Preparation And Electrochemical Performance Of Metal-organic Framework(MOFs) Materials

With increasing environmental pollution and energy shortages,the conversion from a fossil fuel-based energy economy to a sustainable and clean one is a huge challenge.Clean energy,such as hydrogen,wind and solar,is environmentally friendly and renewable,which is rapidly becoming a global concern.In recent years,the storage and conversion technologies used for clean energy have been unprecedentedly developed.Such as lithium-ion batteries,zinc-air batteries and supercapacitors have been applied to real life.Among them,the development of electrode materials and electrode catalysts has always been an important and difficult point.Metal-organic frameworks?MOFs?are porous materials with a periodic network structure formed by metal ions/clusters and organic ligands through coordination bonds.Given their unique properties of high surface area,tunable porous structures,and uniform open cavities,MOFs are gradually utilized to prepare electrode materials and electrocatalyst precursors.The MOFs derived catalysts and electrode materials with significantly activity have been demonstrated in fuel cells and supercapacitors?SCs?,which are likely to be used in the storage and conversion of clean energy.First of all,the organic ligands in MOFs will provide a large amount of carbon for the derived materials.The carbon materials pyrolyzed by high temperature have better conductivity.Secondly,the porous structure and large specific surface area of MOFs are easy to obtain porous derivative materials,which are favorable for proton transport.Finally,MOFs provide active sites?such as P,S,etc.?for the derived materials through surface functionalization or mixing with heteroatom-containing chemicals,which is beneficial to improve the activity of materials.In addition it would further provide the opportunity to tailor the porosity and morphology of the materials,which are induced by the guest molecules during carbonization,for improving their electrochemical performance.Therefore,MOFs as precursors derived electrochemical materials have attracted the attention of scholars.In this paper,porous MOFs were used as precursors to obtain catalytic materials and electrode materials by pyrolysis.The electrochemical properties of the materials were studied by SCs,zinc-air batteries?ZABs?and oxygen evolution reaction?OER?.This article contains following aspects of research work.?1?Using Co-MOF?DUT-58?as a precursor,thioacetamide?TAA?as a guest molecule that is rich in heteroatoms S,we successfully prepared Co₉S₈ nanoparticles?NPs?embedded in carbon co-doped with N and S?Co₉S₈/NS-C-1.5 h?by the nanoconfinement,pyrolysis and CO₂ removal of carbon process.The Co₉S₈/NS-C-1.5 h hybrid exhibited remarkable electrochemical performance for SCs with high specific capacitance of 734 F g^-1 at 1 A g^-1,great rate performance(89%of the capacitance was still maintained even at the current density of 10 A g^-1),and long-term stability with 99.8%of the initial capacitance after 140,000 continuous cycles.?2?Using Co-MOF?DUT-58?as a precursor,guest induced morphological control was studied through nanoconfinement and carbonation processes.Through the regulation of the carbonization temperature and the ratio of heteroatoms,nitrogen and sulfur co-doped porous carbon-coated Co₉S₈ NPs(Co₉S₈/NS₁₀-C-700)were prepared as cathode catalysts for zinc-air batteries.With excellent redox catalytic activity,the starting potential,half-wave potential and electron transfer number were close to commercial Pt/C catalysts.Remarkably,their methanol resistance and stability were superior to those of commercial Pt/C catalysts.Co₉S₈/NS₁₀-C-700 as a zinc-air battery oxygen electrode catalyst material exhibited high specific capacity(specific capacity 800 mAh g^-1 at a current density of 50mA g^-1).?3?Using Co/Ni-MOFs?MOF-74?and graphene oxide?GO?as precursors,the N doped cobalt-nickel bimetallic composite material?CoNi/N-GO?was successfully prepared after ammonia nitrogen treatment.This material was used as an OER catalyst and exhibited excellent catalytic activity.The overpotential at 10 mA cm^-2?0.33 V?is lower than commercial Ir/C catalyst?0.38 V?.