Preparation Of ZIF-67 Derived Cobalt-based Composite Nanofibers And Its Electrocatalytic Oxygen Evolution Performance

With the rapid growth of population,the depletion of fossil fuels and environmental pollution are the main concerns of the research.At present,both foreign and domestic,are actively advocating the use of green and sustainable energy.Hydrogen produced by electrolysis of water is a clean and environmentally friendly fuel that is an ideal alternative to fossil fuels.Water electrolysis can be divided into hydrogen evolution reaction（HER）and oxygen evolution reaction（OER）.OER is one of the key reactions in solar water decomposition,rechargeable metal-air battery,renewable fuel cell,water electrolysis for hydrogen production and other technologies.However,the slow kinetic process restricts the efficiency of the reaction and greatly hinders the improvement of the overall performance of the system.Noble metal catalysts have good catalytic activity for OER,but they cannot be widely used due to high cost of noble metal elements and small natural reserves.Therefore,researchers must develop efficient,low-cost and sustainable alternatives.Designing novel multiple composite material with hierarchical structure has been demonstrated as an effective method to improve the electrochemical properties of electrocatalysts due to the synergistic effects and structural advantages between the ingredients.Here,we designed and synthesized two kinds of composite nanomaterials and studied their electrochemical oxygen evolution properties.（1）First,the polyacrylonitrile（PAN）/2-methylimidazole（C₄H₆N₂）nanofibers were prepared by the electrospinning method.Then,PAN/C₄H₆N₂was chemically soaked to yield the tubular PAN/ZIF-67 nanofibers.Finally,it was annealed in Ar/H₂and air at high temperature to obtain carbon nanotube（CNT）/Co₃O₄nanofibers.The hollow tubular structure of CNT/Co₃O₄nanofibers can increase the active surface area and expose more active sites.Because of its unique structure and composition advantages,the OER performance of CNT/Co₃O₄nanofibers has been significantly improved.When the current density is 10 m A cm^-2,the overpotential of CNT/Co₃O₄nanofibers is only 340 m V,and the Tafel slope is 71 m V dec^-1.Remarkably,these CNT/Co₃O₄can also display excellent long-term stability for more than 48 h electrochemical test in an alkaline medium.This study shows that the material with hollow tubular structure has excellent OER properties.（2）We report highly active electrocatalysts for oxygen evolution reaction（OER）comprising Co S₂nanoparticles embedded in CNT-grafted carbon nanofibers（CNF/Co S₂-CNT）obtained by the pyrolysis of cobalt metal–organic framework（ZIF-67）in a reductive H₂atmosphere and subsequent adjustable sulfuration process.The main advantages of this hierarchical structure are as follows:First,the catalyst is embedded in situ in carbon nanotubes to achieve efficient electron transport.Secondly,the coating effect of carbon nanotubes will inhibit catalyst agglomeration during the reaction.Finally,carbon fiber with three-dimensional cross-linked non-woven fabric structure can effectively anchor carbon nanotubes to avoid agglomeration caused by adsorption.The optimized CNF/Co S₂-CNT have an enlarged electrolyte-accessible surface,abundant mass diffusion pathways,and high structural integrity,which afford the current density of 10 m A cm^-2at a low overpotential of 303 m V for OER in 1.0 M KOH solution.In short,this research demonstrating that CNF/Co S₂-CNT hierarchical structure could be a potential electroactive material in advanced electrocatalysts systems.