基于第一性原理的锂空气电池钌掺杂石墨烯正极 氧还原反应机理研究

双电解液锂空气电池因其高理论能量密度受到广泛研究,但电池正极侧氧还原反应(ORR)速率低,其反应速率是限制锂空气电池发展的主要因素之一.本文提出了以钌(Ru)掺杂单层石墨烯作为正极ORR催化剂,采用第一性原理计算nRu (n=1～3)掺杂石墨烯的电子结构和氧气在Ru掺杂石墨烯表面的吸附性能,并以过渡态搜索方法获得ORR反应路径,研究碱性溶液中Ru掺杂单层石墨烯作用下的ORR机理.研究结果表明,经Ru原子掺杂后,石墨烯能够获得稳定的掺杂结构,且电导率显著提升.同原始单层石墨烯相比,Ru掺杂石墨烯增强了对O₂的吸附能力.在三Ru(n=3)掺杂石墨烯表面进行的ORR无需克服任何能垒.此外,三Ru掺杂石墨烯表面对OH基团的吸附能最低,有利于ORR的连续进行.研究表明三Ru掺杂石墨烯有望成为一种新型的ORR催化剂以提高双电解液锂空气电池的性能.     

二维Li+BC3结构高储氢容量的研究

本文基于第一性原理密度泛函理论, 证实了锂原子可以均匀地吸附在二维结构的BC₃片两侧, 同时被吸附的锂原子不会抱团. 通过计算表明, 被吸附的锂原子浓度达到33.3%时, Li+BC₃体系具有最高的储氢比例12.57 wt.%. 然后, 通过热力学分析预测了在室温 (300 K) 下, 115–250 atm之间, Li+BC₃体系可以达到上述储氢比例, 这不仅符合美国能源部的要求, 也满足了应用中的安全需要. 关键词： 第一性原理 储氢 3二维结构')" href="#">Li+BC₃二维结构     

拉伸形变下BC3纳米管的能带结构

运用紧束缚能带理论,研究拉伸形变下BC₃纳米管的能带结构. 研究表明:随着拉伸和压缩强度的不断增加,BC₃纳米管的导带能级和价带能级逐渐靠近,最终发生能带交叠. 压缩形变下能带的交叠程度可达05 eV,而拉伸形变下只有02 eV. 对于扶手椅型BC₃纳米管,随着拉伸和压缩的不断增加,BC₃纳米管首先由直接半导体转化为间接半导体,进而发生能带的交叠,表现出金属性. 在无形变时,扶手椅型BC₃纳米 关键词： 3纳米管')" href="#">BC₃纳米管 能隙 拉伸形变 半导体     

碳纳米管材料的储锂性能

碳纳米管较低的碳原子密度、管径和管间的空隙可以为锂离子提供大量的嵌入空间,从而拥有更高的储锂能力。本文结合实验与理论研究的最新成果,综述了这一领域的主要进展和前景。实验上,对单壁碳纳米管进行适当处理,可以将锂存储量提高到常规石墨材料的2~3倍。根据密度泛函理论计算,锂在不同碳纳米管束中的最高理论嵌入量可以达到Li0.5C。嵌入后锂和碳纳米管之间发生了完全的电荷转移,碳纳米管的Fermi能级上移到导带中,所有碳纳米管都转变为金属。纳米管自身的电子结构对锂的吸附是至关重要的,缺电子体系更有利于锂的吸附。锂在B掺杂的复合管如BC3纳米管中有很大的吸附能。锂穿透纳米管壁从管壁外进入纳米管内的能垒,随着纳米管壁拓扑缺陷结构的尺寸变大而显著降低,B在纳米管壁的存在会进一步降低锂穿越纳米管壁的能垒。同时B的掺杂会降低相同拓扑缺陷的生成能,导致在BC3纳米管中出现更多的拓扑缺陷,从而有利于锂离子的扩散。实验与理论计算的结合可望加深对锂离子在纳米管材料中嵌入过程的理解,指导设计具有更高储锂性能的新材料。     

碳纳米管材料的储锂性能

碳纳米管较低的碳原子密度、管径和管间的空隙可以为锂离子提供大量的嵌入空间,从而拥有更高的储锂能力。本文结合实验与理论研究的最新成果,综述了这一领域的主要进展和前景。实验上,对单壁碳纳米管进行适当处理,可以将锂存储量提高到常规石墨材料的2~3倍。根据密度泛函理论计算,锂在不同碳纳米管束中的最高理论嵌入量可以达到Li0.5C。嵌入后锂和碳纳米管之间发生了完全的电荷转移,碳纳米管的Fermi能级上移到导带中,所有碳纳米管都转变为金属。纳米管自身的电子结构对锂的吸附是至关重要的,缺电子体系更有利于锂的吸附。锂在B掺杂的复合管如BC3纳米管中有很大的吸附能。锂穿透纳米管壁从管壁外进入纳米管内的能垒,随着纳米管壁拓扑缺陷结构的尺寸变大而显著降低,B在纳米管壁的存在会进一步降低锂穿越纳米管壁的能垒。同时B的掺杂会降低相同拓扑缺陷的生成能,导致在BC3纳米管中出现更多的拓扑缺陷,从而有利于锂离子的扩散。实验与理论计算的结合可望加深对锂离子在纳米管材料中嵌入过程的理解,指导设计具有更高储锂性能的新材料。     

富锂正极材料在全固态锂电池中的研究进展

开发高能量密度、长循环寿命、低成本和高安全性的全固态锂电池是发展下一代锂离子电池的重要方向之一.富锂层状氧化物正极材料由于阴阳离子协同参与氧化还原反应,可以提供更高的放电比容量(>250 mAh/g)和能量密度(>900 Wh/kg),将其应用于全固态锂电池中有望推动锂离子电池能量密度突破500 Wh/kg的中长期目标.然而,富锂正极材料的电子导电性差、阴离子氧的不可逆氧化还原反应以及循环中的结构相变,导致该材料在电化学循环过程中存在初始库仑效率低、循环稳定性差和电压衰退等问题.此外,富锂正极材料的工作电压较高(>4.5 V vs.Li/Li⁺),使正极/电解质之间不仅面临常规的界面化学反应,释放的氧还会加剧界面的电化学反应,对正极/电解质的界面稳定性提出了更高的要求.因此,富锂正极材料的本征特性和富锂正极/电解质间严重的界面反应极大限制了富锂正极材料在全固态锂电池中的应用.本文首先详细阐述了富锂正极材料在全固态锂电池中的失效机制,其次综述了近年来富锂正极材料在不同固态电解质体系下的研究进展,最后总结和展望了富锂全固态锂电池未来的研究重点和发展方...     

单壁BC3纳米管晶格动力学研究

基于力常数模型计算了一系列扶手椅型、锯齿型和手性单壁BC₃纳米管的声子色散关系.描述了单壁BC₃纳米管结构的表征方式,比较详细地给出了其结构、对称性和晶格动力学分析.基于数值计算结果,讨论了拉曼活性模和红外活性振动模的频率与管径的关系.由分析结果做出推断,BC₃纳米管的拉曼光谱和红外光谱比单壁碳纳米管更为复杂. 关键词： 3纳米管')" href="#">BC₃纳米管 声子色散关系 晶格动力学     

氧气在碳化钨负载的铜-金合金单层上吸附与解离的第一性原理研究

采用基于密度泛函理论的第一性原理方法研究了碳化钨负载的铜-金合金单层催化剂对氧气吸附和解离性质的影响.通过比较碳化钨负载的纯金单层与铜掺杂的合金单层的电荷布局,发现掺杂铜可以创造新的活性位点,改变氧气的吸附构型,改善氧气的吸附和解离性质.进一步探究了氧气在Cu₁Au₈/WC(0001),Cu₂Au₇/WC(0001)上的解离过程,发现:氧气在Cu₂Au₇/WC(0001)上解离势垒仅为0.64 eV,远低于在纯金单层上的1.56 eV,表明铜掺杂有效促进了氧气的解离.铜掺杂后的单层结构变化预示了在单层产生了配位效应和局部应力效应.电荷布局和态密度结果表明铜掺杂促进了单层上电荷的重新分布,加强了氧气分子与基底的电荷转移和轨道杂化,从而增强了对氧气的吸附.当前的研究结果阐明了碳化钨负载合金单层对氧气分解的促进作用和机理,为设计更加高效廉价的氧还原反应催化剂奠定理论基础.     

有机电解质锂空气电池放电特性分析

为了研究有机电解质锂空气电池放电过程的内部反应机理,本文以有限元方法为基础,利用有限元软件COMSOL建立了一个耦合了Butler-volmer方程、Fick定律方程、偏微分方程的二维数值模型,研究有机电解质锂空气电池放电过程中的传质规律,分析了沉积物形貌、正极多孔材料厚度对电池放电特性的影响,在一定放电电流密度下,小的过氧化物沉淀形貌系数导致放电电压降低,降低正极厚度有利于电池的放电特性,靠近正极集流体附近电化学反应剧烈,但生成的过氧化物多,阻塞在靠近正极集流体一侧,导致电流密度迅速降低,研究结果对理解有机电解质锂空气电池的工作原理具有重要帮助.     

一代材料，一代电池：正极材料研究推动锂离子动力电池的升级换代

一代材料,一代电池。锂离子电池正极材料的研究不断推动着动力电池的升级换代。第一代动力电池的正极材料为锰酸锂Li Mn₂O₄,其低温性能好、成本低和安全性高,但电池能量密度不够高。第二代动力电池正极材料为磷酸铁锂Li Fe PO₄和三元正极材料镍钴锰NCM/镍钴铝NCA。磷酸铁锂正极材料的优势是长寿命、低成本、高安全性。三元锂正极材料的特点是大容量、高能量密度、快充效率高。第三代动力电池的正极材料是高电压镍锰酸锂Li Ni_0.5Mn_1.5O₄和镍酸锂Li Ni O₂,主要解决第二代面临的低成本和长续航不能兼顾的问题以及更长里程问题。文章首先回顾第一、二代的锰酸锂、磷酸铁锂和三元正极材料的研究历程、优缺点及发展近况,之后介绍和展望下一代高电压镍锰酸锂和镍酸锂正极材料。     

Electrochemical performance of a nonaqueous rechargeable lithium-air battery

Nonaqueous rechargeable lithium-air battery has so high specific capacity and specific energy that it is being widely researched by academia, corporation, and different research institutes. When used in dried air and absorbing oxygen form the air, this battery is called lithium-air battery, and its specific capacity based on cathode active material (oxygen) is infinite. However, its cycle performance is very limited as reported by the state-of-the-art researches. This cycle problem is mainly caused by instability of electrolyte. Based on electroanalysis of materials’ electrochemical property, a stable electrolyte solvent (sulfolane) and a lithium salt LiBF₄ are selected as electrolytes in this work. Coupled with other eligible battery materials and careful assembly, the lithium-air battery exhibits favorable cycle performance. Above all, this lithium-air system is evaluated objectively in this paper.     

Working Mechanism of a BC_3 Nanotube Carbon Monoxide Gas Sensor

Carbon and BN nanotubes have previously demonstrated extreme sensitivity to several molecules, but they cannot be used to detect highly toxic molecules of CO. In this work, we examine the possibility of a BC3 nanotube (BC3NT) as a potential gas sensor for CO detection by using density functional theory calculations. It is found that CO molecule can be absorbed on B and C atoms of BC3 NT wall with adsorption energies in the range of 1.0 to 25.9 kcal/mol and it can donate finite charge to the tube. By comparing the HOMO/LUMO energy gaps of the bare and CO adsorbed nanotubes, we deduce that molecular CO can induce significant change in the electrical conductivity of the tube. The conductivity change can generate an electrical signal, which might be useful for CO detection.     

First-principles study on anatase TiO2（101） surface adsorption of NO

In this paper, the stable structure and the electronic and optical properties of nitric oxide （NO） adsorption on the anatase TiO2 （101） surface are studied using the plane-wave ultrasoft pseudopotential method, which is based on the density functional theory. NO adsorption on the surface is weak when the outermost layer terminates on twofold coordinated oxygen atoms, but it is remarkably enhanced on the surface containing O vacancy defects. The higher the concentration of oxygen vacancy defects, the stronger the adsorption is. The adsorption energies are 3.4528 eV （N end adsorption）, 2.6770 eV （O end adsorption）, and 4.1437 eV （horizontal adsorption）. The adsorption process is exothermic, resulting in a more stable adsorption structure. Furthermore, O vacancy defects on the TiO2 （101） surface significantly contribute to the absorption of visible light in a relatively low-energy region. A new absorption peak in the low-energy region, corresponding to an energy of 0.9 eV, is observed. However, the TiO2 （101） surface structure exhibits weak absorption in the low-energy region of visible light after NO adsorption.     

VO2薄膜表面氧缺陷的修复:F4TCNQ分子吸附反应

VO₂表面氧缺陷的存在对VO₂材料具有显著的电子掺杂效应, 极大地影响材料的本征电子结构和相变性质. 通过2, 3, 5, 6-四氟-7, 7', 8, 8'-四氰二甲基对苯醌(F₄TCNQ)分子表面吸附反应, 可以有效消除表面氧缺陷及其电子掺杂效应. 利用同步辐射光电子能谱和X射线吸收谱原位研究了修复过程中电子结构的变化以及界面的化学反应, 发现这种方式使得VO₂薄膜样品氩刻后得到的V³⁺失去电子成功地被氧化成原先的V⁴⁺, 同时F₄TCNQ分子吸附引起电子由衬底向分子层转移, 界面形成带负电荷的分子离子物种. 受电化学性质的制约, F₄TCNQ分子吸附反应修复氧缺陷较氧气氛退火更安全有效, 不会引起表面过度氧化形成V₂O₅.     

Effect of Oxide Content of Graphene Oxide Membrane on Remarkable Adsorption for Calcium Ions

Graphene oxide membranes(GOMs), as one of the most promising novel materials, have gained great interest in the field of adsorption. However, the oxygen content of graphene oxide is directly related to its adsorption properties, such as suspension stability, adsorption capacity, and reusability of GOMs. Here, a series of reduced GOMs with oxygen content from 28% to 12% were conveniently prepared by the thermally reduced and the corresponding interlayer spacing of these membranes changed from 8.0 ? to 3.7 ?. These prepared GOMs have remarkable Ca~(2+) adsorption capacity, which increases with the oxygen content or interlayer spacing of GOMs.Importantly, the max adsorption capacity of the mass ratio between adsorbed Ca~(2+)and pristine GOMs can reach up to 0.481 g/g, which is about one order of magnitude higher than the adsorption capacity of activated sludge,magnetic Fe_3 O_4, functionalized silica, zeolite molecular sieve, and other reported previously. Moreover, GOMs show excellent stability and the Ca~(2+) can be easily desorbed by water, so that the GOMs can be reused. Our previous theoretical analysis suggests that this remarkable adsorption is attributable to the strong interactions between Ca~(2+) and GO sheets, including the ion- interactions between Ca~(2+) and aromatic graphitic rings as well as the electrostatic interaction between Ca~(2+) and oxygen-containing groups.     

沉淀过程pH值对铈锆复合氧化物结构与性能的影响

采用加热回流老化技术制备了系列组成为0.6CeO₂-0.4ZrO₂的铈锆复合氧化物,通过N₂物理吸附、Raman光谱、UV-Vis 漫反射光谱等方法对沉淀过程pH值对铈锆复合氧化物结构及储氧性能的影响进行了研究。结果表明,沉淀过程pH值不同,将导致铈锆复合氧化物的组成产生波动,进而影响样品的晶相组成、缺陷性质、结晶程度和孔结构性质。控制沉淀pH值为10.5～11.0,可消除Si的影响,改善铈锆复合氧化物的孔结构,提高相均匀性,提高缺陷浓度,降低结晶度,从而可提高样品的储氧性能。     

Effect of surface oxygen vacancy defects on the performance of ZnO quantum dots ultraviolet photodetector

The slower response speed is the main problem in the application of ZnO quantum dots (QDs) photodetector, which has been commonly attributed to the presence of excess oxygen vacancy defects and oxygen adsorption/desorption processes. However, the detailed mechanism is still not very clear. Herein, the properties of ZnO QDs and their photodetectors with different amounts of oxygen vacancy (V_O) defects controlled by hydrogen peroxide (H₂O₂) solution treatment have been investigated. After H₂O₂ solution treatment, V_O concentration of ZnO QDs decreased. The H₂O₂ solution-treated device has a higher photocurrent and a lower dark current. Meanwhile, with the increase in V_O concentration of ZnO QDs, the response speed of the device has been improved due to the increase of oxygen adsorption/desorption rate. More interestingly, the response speed of the device became less sensitive to temperature and oxygen concentration with the increase of V_O defects. The findings in this work clarify that the surface V_O defects of ZnO QDs could enhance the photoresponse speed, which is helpful for sensor designing.