A freestanding MoO2‐decorated carbon nanofibers interlayer for rechargeable lithium sulfur battery

Lithium‐sulfur (Li‐S) battery based on sulfur cathodes is of great interest because of high capacity and abundant sulfur source. But the shuttling effect of polysulfides caused by charge‐discharge process results in low sulfur utilization and poor reversibility. Here, we demonstrate a good approach to improve the utility of sulfur and cycle life by synthesizing carbon nanofibers decorated with MoO₂ nanoparticles (MoO₂‐CNFs membrane), which plays a role of multiinterlayer inserting between the separator and the cathode for Li‐S battery. The S/MoO₂‐CNFs/Li battery showed a discharge capacity of 6.93 mAh cm^?2 (1366 mAh g^?1) in the first cycle at a current density of 0.42 mA cm^?2 and 1006 mAh g^?1 over 150 cycles. Moreover, even at the highest current density (8.4 mA cm^?2), the battery achieved 865 mAh g^?1. The stable electrochemical behaviors of the battery has achieved because of the mesoporous and interconnecting structure of MoO₂‐CNFs, proving high effect for ion transfer and electron conductive. Furthermore, this MoO₂‐CNFs interlayer could trap the polysulfides through strong polar surface interaction and increases the utilization of sulfur by confining the redox reaction to the cathode.     

Embedding Co2P nanoparticles into N&P co-doped carbon fibers for hydrogen evolution reaction and supercapacitor

The demands for highly efficient and low-cost electrochemically active materials are still urgent needs for the fields of electro-catalysis and supercapacitor. Herein, a facile strategy for preparing high-efficient bi-functional electrode material was reported. The electrode material was prepared through embedding Co₂P nanoparticles in the binary co-doped carbon nanofibers (Co₂P@N&P-CNFs). This unique structure can effectively prevent the Co₂P from detaching and provide abundant active sites. Materials prepared in this work showed the superior hydrogen evolution reaction (HER) performance with overpotential of 192 mV at a current density of 10 mA cm^?2 and remarkable stability for 20 h. Moreover, the asymmetric supercapacitor (ASC) was fabricated using the Co₂P@N&P-CNFs as the positive electrode material and carbon nanofibers (CNFs) as the negative electrode material, which shows an outstanding cycle stability (91.5% of the initial capacitance is retained throughout 10,000 charge-discharge tests) and a high E of 22.31 Wh kg^?1 at the P of 225.02 W kg^?1 at 0.3 A g^?1. This work offers an effective route in designing bi-functional active materials for HER and supercapacitor.     

Synthesis of carbon-coated TiO2 nanotubes for high-power lithium-ion batteries

Carbon-coated TiO₂ nanotubes are prepared by a simple one-step hydrothermal method with an addition of glucose in the starting powder, and are characterized by morphological analysis and electrochemical measurement. A thin carbon coating on the nanotube surface effectively suppresses severe agglomeration of TiO₂ nanotubes during hydrothermal reaction and post calcination. This action results in better ionic and electronic kinetics when applied to lithium-ion batteries. Consequently, carbon-coated TiO₂ nanotubes deliver a remarkable lithium-ion intercalation/deintercalation performance, such as reversible capacities of 286 and 150 mAh g⁻¹ at 250 and 7500 mA g⁻¹, respectively.     

A polyanionic anthraquinone organic cathode for pure small-molecule organic Li-ion batteries

Sodium 9,10-anthraquinone-2,6-disulfonate (Na₂AQ26DS, 130 mAh g⁻¹) with polyanionic character and two O–Na ionic bonds is used as an organic cathode for Li-ion batteries. Na₂AQ26DS exhibits highly impressive cycle stability in ether electrolytes due to its polyanionic character and the effective suppression of solvent-molecule co-intercalation. In half cells (1–3.9 V vs. Li⁺/Li) using 1 M bis(trifluoromethanesulphonyl)imide lithium salt (LiTFSI) in 1,3-dioxolane/dimethoxyethane (DOL/DME), Na₂AQ26DS delivers a highly stable specific capacity of 123 mAh g⁻¹ at 50 mA g⁻¹ for 900 cycles (6-month test) and realizes ∼69 mAh g⁻¹ for 2800 cycles at 500 mA g⁻¹. In the full cells with the reduced state (Li₄TP) of lithium terephthalate (Li₂TP) as the organic anode, the resulting Li₄TP II Na₂AQ26DS organic lithium-ion batteries (OLIBs) can display a highly stable average discharge capacity of 120 mAh g⁻¹_cathode for 100 cycles at 50 mA g⁻¹ and ∼63 mAh g⁻¹_cathode for 1200 cycles at 500 mA g⁻¹ in 0.2–3.3 V.     

In-situ construction of Mn–Fe mixed oxides nanoparticles on reduced graphene oxide with superior lithium storage property

In this paper, porous Mn₃O₄–Fe₃O₄ nanoparticles with highly uniform composition are in-situ anchored on reduced graphene oxide (rGO) nanosheets by a simple cyanometallic framework template method. Thanks to the synergistic effects between the porous Mn₃O₄–Fe₃O₄ nanoparticles and the well-conductive rGO nanosheets, the Mn₃O₄–Fe₃O₄/rGO composites present superior electrochemical lithium storage performances with a great reversible capacity of 1013 mAh g^?1 after 100 cycles at 0.1 A g^?1, satisfactory rate capability of 510 mAh g^?1 at 3.0 A g^?1, and eminent long-term cycle stability of 804 mAh g^?1 after 500 cycles at 0.5 A g^?1. It is demonstrated that the rGO can not only act as a conducting matrix, but also buffer the volume expansion and avoid the aggregation of the Mn₃O₄–Fe₃O₄ nanoparticles during charging-discharging. The work provides a simple strategy for designing and fabricating advanced multi-component metal oxide-based anodes for high-performance lithium-ion battery.     

Spatially confined growth of ultrathin NiFe layered double hydroxide nanosheets within carbon nanofibers network for highly efficient water oxidation

The rational design of catalysts with low cost, high efficient and robust stability toward oxygen evolution reaction (OER) is greatly desired but remains a formidable challenge. In this work, a one-pot, spatially confined strategy was reported to fabricate ultrathin NiFe layered double hydroxide (NiFe-LDH) nanosheets interconnected by ultrafine, strong carbon nanofibers (CNFs) network. The as-fabricated NiFe-LDH/CNFs catalyst exhibits enhanced OER catalytic activity in terms of low overpotential of 230 mV to obtain an OER current density of 10 mA cm^?2 and very small Tafel slope of 34 mV dec^?1, outperforming pure NiFe-LDH nanosheets assembly, commercial RuO₂, and most non-noble metal catalysts ever reported. It also delivers an excellent structural and electrocatalytic stability upon the long-term OER operation at a large current of 30 mA cm^?2 for 40 h. Furthermore, the cell assembled by using NiFe-LDH/CNFs and commercial Pt/C as anode (+) and cathode (?) ((+)NiFe-LDH/CNFs||Pt/C(?)) only requires a potential of 1.50 V to deliver the water splitting current of 10 mA cm^?2, 130 mV lower than that of (+)RuO₂||Pt/C(?) couple, demonstrating great potential for applications in cost-efficient water splitting devices.     

Efficient photocatalytic H2 evolution over Cu and Cu3P co-modified TiO2 nanosheet

Schottky junction and p-n heterojunction are widely employed to enhance the charge transfer during the photocatalysis process. Herein, Cu and Cu₃P co-modified TiO₂ nanosheet hybrid (Cu–Cu₃P/TiO₂) was fabricated using an in situ hydrothermal method. The ternary composite achieved the superior H₂ evolution rate of 6915.7 μmol g^?1 h^?1 under simulated sunlight, which was higher than that of Cu/TiO₂ (4643.4 μmol g^?1 h^?1) and Cu₃P/TiO₂ (6315.8 μmol g^?1 h^?1) and pure TiO₂ (415.7 μmol g^?1 h^?1). The enhanced activity can be attributed to the collaboration effect of Schottky junction and p-n heterojunction among Cu/TiO₂ and Cu₃P/TiO₂, which can harvest the visible light, reduce the recombination of charge carriers and lower the overpotential of H₂ evolution, leading to a fast H₂ evolution kinetics. This work develops a feasible method for the exploration of H₂ evolution photocatalyst with outstanding charge separation properties.     

Fabrication of single-walled carbon nanotube/tin nanoparticle composites by electrochemical reduction combined with vacuum filtration and hybrid co-filtration for high-performance lithium battery electrodes

Hybrids consisting of single-walled carbon nanotubes (SWNTs) and tin nanoparticles are prepared on substrates as anode materials for lithium-ion batteries via two different techniques: (i) hybrid co-filtration by simultaneous vacuum filtration of SWNT/tin nanoparticle hybrid solutions and (ii) a combined technique comprised of vacuum filtration and electrochemical reduction. The resulting hybrid composites are of uniform thickness and consist of a homogeneous dispersion of tin nanoparticles in a SWNT network. In the hybrid films, the tin nanoparticles and SWNTs are in close contact with each other and the substrate. The hybrid films exhibit extended cycle life (capacity retention of 80% at 50th cycle), high power characteristics up to 1.75 mA cm⁻², high electrode density up to 5 mg cm⁻², and enhanced reversible capacities (535 mAh g⁻¹ for composite electrode at 50th cycle) because the aggregation of tin nanoparticles is prevented.     

Crystalline CoB: Solid state reaction synthesis and electrochemical properties

Using a facile and effective method based on the solid phase reaction between Co(OH)₂ and KBH₄, we successfully synthesize orthorhombic CoB. It is shown that this CoB obtained is of high purity and thermal stability. A possible formation process for orthorhombic CoB is discussed in detail. In addition, crystalline CoB shows excellent electrochemical reversibility and considerable high charge-discharge capacities when it is used as the anode material for nickel-based secondary batteries. The reversible discharge capacities of the CoB electrode are found to be about 380 mAh g⁻¹ at a discharge current of 25 mA g⁻¹ and 360 mAh g⁻¹ at 100 mA g⁻¹. Moreover, electrochemical reaction mechanism of CoB is investigated in detail.     

Study of the electrochemical properties of Fe3O4/C–Bi composites prepared by spray drying and their use in cylindrical sealed nickel iron batteries

In this paper, Fe₃O₄/C–Bi composites with carbon coating and bismuth added were prepared by step-by-step precipitation, spray carbon coating drying and high temperature treatment. The composite materials are spherical particles, which are composed of primary nanoparticles coated with carbon, and the thickness of the carbon coating layer is 2 nm. Electrochemical test results show that the synergistic effect of Bi and C can effectively inhibit hydrogen evolution and passivation of iron electrodes. The Fe₃O₄/C–Bi composite materials have excellent electrochemical properties, among which the Fe₃O₄/C–Bi(5%) electrode has the best performance. At a current density of 300 mA g^?1, the discharge capacitance is close to 700.0 mAh g^?1, the coulombic efficiency is as high as 95.2%, and the rate performance is also excellent. At a current density of 2400 mA g^?1, the discharge capacity reaches 500.0 mAh g^?1. AA600 cylindrical iron nickel batteries prepared with an Fe₃O₄/C–Bi(5%) composite as the active material for iron negative electrodes realized sealing for the first time.     

Synthesis of polyanionic anthraquinones as new insoluble organic cathodes for organic Na-ion batteries

A new polyanionic organic cathode, namely sodium 2,6-dihydroxyanthraquinone (AQ26ONa), is synthesized and fully characterized for sodium-ion batteries (SIBs). Due to the two ionic Na–O bonds, the polyanionic AQ26ONa is found almost insoluble in ether-type electrolytes. Meanwhile, AQ26ONa can deliver a two-electron redox mechanism and thus a high specific capacity of 189 mAh g⁻¹ for SIB. In half cells, the AQ26ONa electrode delivers a reversible capacity of 217 mAh g⁻¹ for 150 cycles (50 mA g⁻¹) and ~128 mAh g⁻¹ for 2500 cycles (0.5 A g⁻¹). In the full cells with the reduced state (Na₄TP) of sodium terephthalate (Na₂TP) as the organic anode, the resulting Na₄TPIIAQ26ONa organic SIBs (OSIBs) can display an average discharge capacity of 150 mAh g⁻¹_cathode for 50 cycles and ~66 mAh g⁻¹ for 1000 cycles during the working voltage of 0.01–3.0 V. Currently, the performance of the Na₄TPIIAQ26ONa full cells is among one of the best OSIBs reported to date.     

NH4V3O8/carbon nanotubes composite cathode material with high capacity and good rate capability

NH₄V₃O₈/carbon nanotubes (CNTs) composites are synthesized by one-step hydrothermal method. All the samples show the flake-like morphology with the width of up to 5 μm and thickness of 500 nm and the CNTs are clearly observed on the surface of modified NH₄V₃O₈. It is found that incorporation of 0.5 wt% CNTs into NH₄V₃O₈ could greatly improve its discharge capacity and cycling stability. It delivers a maximum discharge capacity of 358.7 mAh g⁻¹ at 30 mA g⁻¹, 55 mAh g⁻¹ larger than that of the pristine one. At 150 mA g⁻¹, the composite shows 226.2 mAh g⁻¹ discharge capacity with excellent capacity retention of 97% after 100 cycles. The much improved electrochemical performance of NH₄V₃O₈ is attributed to incorporation of CNTs, which facilitates the interface charge transfer and Li⁺ diffusion.     

Autogenic reactions for preparing carbon-encapsulated, nanoparticulate TiO2 electrodes for lithium-ion batteries

We report an anhydrous, autogenic technique for synthesizing electronically interconnected, carbon-encapsulated, nanoparticulate anatase anode materials (TiO₂-C) for lithium-ion batteries. The TiO₂-C nanoparticles provide a reversible capacity of ∼200 mAh g⁻¹, which exceeds the theoretical capacity of the commercially attractive spinel anode, Li₄Ti₅O₁₂ (175 mAh g⁻¹) and is competitive with the capacity reported for other TiO₂ products. The processing method is extremely versatile and has implications for preparing, in a single step, a wide variety of electrochemically active compounds that are coated, in situ, with carbon.     

Enhanced performance for photocatalytic hydrogen evolution using MoS2/graphene hybrids

A MoS₂/graphene hybrid (MSG) is synthesized by microwave hydrothermal method. Both of the charge transfer resistance and the photocurrent are tuned in graphene modified MoS₂ by enhancing photocatalytic nature, where the charge transfer resistance significantly decreases from 36,000 Ω–8.49 Ω and the photocurrent promotes from 0.29 mA cm^?2 to 16.47 mA cm^?2. In this article, the result reveals that the appropriate modification of graphene can reach the maximum yield of hydrogen gas. In addition, the appropriate conditions, such as the concentration of 0.32 M formic acid and the MoS₂ photocatalyst with 0.8 wt% graphene (MSG_0.8) dose of 0.013 g L^?1, can complete the outstanding photocatalytic hydrogen evolution, where the hydrogen evolution using MSG_0.8 composite photocatalyst has the maximum yield of 667.2 μmol h^?1 g^?1.     

Silicon-coated carbon nanofiber hierarchical nanostructures for improved lithium-ion battery anodes

Silicon-coated carbon nanofibers (CNFs) are a viable method of exploiting silicon's capacity in a battery anode while ameliorating the complications of silicon expansion as it alloys with lithium. Silicon-coated CNFs were fabricated through chemical vapor deposition and deposited onto a carbon fiber mesh. This novel anode material demonstrated a capacity of 954 mAh g⁻¹ in the first cycle, but faded to 766 mAh g⁻¹ after 20 cycles. Structural characterization of the samples before and after cycling was carried out using field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The results suggest that a portion of the fade may be due to separation of the silicon coating from the CNFs. Enough silicon remains in contact with the conductive network of CNFs to allow a usable reversible capacity that well exceeds that of graphite. An anode of this material can double the capacity of a lithium-ion battery or allow a 14% weight reduction.     

Aligned nickel–cobalt oxide nanosheet arrays for lithium ion battery applications

Aligned nickel–cobalt nanosheet arrays are deposited on nickel foam substrates by means of chemical bath deposition technique. The nanosheet arrays are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The electrochemical performances as anode materials of lithium ion batteries are investigated by galvanostatic charge–discharge cycle and cyclic voltammetry (CV) tests. The results show that the nickel–cobalt oxide film prepared from the solution in which Ni/Co = 3/1 has the best performance. Its initial charge capacity at 0.1 A g⁻¹ is 798 mAh g⁻¹. When cycled at higher current densities of 0.5 and 1.0 A g⁻¹, the initial charge capacities are 570 and 500 mAh g⁻¹, and 84% and 86% can be retained after 50 cycles, respectively. It is believed that the interconnected nanosheet-array structure and the nickel–cobalt binary composition play important roles in their electrochemical performances.     

Electrochemical hydrogen storage behavior of Ni-Ceria impregnated carbon micro-nanofibers

A hierarchical porous structured carbon micro-nanofiber containing the bimetallic configuration of the nickel (Ni) and ceria (CeO₂) nanoparticles (NPs) was synthesized and tested for the electrochemical hydrogen (H₂) storage capacity. The electrode exhibited a high H₂ storage capacity of 498 mA h/g or 1.858% (w/w) at the charge-discharge current density of 500 mA/g. A mechanistic insight showcased the combined contributions of the high surface area containing activated carbon microfiber (ACF) substrate, the graphitic carbon nanofibers (CNFs), and the Ni and CeO₂ NPs, towards the augmented electrochemical H₂ storage capacity and cyclic stability of the fabricated Ni–CeO₂–CNF/ACF electrode. Ni served as the catalyst for growing the CNFs via chemical vapor deposition as well as for storing H₂ via spillover mechanism, while CeO₂ created the charge carrier vacancies in the material. The measured cycle retention capacity of 99% and charge-discharge efficiency of 97.6% confirm the electrochemically stable characteristics of Ni–CeO₂–CNF/ACF, and clearly indicate it to be an economically viable and efficient H₂-storage material.     

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.     

Effect of synthetic conditions on the electrochemical properties of LiMn0.4Fe0.6PO4/C synthesized by sol–gel technique

Carbon-coated LiMn_0.4Fe_0.6PO₄ (LMFP) was synthesized by sol–gel technique using citric acid as foaming agent and carbon precursor. To evaluate the effect of synthetic conditions on the electrochemical properties of LMFP for use as cathode active material, the carbon-coated olivines were synthesized by a two-step thermal treatment at different temperatures. The composites were characterized by elemental analysis, XRD, SEM, TEM, Raman microprobe spectroscopy and their electrochemical properties were also studied. The composite that shows the better electrochemical performance has more porous structure, lower D/G band ratio in Raman spectra, and charge and discharge capacities of same 155 mAh g⁻¹ with higher material utilization of 97% at 0.1 C-rate (0.05 mA cm⁻²). The material exhibiting the better performance was also incorporated in a polymer electrolyte hosted in an electrospun P(VdF-HFP) membrane. The lithium polymer battery composed of LiMn_0.4Fe_0.6PO₄ cathode and polymer electrolyte showed a good cycling performance with the initial discharge capacity of 146 mAh g⁻¹.