Porous carbon framework nested nickel foam as freestanding host for high energy lithium sulfur batteries

Constructing 3 D multifunctional conductive framework as stable sulfur cathode contributes to develop advanced lithium-sulfur(Li-S) batteries.Herein,a freestanding electrode with nickel foam framework and nitrogen doped porous carbon(PC) network is presented to encapsulate active sulfur for Li-S batteries.In such a mutually embedded architecture with high stability,the interconnected carbon network and nickel foam matrix can expedite ionic/electro nic tra nsport and sustain volume variations of sulfur.Furthermore,rationally designed porous structures provide sufficient internal space and large surface area for high active sulfur loading and polar polysulfides anchoring.Benefiting from the synergistic superiority,the Ni/PC-S cathode exhibits a high initial capacity of around 1200 mAh/g at 0.2 C,excelle nt rate perfo rmance,and high cycling stability with a low decay rate of 0.059% per cycle after 500 cycles.This work provides a useful strategy to exploit freestanding porous framework for diverse applications.     

Improving breakdown strength and energy storage efficiency of poly(vinylidene fluoride-co-chlorotrifluoroethylene) and polyurea blend films by double layer structure design

All-organic composites are widely used in energy storage application due to the high breakdown strength performance, but the improvement of energy storage was limited by the relatively low dielectric constant. Therefore, to satisfy the high demands of dielectric materials, energy storage properties of polymer composites should be further enhanced. In this article, poly(vinylidene fluoride-co-chlorotrifluoroethylene) (P(VDF-CTFE)) and polyurea (PUA), which are known as high dielectric ferroelectric material and linearly high energy storage efficiency material respectively, are composited through double layer (DL) casting method for the first time. The properties of DL structured composite film is contrasted with solution blending structure especially in energy storage efficiency, and the results demonstrate that DL structure design can make great use of advantages of two materials and also can avoid the influence of phase separation between P(VDF-CTFE) and PUA efficiently. Moreover, high breakdown strength (6180 kV/cm) and high energy storage efficiency (77%) of DL composites can be realized simultaneously by incorporating PUA as an insulating layer, and the mechanism is discussed in detail. This work provides an effective route to improve the energy storage properties of polymer dielectric materials and shows great application potential.     

原子层沉积制备掺氮碳膜修饰的 Pt/CNTs 实现甲醇高效电催化氧化

甲醇燃料电池作为一种清洁、高效的能源转化形式广受关注. 贵金属 Pt 是甲醇燃料电池阳极催化剂不可缺少的活性组分, 但 Pt 价格昂贵, 易与 CO 等中间体强相互作用而中毒失活, 从而限制了甲醇燃料电池的广泛应用. 因此, 如何提高Pt 的利用率成为一个关键问题. 研究表明, 在碳材料载体中掺杂氮元素, 改变了载体本身的表面结构和电子性质, 有利于Pt 颗粒的成核和生长, 可获得尺寸小、分布均匀的 Pt 纳米颗粒, 能显著提升催化反应活性和 Pt 利用率. 然而, 传统的氮掺杂方法需要在高温、高压及氨气条件下进行, 增加了催化剂制备难度和成本.原子层沉积技术是逐层超薄沉积技术, 能够在原子级别精确控制膜的厚度, 既可制备尺度均一、高度可控的纳米粒子,也能实现材料表面的可控超薄修饰. 本课题组利用原子层沉积技术优势, 首先在碳纳米管表面沉积了直径 2 nm 左右的 Pt纳米颗粒, 然后在 Pt 纳米颗粒外表面超薄修饰聚酰亚胺膜, 通过后处理得到多孔掺氮碳膜修饰的 Pt/CNTs 催化剂. 碳膜的厚度可简单通过调控聚酰亚胺膜的沉积厚度来控制. 结果表明, 适当厚度的碳膜修饰 Pt/CNTs 催化剂可显著提升其甲醇电氧化性能, 电流密度可达商业 20% Pt/C 的 2.7 倍, 催化剂稳定性也显著改善. 然而碳膜修饰过厚会导致催化剂活性降低.通过计算催化剂电化学活性表面积发现, 超薄修饰碳膜后催化剂活性表面积有所降低, 这是由于碳膜的覆盖导致表面 Pt原子数减少. 修饰前后催化剂颗粒尺度变化不大, 推测催化剂活性的提高与形成了有利于催化反应的 Pt-碳膜界面有关.然而, 当碳膜修饰层过厚时, 会导致反应物分子难以扩散到 Pt 颗粒表面, 使催化剂活性降低. 预吸附单层 CO 溶出实验结果表明, 多孔掺氮碳膜超薄修饰 Pt/CNTs 催化剂后, CO 氧化峰的起始电位和峰值电位都向低电位处偏移, 这表明 Pt 表面吸附的 CO 在较低电位下即可被氧化, CO 更容易从 Pt 表面移除, 从而提高了催化剂的抗 CO 毒化能力. X 射线光电子能谱实验结果进一步表明, 经多孔掺氮碳膜修饰后, Pt 的 4f 电子向高结合能处偏移, 表明 Pt 原子周围的电子密度减小, 从而弱化了 Pt 对 CO 吸附的σ-π键反馈作用, 即减弱了 Pt 原子对 CO 的吸附, 这是导致掺氮碳膜修饰后催化剂活性及稳定性都大幅提高的原因.     

Destabilizing role of the double layer for a dissolution–depassivation mechanism

A new dissolution–depassivation mechanism showing a non-trivial complex S-shaped polarization curve due to the Frumkin isotherm hypothesis has been studied. A potential domain exists for sufficiently low values of the Frumkin interaction parameter where a negative differential resistance is observed. For this mechanism, the electrode potential acts as an essential system variable due to the double layer capacitance. Harmonic and relaxation oscillations can be observed for the dissolution–depassivation mechanism under galvanostatic control (GC). Hopf bifurcation gives rise to oscillations under GC only for sufficiently high values of the double layer capacitance. Bifurcation diagrams are plotted.     

Fluorination effect of activated carbon electrodes on the electrochemical performance of electric double layer capacitors

The surface of phenol-based activated carbon (AC) was fluorinated at room temperature with different F₂:N₂ gas mixtures for use as an electrode material in an electric double-layer capacitor (EDLC). The effect of surface fluorination on EDLC electrochemical performance was investigated. The specific capacitance of the fluorinated AC-based EDLC was measured in a 1 M H₂SO₄ electrolyte, in which it was observed that the specific capacitances increased from 375 and 145 F g⁻¹ to 491 and 212 F g⁻¹ with the scan rates of 2 and 50 mV s⁻¹, respectively, in comparison to those of an unfluorinated AC-based EDLC when the fluorination process was optimized via 0.2 bar partial F₂ gas pressure. This enhancement in capacitance can be attributed to the synergistic effect of increased polarization on the AC surface, specific surface area, and micro and mesopore volumes, all of which were induced by the fluorination process. The observed increase in polarization was derived from a highly electronegative fluorine functional group that emerged due to the fluorination process. The increased surface area and pore volume of the AC was derived from the physical function of the fluorine functional group.     

Probing the electrochemical double layer of an ionic liquid using voltammetry and impedance spectroscopy: A comparative study of carbon nanotube and glassy carbon electrodes in [EMIM][EtSO4]

Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) are compared as techniques for analyzing double layer capacitances of ionic liquids (ILs) at the surfaces of two carbon-based electrodes. These systems are relevant for energy storage supercapacitors and often are associated with unconventional electrochemical properties. Certain theoretical and experimental aspects of CV and EIS necessary for quantitative evaluation of the capacitance characteristics of such systems are explored. The experiments use 1-ethyl-3-methyl imidazolium ethylsulfate as a model IL electrolyte in combination with a porous electrode of carbon nanotubes (CNTs). The results are compared with those obtained with a nonporous glassy carbon (GC) electrode. The time is constant, and hence the power delivery characteristics of the experimental cell are affected by the electrolyte resistance and residual faradaic reactions of the IL, as well as by the spatially inhomogeneous electrode surfaces. It is shown that adequate characterization of these IL-electrode systems can be achieved by combining CV with EIS. A phenomenological framework for utilizing this combination is discussed.     

Humic acid‐derived hierarchical porous carbon preparation using vacuum freeze‐drying for electric double layer capacitors

Electric double layer capacitors (EDLCs) preserve charge by reversible physisorption of electrolyte ions on the surface of porous active materials. Therefore, engineering a reasonable pore structure and reducing oxygen‐containing groups of carbon materials are efficient approaches to enable rapid ion diffusion pathways and long life span, respectively. Here, humic acid (HA)‐derived hierarchical porous carbon was fabricated by vacuum freeze‐drying, KOH activation, and subsequent annealing. The macropores were generated from the vacancies where the ice crystals in the HA–KOH gels initially occupied during vacuum‐freeze drying, while abundant micropores were created from homogeneous KOH activation. In addition, subsequent annealing further reduced the oxygen‐containing groups. When used as EDLC electrodes in 1 mol/L TEABF₄/PC organic electrolyte, they could give a high capacitance of 150 F/g at 0.05 A/g and excellent rate performance of 81% (with capacitance of 121.46 F/g at 10 A/g). More importantly, the hierarchical porous carbon displays superior capacity retention of 85.6% after 10,000 cycles at 1 A/g at 2.7 V.     

The loading of polyoxometalates compound on a biomass derived N-doped mesoporous carbon matrix,a composite material for electrical energy storage

Abstract

A polyoxometalate (POM)-based composite material (NiPW₁₂NP/NMC) was synthesized, in which the nanoparticle of a POM compound (NiPW₁₂NP) distributes on orange juice derived nitrogen doped mesoporous carbon matrix (NMC) homogenously. When employed as a cathode material, NiPW₁₂NP/NMC exhibits high specific capacitance, remarkable rate capability and long-term stability. When the current density is 4?A·g^?1, a specific capacitance as high as 547 F·g^?1 is achieved by NiPW₁₂NP/NMC. With NiPW₁₂NP/NMC serving as cathode and MnO₂ acting as anode, a high performance asymmetric supercapacitor is assembled, which possesses a high energy density of 10.88?Wh·kg^?1 at 0.64?kW·kg^?1. It also shows a good rate capability, when the current density increases from 4 to 12?A·g^?1, its specific capacitance decreases from 113 to 88 F·g^?1, with 77.9% capacitance retention. After 5000 cycles charge-discharge experiments, 92.8% of its capacitance can be maintained, which exhibits good stability.     

Atomic layer deposition: An efficient tool for corrosion protection

Atomic layer deposition (ALD) is now a widely implemented thin film growing method. It is currently used in industrial fabrication processes of microelectronics and luminescent display technologies. Since compact and conformal films can be grown with perfect control of the thickness, ALD is envisioned in numerous other applications fields such as energy, sensing, biomaterials, and photonics. Although few reports can be found on its application to corrosion protection, it has been shown that the qualities of ALD can be highly beneficial to this field. After a brief review of the principle of ALD and the effect of the main parameters on the properties of the films, this report attempts to show the interest of this technique to mitigate corrosion. Various examples of successful uses of ALD to protect metallic and non-metallic surfaces in different fields are reviewed.     

Ferrocene-mediated carbon paste electrode modified with d-fructose dehydrogenase for batch mode measurement of d-fructose

A mediated modified carbon paste and renewable surface electrode for fructose amperometric measurement based on d-fructose dehydrogenase (FDH) was prepared and optimized. Commercially available ferrocene (FcH) and hydroxymethyl ferrocene (FcCH₂OH) were used as mediators. The substituted FcH showed better linearity and higher sensitivity. The influence of different experimental parameters was studied for optimum analytical performance. The final FDH-modified electrode showed good analytical performance for batch mode measurements of fructose.     

A review on the development of a porous carbon-based as modeling materials for electric double layer capacitors

Carbon electrodes are a key factor for electric double layer capacitors (EDLCs). Carbon gels have high porosity with a controllable pore structure by changing synthesis conditions and modifying preparation processing to improve the electrochemical performance of EDLCs. This review summarizes the preparation of carbon gels and their derivatives, the criteria to synthesize high surface area in each process, the development by some carbon forms, and EDLC applications. Porous carbons are also prepared as model materials by concentrating on how pore structure increases electrochemical capacitance, such as electronic and ion resistance, the tortuosity of pore channel, suitable micropore and mesopore sizes, and mesopore size distribution. This review emphasizes the significance of pore structures as the key factor to allow for the design of suitable pore structures that are suitable as the carbon electrode for EDLCs.     

绿色碳科学——化石能源增效减排的科学基础

尝试提出碳科学这一理念,就碳科学的定义、要点及碳原子经济性的涵义进行论述.在此基础上,以碳科学的理念探讨四个典型的碳资源转化过程中所涉及的相关科学和技术.     

Preparation of activated carbon with high surface area for high-capacity methane storage

Activated carbon （AC） was fabricated from corncob, which is cheap and abundant. Experimental parameters such as particle size of corncob, KOHlchar weight ratio, and activation temperature and time were optimized to generate AC, which shows high methane sorption capacity. AC has high specific surface area （3227 m^2/g）, with pore volume and pore size distribution equal to 1.829 cm^3/g and ca. 1.7-2.2 nm, respectively. Under the condition of 2℃ and less than 7.8 MPa, methane sorption in the presence of water （Rw = 1.4） was as high as 43.7 wt% methane per unit mass of dry AC. The result is significantly higher than those of coconut-derived AC （32 wt%） and ordered mesoporous carbon （41.2 wt%, Rw = 4.07） under the same condition. The physical properties and amorphous chaotic structure of AC were characterized by N2 adsorption isotherms, XRD, SEM and HRTEM. Hence, the corncob-derived AC can be considered as a competitive methane-storage material for vehicles, which are run by natural gas.

Key words     

Modification of carbon paste with congo red supported on multi-walled carbon nanotube for voltammetric determination of uric acid in the presence of ascorbic acid

A chemically modified carbon-paste electrode (CPE) is prepared by incorporating congo red (CR) immobilized on multi-walled carbon nanotube (MWCNT). The results show that CR is effectively immobilized on the surface of MWCNT under the ultrasonic agitation in aqueous solution and further incorporating the nafion. The prepared electrode, due to the electrostatic repulsions between the CR and ascorbate anion, is capable to mask the response of the ascorbic acid (AA) completely and provide an effective method for the detection of minor amounts of uric acid (UA) in the presence of high concentrations of AA. On the other hand, an increase in the microscopic area of the electrode by addition of MWCNT together with the electrocatalytic activity caused to a significant enhancement in the voltammetric response to UA. Optimization of the amounts of composite modifier in the matrix of CPE is performed by cyclic and differential pulse voltammetric measurements. The modified electrode shows a linear response to UA in the range of 1.0 × 10⁻⁷–1.0 × 10⁻⁴ M with a detection limit of 1.0 × 10⁻⁸ M. The electrode exhibits excellent accuracies for the determination of UA in the presence of high concentrations of AA (a recovery of 97.6%). The response of the electrode toward sulfhydryl compounds such as cysteine, penicillamine, and glutathione is not considerable. This reveals a good selectivity for the voltammetric response toward UA. The effective electrocatalytic property, ability for masking the voltammetric responses of the other biologically reducing agents, ease of preparation, and surface regeneration by simple polishing together with high reproducibility and stability of the responses make the modified electrode suitable for the selective and sensitive voltammetric detection of sub-micromolar amounts of UA in clinical and pharmaceutical preparations.     

Synthesis and application of a natural-based nanocomposite with carbon nanotubes for sensitive voltammetric determination of lead (II) ions

ABSTRACT

A modified carbon paste electrode has been developed for the determination of Pb(ΙΙ) ions based on Fe₃O₄/eggshell magnetic nanocomposite. The structure and morphology of Fe₃O₄/eggshell were analysed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The prepared nanocomposite was also characterized by Fourier transform infrared spectroscopy (FT-IR) and vibrating sample magnetometer (VSM). The electrochemical procedure was based on the accumulation and determination of Pb(ΙΙ) ions at the surface of the modified carbon paste electrode with Fe₃O₄/eggshell nanocomposites and carbon nanotubes by differential pulse anodic stripping voltammetry (DPASV). Various experimental parameters involved in the preconcentration of Pb(ΙΙ) ions and voltammetric stripping step were studied. Under the optimum conditions, the voltammetric peak current of Pb(ΙΙ) occurs at a potential about ?0.5 V. Also, the voltammetric peak current increased linearly with Pb(ΙΙ) concentration in the range of 0.5–200 ng mL^?1 and a detection limit of 0.15 ng mL^?1 was obtained for Pb(ΙΙ). The selectivity of the proposed electrode for Pb(ΙΙ) ions in the presence of some cations was also examined. The practical application of the proposed modified electrode was evaluated by the determination of Pb(ΙΙ) ions in human hair and water samples. The results were satisfactory for the spiked samples.     

Precise regulation of Ultra-thin platinum decorated Gold/Graphite carbon nitride photocatalysts by atomic layer deposition for efficient degradation of Rhodamine B under simulated sunlight

Atomic Layer Deposition (ALD) precise controlling ultra-thin platinum (Pt) modified Graphite carbon nitride (g-C₃N₄) photocatalysts, which had been doped with gold nanoparticles (Au NPs) by photodeposition, were successfully synthesized. The experimental results showed that precise regulation of platinum decorated C₃N₄-Au(C₃N₄-Au/nPt (n is the number of Pt ALD cycles, 1 Å per cycle)) exhibited excellent photocatalytic degradation ability for Rhodamine B (RhB). Under simulated sunlight irradiation, the degradation rate of 10 mg/L RhB(100 mL) by 1.5 mg C₃N₄-Au/10Pt catalysts was 95.8% within 60 min that is much better than other photocatalysts for the degradation of RhB. The efficient degradation mechanism of RhB by C₃N₄-Au/10Pt photocatalysts was studied and the experiments demonstrated the ·O₂^– as main active species played an important role in the photocatalytic process. Local surface plasmon resonance (LSPR) of Au NPs and Schottky barrier between Pt clusters and g-C₃N₄ may be the reasons for enhanced C₃N₄-Au/10Pt photocatalytic performances. Furthermore, the successive catalytic cycles revealed the excellent stability of C₃N₄-Au/10Pt photocatalyst.     

Functionalization of mesoporous carbon with superbasic MgO nanoparticles for the efficient synthesis of sulfinamides

Highly basic MgO nanoparticles with different sizes have been successfully immobilized over mesoporous carbon with different pore diameters by a simple wet-impregnation method. The prepared catalysts have been characterized by various sophisticated techniques, such as XRD, nitrogen adsorption, electron energy loss spectroscopy, high-resolution TEM, X-ray photoelectron spectroscopy, and the temperature-programmed desorption of CO(2). XRD results reveal that the mesostructure of the support is retained even after the huge loading of MgO nanoparticles inside the mesochannels of the support. It is also demonstrated that the particle size and dispersion of the MgO nanoparticles on the support can be finely controlled by the simple adjustment of the textural parameters of the supports. Among the support materials studied, mesoporous carbon with the largest pore diameter and large pore volume offered highly crystalline small-size cubic-phase MgO nanoparticles with a high dispersion. The basicity of the MgO-supported mesoporous carbons can also be controlled by simply changing the loading of the MgO and the pore diameter of the support. These materials have been employed as heterogeneous catalysts for the first time in the selective synthesis of sulfinamides. Among the catalysts investigated, the support with the large pore diameter and high loading of MgO showed the highest activity with an excellent yield of sulfinamides. The catalyst also showed much higher activity than the pristine MgO nanoparticles. The effects of the reaction parameters, including the solvents and reaction temperature, and textural parameters of the supports in the activity of the catalyst have also been demonstrated. Most importantly, the catalyst was found to be highly stable, showing excellent activity even after the third cycle of reaction.     

The selectivity and polarity of carbon layer open tubular capillary columns modified with a polar liquid phase

The polarity of carbon layer open tubular (CLOT) columns coated with a layer of non-porous graphitized carbon black (Carbopack B) modified with an appropriate amount of polar polyglycol liquid phase has been evaluated and compared with that of standard polar (Supelcowax-10) and non-polar (SPB-1) bonded phase open tubular columns. The efficiency and selectivity were measured at various temperatures and the polarity of the columns was evaluated by use of McReynolds' constants and the difference in apparent carbon number, ΔC of linear alkanes and alcohols. The polarity of the CLOT column was found to depend on temperature, and changing the analytical conditions therefore enabled the separation of compounds of different polarity whose reciprocal position and resolution were affected by temperature. The application of calculation methods which enable programmed temperature retention times to be predicted from isothermal data was also found to be possible when the polarity of the CLOT column changes with temperature.     

基于有机溶剂原位制备的致密疏水铜金属层在保护锌负极中的应用

通过在 N-甲基吡咯烷酮(NMP)有机溶剂中锌电极与 CuI之间的置换反应,在锌电极上原位构建了一层致密且疏水的铜金属保护层(Cu@Zn)。铜金属保护层能有效地隔离锌电极与电解液的接触,减少锌电极-电解液界面的析氢和腐蚀等副反应。同时,铜金属保护层还具有较好的亲锌性,更小的界面电阻,更低的成核能垒,有利于锌离子均匀沉积,从而有效抑制了锌枝晶的生成。Cu@Zn对称电池实现了超过 1 700 h(1 mA·cm^-2)和 1 330 h(3 mA·cm^-2)的循环寿命。采用商用 MnO₂与之匹配得到的Cu@Zn||MnO₂全电池不仅在1 A·g^-1下具有168.5 mAh·g^-1的可逆比容量,还可稳定循环2 000次以上。