Nanoarchitectured Graphene‐Based Supercapacitors for Next‐Generation Energy‐Storage Applications

Tremendous development in the field of portable electronics and hybrid electric vehicles has led to urgent and increasing demand in the field of high‐energy storage devices. In recent years, many research efforts have been made for the development of more efficient energy‐storage devices such as supercapacitors, batteries, and fuel cells. In particular, supercapacitors have great potential to meet the demands of both high energy density and power density in many advanced technologies. For the last half decade, graphene has attracted intense research interest for electrical double‐layer capacitor (EDLC) applications. The unique electronic, thermal, mechanical, and chemical characteristics of graphene, along with the intrinsic benefits of a carbon material, make it a promising candidate for supercapacitor applications. This Review focuses on recent research developments in graphene‐based supercapacitors, including doped graphene, activated graphene, graphene/metal oxide composites, graphene/polymer composites, and graphene‐based asymmetric supercapacitors. The challenges and prospects of graphene‐based supercapacitors are also discussed.     

MgH_2+20%(w)MgTiO_3复合材料的吸/放氢性能(英文)

为了降低MgH2的吸放氢温度,提高其吸放氢动力学性能,本文通过球磨方法制备了MgH2+20%(w)MgTiO3复合储氢材料,并研究了其储氢性能.X射线衍射(XRD)结果表明,MgTiO3在与MgH2球磨过程中生成Mg2TiO4和TiO2,并且Mg2TiO4和TiO2在体系的吸放氢过程中保持稳定,能够对MgH2的吸放氢过程产生催化作用.程序升温脱附和吸/放氢动力学测试结果表明,添加MgTiO3后MgH2的初始放氢温度从389°C降至249°C.150°C下的吸氢量从0.977%(w)提高到2.902%(w),350°C下的放氢量从2.319%(w)提高到3.653%(w).同时,MgH2放氢反应的活化能从116kJ·mol-1降至95.7kJ·mol-1.与MgH2相比,MgH2+20%(w)MgTiO3复合材料的热力学与动力学性能均有显著提高,这主要是由于球磨和放氢过程中原位生成的TiO2和Mg2TiO4具有良好的催化活性.     

新型掺杂多孔芳香骨架材料的储氢性能模拟

基于PAF-301分子模型通过Li掺杂或B取代等模式设计了几种新型多孔芳香骨架(PAFs)材料,采用量子力学和分子力学方法对新材料的储氢性能进行研究.由量子力学计算得到了不同分子片段与H2之间的结合能,并结合DDEC方法计算了各分子片段的原子电荷分布.利用巨正则蒙特卡洛(GCMC)模拟方法计算了77和298 K下H2在不同PAFs材料中的吸附平衡性质.结果表明,H2直接与苯环的结合能较低,但掺杂Li原子能够提高H2与六元环的结合能,同时Li原子体现出较高的正电性质,B原子取代苯环中的两个C原子后,使得原有C原子电负性增强;77 K下PAF-301Li具有最高的储氢性能,而PAF-C4B2H4-Li2-Si和PAF-C4B2H4-Li2-Ge体现出较好的常温储氢性能,各种材料的常温储氢性能远低于其低温储氢性能.通过77 K下H2在PAFs材料中的等位能面分布和吸附平衡质心密度分布对H2在PAFs材料中的优先吸附位置进行分析,发现在PAF-301和PAF-301Li骨架中,由于中心能量较低的等位能区域范围较宽,H2在其中存在四个明显的吸附高密度分布区域,而其它三种PAFs晶胞中心能量较低的等位能区域范围较窄,使得H2在其中只存在两个明显的吸附高密度分布区域.     

低于300℃时两种氧化铈材料对稀燃阶段NOx存储性能的影响

The present work investigated the effects of two types of CeO₂ materials on the lean NO_x trap (LNT) performance over NO_x storage reduction (NSR) catalysts below 300 ℃. These materials were obtained by mechanical mixing of 2% (w) Pt/Al₂O₃ (PA) with CeO₂-X (X=S, I). X-ray diffraction (XRD), BET surface area measurements, and scanning electron microscopy (SEM) were used to characterize the physical structures of the catalysts, while X-ray photoelectron spectroscopy (XPS) and H₂ temperature-programmed reduction (H₂-TPR) were employed to identify and quantify the surface Ce³⁺ concentrations and the amounts of surface-active oxygen. In-situ diffuse reflectance infrared Fourier transform spectroscopy (In-situ DRIFTS) was applied to analyze the surface adsorbed NO_x species. Compared with CeO₂-I, CeO₂-S presented superior physico-chemical properties, including higher surface area, richer porous texture, stronger aging-resistance, and higher surface Ce³⁺ concentration. As a result, the PA+CeO₂-S sample also exhibited outstanding NO_x trapping capacity. Furthermore, interaction between Pt and CeO₂ was observed in the PA+CeO₂-X mixtures, which facilitates NO oxidation and the NO_x trapping process owing to the accompanying increase in the activity of surface active oxygen on the CeO₂. This interaction was stronger in the case of the PA+CeO₂-S sample as compared with the PA+CeO₂-I. The Ce³⁺ content and presence of active oxygen species on the CeO₂ surface both play critical roles in the NO_x trapping process and hydrothermal treatment of the CeO₂ significantly decreased the NO_x trapping capacity of both PA+CeO₂ samples. It was also determined that the interaction between Pt and aged CeO₂ is weakened and that the NO_x trapping capacity of aged CeO₂ is enhanced after loading a small amount of Pt, which is attributed to the promotion of nitrate formation by increased surface oxygen activity.     

混合稀土对A_2B_7型储氢合金结构和电化学性能的影响

采用感应熔炼方法制备了A2B7型La0.83-0.5x(Pr0.1Nd0.1Sm0.1Gd0.2)xMg0.17Ni3.1Co0.3Al0.1(x=0~1.66)储氢合金,并在He+Ar气氛和1 173 K下进行退火处理。通过X射线衍射(XRD)、扫描电子显微镜(SEM)和电化学方法,研究了混合稀土(Pr,Nd,Sm,Gd)替代La元素对合金物相结构和电化学性能的影响。合金相结构分析表明,混合稀土含量对合金组成和相结构有重要的影响,随混合稀土含量x的增加,合金中主相A2B7型(2H-Ce2Ni7型+3R-Gd2Co7型)相丰度逐渐增多,其中2H-Ce2Ni7型相丰度先增多后减少,3RGd2Co7型相丰度则逐渐增加,主相晶胞参数随x增加而减小。电化学结果表明,随混合稀土含量增加,放氢平台压逐渐升高,合金电极的最大放电容量和循环稳定性均呈先增大后减小的规律,其中x=0.4合金电极具有最高的电化学放电容量(389.8 mAh·g-1)和最佳的循环寿命(S100=91.30%);合金电极的高倍率放电性能(HRD)则随x的增加获得显著提高。适量的混合稀土替代量可显著改善合金电极的综合电化学性能。     

Synergetic effects of NaAlH4-TiF3 co-additive on dehydriding reaction of Mg(AlH4)2

The effects of Na Al H4, Ti F3 and Na Al H4-Ti F3co-additive on dehydriding reaction of Mg(Al H4)2are systematically investigated. The onset dehydrogenation temperature of the co-doped Mg(Al H4)2composites decreased to 74°C, which is about 59°C lower than that of pure Mg(Al H4)2. The dehydrogenation kinetics of Na Al H4-Ti F3co-doped Mg(Al H4)2sample was also improved, which released about 94%hydrogen within 48 min, but no visible hydrogen was released from pure Mg(Al H4)2under the same conditions. The activation energy of co-doped Mg(Al H4)2was 85.6 k J mol-1, which was significantly lower than that of additive-free Mg(Al H4)2sample. The synergetic effects of Na Al H4 and Ti F3 on the dehydrogenation performance of Mg(Al H4)2were confirmed. In addition, a possible catalytic mechanism is discussed, regarding the different roles of Na Al H4 and Ti F3 on Mg(Al H4)2.     

Facile synthesis and performance of polypyrrole-coated sulfur nanocomposite as cathode materials for lithium/sulfur batteries

In situ chemical oxidation polymerization of pyrrole on the surface of sulfur particles was carried out to synthesize a sulfur/polypyrrole （SIPPy） nanocomposite with core-shell structure. The composite was characterized by elemental analysis, X-ray diffraction, scanning/transmission electron microscopy, and electrochemical measurements. XRD and FTIR results showed that sulfur well dispersed in the core-shell structure and PPy structure was successfully obtained via in situ oxidative polymerization of pyrrole on the surface of sulfur particles. TEM observation revealed that PPy was formed and fixed to the surface of sulfur nanoparticle after polymerization, developing a well-defined core-shell structure and the thickness of PPy coating layer was in the range of 20-30 nm. In the composite, PPy worked as a conducting matrix as well as a coating agent, which confined the active materials within the electrode. Consequently, the as prepared SIPPy composite cathode exhibited good cycling and rate performances for rechargeable lithium/sulfur batteries. The resulting cell containing SIPPy composite cathode yields a discharge capacity of 1039 mAh·g^-1 at the initial cycle and retains 59% of this value over 50 cycles at 0.1 C rate. At 1 C rate, the SIPPy composite showed good cycle stability, and the discharge capacity was 475 mAh·g^-1 after 50 cycles.     

Fluorine‐Doped Fe2O3 as High Energy Density Electroactive Material for Hybrid Supercapacitor Applications

Nanostructured α‐Fe₂O₃ with and without fluorine substitution were successfully obtained by a green route, that is, microwave irradiation. The hematite phase materials were evaluated as a high‐performance electrode material in a hybrid supercapacitor configuration along with activated carbon (AC). The presence of fluorine was confirmed through X‐ray photoelectron spectroscopy and transmission electron microscopy. Fluorine‐doped Fe₂O₃ (F‐Fe₂O₃) exhibits an enhanced pseudocapacitive performance compared to that of the bare hematite phase. The F‐Fe₂O₃/AC cell delivered a specific capacitance of 71 F g^?1 at a current density of 2.25 A g^?1 and retained approximately 90 % of its initial capacitance after 15 000 cycles. Furthermore, the F‐Fe₂O₃/AC cell showed a very high energy density of about 28 W h kg^?1 compared to bare hematite phase (～9 W h kg^?1). These data clearly reveal that the electrochemical performance of Fe₂O₃ can be improved by fluorine doping, thereby dramatically improving the energy density of the system.     

Steady-state solutions of a reaction–diffusion system arising from intraguild predation and internal storage

Intraguild predation is added to a mathematical model of competition between two species for a single nutrient with internal storage in the unstirred chemostat. At first, we established the sharp a priori estimates for nonnegative solutions of the system, which assure that all of nonnegative solutions belong to a special cone. The selection of this special cone enables us to apply the topological fixed point theorems in cones to establish the existence of positive solutions. Secondly, existence for positive steady state solutions of intraguild prey and intraguild predator is established in terms of the principal eigenvalues of associated nonlinear eigenvalue problems by means of the degree theory in the special cone. It turns out that positive steady state solutions exist when the associated principal eigenvalues are both negative or both positive.     

基于改进NSGA-II算法的多级服务设施备用覆盖选址决策模型

为了应对跨区域突发事件过程中受灾点服务差异化需求的问题,建立了应急储备设施点的多级备用覆盖选址决策模型,即一个需求点由多个应急设施提供不同质量水平的服务,并考虑设施繁忙状态下由其他设施点提供服务的状况,使模型更加符合实际应用。首次通过设计分段的染色体编码方式改进NSGA-II算法提升运算效率以更好地解决多目标选址决策问题,将改进方法下得到的Pareto解分布与NSGA-II算法下的仿真结果进行对比分析,结合设施点的部署策略得到不同的空间布局方案。证明了模型的可行性及改进NSGA-II算法在解决设施点多目标选址决策问题时的有效性。