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81.
Chemical and structural changes preceding electrocatalysis obfuscate the nature of the active state of electrocatalysts for the oxygen evolution reaction (OER), which calls for model systems to gain systematic insight. We investigated the effect of bulk oxidation on the overpotential of ink-casted LiMn2O4 electrodes by a rotating ring-disk electrode (RRDE) setup and X-ray absorption spectroscopy (XAS) at the K shell core level of manganese ions (Mn−K edge). The cyclic voltammogram of the RRDE disk shows pronounced redox peaks in lithium hydroxide electrolytes with pH between 12 and 13.5, which we assign to bulk manganese redox based on XAS. The onset of the OER is pH-dependent on the scale of the reversible hydrogen electrode (RHE) with a Nernst slope of −40(4) mV/pH at −5 μA monitored at the RRDE ring. To connect this trend to catalyst changes, we develop a simple model for delithiation of LiMn2O4 in LiOH electrolytes, which gives the same Nernst slope of delithiation as our experimental data, i. e., 116(25) mV/pH. From this data, we construct an ERHE-pH diagram that illustrates robustness of LiMn2O4 against oxidation above pH 13.5 as also verified by XAS. We conclude that manganese oxidation is the origin of the increase of the OER overpotential at pH lower than 14 and also of the pH dependence on the RHE scale. Our work highlights that vulnerability to transition metal redox may lead to increased overpotentials, which is important for the design of stable electrocatalysts. 相似文献
82.
Yongseon Kim 《International journal of quantum chemistry》2019,119(24):e26028
The doping behavior of Zr in LiNi8/12Co2/12Mn2/12O2 (LNCM) is investigated by a simulation of the phase equilibria for the Li-(M*,Zr)-O system (M* = Ni, Co, Mn) based on first-principles calculations followed by a thermochemical post-analysis of the resultant phase diagrams. The results indicate that the stable state at the synthetically stoichiometric composition of LNCM with Zr is a mixture of undoped LNCM with a Li2ZrO3 secondary phase; doping of Zr in the LNCM crystal is not thermodynamically favored. The energies of various states comprising LNCM supercells with defects, secondary phases, and Zr doping are examined, and the equilibrium doping concentration of Zr is calculated by considering the entire LNCM:Zr crystal as a statistical combination of these states. The doping concentration of Zr in the LNCM crystal is calculated to be very low, which enables balanced control between doping and coating, as recently reported through experimentation. The dopability of Zr is expected to increase with the depletion of O2 supply during the heating of a system with a precisely controlled Li to M* ratio, but this behavior is affected by the formation of defects, especially by M* substitution for Li. 相似文献
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本文首次提出采用升华物质为模板,制备聚苯胺包覆的中空硫电极材料. 首先通过Na2S2O3和稀HCl反应,在具有升华特性的ADD(2,4,6-三异丙基-1,3,5-三氧杂环己烷)微粒表面沉积一层S,然后在S的表面再沉积聚苯胺包覆层. 在经60 oC干燥12小时后,其中的ADD自然挥发,得到聚苯胺壳体包覆的中空硫复合物. SEM、TEM和TG分析表明,制得的聚苯胺包覆中空硫的粒径约为2 μm,硫含量为61.1%. 在500 mA·g-1充放电电流下,首次放电比容量为776.2 mAh·g-1,库仑效率为95.9%. 100次充放电循环后,放电比容量为524.7 mAh·g-1. 由于聚苯胺包覆物的聚苯胺膜具有抑制聚硫锂向外的扩散作用,以及包覆物中的空间对放电时S的膨胀具有缓冲作用,聚苯胺包覆中空硫粉末的放电比容量和充放电稳定性均明显高于未包覆聚苯胺的中空硫和化学制备的硫. 这种制备导电聚合物包覆中空硫的新方法具有操作简单、成本低廉的优点,有进一步发展的前景. 相似文献
87.
Yoshiki Shibuya Ryoichi Tatara Yivan Jiang Yang Shao‐Horn Jeremiah A. Johnson 《Journal of polymer science. Part A, Polymer chemistry》2019,57(3):448-455
The properties of polymeric materials are dictated not only by their composition but also by their molecular architecture. Here, by employing brush‐first ring‐opening metathesis polymerization (ROMP), norbornene‐terminated poly(ethylene oxide) (PEO) macromonomers ( MM‐n , linear architecture), bottlebrush polymers ( Brush‐n , comb architecture), and brush‐arm star polymers ( BASP‐n , star architecture), where n indicates the average degree of polymerization (DP) of PEO, are synthesized. The impact of architecture on the thermal properties and Li+ conductivities for this series of PEO architectures is investigated. Notably, in polymers bearing PEO with the highest degree of polymerization, irrespective of differences in architecture and molecular weight (~100‐fold differences), electrolytes with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as an Li+ source exhibit normalized ionic conductivities (σn) within only 4.9 times difference (σn = 29.8 × 10?5 S cm?1 for MM‐45 and σn = 6.07 × 10?5 S cm?1 for BASP‐45 ) at a concentration of Li+ r = [Li+]/[EO] = 1/12 at 50 °C. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 448–455 相似文献
88.
Lifen Xiao Yanyan Yang Yanqiang Zhao Xinping Ai Hanxi Yang Yuliang Cao 《Journal of Solid State Electrochemistry》2008,12(2):149-153
Submicron LiCoO2 was synthesized by a polymer pyrolysis method using LiOH and Co(NO3)2 as the precursor compounds. Experimental results demonstrated that the powders calcined at 800 °C for 12 h appear as well-crystallized,
uniform submicron particles with diameter of about 200 nm. As a result, the as-prepared LiCoO2 electrode displayed excellent electrochemical properties, with an initial discharge capacity of 145.5 mAh/g and capacity
retention of 86.1% after 50 cycles when cycled at 50 mA/g between 3.5 and 4.25 V. When cycled between 3.5 and 4.5 V, the discharge
capacity increased to 177.9 mAh/g with capacity retention of 85.6% after 50 cycles. 相似文献
89.
Jiaqing Dong Daocong Li Zhenghe Peng Yunhong Zhou 《Journal of Solid State Electrochemistry》2008,12(2):171-174
The anode material cobalt disulfide for lithium-ion batteries was synthesized using the hydrothermal method at a lower temperature.
The microstructure and surface morphology of the powders were characterized by means of X-ray diffraction (XRD) and scanning
electron microscopy (SEM). Electrochemical tests showed that this sample had superior electrochemical properties. The first
discharge capacity is up to 1313.9 mAh/g in the voltage range of 3.00–0.02 V at a current density of 50 mA/g. Adjusting the
voltage range to 3.00–0.50 V, the first discharge capacity decreases, but the 20th discharge capacity is 435.5 mAh/g, which
is better than what has been reported in the literature. 相似文献
90.
多孔硅纳米材料具有巨大的比表面积,可调控的物理化学性质,在药物治疗、传感、能源储存与转化等领域拥有巨大的应用前景。尤其在高能量密度锂离子电池领域,多孔硅由于其丰富的孔道结构能有效释放充放电过程中硅体积变化带来的巨大应力以及大大地缩短锂离子传输距离,而引起了人们的广泛研究兴趣。但是,开发简便快速的方法来合成结构可调变的多孔硅纳米材料仍是当前研究的挑战。近年来,一些用来合成多孔硅纳米材料的方法已有报道。我们基于本课题组最近的研究进展和近年来相关文献,比较详细综述了近年来多孔硅纳米材料的制备方法以及重点关注其在高能锂电池领域的应用。最后,对多孔硅纳米材料的未来发展方向做了进一步的展望。 相似文献