Preparation Of Transition Metal-based Electrocatalytic Composite Materials For Catalytic Reaction

The increasing consumption of fossil fuels and related environmental issues such as air pollution,global warming and rising sea levels have prompted people to explore and develop safe,clean and renewable energy systems.As a zero-carbon energy carrier,hydrogen with high energy density is considered a promising energy option,which can be directly obtained through electrochemically driven water splitting.In particular,the overall water splitting can be divided into two half reactions,including the hydrogen escape reaction（HER）at the cathode and the oxygen escape reaction（OER）at the anode.A larger voltage will inevitably increase the cost and hinder the efficiency of the overall water splitting reaction,thereby inhibiting the economic industrial production of hydrogen from water splitting.To date,a variety of electrocatalysts have been developed to enhance the kinetics of HER and OER,such as metal phosphides,metal oxides,and metal chalcogenides.In this category,metal materials have received great attention due to their relatively high activity and conductivity.However,mainly due to their unsatisfactory performance away from industry standards and high cost（especially for precious metals）,there is still a big gap in realizing the practical application of these metal electrocatalysts.Therefore,the development of no precious metal materials as an alternative electrocatalyst is of great significance for the realization of large-scale commercialization of water electrolysis.As a highly ordered coordination polymer,the Metal-Organic Frameworks（MOFs）as a self-assembled form of metal ions and organic linkers has homogeneous and heterogeneous catalytic properties.Due to its high surface area and concentration,its porous structure and diverse composition of well-defined metal centers make it a promising candidate for electrocatalysts.In particular,the high surface area facilitates exposure of more active sites,and the porous structure allows rapid mass transfer.However,conventional MOFs have drawbacks such as low conductivity,low stability,and slow reaction rate,which hinders the development of catalysts prepared in the fields of industrial production and catalysis.Transition metal sulfides and phosphides have become research hotspots in derivative materials due to their high stability and good conductivity.In order to solve the above problems,starting with transition metal-based MOFs materials,MOFs derivatives are obtained by morphology control,multidimensional formulation,phosphorylation,low temperature vulcanization,etc.,with adjustable morphology and size,and high catalytic performance.Prepare an efficient electrode catalyst.We also use scanning electron microscopy,transmission electron microscopy,X-ray diffraction,and other characterization methods to investigate the morphology and crystalline phase of the catalytic material.X-ray photoelectron spectroscopy was used to analyze the valence state of the catalytic elements,to investigate the internal relationship between catalyst performance and reaction morphology and structure,and to investigate possible reaction mechanisms.The specific work contents are as follows.（1）Venus flytrap-like NiCoP/NF 1D/2D bi-functional catalyst for overall water splittingUsing foamed nickel as the base support material,sheet-shaped nickel cobalt hydroxide is synthesized through hydrothermal,and 2-methylimidazole vapor is exposed to the furnace through the furnace.The introduction of organic ligands involves the in-situ conversion of flake nickel-cobalt hydroxide into Ni CoMOF with a unique bionic structure（that is,Venus flytrap-like,one-dimensional nanowires fixed on two-dimensional nanosheets）.And further make the precursor phosphorylated into NiCoP with similar and unique structure.One-dimensional nanowires provide a fast path with its unique structure,and the resistance of charge transfer is small,while 2D nanosheets enhance the mechanical stability of the catalyst.At the same time,the NiCoP formed after the phosphating reaction produces more catalytically active sites.Due to its unique bionic Venus flytrap-like structure and the synergistic effect of one-dimensional nanowires and two-dimensional nanosheets,the prepared material has the advantages of multiple dimensions,a large number of active sites and abundant electron transfer channels.NiCoP/NF shows good hydrogen and oxygen evolution performance in alkaline solution.When the current density is 10 m A cm^-2,the overpotentials for hydrogen evolution and oxygen evolution are 78 m V and 268 m V,respectively.When it is used as a bifunctional electrocatalyst for the overall water splitting,the electrode voltage only needs 1.60 V and maintains stability for up to 24 h.This work has opened up a new path for the rational design of high-efficiency and stable bifunctional electrocatalysts for water electrolysis.（2）Pod-like 2D/3D-CoS₂@CC composite for enhancing electrocatalytic hydrogen evolutionUsing conductive carbon cloth as a support material,two-dimensional CoMOF precursors were synthesized at room temperature,and 2-methylimidazole steam was introduced into the tube furnace to convert the two-dimensional CoMOF into pod-like two-dimensional/three-dimensional CoMOF in situ.With the help of low-temperature vulcanization treatment,MOFs precursors are converted into metal sulfides with similar structures.The prepared material has the advantages of multiple dimensions.The formed two-dimensional nanosheet and three-dimensional nanocube have a coupling structure.The synergistic effect between the two provides a large number of active sites for the catalytic reaction,while maintaining the overall structure of the catalyst.stability.It provides more channels for electron transmission,reduces the resistance of electron transmission,shows great structural advantages in the hydrogen production reaction of electrolyzed water,and significantly enhances the reaction performance.In the prepared materials,S-800 shows excellent HER properties.In alkaline medium,the optimized S-800 material only needs 131 m V and 245 m V overpotential when the current density is 10 m A cm^-2and 50 m A cm^-2,respectively.This work provides a new strategy for the development of high-performance MOFs-derived electrocatalysts.