| Hydrogen energy,as a green and environmentally friendly energy,is considered to be an ideal substitute for fossil fuels.Electrocatalytic water splitting which is an efficient and green technology to obtain hydrogen energy,has important research significance.However,the oxygen evolution reaction（OER）as a half-reaction of water splitting exhibits slow kinetic process,thus limiting the industrial application of electrocatalytic water splitting.Therefore,it is crucial to design an efficient electrocatalyst to facilitate the proton coupling-four-electron transport process.Zeolitic imidazolate framework（ZIF-67）as a metal-organic framework（MOFs）,is assembled by metal centers（Co）and organic ligands（dimethylimidazole）,thus possessing the advantages like high stability,high porosity and adjustable composition.The preparation of transition metal/carbon composites by using MOFs as precursors can improve the specific surface area and electrical conductivity of catalysts,which receive extensive attention.Cobalt sulfide-based materials are promising OER electrocatalysts due to their unique structures and tunable electronic properties.However,it still suffers from low intrinsic activity,insufficient active sites,and unsatisfactory crystal structure.Based on this,in this paper,a series of ZIF-67-derived cobalt sulfide-based electrocatalysts were prepared by transition metal doping and morphology control.The effects of doped transition metal elements and geometry structure on the OER performance were systematically investigated.And the OER performance of ZIF-67-derived cobalt sulfide-based catalysts is improved as a result.The specific research is as follows:（1）By using ZIF-67 and ZIF-8 as templates,Fe-doped Co S2/nitrogen-doped carbon nanotube hollow polyhedral composites（Fe-Co S2/CNT CPs）were synthesized via epitaxial growth method.Through adsorption,pyrolysis and sulfurization treatment.ZIF-8 with Zn as the metal center can form a hollow polyhedron structure,and the volatilization of Zn can promote the formation of carbon nanotubes.The effects of Fe doping on the catalytic performance were analysed by systematic characterization tests.On the one hand,the introduction of Fe optimizes the electronic structure of Co S2,enriches the catalytic sites of Co S2,and enhances the degree of graphitization of the material.On the other hand,the formation of carbon nanotubes can further improve the specific surface area and electrical conductivity of the catalyst.Therefore,Fe-Co S2/CNT CPs can expose more active sites,which is beneficial to the OER process.（2）ZIF-67 derived Mo-doped Co S2 hollow spherical catalyst（Mo-Co S2/NC（H））was synthesized by using polystyrene microspheres as templates and introducing transition metal Mo.Compared with the original polyhedral morphology,the construction of the hollow spherical structure can expose more active sites.Experimental characterization combined with theoretical calculation confirm that the introduction of Mo optimizes the electronic structure of Co S2,accompanied with enhanced intrinsic catalytic activity.Mo-Co S2/NC（H）exhibits good electrocatalytic performance and good stability owing to the synergistic effect of geometric modification and electronic structure modulation.（3）Mn-doped Co9S8/nitrogen-doped porous carbon polyhedral composites（Mn-Co9S8/NC）were prepared by adsorption-pyrolysis-sulfidation treatment using ZIF-67 as the template.The introduction of Mn can optimize the electronic structure of Co,thus improving intrinsic activity,specific surface area and the degree of graphitization of the carbon framework.Hence,the electrocatalytic activity of the material is enhanced in return.Meanwhile,the formation of Co9S8 can further improve the electrical conductivity and catalytic activity of the material for superior OER performance... |
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