Recent Progress of Conductive Metal-Organic Frameworks for Electrochemical Energy Storage

The development of reliable and low-cost energy storage systems is of considerable value in using renewable and clean energy sources,and exploring advanced electrodes with high reversible capacity,excellent rate performance,and long cycling life for Li/Na/Zn-ion batteries and supercapacitors is the key problem.Particularly because of their diverse structure,high specific surface area,and adjustable redox activity,electrically conductive metal-organic frameworks(c-MOFs)are considered promising candidates for these electrochemical applications,and a detailed overview of the recent progress of c-MOFs for electrochemical energy storage and their intrinsic energy storage mechanism helps realize a comprehensive and systematic understanding of this progress and further achieve highly efficient energy storage and conversion.Herein,the chemical structure of c-MOFs and their conductive mechanism are first introduced.Subsequently,a comprehensive summarization of the current applications of c-MOFs in energy storage systems,namely supercapacitors,LIBs,SIBs,and ZIBs,is presented.Finally,the prospects and challenges of c-MOFs toward much higher-performance energy storage devices are presented,which should illuminate the future scientific research and practical applications of c-MOFs in energy storage fields.

Conductive metal-organic frameworks promoting polysulfides transformation in lithium-sulfur batteries

Metal organic frameworks(MOFs) have been extensively investigated in Li-S batteries owing to high surface area, adjustable structures and abundant catalytic sites. Nevertheless, the insulating nature of traditional MOFs render retarded kinetics of polysulfides conversion, leading to insufficient utilization of sulfur. In comparison, conductive MOFs(c-MOFs) show great potential for promoting polysulfides transformation due to superb electronic conductivity. In this work, a nickel-catecholates based c-MOF, NiHHTP(HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene), is designed to regulate surface chemistry of self-supported carbon paper for advanced Li-S batteries. Taking advantage of the porous structure and high conductivity, the as-prepared Ni-HHTP is conducive to synergising strengthening the chemisorption of polysulfides and accelerating the reaction kinetics in Li-S batteries, significantly mitigating the polysulfides diffusion from the non-encapsulated sulfur cathode, therefore promoting polysulfides transformation in Li-S batteries. This work points out a promising modification strategy for developing advanced sulfur cathode in Li-S batteries.

Conductive metal-organic frameworks: Recent advances in electrochemical energy-related applications and perspectives

Metal-organic frameworks(MOFs),typically constructed with metallic nodes and organic linkers,have influenced the development of modular solid materials.Their adjustable molecular structure provides a remarkable variety of MOF-based solid-state structures towards diverse applications.However,the low conductivity of traditional MOFs extremely hinders their applications in electronic and electrochemical devices.The emerging conductive MOFs,generally possessing twodimensional layered structures,are endowed with both the structural merits of common MOFs and exceptional electronic/ionic conductivities.Besides,the selection and optimization of ligands and metal centers,as well as synthetic methods enormously affects the intrinsic conductivity of conductive MOFs.The distinctive crystal structures and superb conductivity promise their appealing applications in electrochemical energy-related fields.In the review,we mainly summarize representative crystal features,conducting mechanisms and recent advances in rational design and synthesis of conductive MOFs,along with their versatile applications as electrodes for electrochemical capacitors and rechargeable batteries,and as catalysts towards electrocatalysis.Finally,the involved challenges and future trends/prospects of the conductive MOFs for electrochemical energyrelated applications are further proposed.

V-MOF-derived V_(2)O_(5) nanoparticles-modified carbon fiber cloth-based dendrite-free anode for high-performance lithium metal batteries

At present,commercial Li-ion batteries are hardly to satisfy the growing demand for high energy density,for this purpose,lithium metal batteries have attracted worldwide attention in recent years.However,its practical applications are hindered by the formation of Li dendrites and volume effect during Li plating/stripping process,which leads to a lot of safety hazards.Herein,we first employed MOF-derived V_(2)O_(5) nanoparticles to decorate the carbon fiber cloth(CFC)backbone to acquire a lithiophilic 3D porous conductive framework(CFC@V_(2)O_(5)).Subsequently,the CFC@V_(2)O_(5) skeleton was permeated with molten Li to prepare CFC@V_(2)O_(5)@Li composite anode.The CFC@V_(2)O_(5)@Li composite anode can be stably cycled for more than 1650 h at high current density(5 mA·cm^(-2))and areal capacity(5 mA·h·cm^(–2)).The prepared full cell can initially maintain a high capacity of about 143 mA·h·g^(-1) even at a high current density of 5 C,and can still maintain 114 mA·h·g^(-1) after 1000 cycles.

Two-Dimensional Conductive Metal-Organic Framework Reinforced Spinterface in Organic Spin Valves

Interface engineering in device fabrication is a significant but complicated issue.Although great successes have been achieved by conventional physical in situ or ex situ methods,it still suffers from complicated procedures.In this work,we present a facile method for fabricating phthalocyanine(Pc)-based two-dimensional conductive metal–organic framework(MOF)films.Based on PcM-Cu(M=Ni,Cu,H_(2))MOF films,spin valves with a vertical configuration of La_(0.67)Sr_(0.33)MnO_(3)/PcM-Cu MOFs/Co were constructed successfully,and exhibited notably high negative magnetoresistance(MR)up to -22% at 50 K.The penetrated Co atoms coordinated with the dehydrogenated hydroxy groups in the MOFs resulting in an antiferromagnetic layer of the PcM-Cu-Co hybrid structure.Interestingly,a significant exchange bias effect was demonstrated at the PcM-Cu MOF/Co interface,beneficial for the MR behavior.Thus,our present study provides new insights into developing high-performance organic spin valves via de novo molecular design.

Metal and ligand modification modulates the electrocatalytic HER,OER,and ORR activity of 2D conductive metal-organic frameworks

It is highly desirable to design efficient and stable hydrogen evolution reaction(HER)and oxygen evolution/reduction reaction(OER/ORR)electrocatalysts for the development of renewable energy technologies.Herein,density functional theory(DFT)calculations were conducted to systematically investigate a series of TMN_(x)O_(4-x)-HTT(TM=Fe,Co,Ni,Ru,Rh,Pd,Ir and Pt;HTT=hexahydroxy tetraazanaphthotetraphene)analogs of two-dimensional(2D)conductive metal-organic frameworks(MOFs)as potential electrocatalysts for the HER,OER and ORR.The thermodynamic and electrochemical stability simulations suggest that these designed catalysts are stable.Remarkably,CoO_(4)-HTT,RhN_(3)O_(1)-HTT and IrN3O1-HTT are predicted to be the most promising catalysts for the HER,OER and ORR,respectively,surpassing the catalytic activity of corresponding benchmark catalysts.The volcano plots were established based on the scaling relationship of adsorption Gibbs free energy of intermediates.The results reveal that regulating combinations of metal active centers and local coordination environments could effectively balance the interaction strength between intermediates and catalysts,thus achieving optimal catalytic activity.Our findings not only opt for the promising HER/OER/ORR electrocatalysts but also guide the design of efficient electrocatalysts based on 2D MOFs materials.

A Pyrazine-Based 2D Conductive Metal-Organic Framework for Efficient Lithium Storage

The merits of intrinsic electrical conductivity, high specific surface area, tunable chemical composition and tailor-made properties enable two-dimensional conductive metal-organic frameworks (2D c-MOFs) as promising next-generation electrode materials in the field of energy storage and conversion. Herein, we have designed and synthesized a novel pyrazine-based 2D c-MOF (TPQG-Cu-MOF) bearing extended π-conjugated structure and abundant redox active sites. Thanks to the excellent redox reversibility of pyrazine units and CuO2 units, as well as the insolubility of the rigid framework skeleton, TPQG-Cu-MOF as the cathode material of lithium-ion battery exhibits a reversible specific capacity (150.2 mAh·g–1 at 20 mAh·g–1), good cycling stability (capacity retention of 82.6% after 500 cycles at 1 A·g–1) and excellent rate performance. Comprehensive ex-situ spectroscopic studies revealed the reversible redox activity of pyrazine units and CuO2 units of TPQG-Cu-MOF during the Li+ insertion/extraction process. The deepening fundamental understanding of the structure-property relationship was proposed, which might pave the way for further development of efficient MOF-based energy storage devices.

Conductive Metal/Covalent Organic Frameworks for CO_(2) Electroreduction

Porous crystalline metal-organic frameworks(MOFs)and covalent organic frameworks(COFs)are promising platforms for electrocatalytic reduction of CO_(2)(CO_(2)RR)due to their large CO_(2)adsorption uptakes and periodically arranged single active sites.However,the applications in CO_(2)RR of the traditional MOFs and COFs are greatly limited by their low electron conductivity.In recent years,numerous types of MOFs and COFs with high intrinsic conductivity have been rationally designed and successfully constructed,and some of them have been applied in CO_(2)RR.In this review,the applications of conductive MOFs and COFs in CO_(2)RR have been summarized.The conductive MOFs and COFs can be categorized according to the methods,in which the conductivity is enhanced,such as constructing fullyπ-conjugated backbones,donor-acceptor heterojunction,enhancing theπ-πstacking interactions between organic moieties and/or the introduction of guest molecules.

Co3(hexahydroxytriphenylene)2:A conductive metal-organic framework for ambient electrocatalytic N2 reduction to NH3

As a carbon-neutral alternative to the Haber-Bosch process,electrochemical N2 reduction enables environment-friendly NH3 synthesis at ambient conditions but needs active electrocatalysts for the N2 reduction reaction.Here,we report that conductive metal-organic framework CO3(hexahydroxytriphenylene)2(Co3 HHTP2)nanoparticles act as an efficient catalyst for ambient electrochemical N2-to-NH3 fixation.When tested in 0.5 M LiClO4,such Co3 HHTP2 achieves a large NH3 yield of 22.14μg·h^-1·mg^-1 cat.with a faradaic efficiency of 3.34%at-0.40 V versus the reversible hydrogen electrode.This catalyst also shows high electrochemical stability and excellent selectivity toward NH3 synthesis.

2D conductive metal-organic frameworks for electronics and spintronics

Two-dimensional(2D)materials showcase great potentials in both fundamental research and technology development,thanks to their unique chemical and physical properties that are usually not available in corresponding bulk counterparts.As an emerging class of 2D materials,2D conductive metal-organic frameworks(2D c-MOFs)exhibit the characteristics of pre-designable and tunable structures,excellent crystallinity,intrinsic porosity and superior conductivity.During the past decade,2D c-MOFs have been rapidly developed in electronics,sensors,energy storage devices,etc.In this review,the electrical,magnetic and quantum properties of 2D c-MOFs are surveyed in detail.Their applications in semiconductor,metal,superconductor,topological insulator and porous magnet are highlighted.We envision that the combination of 2D c-MOFs with quantum materials could evoke rich physics,flexible chemistry and potential applications in both electronics and spintronics.

双配体基二维导电金属-有机框架的一步合成及其储锂性能研究

基于双氧化还原活性有机配体的二维导电金属-有机框架(2D c-MOFs)是极具潜力的锂离子电池(LIBs)电极材料.然而,双配体竞争配位导致该类材料合成具有极大挑战性.本文以乙二胺为调节剂,发展了一步法合成双配体基2D c-MOF Cu_(3)(HHTP)(THQ)(HHTP=2,3,6,7,10,11-六羟基三亚苯,THQ=四羟基-1,4-苯醌).所得Cu_(3)(HHTP)(THQ)具有良好的导电性、丰富的活性位点和优异的化学稳定性,其作为LIBs负极材料展现出高比容量、良好的倍率性能和长循环稳定性.实验结果和理论计算表明,Cu_(3)(HHTP)(THQ)中CuO_(4)活性位点和苯环单元均参与了锂存储,从而优化了储锂性能.该工作为构筑双配体基2D c-MOFs和高性能LIBs电极材料提供了新的途径.