全钒氧化还原液流电池用电极材料的研究进展

全钒氧化还原液流电池系统作为电化学系统现已在国外得到了很好的发展.本文归纳了全钒氧化还原液流电池电极的功能和性能要求,介绍了电极材料的研究进展情况,并提出了当前最有应用前景的电极材料及其结构.     

全钒液流电池用新型全氟磺酸离子交换膜制备及性能研究

通过溶液流延成膜法制备了具有不同离子交换容量(IEC)的全氟磺酸(PFSA)离子交换膜,并测试了其吸水率、电导率、钒离子(Ⅴ(Ⅳ))透过率和选择性系数。研究发现,具有高IEC值的PFSA离子交换膜具有相对较低的Ⅴ(Ⅳ)离子透过率和较高的质子电导率。其中IEC值为1.10mmol/g的PFSA离子交换膜对Ⅴ(Ⅳ)离子具有最高的选择性,其选择性系数为Nafion 117膜的2.97倍。     

Nanocarved vanadium nitride nanowires encapsulated in lamellar graphene layers as supercapacitor electrodes

Supercapacitors have the characteristics of high specific capacitance, long cycle life and fast charging ability, which have shown extremely valuable applications in energy storage fields. Improving the electrode materials is a crucial approach to achieve high capacity. Vanadium nitride (VN) has higher theoretical capacitance than noble metal oxides, as well as better chemical stability and good electrical conductivity. Herein, a composite of VN nanowires with multiple cavities encapsulated in N-doped reduced graphene oxide lamellar layers (VNNWs@rGO) has been synthesized by facile freeze-casting and subsequent nitridation technique. The hierarchical VNNWs@rGO composite exhibited excellent supercapacitor performance: high capacitances of 222 and 65 F g^?1 were achieved at current densities of 0.5 and 10 A g^?1, respectively. The improved electrochemical performance is associated with the unique structural design: the N-doped rGO sheets endowed enhanced electric conductivity and chemical stability for VN, the interconnected laminar network of VNNWs@rGO are crucial for electrolyte penetration and charge transfer, and the cavities and nanoparticles inside the VN nanowires can provide abundant active sites for electric double-layer capacitor and pseudocapacitance.

     

Recent advances in metals and metal oxides as catalysts for vanadium redox flow battery:Properties,structures,and perspectives

Vanadium redox flow battery(VRFB)is a kind of battery with wide application prospect.Electrode mate-rial is one of the key components of VRFB,and its stability directly affects the performance of battery.Among all kinds of electrode materials,carbon-based material has the best comprehensive properties.However,carbon-based electrodes still have disadvantages such as poor hydrophilicity and low electro-chemical activity which need to be improved.One of the effective ways to improve the performance of electrode is to modify carbon-based material with metals and metal oxides.The metal catalysts have excellent electrical conductivity and high catalytic activity.The metal oxide catalysts have the advan-tages of low cost,wide variety and strong oxidizing properties.This work introduced the application of metal and metal oxide modified electrodes in VRFB in recent years,classified the catalysts,studied their catalytic performance and mechanism.The metal catalysts were reviewed from precious metals and base metals.The metal oxide catalysts were classified and discussed according to the similar proper-ties of the same group elements.This work compared different modification methods,summarized the research progress of metal and metal oxide modification,and proposes the future development direction of electrodes and catalysts.     

全钒液流氧化还原电池中隔膜的研究

Nafion 117和PE-01阳离子交换膜均可作为全钒液流氧化还原电池的隔膜用材料,PE-01在机械性能和化学稳定性方面优于Nafion 117.探讨PE-01作为钒电池隔膜材料的优势和劣势,测定PE-01膜和Nafion 117的离子交换容量、4价钒离子在其中的扩散能力以及膜面电阻.实验表明,Nafion 117具有导电性能优良、较大的离子交换容量以及较小的面电阻;PE-01具有很好的物理性能和阻钒离子渗透能力.     

MOS photodetectors based on Au-nanorod doped graphene electrodes

By using Au-nanorod (Au-NR) doped graphene as a transparent conducting electrode, Si-based metal-oxide-semiconductor (MOS) photodetectors (PDs) exhibit high external quantum efficiency (EQE) and fast response time. It is found that upon adding Au-NRs to the graphene, a significant increase in EQE is observed for both planar and Si-nanotip (Si-NT) MOS PDs. The planar Si-based MOS PDs reveal a notable photoresponse with an EQE of 49% at the peak wavelength of 530 nm under zero bias and an EQE of 66% at the peak wavelength of 600 nm under - 0.4 V bias. For the Si-NTs MOS PD, it exhibits a relatively high EQE of 71% under - 4 V bias due to the effect of light trapping arising from the nature of the Si-NT array.     

A soluble-lead redox flow battery with corrugated graphite sheet and reticulated vitreous carbon as positive and negative current collectors

A soluble-lead redox flow battery with corrugated-graphite sheet and reticulated-vitreous carbon as positive and negative current collectors is assembled and performance tested. In the cell, electrolyte comprising of 1·5 M lead (II) methanesulfonate and 0·9 M methanesulfonic acid with sodium salt of lignosulfonic acid as additive is circulated through the reaction chamber at a flow rate of 50 ml min^???1. During the charge cycle, pure lead (Pb) and lead dioxide (PbO₂) from the soluble lead (II) species are electrodeposited onto the surface of the negative and positive current collectors, respectively. Both the electrodeposited materials are characterized by XRD, XPS and SEM. Phase purity of synthesized lead (II) methanesulfonate is unequivocally established by single crystal X-ray diffraction followed by profile refinements using high resolution powder data. During the discharge cycle, electrodeposited Pb and PbO₂ are dissolved back into the electrolyte. Since lead ions are produced during oxidation and reduction at the negative and positive plates, respectively there is no risk of crossover during discharge cycle, preventing the possibility of lowering the overall efficiency of the cell. As the cell employs a common electrolyte, the need of employing a membrane is averted. It has been possible to achieve a capacity value of 114 mAh g^???1 at a load current-density of 20 mA cm^???2 with the cell at a faradaic efficiency of 95%. The cell is tested for 200 cycles with little loss in its capacity and efficiency.     

全钒液流电池的质子传导膜研究

研究质子传导膜对全钒液流电池性能的影响,包括膜面电阻、阻钒性以及质子传导膜厚度,为研究开发适用于全钒液流电池的质子传导膜提供依据.通过测定钒电池循环充电/放电过程的效率、暂态极化曲线、静态交叉放电曲线,建立选择与优化膜材料的评价方法;在考察膜电导率、膜厚、阻钒性和机械强度的综合性能指标后,认为膜面电阻在0.3～0.5 Ω·cm2范围,具备优良阻钒性能条件下,膜厚约150 μm比较合适.使用符合该性能的聚偏氟乙烯质子传导膜时,钒电池能量效率超过70％,有望满足发展大容量蓄电储能装备的需要.     

An overview of amphoteric ion exchange membranes for vanadium redox flow batteries

Vanadium redox flow battery(VRB),as the most promising large-scale electrical energy storage units,has attracted extensive attention.Amphoteric ion exchange membrane(AIEM),as the core part of VRB,separates electrolyte on both sides of electrolytic tank and conducts H~+.The AIEM with cation and anion groups possesses excellent performances,such as high ion conductivity(σ),low vanadium ion permeability(Pvn+),relative stability and low cost.However,the performance of AIEM directly depends on the chemical structure of polymers.In addition to ensuring foundational physical performance,ion selectivity of AIEM is significant since the crossover of vanadium ion with various valences may reduce the battery capacity.In this paper,AIEMs for VRB and their chemical structures as well as synthesis approaches to realize all kinds of high-performing AIEMs are reviewed.The current trend and future direction of prospective materials for the VRB separators are documented in detail as well.     

Enhanced microwave absorption performance of graphene/doped Li ferrite nanocomposites

In the present study, Microwave absorbing Li-Sr, Li-Co ferrite nanoparticles and RGO/Li-Sr, RGO/Li-Co ferrite nanocomposites containing Li ferrite and reduced graphene oxide (RGO) were synthesized to further improve the microwave absorption performance of Li ferrite nanoparticles (LiFe₅O₈). The Li-Sr and Li-Co nanoparticles were synthesized by thermal treatment method, the RGO/Li-Sr and RGO/Li-Co nanocomposites were obtained by a polymerization method and were characterized by different techniques. The electromagnetic wave absorption properties of the samples were evaluated by vector network analyzer (VNA) in the frequency range of 2–18 GHz. The magnetic and dielectric loss, impedance matching, and electromagnetic wave absorption of the samples are significantly improved through the addition of RGO. Experimental results revealed that the RGO/Li-Co nanocomposite considerably increased microwave absorption. The minimum reflection loss (RL) of RGO/Li-Co also was found to reach −46.80 dB at the thickness of 3 mm and the effective absorption bandwidth (≤-10 dB) amounted to 6.80 GHz (from 10.52 to 17.32 GHz), which was much higher in comparison with pure Li and Li-Co ferrites nanoparticles. Due to the synergistic effect between magnetic loss and dielectric loss and the good impedance matching, the RGO/Li-Co nanocomposite may be regarded as a new candidate for microwave absorbing materials characterized with a broad effective absorption bandwidth at thin thicknesses.     

Hierarchically porous graphene as a lithium-air battery electrode

The lithium-air battery is one of the most promising technologies among various electrochemical energy storage systems. We demonstrate that a novel air electrode consisting of an unusual hierarchical arrangement of functionalized graphene sheets (with no catalyst) delivers an exceptionally high capacity of 15000 mAh/g in lithium-O(2) batteries which is the highest value ever reported in this field. This excellent performance is attributed to the unique bimodal porous structure of the electrode which consists of microporous channels facilitating rapid O(2) diffusion while the highly connected nanoscale pores provide a high density of reactive sites for Li-O(2) reactions. Further, we show that the defects and functional groups on graphene favor the formation of isolated nanosized Li(2)O(2) particles and help prevent air blocking in the air electrode. The hierarchically ordered porous structure in bulk graphene enables its practical applications by promoting accessibility to most graphene sheets in this structure.     

Functionalized graphene sheets for polymer nanocomposites

Polymer-based composites were heralded in the 1960s as a new paradigm for materials. By dispersing strong, highly stiff fibres in a polymer matrix, high-performance lightweight composites could be developed and tailored to individual applications. Today we stand at a similar threshold in the realm of polymer nanocomposites with the promise of strong, durable, multifunctional materials with low nanofiller content. However, the cost of nanoparticles, their availability and the challenges that remain to achieve good dispersion pose significant obstacles to these goals. Here, we report the creation of polymer nanocomposites with functionalized graphene sheets, which overcome these obstacles and provide superb polymer-particle interactions. An unprecedented shift in glass transition temperature of over 40 degrees C is obtained for poly(acrylonitrile) at 1 wt% functionalized graphene sheet, and with only 0.05 wt% functionalized graphene sheet in poly(methyl methacrylate) there is an improvement of nearly 30 degrees C. Modulus, ultimate strength and thermal stability follow a similar trend, with values for functionalized graphene sheet- poly(methyl methacrylate) rivaling those for single-walled carbon nanotube-poly(methyl methacrylate) composites.     

Designed synthesis of ordered mesoporous graphene spheres from colloidal nanocrystals and their application as a platform for high-performance lithium-ion battery composite electrodes

Three-dimensional (3D) graphene has recently attracted enormous attention for electrochemical energy storage applications. However, current methods suffer from an inability to simultaneously control and engineer the porosity and morphology of the graphene frameworks. Here, we report the designed synthesis of ordered mesoporous graphene spheres (OMGSs) by transformation of self-assembled Fe₃O₄ nanocrystal superlattices. The resultant OMGSs have an ultrathin framework comprising few-layered graphene, with highly ordered and interconnected mesoporosity and a high surface area. These advantageous structural and textural features, in combination with the excellent electrical conductivity of the graphitic frameworks, render the OMGSs an ideal and general platform for creating hybrid materials that are well suited for use as composite electrodes in lithium-ion batteries (LIBs). As a proof-of-concept demonstration, SnO₂ and GeO₂ nanoparticles are incorporated into the OMGSs to afford SnO₂@OMGSs and GeO₂@OMGSs, respectively, both of which exhibit outstanding lithium storage properties when used as LIB anodes.

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Graphene-multilayer graphene nanocomposites as highly efficient thermal interface materials

We found that the optimized mixture of graphene and multilayer graphene, produced by the high-yield inexpensive liquid-phase-exfoliation technique, can lead to an extremely strong enhancement of the cross-plane thermal conductivity K of the composite. The "laser flash" measurements revealed a record-high enhancement of K by 2300% in the graphene-based polymer at the filler loading fraction f = 10 vol %. It was determined that the relatively high concentration of the single-layer and bilayer graphene flakes (~10-15%) present simultaneously with the thicker multilayers of large lateral size (~1 μm) were essential for the observed unusual K enhancement. The thermal conductivity of the commercial thermal grease was increased from an initial value of ~5.8 W/mK to K = 14 W/mK at the small loading f = 2%, which preserved all mechanical properties of the hybrid. Our modeling results suggest that graphene-multilayer graphene nanocomposite used as the thermal interface material outperforms those with carbon nanotubes or metal nanoparticles owing to graphene's aspect ratio and lower Kapitza resistance at the graphene-matrix interface.     

Anodic oxidation with doped diamond electrodes: a new advanced oxidation process

Boron-doped diamond anodes allow to directly produce OH* radicals from water electrolysis with very high current efficiencies. This has been explained by the very high overvoltage for oxygen production and many other anodic electrode processes on diamond anodes. Additionally, the boron-doped diamond electrodes exhibit a high mechanical and chemical stability. Anodic oxidation with diamond anodes is a new advanced oxidation process (AOP) with many advantages compared to other known chemical and photochemical AOPs. The present work reports on the use of diamond anodes for the chemical oxygen demand (COD) removal from several industrial wastewaters and from two synthetic wastewaters with malic acid and ethylenediaminetetraacetic (EDTA) acid. Current efficiencies for the COD removal between 85 and 100% have been found. The formation and subsequent removal of by-products of the COD oxidation has been investigated for the first time. Economical considerations of this new AOP are included.     

Active carbon/graphene hydrogel nanocomposites as a symmetric device for supercapacitors

Activated carbons (ACs) are successfully synthesized from Elaeagnus grain by a simple chemical synthesis methodology and demonstrated as novel, suitable supercapacitor electrode materials for graphene hydrogel (GH)/AC nanocomposites. GH/AC nanocomposites are synthesized via hydrothermal process at temperature of 180°C. The low-temperature thermal exfoliation approach is convenient for mass production of graphene hydrogel (GH) at low cost and it can be used as electrode material for energy storage applications. The GH/AC nanocomposites exhibit better electrochemical performances than the pure GH. Electrochemical performance of the electrodes is studied by cyclic voltammetry, and galvanostatic charge-discharge measurements in 1.0 M H₂SO₄ solution. A remarkable specific capacitance of 602.36 Fg^?1 (based on GH/AC nanocomposites for 0.4 g AC) is obtained at a scan rate of 1 mVs^?1 in 1 M H₂SO₄ solution and 155.78 Fg^?1 for GH. The specific capacitance was increased 3.87 times for GH/AC compared to GH electrodes. Moreover, the GH/AC nanocomposites for 0.2 g AC present excellent long cycle life with 99.8% specific capacitance retained after 1000 charge/discharge processes. Herein, ACs prepared from Elaeagnus grain are synthesized GH and AC supercapacitor device for high-performance electrical energy storage devices as a promising substitute to conventional electrode materials for EDLCs.     

全钒液流电池的质子传导膜研究进展

全钒液流电池(VRB)作为一种大规模的蓄电储能设备,在新能源发电和电网调峰等方面有重要应用.质子传导膜是钒电池的关键材料,对电池的性能、成本和寿命有着十分重要的影响.文章在简单介绍VRB的基本组成和原理以及对隔膜的性能要求的基础上,主要论述了目前报道的几种VRB隔膜材料及其改性方法,以及对电池性能的影响,最后对质子交换膜的发展方向和前景进行了总结和展望.     

Silane-functionalized graphene nanoplatelets for silicone rubber nanocomposites

Journal of Materials Science - Silane-functionalized graphene nanoplatelets (GNPs) were prepared using a newly developed approach based upon a simple two-step strategy. The effect of their...