垂直自支撑式金属有机框架多级结构单晶用于锂定向沉积

金属有机框架材料(MOF)是由金属离子或簇和有机配体通过配位键自组装形成的多孔晶体材料.MOF及其衍生物具有开放金属位点和极大的比表面积,广泛地应用在催化领域.然而,MOF材料由于存在暴露活性位点较少,传质受限或易发生不可控制的聚集等问题,会导致活性位点的损失,极大地限制了其在催化领域的应用.多级结构不仅提供更多的暴露活性位点,而且提升传质效率及稳定性.因此,设计和构造分层多级结构的MOF材料是解决上述问题的有效途径.本文制备了一种垂直自支撑式MOF多级结构材料.该多级结构材料由相互垂直自支撑式纳米片所构成;通过三维电子衍射表征显示,单个垂直自支撑式MOF多级结构颗粒显示单晶特性.因此,可以确定垂直自支撑式MOF多级结构是ZIF-67的单晶.本文也对这种结构的形成机理进行了初步探究,两种具有结构相关性ZIF在混合溶液中的相互转化是主要驱动力.这种垂直穿插的多级结构具有优异的传质/传荷能力和增强反应动力学的特性,扩展了传统多孔晶体材料的应用领域.本文通过温和的溶液硫化法,制备了保留垂直穿插结构的硫化钴,并进一步将这种垂直穿插结构的硫化钴应用在锂金属电池中.这类材料显示出多个优点:(1)具有高比表面积,提升了离子通量和传质;(2)锂离子的结合将硫化钴物种还原为钴金属颗粒;(3)垂直穿插结构引导金属沿着二维纳米片的方向沉积,避免树枝状晶体的生成.将这种垂直自支撑式硫化钴多级结构材料用作电极材料时,所组装的锂金属电池显示出有效的电流密度、高库伦效率(99%)、低成核过电位(30 mV于5 mA cm^(−2))和较好的稳定循环性(510 h).本文对于垂直穿插结构材料的设计及研究其在金属电池中的应用具有重大意义.

Inherent mass transfer engineering of a Co,N co-doped carbon material towards oxygen reduction reaction

Oxygen reduction reaction (ORR) is an important process for the conversion and utilization of a wide range of renewable energy sources, and is critical for the shape of future energy scenario [1–10]. However, ORR is a complex four-electron transfer process and is kinetically sluggish. It is urgent to develop high-efficient electrocatalysts to solve this problem [11–15]. Up to now, precious metal-based catalysts such as Pt-based electrocatalysts have been widely studied and found to be one of the most efficient electrocatalysts for ORR. However, the high price and the small reserves limit their large-scale commercialization [10,16–23]. Therefore, in order to fulfill needs for the practical applications, it is necessary to develop low-cost electrocatalysts, also with high activity and great stability [19,24–28].

Two-Dimensional Metal-Organic Frameworks with Unique Oriented Layers for Oxygen Reduction Reaction:Tailoring the Activity through Exposed Crystal Facets

As one of the most important families of porous materials,metal–organic frameworks(MOFs)have well-defined atomic structures.This provides ideal models for investigating and understanding the relationships between structures and catalytic activities at the molecular level.However,the active sites on the edges of two-dimensional(2D)MOFs have rarely been studied,as they are less exposed to the surfaces.Here,for the first time,we synthesized and observed that the 2D layers could align perpendicular to the surface of a 2D zeolitic imidazolate framework L(ZIF-L)with a leaf-like morphology.Owing to this unique orientation,the active sites on the edges of the 2D crystal structure could mostly be exposed to the surfaces.Interestingly,when another layer of ZIF-L-Co was grown heteroepitaxially onto ZIF-L-Zn(ZIF-L-Zn@ZIF-L-Co),the two layers shared a common b axis but rotated by 90°in the ac plane.This demonstrated that we could control exposed facets of the 2D MOFs.The ZIF-L-Co with more exposed edge active sites exhibited high electrocatalytic activity for oxygen reduction reaction.This work provides a new concept of designing unique oriented layers in 2D MOFs to expose more edge-active sites for efficient electrocatalysis.