水溶性带电聚合物黏结剂修饰炭电极用于增强电容去离子性能

电容去离子技术（capacitive deionization,CDI）是一种基于电吸附原理的新型脱盐技术,具有成本低、无污染、能耗小等优点。采用亲水性的羧甲基纤维素钠（CMC）和聚乙烯醇（PVA）黏结剂及其化学修饰得到的具有更多带电基团的磺化羧甲基纤维素（SCMC）和季铵化聚乙烯醇（QPVA）黏结剂制备活性炭电极,能进一步增强活性炭（AC）电极的亲水性和离子选择性。亲水性带电聚合物黏结剂依靠自身的电荷可以有效抑制阳极氧化的副反应,并增强离子吸附驱动力。在500 mg/L NaCl盐溶液,1.2/0 V电压下,AC-CMC//AC-PVA和AC-SCMC//AC-QPVA可分别获得14.58和17.39 mg/g的脱盐量,且在0.8/0 V电压下循环100圈之后,脱盐量的保持率分别为65.48%和80.53%。     

Enhanced capacitive deionization of graphene/mesoporous carbon composites

Capacitive deionization (CDI) with low-energy consumption and no secondary waste is emerging as a novel desalination technology. Graphene/mesoporous carbon (GE/MC) composites have been prepared via a direct triblock-copolymer-templating method and used as CDI electrodes for the first time. The influences of GE content on the textural properties and electrochemical performance were studied. The transmission electron microscopy and nitrogen adsorption-desorption analysis indicate that mesoporous structures are well retained and the composites display improved specific surface area and pore size distribution, as well as pore volume. Well dispersed GE nanosheets are deduced to be beneficial for enhanced electrical conductivity. The electrochemical performance of electrodes in an NaCl aqueous solution was characterized by cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy measurements. The composite electrodes perform better on the capacitance values, conductive behaviour, rate performance and cyclic stability. The desalination capacity of the electrodes was evaluated by a batch mode electrosorptive experiment and the amount of adsorbed ions can reach 731 μg g(-1) for the GE/MC composite electrode with a GE content of 5 wt%, which is much higher than that of MC alone (590 μg g(-1)). The enhanced CDI performance of the composite electrodes can be attributed to the better conductive behaviour and higher specific surface area.     

High performance graphene composite microsphere electrodes for capacitive deionisation

Graphene oxide/resorcinol–formaldehyde microsphere (GORFM) was synthesised by a simple-inverse suspension polymerisation under ambient pressure drying and the graphene composite microsphere (GCM) was obtained by carbonisation in a nitrogen atmosphere. The morphologies and microstructures of GORFM and GCM samples were characterised by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and surface area analysis. The results showed that the diameters of GORFM were controlled in the range of 5–10 μm with perfect sphericity. The inner layer of GORFM was composed of resorcinol–formaldehyde (RF) particles, and the outer layer was the wrinkled GO sheets intercalated with RF through chemical and physical interactions. The GCM-1.5 sample achieved the highest specific surface area of 1128 m²/g and the mesopore area was 699 m²/g. The electrochemical behaviours of GCM as an electrode were investigated by cyclic voltammograms, electrochemical impedance spectroscopy and capacitive deionisation (CDI). The specific capacitance and electrosorption capacity of GCM-1.5 was 290.2 F/g and 33.52 mg/g, respectively. The current efficiencies were in the range of 77.75–81.41%. These results implied that GCM had a potential application in CDI due to its low-cost and high performance.     

Towards high purity graphene/single-walled carbon nanotube hybrids with improved electrochemical capacitive performance

CoMgAl layered double hydroxides were prepared as catalysts for the in situ synchronous growth of graphene and single-walled carbon nanotubes (SWCNTs) from methane by chemical vapor deposition. The as-calcined CoMgAl layered double oxide (LDO) flakes served as the template for the deposition of graphene, and Co nanoparticles (NPs) embedded on the LDOs catalyzed the growth of SWCNTs. After the removal of CoMgAl LDO flakes, graphene (G)/SWCNT/Co₃O₄ hybrids with SWCNTs directly grown on the surface of graphene and 27.3 wt.% Co₃O₄ NPs encapsulated in graphene layers were available. Further removal of the Co₃O₄ NPs by a CO₂-oxidation assistant purification method induced the formation of G/SWCNT hybrids with a high carbon purity of 98.4 wt.% and a high specific surface area of 807.0 m²/g. The G/SWCNT/Co₃O₄ hybrids exhibited good electrochemical performance for pseudo-capacitors due to their high Co₃O₄ concentration and the high electrical conductivity of SWCNTs and graphene. In another aspect, the G/SWCNT hybrids can be used as excellent electrode materials for double-layer capacitors. A high capacity of 98.5 F/g_electrode was obtained at a scan rate of 10 mV/s, 78.2% of which was retained even when the scan rate increased to 500 mV/s.     

聚间苯二胺/碳纳米管复合材料制备及其电容法脱盐研究

采用原位氧化聚合方法制备聚间苯二胺（PmPD）和碳纳米管（CNT）复合电极材料（PmPD@CNT）,考察了PmPD的添加对复合材料亲水性、电化学性能的影响,研究了以PmPD@CNT为电极的电容法脱盐（Capacitive Deionization,CDI）性能。扫描电镜和透射电镜分析表明PmPD的球形形貌保留在复合材料中且均匀包裹在CNT外表面。接触角测试证明,与CNT （107°）相比,PmPD@CNT的接触角（61°）显著降低,亲水性明显提高。X射线衍射和拉曼光谱图的测试结果证明PmPD@CNT相比CNT有更多的缺陷点位,有利于提高离子吸附能力。电化学测试证明,PmPD@CNT （72.5 F·g^-1,0.071 Ω）比CNT （27.4 F·g^-1,0.089 Ω）具有更高的比电容和较低的电阻。将PmPD@CNT制备成固体电极用于CDI组件进行饱和脱盐测试,结果表明以500 mg·L^-1的NaCl溶液为原料液及1.4 V操作电压条件下,该复合电极的盐吸附量为16.64 mg,对应的比吸附量为35.40 mg·g^-1,平均吸附速率为10.11 mg·g^-1·min^-1,PmPD@CNT的比吸附量和平均吸附速率分别是CNT的2.4和1.4倍。PmPD@CNT因其良好的亲水性,优异的电化学性能和脱盐性能,有望成为有竞争力的CDI电极材料。     

Influence of microstructure on the capacitive performance of polyaniline/carbon nanotube array composite electrodes

A series of polyaniline/carbon nanotube array (PANI/CNTA) composite electrodes are prepared by electrodeposition of PANI onto CNTA electrodes by 100-500 cyclic voltammetry (CV) cycles, with the aim to investigate the influence of microstructure on the capacitive performance of PANI/CNTA composites. The morphology of PANI/CNTA composites varies remarkably with the CV cycles of electrodeposition. The optimum condition is obtained for the PANI/CNTA composite prepared by 100 CV cycles, corresponding to the highest specific capacitance, best rate performance, and longest cycle life, which are much better than that of activated carbon fiber cloth, the PANI electrodeposited on stainless steel substrate, and CNTA electrode. The forming process of the microstructure and its influence on the capacitive performance of PANI/CNTA composites are presented in this paper.     

石墨烯气凝胶/MnO2复合材料强化电容去离子性能研究

选用石墨烯气凝胶(GA)作为载体,负载MnO2纳米颗粒,构建新型石墨烯气凝胶-MnO2复合材料(MnGA),并制备电容电极,研究复合材料的电容去离子性能。结果表明,MnO2在石墨烯片层上可形成一维线状结构,减弱石墨烯片层间的堆叠效应,提升材料电容,从而提高了电极的脱盐性能,最大电容脱盐量达到25.78 mg/g;NaCl溶液的初始浓度、供电电压和进水流速均会对电容脱盐量产生影响。     

Ag nanoparticles anchored NiO/GO composites for enhanced capacitive performance

Hierarchical nickel oxide/graphene oxide (NiO/GO) and nickel oxide/graphene oxide/silver (NiO/GO/Ag) heterostructures were sucessfully fabricated as high-performance supercapacitors electrode materials by using a hydrothermal process and a photoreduction process. The experimental results showed that the NiO/GO/Ag heterostructure electrodes showed better electrochemical performance than those of NiO/GO and bare NiO nanosheets. The NiO/GO/Ag electrode exhibited a higher specific capacitance of 229 F g⁻¹ at a current density of 1 A g⁻¹, higher than that of 161 F g⁻¹ for NiO/GO composites. Furthermore, NiO/GO/Ag electrode also showed good rate capability (still 200 F g⁻¹ at 6 A g⁻¹) and cycling stability (24% loss after 2000 repetitive cycles at a scan rate of 20 mV s⁻¹). The enhanced capacitive performance of the NiO/GO/Ag composites was mainly attributed to the introduction of Ag nanoparticles, which increased the electrical conductivities of the composites, and promoted the electron transfer between the active components. This study suggested that NiO/GO/Ag composites were a promising class of electrode materials for high performance energy storage applications.     

Electrospun porous carbon nanofibers/TiO2 composite coated over carbon cloth- A flexible electrode for capacitive deionization

The combination of porous carbon matrix and metal oxide is trending for capacitive deionization (CDI) due to their synergistic electrochemical behaviour and properties. In this research, a flexible electrode based on electrospun porous carbon nanofibers and TiO₂ nanoparticles (particle size ～7 nm) i.e., PCNFs/TiO₂ composite coated over carbon cloth is developed. A facile in-situ activation procedure using sacrificial polymer is adopted over typical chemical activation treatment to synthesize PCNFs/TiO₂ composite. PCNFs/TiO₂ composite is prepared in two steps, possessing a high specific surface area of ～343 m² g^?1 and pore volume of 0.038 cm³ g^?1. Interestingly, CDI unit assembled with PCNFs/TiO₂ composite based flexible electrodes delivers the large salt electrosorption capacity of 204.8 mg g^?1 at voltage 1.2 V in a salt solution of concentration 500 ppm and conductivity 880 μS cm^?1. The excellent adsorption capacity retention of 96.4% up to ten adsorption-regeneration cycles can be a tempting option for future flexible CDI applications.     

Carbon nanotube wires for high-temperature performance

We developed carbon nanotube wires (CNWs) and monitored in situ their electrical properties at high temperature conditions for the first time. The dominant type of CNTs present in the material and packing density of thereof proved to have a dominant effect on the thermal stability of CNWs. Furthermore, we showed that kinetics of CNW oxidation plays an important role and slow heating rates or prolonged heating times are essential for the proper determination of thermal stability of CNTs. To enhance the stability at high temperatures, we applied SiC coating onto the CNWs, what allowed a 300 °C improvement to the operational window, eventually reaching 700 °C in the long-haul. Correlation of the change in electrical properties with thermogravimetric response showed that the loss of electrical percolation takes place at 100 °C lower temperature than the last observed weight loss in CNTs content. Finally, we demonstrated feasibility of SiC-coated CNWs under high temperature conditions, by creating a heating device out of them. The presence of SiC layer gave rise to a significant improvement to the thermal stability of the CNT heaters, which now offer unprecedented range of operation reaching 700 °C, as compared to 400 °C when uncoated.     

Plasma sprayed graphene/carbon nanotube reinforced lanthanum-cerate hybrid composite coating

Lanthanum cerate (LC: La₂Ce₂O₇) is a potential material for thermal barrier coating, whose improved toughness is a crucial necessity for the pathway of its industrialization. Herein, we demonstrated a promising approach to develop graphene/carbon nanotube hybrid composite coating using a large throughput and atmospheric plasma spraying method. Graphene nanoplatelets (GNP: 1 wt %) and carbon nanotube (CNT: 0.5 wt %) reinforced lanthanum cerate (LCGC) hybrid composite coatings were deposited on the Inconel substrate. Addition of 1 wt % GNP and 0.5 wt % CNT in LC matrix has significantly increased its relative density, hardness, and elastic modulus up to 97.2%, 2–3 folds, 3–4 folds, respectively. An impressive improvement of indentation toughness (8.04 ± 0.2 MPa m^0.5) was observed on LCGC coating, which is ～8 times higher comparing the LC coating. The toughening was attributed to the factors: such as the distribution of GNPs and CNTs in the LC matrix, synergistic toughening offered by the GNPs and CNTs; (i) GNP/CNT pull-out, (ii) crack bridging and arresting, (iii) splat sandwiching, mechanical interlocking, etc. Finally, this improved toughness offered an exceptional thermal shock performance up to 1721 cycles at 1800 °C, without any major failure on the coating. Therefore, the GNP and CNT-reinforced LC hybrid composite coating can be recommended to open a path for turbine industries.     

KOH改性活性炭涂层电极的电容去离子性能研究

用KOH对市售的粉末活性炭进行表面改性。采用BET分析改性前后活性炭的表面结构,并采用活性炭涂层电极构建电容去离子吸附装置,研究改性后电极的去离子效果。研究表明:经过KOH改性后,活性炭的比表面积从519.25 m2/g增加到975.07 m2/g,提高了87.78%,中孔孔容占总孔孔容的百分比提高了48.28%,改性后活性炭的孔隙结构和孔径的分布更有利于溶液中的Na+和Cl-通过,提高了电极的吸附速率。     

Subsize Ti3C2Tx derived from molten-salt synthesized Ti3AlC2 for enhanced capacitive deionization

Ti₃C₂T_x is a promising intercalation-type electrode material for capacitive deionization (CDI). However, Ti₃C₂T_x, obtained from traditional synthesized Ti₃AlC₂, is with large particle size and undersized interlayer space, which can easily lead to the longer ion diffusion path, fewer adsorption sites, and higher ion diffusion barrier in CDI process. In this work, subsize and Na⁺ intercalated Ti₃C₂T_x (Na⁺-Ti₃C₂T_x-MS) was prepared by HF etching KCl-assisted molten-salt synthesized Ti₃AlC₂ and following NaOH treatment. The Na⁺-Ti₃C₂T_x-MS achieves a high electrosorption capacity of 14.8 mg/g and a high charge efficiency of 0.81 at the applied voltage of 1.2 V in 100 mg/L NaCl solution. Besides, the stable desalination performance of Na⁺-Ti₃C₂T_x-MS has been confirmed. The superior performance of Na⁺-Ti₃C₂T_x-MS can be attributed to the subsize particle and larger interlayer space. Both two factors can effectively increase ions adsorption sites, shorten diffusion path lengths, and reduce diffusion barriers in the CDI process.     

CNTs/PANI/NiHCF复合膜的共聚制备与电容性能

采用循环伏安一步共聚法在碳纳米管修饰的铂基体上制备出电活性CNTs/PANI/NiHCF复合膜;用循环伏安(CV)、恒电流充放电和电化学阻抗(EIS)等测试了复合膜的循环稳定性与电化学容量性能.研究表明,在电流密度为2 mA/cm~2时,CNTs/PANI/NiHCF复合膜的比容量高达217.69 F/g,比能量高达24.49 Wh/ks,当电流密度为10mA/cm~2时比容量仍可达212.98F/g,比功率可达8 489.75 W/kg,具有良好的功率特性和快速克放电能力;在2000次循环充放电过程中,CNTs/PANI/NiHCF/复合膜的容量仅衰减19.92%,电荷充放电效率一直保持在99%以上,是一种优异的超级电容器材料.     

Fabrication and electrochemical capacitance of hierarchical graphene/polyaniline/carbon nanotube ternary composite film

A film composed of graphene (GN) sheets, polyaniline (PANI) and carbon nanotubes (CNTs) has been fabricated by reducing a graphite oxide (GO)/PANI/CNT precursor prepared by flow-directed assembly from a complex dispersion of GO and PANI/CNT, followed by reoxidation and redoping of the reduced PANI in the composite to restore the conducting PANI structure. Scanning electron microscope images indicate that the ternary composite film is a layered structure with coaxial PANI/CNT nanocables uniformly sandwiched between the GN sheets. Such novel hierarchical structure with high electrical conductivity perfectly facilitates contact between electrolyte ions and PANI for faradaic energy storage and efficiently utilizes the double-layer capacitance at the electrode–electrolyte interfaces. The specific capacitance of the GN/PANI/CNT estimated by galvanostatic charge/discharge measurement is 569 F g⁻¹ (or 188 F cm⁻³ for volumetric capacitance) at a current density of 0.1 A g⁻¹. In addition, the GN/PANI/CNT exhibits good rate capability (60% capacity retention at 10 A g⁻¹) and superior cycling stability (4% fade after 5000 continuous charge/discharge cycles).     

Self-assembled flower-like FeS2/graphene aerogel composite with enhanced electrochemical properties

Graphene aerogel (GA) supported flower-like ferrous disulfide (FeS₂) composite was synthesis by a two-step self-assembly method using eco-friendly and low-cost precursors. The formation of well-crystallized pyrite FeS₂ and the reduction of graphene oxide (GO) was demonstrated by X-ray diffraction, Fourier transform infrared spectroscopy and Raman spectroscopy. According to the scanning electron microscopy images, the flower-like FeS₂ distributes uniformly on the inter-linking GA networks. The electrochemical tests indicate that the as-prepared GA-FeS₂ exhibits enhanced specific capacitance (313.6 F/g at the current density of 0.5 A/g), which is almost twice as high as that of bare FeS₂ (163.5 F/g). It is noticed that this composite also has excellent cyclability (88.2% retention after 2000 cycles at 10 A/g) and low transfer resistance. A symmetric supercapacitor device with wide potential range was assembled using GA-FeS₂, while its energy density could reach 22.86 Wh/kg. The excellent specific capacitance, good rate capability, and high energy density make it a promising candidate for next generation supercapacitors.     

流动电极电容去离子去除铵根离子模型及优化

为了更直观地研究流动电极电容去离子（flow electrode capacitive deionization, FCDI）除氨工艺的机理并进行高效改进,本文构建了FCDI装置去除NH{}_{\mathrm{4}}^{+}的电化学稳态模型,实验结果模拟准确率达到93.8%。利用该模型研究了FCDI除氨工艺在进水流量、电流密度、电极液中活性炭质量分数等工况条件下的能耗和去除效率变化趋势,计算离子选择性和去除速率两个指标,定性阐明操作参数对去除氨的影响机理,筛选出较优化工况。研究结果表明,FCDI除氨工艺在进水流量1.25mL/min、电流密度21.26A/m²、活性炭质量分数为10%时,除氨效率为74.5%,能耗为29.62kWh/kg N,达到较为理想的状态。在优化的工况条件下,讨论了NH{}_{\mathrm{4}}^{+}在FCDI装置内部的微观传输情况,考虑到过长的流道长度会增强电流密度的极化现象,降低装置除氨性能,提出了串联装置的建议。保持流道长度和工况条件不变,串联的装置可以比原装置的去除效率提升32.9%,同时去除单位质量N的能耗降低22.0%,表明装置的改进是有效的。优化后的FCDI除氨工艺比同类处理工艺更有优势,NH{}_{\mathrm{4}}^{+}去除效率更高,能耗更低,具有广泛应用前景。     

Continuous capacitive deionization-electrodialysis reversal through electrostatic shielding for desalination and deionization of water

We report a new concept for capacitive deionization with simple and cheap porous bipolar intermediate graphite electrodes which is operated continuously by constant or alternating polarity without any down time for electrode saturation, regeneration and rinsing steps and certainly without any permselective ion exchange membranes. The proposed process utilizes the advantages of the classical electrodeionization technologies combining them all to a unified continuous capacitive deionization-continuous electrodeionization-electrodialysis-electrodialysis reversal process. Separate and unchanged diluate and concentrate compartments are created in two modes, first by periodical charging/discharging the bipolar intermediate electrodes through a pulsating electric field and second by simultaneous charging/discharging them through a constant or pulsating electric field and electrostatic shielding. Because of coion permeation and the convenience of alternating the polarity without any negative impact on the deionization process, the new technique is less affected by the known membrane associated limitation, such as concentration polarization, limiting current density or scaling. The new electrochemical deionization technique is suitable for regeneration of ion exchange resins and production of high purity deionized water, removal of heavy metal ions from industrial effluents and desalination of brackish or seawater.     

1D/2D carbon nanotube/graphene nanosheet composite anodes fabricated using electrophoretic assembly

This study examines the direct assembly of hybrid graphene nanosheets (GNSs) and multiwalled carbon nanotubes (MWCNTs) onto Ni current collectors in the presence of an electric field. The dissociation of Ni nitrate salt, which provides ions to charge the GNSs and MWCNTs positively, facilitates the homogeneous dispersion of each powder and assists in electrophoretic deposition. Direct assembly by this electrophoretic deposition results in the effective packing of GNS/MWCNT composites without any appreciable agglomeration, which is desirable for achieving high electrochemical performance of the composite electrodes in Li-ion batteries. Hence, GNS/MWCNT composite electrodes exhibit higher specific capacity compared to electrodes made of pure GNSs or MWCNTs owing to better realization of electrolyte permeability and Li-ion transfer.