Study On Transition Metal Nanomaterials And Their Electrocatalytic Performance

Non-precious metals such as iron,cobalt,nickel,zinc and their sulfides,nitrides,phosphides etc.,as new electrocatalyst materials,have the characteristics of low cost,high abundance,high efficiency,good environmental compatibility,etc.,making them widely used electrocatalytic hydrogen evolution,oxygen evolution,oxygen reduction and other fields.The low surface area of iron sulfide,the lack of active sites and further surface modifications make it rarely exhibit excellent electrocatalytic performance.The Co:FeS₂/CoS₂ heterostructure nanoflowers and heterostructure nanowires,and Co:ZnS/CoS₂ heterostructure nanowires have the large specific surface area and rich heterostructure interface,making them more excellent electrocatalytic performance.Therefore,the preparation of Co:FeS₂/CoS₂ heterostructure nanoflowers,nanowires and Co:ZnS/CoS₂ nanowires provide a promising method for replacing electrocatalysts based on precious metals in water decomposition.This paper mainly takes Co:FeS₂/CoS₂ heterostructure nanoflowers,nanowires and Co:ZnS/CoS₂ nanowire materials synthesized by hydrothermal method as the main research objects.The X-ray diffraction?XRD?,Raman spectroscopy,scanning electron microscope?SEM?,transmission electron microscope?TEM?,X-ray photoelectron spectroscopy?XPS?and other characterization methods were used to characterize the microscopic morphology and structure.Subsequently,the electrocatalytic performances of these materials were further studied by an electrochemical workstation?Chen Hua 760?.The detailed research contents are as follows:First,the hydrothermal synthesis method was used to prepare Co:FeS₂/CoS₂ heterostructure nanoflowers with size of 3-10 microns,benefiting from its unique three-dimensional hierarchical nanostructure and the heterostructure formed by FeS₂ and CoS₂ on the petals.The Co:FeS₂/CoS₂nanoflowers are endowed with excellent electrocatalytic hydrogen evolution and oxygen evolution performance.The overpotential of oxygen evolution of Co:FeS₂/CoS₂ in 1M KOH solution with a current density of 10 mA cm^-2 is 278 mV,And the overpotential of electrocatalytic hydrogen evolution in 0.5 MH₂SO₄ solution at a current density of 10 m A cm^-2 was 103 mV.After 1000cycles of cyclic voltammetry scanning,the overpotentials of hydrogen evolution and oxygen evolution increased by only 5mV and 3mV.The catalytic performance of Co:FeS₂/CoS₂ nanoflowers is better than most reported similar materials.Secondly,by improving the experimental method,the Co:FeS₂/CoS₂ nanowires were synthesized with diameter of 5?20 nm.Benefiting from the ultra-large specific surface area brought by its ultrafine one-dimensional nano-structures and the adjustment of the electrocatalytic barrier by the heterostructure between FeS₂ and CoS₂,which makes it have superior electrocatalytic hydrogen evolution performance.The electrocatalytic hydrogen evolution potential of Co:FeS₂/CoS₂nanowires in 0.5 MH₂SO₄ solution at a current density of 10 m A cm^-2 is 69 mV,and the tafel slope is only 46 mV dec^-1.After 1000 cycles of cyclic voltammetry,the potential has only increased by3mV.This ultrafine Co:FeS₂/CoS₂ nanowire is a promising alternative to platinum-based electrocatalysts in water decomposition.Finally,based on above two experiments,we used zincto replace the iron in Co:FeS₂/CoS₂ to prepare ultrafine Co:ZnS/CoS₂ nanowires with diameter of about 5 nm.It also benefits from the ultrafine one-dimensional nanostructure and the adjustment of the electrocatalytic barrier by the heterostructure between ZnS and CoS₂,so that Co:ZnS/CoS₂ nanowires only need to drive 10 m A cm^-2 current in 0.5 MH₂SO₄ solution.With 78 mV overpotential and a tafel slope of 56 mV dec^-1,the hydrogen evolution overpotential increased by only 5mV after 1000 cycles of cyclic voltammetry.This ultrafine Co:ZnS/CoS₂ heterostructure nanowire may be another effective substitute for noble metal electrocatalysts for water decomposition.Summary,Co:FeS₂/CoS₂ heterostructure nanoflowers,nanowires and Co:ZnS/CoS₂ nanowires all exhibit superior electrocatalytic performance,and both have relatively low overpotential,tafel slope and high stability.Our work shows that non-noble metal electrocatalysts can effectively improve the electrocatalytic performance of materials by increasing the specific surface area of nanomaterials and optimizing the electronic structure between different components of the materials.We believe that the development of new electrocatalysts with low cost,high abundance and high activity is of great significance.This is an important part of establishing an environment-friendly and sustainable energy strategy.