Synthesis,Characterization And Electrochemical Oxygen Reactivity Properties Of MOFs Derived Transition Metal Sulfide Nanocomposites

With the energy resources crisis gradually intensified in the world,people have deepened the development of clean energy such as wind and solar energy.The efficient storage and utilization of the electric energy generated by wind and solar energy is a hot topic at present.The most effective stroge method is fuel cell or metal-air cell,in which two important reactions are involved:electrocatalytic oxygen evolution reaction?OER?and electrocatalytic oxygen reduction reaction?ORR?.At present,the effective electrocatalysts for the above two reactions are precious metal based materials,such as RuO₂ and Pt/C,but neither RuO₂ nor Pt/C can act as OER and ORR catalysts at the same time.Pt and Ru are rare precious metals on earth,which seriously hinder their extensive application.Earth abundant transition metal sulphides have been proven to have catalytic activities for OER and ORR and are ideal substitutes for noble metal-based catalysts.In addition,the synergistic effect of these active nanoparticles with heteroatom-doped graphene-like nanomaterials can significantly improve OER and ORR catalytic activity.Metal organic framework?MOFs?constructed from transition metals?Fe,Co,Ni?are ideal precursors for the preparation of carbon nanocomposites.Until now,various MOFs have been used as self-sacrificing templates or precursors to prepare functional MOF derivatives.Despite amounts of encouraging results have been obtained from these studies,some limitations such as poor catalytic activity and complex preparation procedures are still remained.In this work,we used Co-MOF and Co/Ni-MOF-4:1,Co/Ni-MOF-8:1,Co/Ni-MOF-10:1,Co/Ni-MOF-15:1;as precursor,which constructed by transition metal Co and different proportions of Co/Ni bimetal respectively.Calcining them in the atmosphere of nitrogen by one step,successfully prepared bifunctional ORR/OER electrocatalysts.The effects of calcination temperature,metal doping ratio on the electro-catalytic performance of dual-function ORR/OER and the application of Zn-air battery was studied.The research are as follows:?1?Co-MOF were synthesized by hydrothermal reaction after dispersion and dissolution of terephthalic acid?H₂BDC?,4,4'-?sulfonylbis?4,1-phenylene??dipyridine?SPDP?and cobalt nitrate in a mixture solution of N,N'-dimethylformamide?DMF?and H₂O.By changing the metal center of the above MOF,the metal Ni and Co were introduced into the MOF in different proportions to obtain the Co/Ni-MOF with the homomorphic structure of the Co-MOF.The purity of the samples was verified by elemental analysis and ICP.?2?The obtained Co-MOF was calcined in the atmosphere of nitrogen at different temperatures to obtain N,O and S doped carbon encapsulated Co₉S₈ nanoparticle composites.The chemical composition and structure were characterized by XRD,XPS,Raman spectrum,Nitrogen adsorption,SEM and TEM.The electrocatalytic performance was tested by electrochemical workstation.The experimental results showed that the sample calcinated at 900?have good bifunctional ORR/OER electric catalytic activity,which was used as the positive electrode material of Zn-air battery,which showed extremely high open circuit voltage and good charging and discharging stability.?3?N,O and S-tridoped carbon encapsulated?Co_XNi_Y?₉S₈ nanocomposites were prepared by calcining Co/Ni-MOF with different Co/Ni ratio in nitrogen atmosphere at900?,respectively.Its structure and chemical composition were analyzed by different characterization methods,and its bifunctional ORR/OER electrocatalytic activity was tested by electrochemical workstation.The experimental results showed that the?Co_XNi_Y?₉S₈-8:1 greatly improved OER catalytic performance and ORR catalytic performance to some extent.The?Co_XNi_Y?₉S₈-8:1 was used as the positive electrode materials of Zn-air battery,which showed high open circuit voltage and good charging and discharging stability.