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.

In situ growth CNT@MOFs core-shell structures enabling high specific supercapacitances in neutral aqueous electrolyte

Conductive metal-organic frameworks(c-MOFs)are promising active electrode materials for electrochemical double-layer capacitors with a performance that already exceeds most carbon-based materials.However,their excellent supercapacitance is primarily based on organic or alkaline electrolytes,which largely impede their broad applications and sustainabilities.In this work,we propose a new synthesis approach for fabricating carbon nanotubes and c-MOFs(CNT@MOFs)core–shell structures,which result in high supercapacitance in neutral aqueous electrolytes.We identify that CNTs provide abundant active sites to ensure high capacitance,and Ni3(2,3,6,7,10,11-hexaiminotriphenylene(HITP))2 nanoarrays that in situ grow on the surface of CNTs bundles can significantly improve the conductivity and provide enough ion transport pathways in aqueous electrolytes.Specifically,using CNT@MOFs core-shell structures as an electrode,we obtained a high initial capacitance of 150.7 F·g^(−1) at 0.1 A·g^(−1) in 1 M Na2SO4 solution and good capacity retention of 83.5%after 10,000 cycles at 4 A·g^(−1).We also found that the carboxyl groups on the surface of CNTs provide better anchor sites for the in situ growth of c-MOF,which promotes the uniform growth of c-MOF shells on the CNT surface and improves aqueous electrolyte accessibility.We believe that the high supercapacitance in aqueous electrolytes reported in this work would provide a good prospect for deploying c-MOF based energy storage devices into biomedical and other healthcare electronic applications.

Two-dimensional d-πconjugated metal-organic framework based on hexahydroxytrinaphthylene

The development of new two-dimensional(2D)d-πconjugated metal-organic frameworks(MOFs)holds great promise for the construction of a new generation of porous and semiconductive materials.This paper describes the synthesis,structural characterization,and electronic properties of a new d-πconjugated 2D MOF based on the use of a new ligand 2,3,8,9,14,15-hexahydroxytrinaphthylene.The reticular self-assembly of this largeπ-conjugated organic building block with Cu(II)ions in a mixed solvent system of 1,3-dimethyl-2-imidazolidinone(DMI)and H2 O with the addition of ammonia water or ethylenediamine leads to a highly crystalline MOF Cu3(HHTN)2,which possesses pore aperture of 2.5 nm.Cu3(HHTN)2 MOF shows moderate electrical conductivity of 9.01×10^(-8)S·cm^(-1)at 385 K and temperature-dependent band gap ranging from 0.75 to 1.65 eV.After chemical oxidation by l2,the conductivity of Cu3(HHTN)2 can be increased by 360 times.This access to HHTN based MOF adds an important member to previously reported MOF systems with hexagonal lattice,paving the way towards systematic studies of structure-property relationships of semiconductive MOFs.

Preparation of metal‐organic frameworks and their derivatives for supercapacitors

To satisfy the requirements of social power development,it is urgently necessary to develop innovative and sustainable new energy storage devices.Supercapacitors have attracted considerable attention as a new type of energy storage device,owing to their high energy density,high power density,fast charging and discharging speeds,and long cycle life.The electrode material is an important factor in determining the electrochemical performance of supercapacitors.In recent years,researchers explored the application of metal‐organic frameworks(MOFs)and their derivatives as electrode materials for supercapacitors.In this paper,the preparation of monometallic,bimetallic,and conductive MOFs,and their derivatives for application in supercapacitors are reviewed.In addition,challenges facing MOFs in the field of supercapacitors and their future development prospects are discussed.