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].

Flexibility in DUT-8(Cu)Metal-Organic Framework:Impact of Cluster,Stress,History,and Hierarchical Texture

The flexibility of metal-organic frameworks(MOFs)featuring stimuli-responsive structural transitions is often governed not only by the chemical composition and topology but also by orthogonal factors such as particle size,desolvation method,and history of the sample.A precise understanding of the mechanism behind such observations has been lacking up to now,and there are still substantial open questions concerning the impact of sample treatment history.The DUT-8(M)family([M_(2)(2,6-ndc)2(dabco)]n,2,6-ndc=2,6-naphthalene dicarboxylate,dabco=1,4-diazabicyclo-[2.2.2]-octane),encompasses isostructural compounds based on Ni,Zn,Co,and Cu in the cluster node and is representative of pillared layer MOFs,often showing flexible behavior.In this contribution,we discuss a possible explanation for the differences in flexibility observed in desolvated phases of DUT-8(Cu).Theoretical calculations and crystallographic data shed light on the preferred formation of interpenetrated confined closed pore phases in DUT-8(Cu)in contrast to DUT-8(Ni,Co,Zn)where the closed pore phases are formed.

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.