million std ft³ y^?1). Projected costs to the end user were determined for: the product of dissociated ammonia (N₂+H₂)/NH₃, and the 99.999% pure H₂ obtained by separation of the nitrogen (H₂/NH₃); hydrogen produced by the steam reforming of natural gas (H₂/NG); electrolytic hydrogen (EH₂); purchased (merchant) liquid hydrogen (LH₂); OTEC (ocean thermal energy conversion) LH₂; as well as OTEC NH₃ and the H₂ products derived from it. Future costs are projected as $ GJ^?1 and as $ MBTU^?1 (1980$ in 1990) using two sets of forecast energy prices. The results show that merchant LH₂ was substantially higher in cost than the other options, and that until EH₂ is available at the projected costs, H₂/NH₃ would be the preferred option for the smallest plant sizes where it is projected to be competitive with H₂/NG of comparable purity. Thus, via state-of-the-art technology, industrial NH₃ can now serve as a viable H₂ carrier for some small-scale users. The availability of OTEC NH₃ at the projected costs would substantially increase the competitive position of H₂/NH₃. Consideration of safety and environmental factors are among the important items listed in recommendations for future work.     

Post-synthetic Ti exchanged UiO-66-NH2 metal-organic frameworks with high faradaic efficiency for electrochemical nitrogen reduction reaction

Electrochemical nitrogen reduction reaction (NRR) is a promising approach for NH₃ production to take place of the traditional Haber-Bosch process, which is still limited by the low NH₃ yield rate and low Faradaic efficiency. Herein, Ti was post-synthetic exchanged into Zr-based metal organic frameworks to synthesize UiO-Zr-Ti as NRR electrocatalysts. The incorporated Ti is found to function as active sites for NRR and benefit the improved charge-transfer efficiency, which has a positive effect on the high NH₃ yield rate. Moreover, the existence of Zr and Ti species can effectively suppress the competing HER, thus leading to high Faradaic efficiency. Therefore, the modified UiO-Zr-Ti-5d shows the highest NH₃ yield rate of 1.16 × 10⁻¹⁰ mol cm⁻² s⁻¹ and the highest Faradaic efficiency of 80.36%, which is comparable to recently reported NRR electrocatalysts.     

Improved dehydrogenation properties of the combined Mg(BH4)2·6NH3–nNH3BH3 system

A combined strategy via mixing Mg(BH₄)₂·6NH₃ with ammonia borane (AB) is employed to improve the dehydrogenation properties of Mg(BH₄)₂·6NH₃. The combined system shows a mutual dehydrogenation improvement in terms of dehydrogenation temperature and hydrogen purity compared to the individual components. A further improved hydrogen liberation from the Mg(BH₄)₂·6NH₃–6AB is achieved with the assistance of ZnCl₂, which plays a crucial role in stabilizing the NH₃ groups and promoting the recombination of NH^δ+?HB^δ−. Specifically, the Mg(BH₄)₂·6NH₃–6AB/ZnCl₂ (with a mole ratio of 1:0.5) composite is shown to release over 7 wt.% high-pure hydrogen (>99 mol%) at 95 °C within 10 min, thereby making the combined system a promising candidate for solid hydrogen storage.     

From piggery wastewater nutrients to biogas: Microalgae biomass revalorization through anaerobic digestion

Microalgae grown in swine wastewater were used as a promising strategy to produce renewable energy by coupling wastewater bioremediation and biomass revalorization. The efficiency of a microalgae consortium treating swine slurry at different temperature (15 and 23 °C) and illumination periods (11 and 14 h) was assessed for biomass growth and nutrient removal at two NH₄⁺ initial concentrations (80 and 250 mg L⁻¹ NH₄⁺). Favourable culture conditions (23 °C and 14 h of illumination) and high ammonium loads resulted in higher biomass production and greater nutrients removal rates. The initial N–NH₄⁺ load determined the removal mechanism, thus ammonia stripping and nitrogen uptake accounted similarly in the case of high NH₄⁺ load, while nitrogen uptake prevailed at low NH₄⁺ load. Under favourable conditions, nitrogen availability in the media determined the composition of the biomass. In this context, carbohydrate-rich biomass was obtained in batch mode while semi-continuous operation resulted in protein-rich biomass. The revalorization of the resultant biomass was evaluated for biogas production. Methane yields in the range of 106–146 and 171 ml CH₄ g COD⁻¹ were obtained for the biomasses grown in batch and semi-continuous mode, respectively. Biomass grown under favourable conditions resulted in higher methane yields and closer to the theoretically achievable.     

Thermodynamic analysis of low-temperature and high-pressure (cryo-compressed) hydrogen storage processes cooled by mixed-refrigerants

Cryo-compressed hydrogen (CcH₂) is a promising hydrogen storage method with merits of high density with low power consumption. Thermodynamic analysis and comparison of several CcH₂ processes are conducted in this paper, under hydrogen storage conditions of 10–100 MPa at 60–100 K. Mixed-refrigerant J-T (MRJT), nitrogen/neon reverse Brayton (RBC) and hydrogen expansion are employed for cooling hydrogen, respectively. Combined CcH₂ processes such as MRJT + neon-RBC are proposed to reach higher CcH₂ density at lower temperatures (<80 K). It was indicated that the specific power consumptions (SPC) of MRJT processes are obviously lower than those of nitrogen/neon-RBC or hydrogen expansion processes. For a typical storage condition of 50 MPa at 80 K, MRJT CcH₂ process could achieve hydrogen density of 71.59 kg m^?3, above liquid hydrogen. While its SPC of 6.42 kWh kg^?1 is about 40% lower than current dual-pressure Claude hydrogen liquefaction processes (10.85 kWh kg^?1).     

Enhanced catalytic behavior of h-BN supported CuNi bimetallic catalysts in hydrolytic dehydrogenation of NH3BH3

The hydrolysis of ammonia borane (NH₃BH₃, AB) is an efficient strategy for high-purify hydrogen evolution. However, it is indispensable to develop a suitable catalyst because this reaction is kinetically infeasible at room temperature. In this work, we prepared a series of nano hexagonal boron nitride (h-BN) supported CuNi bimetallic catalysts through a facile adsorption-chemical reduction procedure. The effects of various molar ratios of Cu to Ni and CuNi loadings on AB hydrolysis were investigated in details. Benefitting from the proper porous structure, the interesting alloy effect of Cu and Ni, as well as the synergistic effect between h-BN and CuNi, 20 wt% Cu_0.5Ni_0.5/h-BN displays the highest catalytic activity among the as-prepared catalysts. Apart from satisfactory durability, the corresponding hydrogen generation rate, turnover frequency at 303 K in base solution and apparent activation energy are 2437.0 mL g^?1 min^?1, 6.33 min^?1 and 23.02 kJ mol^?1, respectively, which are very outstanding compared with many previous results. Our work not only provides a proper non-precious metal catalyst for hydrogen generation from the hydrolysis of chemical hydrogen storage materials but also offers a facile strategy for synthesizing metallic functional materials.     

The influence of nitrogen doping on reduced graphene oxide as highly cyclable Li-ion battery anode with enhanced performance

A straightforward, one-step route has been established to fabricate reduced- (rGO) and nitrogen-doped reduced graphene oxide (NrGO) with remarkable lithium-ion storage properties. The graphene oxide (GO) was synthesized as starting material by improved Hummers’ method. Thereafter, thermally annealing GO with NH₃ at elevated temperature to synthesize NrGO was yielded a more open structure with nitrogen sites suitable for enhanced Li intercalation. NrGO exhibited a reversible capacity of 240 mAhg^?1 at 10 Ag^-1 after 500 cycles with 90% capacity retention, which is the best result achieved among graphene oxide-based anodes at this current density. In contrast to rGO, NrGO cells exhibited a gradually increasing capacity profile, reaching up to 114% of the initial capacity at 0.1, 2, and 10 Ag^-1 current densities. Results showed that high occupancy of pyridinic N within NrGO enhanced battery performance and cell kinetics upon cycling which offers long-time operability at high current density.     

Evaluation of the composition of continuously-cultivated Arthrospira (Spirulina) platensis using ammonium chloride as nitrogen source

This work is focused on the influence of dilution rate (0.08 ≤ D ≤ 0.32 d^?1) on the continuous cultivation and biomass composition of Arthrospira (Spirulina) platensis using three different concentrations of ammonium chloride (c_No = 1.0, 5.0 and 10 mol m^?3) as nitrogen source. At c_No = 1.0 and 5.0 mol m^?3 the biomass protein content was an increasing function of D, whereas, when using c_No = 10 mol m^?3, the highest protein content (72.5%) was obtained at D = 0.12 d^?1. An overall evaluation of the process showed that biomass protein content increased with the rate of nitrogen supply (D c_No) up to 72.5% at D c_No = 1.20 mol m^?3 d^?1. Biomass lipid content was an increasing function of D only when the nitrogen source was the limiting factor for the growth (D c_No ≤ 0.32 mol m^?3 d^?1), which occurred solely with c_No = 1.0 mol m^?3. Under such conditions, A. platensis reduced its nitrogen reserve in the form of proteins, while maintaining almost unvaried its lipid content. The latter was affected only when the concentration of nitrogen was extremely low (c_No = 1.0 mol m^?3). The most abundant fatty acids were the palmitic (45.8 ± 5.20%) and the γ-linolenic (20.1 ± 2.00%) ones. No significant alteration in the profiles either of saturated or unsaturated fatty acids was observed with c_No ≤ 5.0 mol m^?3, prevailing those with 16 and 18 carbons.     

Electrospun zeolitic imidazolate framework‐derived nitrogen‐doped carbon nanofibers with high performance for lithium‐sulfur batteries

Three‐dimensional (3D) nitrogen‐doped carbon nanofibers (N‐CNFs) which were originating from nitrogen‐containing zeolitic imidazolate framework‐8 (ZIF‐8) were obtained by a combined electrospinning/carbonization technique. The pores uniformly distributed in N‐CNFs result in the improvement of electrical conductivity, increasing of BET surface area (142.82 m² g^?1), and high porosity. The as‐synthesized 3D free‐standing N‐CNFs membrane was applied as the current collector and binder free containing Li₂S₆ catholyte for lithium‐sulfur batteries. As a novel composite cathode, the free‐standing N‐CNFs/Li₂S₆ membrane shows more stable electrochemical behavior than the CNFs/Li₂S₆ membrane, exhibiting a high first‐cycle discharge specific capacity of 1175 mAh g^?1at 0.1 C and keeping discharge specific capacity of 702 mAh g^?1 at higher rate. More importantly, as the sulfur mass in cathodes was increased at 7.11 mg, the N‐CNFs/Li₂S₆ membrane delivered 467 mAh g^?1after 150 cycles at 0.2 C. The excellent electrochemical properties of N‐CNFs/Li₂S₆ membrane can be ascribed to synergistic effects of high porosity and nitrogen‐doping in N‐CNFs from carbonized ZIF‐8, illustrating collective effects of physisorption and chemisorption for lithium polysulfides in discharge‐charge processes.