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1.
Engineering Temperature‐Dependent Carrier Concentration in Bulk Composite Materials via Temperature‐Dependent Fermi Level Offset 下载免费PDF全文
Si Hui Wenpei Gao Xu Lu Anurag Panda Trevor P. Bailey Alexander A. Page Stephen R. Forrest Donald T. Morelli Xiaoqing Pan Kevin P. Pipe Ctirad Uher 《Liver Transplantation》2018,8(3)
Precise control of carrier concentration in both bulk and thin‐film materials is crucial for many solid‐state devices, including photovoltaic cells, superconductors, and high mobility transistors. For applications that span a wide temperature range (thermoelectric power generation being a prime example) the optimal carrier concentration varies as a function of temperature. This work presents a modified modulation doping method to engineer the temperature dependence of the carrier concentration by incorporating a nanosize secondary phase that controls the temperature‐dependent doping in the bulk matrix. This study demonstrates this technique by de‐doping the heavily defect‐doped degenerate semiconductor GeTe, thereby enhancing its average power factor by 100% at low temperatures, with no deterioration at high temperatures. This can be a general method to improve the average thermoelectric performance of many other materials. 相似文献
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Yonghyun Cho Sanghan Lee Yongseok Lee Taeeun Hong Jaephil Cho 《Liver Transplantation》2011,1(5):821-828
In an attempt to overcome the problems associated with LiNiO2, the solid solution series of lithium nickel‐metal oxides, Li[Ni1–xMx]O2 (with M = Co, Mn, Al, Ti, Mg, etc.), have been investigated as favorable cathode materials for high‐energy and high‐power lithium‐ion batteries. However, along with the improvement in the electrochemical properties in Ni‐based cathode materials, the thermal stability has been a great concern, and thus violent reaction of the cathode with the electrolyte needs to be avoided. Here, we report a heterostructured Li[Ni0.54Co0.12Mn0.34]O2 cathode material which possesses both high energy and safety. The core of the particle is Li[Ni0.54Co0.12Mn0.34]O2 with a layered phase (R3‐m) and the shell, with a thickness of < 0.5 μm, is a highly stable Li1+x[CoNixMn2–x]2O4 spinel phase (Fd‐3m). The material demonstrates reversible capacity of 200 mAhg‐1 and retains 95% capacity retention under the most severe test condition of 60 °C. In addition, the amount of oxygen evolution from the lattice in the cathode with two heterostructures is reduced by 70%, compared to the reference sample. All these results suggest that the bulk Li[Ni0.54Co0.12Mn0.34]O2 consisting of two heterostructures satisfy the requirements for hybrid electric vehicles, power tools, and mobile electronics. 相似文献
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Qian Zhang Eyob Kebede Chere Jingying Sun Feng Cao Keshab Dahal Shuo Chen Gang Chen Zhifeng Ren 《Liver Transplantation》2015,5(12)
Iodine‐doped n‐type SnSe polycrystalline by melting and hot pressing is prepared. The prepared material is anisotropic with a peak ZT of ≈0.8 at about 773 K measured along the hot pressing direction. This is the first report on thermoelectric properties of n‐type Sn chalcogenide alloys. With increasing content of iodine, the carrier concentration changed from 2.3 × 1017 cm?3 (p‐type) to 5.0 × 1015 cm?3 (n‐type) then to 2.0 × 1017 cm?3 (n‐type). The decent ZT is mainly attributed to the intrinsically low thermal conductivity due to the high anharmonicity of the chemical bonds like those in p‐type SnSe. By alloying with 10 at% SnS, even lower thermal conductivity and an enhanced Seebeck coefficient were achieved, leading to an increased ZT of ≈1.0 at about 773 K measured also along the hot pressing direction. 相似文献
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Synthesis and Characterization of High‐Energy,High‐Power Spinel‐Layered Composite Cathode Materials for Lithium‐Ion Batteries 下载免费PDF全文
Steffen Krueger Vassilios Siozios Jie Li Sascha Nowak Martin Winter 《Liver Transplantation》2015,5(5)
Spinel‐layered composites, where a high‐voltage spinel is incorporated in a layered lithium‐rich (Li‐rich) cathode material with a nominal composition x{0.6Li2MnO3 · 0.4[LiCo0.333Mn0.333Ni0.333]O2} · (1 – x) Li[Ni0.5Mn1.5]O4 (x = 0, 0.3, 0.5, 0.7, 1) are synthesized via a hydroxide assisted coprecipitation route to generate high‐energy, high‐power cathode materials for Li‐ion batteries. X‐ray diffraction patterns and the cyclic voltammetry investigations confirm the presence of both the parent components in the composites. The electrochemical investigations performed within a wide potential window show an increased structural stability of the spinel component when incorporated into the composite environment. All the composite materials exhibit initial discharge capacities >200 mAh g–1. The compositions with x = 0.5 and 0.7 show excellent cycling stability among the investigated materials. Moreover, the first cycle Coulombic efficiency achieve a dramatic improvement with the incorporation of the spinel component. More notably, the composite materials with increased spinel component exhibit superior rate capability compared with the parent Li‐rich material especially together with the highest capacity retention for x = 0.5 composition, making this as the optimal high‐energy high‐power material. The mechanisms involved in the symbiotic relationship of the spinel and layered Li‐rich components in the above composites are discussed. 相似文献
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Single‐Crystalline Nanomesh Tantalum Nitride Photocatalyst with Improved Hydrogen‐Evolving Performance 下载免费PDF全文
Tantalum nitride (Ta3N5) with a suitable bandgap (≈2 eV) is regarded as one of the most promising photocatalysts for efficient solar energy harvesting and conversion. However, Ta3N5 suffers from low hydrogen production activity due to the low carrier mobility and fast carrier recombination. Thus, the design of Ta3N5 nanostructures to facilitate charge carrier transport and improve photocatalytic performance remains a challenge. This study reports a new type of ultrathin (≈2 nm) Ta3N5 nanomesh with high specific surface area (284.6 m2 g?1) and excellent crystallinity by an innovative bottom‐up graphene oxide templated strategy. The resulting Ta3N5 nanomeshes demonstrate drastically improved electron transport ability and prolonged lifetime of charge carriers, due to the nature of high surface area and excellent crystallinity. As a result, when used as photocatalysts, the Ta3N5 nanomeshes exhibit a greater than tenfold improvement in solar hydrogen production compared to bulk counterparts. This work provides an effective and generic strategy for designing 2D ultrathin nanomesh structures for nonlayered materials with improved catalytic activity. 相似文献
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Andreas Wild Maria Strumpf Bernhard Häupler Martin D. Hager Ulrich S. Schubert 《Liver Transplantation》2017,7(5)
An all‐organic battery consisting of two redox‐polymers, namely poly(2‐vinylthianthrene) and poly(2‐methacrylamide‐TCAQ) is assembled. This all‐organic battery shows excellent performance characteristics, namely flat discharge plateaus, an output voltage exceeding 1.3 V, and theoretical capacities of both electrodes higher than 100 mA h g?1. Both organic electrode materials are synthesized in two respective three synthetic steps using the free‐radical polymerization technique. Li‐organic batteries manufactured from these polymers prove their suitability as organic electrode materials. The cathode material poly(2‐vinylthianthrene) (3) displays a discharging plateau at 3.95 V versus Li+/Li and a discharge capacity of 105 mA h g?1, corresponding to a specific energy of about 415 mW h g?1. The anode material poly(2‐methacrylamide‐TCAQ) (7) exhibits an initial discharge capacity of 130 mA h g?1, corresponding to 94% material activity. The combination of both materials results in an all‐organic battery with a discharge voltage of 1.35 V and an initial discharge capacity of 105 mA h g?1 (95% material activity). 相似文献
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Triple‐Layer Structured Composite Separator Membranes with Dual Pore Structures and Improved Interfacial Contact for Sustainable Dye‐Sensitized Solar Cells 下载免费PDF全文
Soo Bong Hong So Hyun Park Jeong‐Hoon Kim Sang‐Young Lee Young Soo Kwon Taiho Park Phil‐Hyun Kang Sung Chul Hong 《Liver Transplantation》2014,4(13)
A composite separator membrane (CSM) with an A/B/A type layered structure, composed of a microporous electrolyte‐philic poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVdF‐HFP) gel layer (A) and a submicrometer porous polyethylene (PE) or a macroporous poly(ethylene terephthalate) (PET) non‐woven matrix (B), is introduced in a dye‐sensitized solar cell (DSSC). Commercially available PE and PET separator membranes (SMs) act as matrices that provide mechanical stability to the DSSC and permanent pore structures for facilitated ion transport. PVdF‐HFP is used as a microporous gelator for improved interfacial contact between the solid SM and the electrodes. The PVdF‐HFP gel impedes the charge recombination process between electron and I3 ? at the TiO2/electrolyte interface, resulting in improved electron lifetimes. The DSSC assembled with the CSM exhibits high initial solar energy conversion efficiency (η, 6.1%) and stable η values over 1400 h, demonstrating good long term stability. The behaviors of the DSSC are attributed to the synergistic factors of the CSM, such as improved ion conductivity, electrolyte affinity, electrolyte retention capability, effective interfacial contact, and plausible passivation of the dyes. This study demonstrates a practical combination of short‐ and long‐term DSSC performance through the introduction of the CSM. 相似文献
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Understanding the Rate Capability of High‐Energy‐Density Li‐Rich Layered Li1.2Ni0.15Co0.1Mn0.55O2 Cathode Materials 下载免费PDF全文
Xiqian Yu Yingchun Lyu Lin Gu Huiming Wu Seong‐Min Bak Yongning Zhou Khalil Amine Steven N. Ehrlich Hong Li Kyung‐Wan Nam Xiao‐Qing Yang 《Liver Transplantation》2014,4(5)
The high‐energy‐density, Li‐rich layered materials, i.e., xLiMO2(1‐x)Li2MnO3, are promising candidate cathode materials for electric energy storage in plug‐in hybrid electric vehicles (PHEVs) and electric vehicles (EVs). The relatively low rate capability is one of the major problems that need to be resolved for these materials. To gain insight into the key factors that limit the rate capability, in situ X‐ray absorption spectroscopy (XAS) and X‐ray diffraction (XRD) studies of the cathode material, Li1.2Ni0.15Co0.1Mn0.55O2 [0.5Li(Ni0.375Co0.25 Mn0.375)O2·0.5Li2MnO3], are carried out. The partial capacity contributed by different structural components and transition metal elements is elucidated and correlated with local structure changes. The characteristic reaction kinetics for each element are identified using a novel time‐resolved XAS technique. Direct experimental evidence is obtained showing that Mn sites have much poorer reaction kinetics both before and after the initial activation of Li2MnO3, compared to Ni and Co. These results indicate that Li2MnO3 may be the key component that limits the rate capability of Li‐rich layered materials and provide guidance for designing Li‐rich layered materials with the desired balance of energy density and rate capability for different applications. 相似文献
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Jingyang Wang Yan Wang Dong‐Hwa Seo Tan Shi Shouping Chen Yaosen Tian Haegyeom Kim Gerbrand Ceder 《Liver Transplantation》2020,10(10)
Over the last decade, Na‐ion batteries have been extensively studied as low‐cost alternatives to Li‐ion batteries for large‐scale grid storage applications; however, the development of high‐energy positive electrodes remains a major challenge. Materials with a polyanionic framework, such as Na superionic conductor (NASICON)‐structured cathodes with formula NaxM2(PO4)3, have attracted considerable attention because of their stable 3D crystal structure and high operating potential. Herein, a novel NASICON‐type compound, Na4MnCr(PO4)3, is reported as a promising cathode material for Na‐ion batteries that deliver a high specific capacity of 130 mAh g?1 during discharge utilizing high‐voltage Mn2+/3+ (3.5 V), Mn3+/4+ (4.0 V), and Cr3+/4+ (4.35 V) transition metal redox. In addition, Na4MnCr(PO4)3 exhibits a high rate capability (97 mAh g?1 at 5 C) and excellent all‐temperature performance. In situ X‐ray diffraction and synchrotron X‐ray diffraction analyses reveal reversible structural evolution for both charge and discharge. 相似文献
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Zhi Zhu Rui Gao Iradwikanari Waluyo Yanhao Dong Adrian Hunt Jinhyuk Lee Ju Li 《Liver Transplantation》2020,10(35)
Li‐rich metal oxide (LXMO) cathodes have attracted intense interest for rechargeable batteries because of their high capacity above 250 mAh g?1. However, the side effects of hybrid anion and cation redox (HACR) reactions, such as oxygen release and phase collapse that result from global oxygen migration (GOM), have prohibited the commercialization of LXMO. GOM not only destabilizes the oxygen sublattice in cycling, aggravating the well‐known voltage fading, but also intensifies electrolyte decomposition and Mn dissolution, causing severe full‐cell performance degradation. Herein, an artificial surface prereconstruction (ASR) for Li1.2Mn0.6Ni0.2O2 particles with a molten‐molybdate leaching is conducted, which creates a crystal‐dense anion‐redox‐free LiMn1.5Ni0.5O4 shell that completely encloses the LXMO lattice (ASR‐LXMO). Differential electrochemical mass spectroscopy and soft X‐ray absorption spectroscopy analyses demonstrate that GOM is shut down in cycling, which not only stabilizes HACR in ASR‐LXMO, but also mitigates the electrolyte decomposition and Mn dissolution. ASR‐LXMO displays greatly stabilized cycling performance as it retains 237.4 mAh g?1 with an average discharge voltage of 3.30 V after 200 cycles. More crucially, while the pristine LXMO cycling cannot survive 90 cycles in a pouch full‐cell matched with a commercial graphite anode and lean (2 g A?1 h?1) electrolyte, ASR‐LXMO shows high capacity retention of 76% after 125 cycles in full‐cell cycling. 相似文献
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Yujie Ke Jingwei Chen Gaojian Lin Shancheng Wang Yang Zhou Jie Yin Pooi See Lee Yi Long 《Liver Transplantation》2019,9(39)
A smart window that dynamically modulates light transmittance is crucial for building energy efficiently, and promising for on‐demand optical devices. The rapid development of technology brings out different categories that have fundamentally different transmittance modulation mechanisms, including the electro‐, thermo‐, mechano‐, and photochromic smart windows. In this review, recent progress in smart windows of each category is overviewed. The strategies for each smart window are outlined with particular focus on functional materials, device design, and performance enhancement. The advantages and disadvantages of each category are summarized, followed by a discussion of emerging technologies such as dual stimuli triggered smart window and integrated devices toward multifunctionality. These multifunctional devices combine smart window technology with, for example, solar cells, triboelectric nanogenerators, actuators, energy storage devices, and electrothermal devices. Lastly, a perspective is provided on the future development of smart windows. 相似文献
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High Band Degeneracy Contributes to High Thermoelectric Performance in p‐Type Half‐Heusler Compounds 下载免费PDF全文
Chenguang Fu Tiejun Zhu Yanzhong Pei Hanhui Xie Heng Wang G. Jeffrey Snyder Yong Liu Yintu Liu Xinbing Zhao 《Liver Transplantation》2014,4(18)
Half‐Heusler (HH) compounds are important high temperature thermoelectric (TE) materials and have attracted considerable attention in the recent years. High figure of merit zT values of 0.8 to 1.0 have been obtained in n‐type ZrNiSn‐based HH compounds. However, developing high performance p‐type HH compounds are still a big challenge. Here, it is shown that a new p‐type HH alloy with a high band degeneracy of 8, Ti‐doped FeV0.6Nb0.4Sb, can achieve a high zT of 0.8, which is one of the highest reported values in the p‐type HH compounds. Although the band effective mass of this system is found to be high, which may lead to a low mobility, its low deformation potential and low alloy scattering potential both contribute to a reasonably high mobility. The enhanced phonon scattering by alloying leads to a reduced lattice thermal conductivity. The achieved high zT demonstrates that the p‐type Ti doped FeV0.6Nb0.4Sb HH alloys are promising as TE materials and offer an excellent TE performance match with n‐type ones for high temperature power generation. 相似文献
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A New Spinel‐Layered Li‐Rich Microsphere as a High‐Rate Cathode Material for Li‐Ion Batteries 下载免费PDF全文
Dong Luo Guangshe Li Chaochao Fu Jing Zheng Jianming Fan Qi Li Liping Li 《Liver Transplantation》2014,4(11)
Li‐rich layered materials are considered to be the promising low‐cost cathodes for lithium‐ion batteries but they suffer from poor rate capability despite of efforts toward surface coating or foreign dopings. Here, spinel‐layered Li‐rich Li‐Mn‐Co‐O microspheres are reported as a new high‐rate cathode material for Li‐ion batteries. The synthetic procedure is relatively simple, involving the formation of uniform carbonate precursor under solvothermal conditions and its subsequent transformation to an assembled microsphere that integrates a spinel‐like component with a layered component by a heat treatment. When calcined at 700 °C, the amount of transition metal Mn and Co in the Li‐Mn‐Co‐O microspheres maintained is similar to at 800 °C, while the structures of constituent particles partially transform from 2D to 3D channels. As a consequence, when tested as a cathode for lithium‐ion batteries, the spinel‐layered Li‐rich Li‐Mn‐Co‐O microspheres obtained at 700 °C show a maximum discharge capacity of 185.1 mA h g?1 at a very high current density of 1200 mA g?1 between 2.0 and 4.6 V. Such a capacity is among the highest reported to date at high charge‐discharge rates. Therefore, the present spinel‐layered Li‐rich Li‐Mn‐Co‐O microspheres represent an attractive alternative to high‐rate electrode materials for lithium‐ion batteries. 相似文献
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Molecular Engineered Hole‐Extraction Materials to Enable Dopant‐Free,Efficient p‐i‐n Perovskite Solar Cells 下载免费PDF全文
Huanle Chen Weifei Fu Chuyi Huang Zhongqiang Zhang Shuixing Li Feizhi Ding Minmin Shi Chang‐Zhi Li Alex K.‐Y. Jen Hongzheng Chen 《Liver Transplantation》2017,7(18)
Two hole‐extraction materials (HEMs), TPP‐OMeTAD and TPP‐SMeTAD, have been developed to facilitate the fabrication of efficient p‐i‐n perovskite solar cells (PVSCs). By replacing the oxygen atom on HEM with sulfur (from TPP‐OMeTAD to TPP‐SMeTAD), it effectively lowers the highest occupied molecular orbital of the molecule and provides stronger Pb? S interaction with perovskites, leading to efficient charge extraction and surface traps passivation. The TPP‐SMeTAD‐based PVSCs exhibit both improved photovoltaic performance and reduced hysteresis in p‐i‐n PVSCs over those based on TPP‐OMeTAD. This work not only provides new insights on creating perovskite‐HEM heterojunction but also helps in designing new HEM to enable efficient organic–inorganic hybrid PVSCs. 相似文献