Preparation And Electrochemical Performance Of （Co,Ni）₂P And Terephthalate-based Metal-organic Frameworks For Hydrogen Evolution Reaction

With the rapid economic development,people’s demand for energy is increasing.Currently,the energy used is usually coal,oil,natural gas,etc.These energy sources are primary energy sources,and will cause serious environmental pollution and endanger human health in the process of use.Therefore,the development of clean and renewable energy is urgent.In recent years,the hydrogen evolution of electrolyzed water has attracted widespread attention due to its zero-emission and environmentally friendly advantages.At present,the hydrogen evolution catalysts commonly used in industry are usually Pt-based catalysts,but its small reserves and high cost make it difficult to realize large-scale commercial applications.Therefore,the development of abundant and inexpensive catalysts with excellent hydrogen evolution performance is the key at present.The three transitional metals iron,cobalt and nickel have high reserves,safety and non-toxicity,and have obvious hydrogen evolution performance,which is expected to replace Pt-based catalysts in the process of electrolysis of water for hydrogen evolution.At present,a series of transitional metal oxides,nitrides,and sulfides have been developed as hydrogen evolution catalysts.However,these electrode materials have high overpotentials and poor stability during the process of electrolysis of water for hydrogen evolution.P atom has high electronegativity,which can modulate the electron density around metal atoms and improve the hydrogen evolution performance of the catalyst.Therefore,transitional metal phosphides have been attracted people’s attention in recent years.Metal-organic frameworks have the advantages of large surface area and adjustable porous structure.However,this kind of material has less application in the field of electrocatalysis.Therefore,it is of research significance to explore the application of metal-organic framework materials in the process of hydrogen evolution in electrolysis of water.Based on the above considerations,in this paper,we synthesized a series of cobalt and nickel based phosphides and metal-organic frameworks of iron,cobalt and nickel via solvothermal technique,vapor deposition method,and electrodeposition method.At the same time,they have been characterized by powder X-ray diffraction（XRD）,scanning electron microscope（SEM）,transmission electron microscope（TEM）,selected area electron diffraction（SAED）,element energy spectra（EDS mappings）,X-ray photoelectron spectroscopy（XPS）,specific surface area（BET）analyses,et al.And their electrochemical performance have been investigated.The main contents are as follows:1)By controlling the amount of NH₄F（x mg）,a series of（Co,Ni）₂P-x F electrocatalysts with different compositions and morphologies were grown on a nickel foam（NF）substrate.Post-（Co,Ni）₂P-x F showed different HER electrocatalytic activity after 10 h of electrolysis.Among them,Post-（Co,Ni）₂P-10F shows excellent HER activity,and at a current density of-10 m A cm^-2 its overpotentialη₁₀is 85 m V,and Post-（Co,Ni）₂P-10F has good stability in 1.0 mol L^-1 KOH solution.This is related to the morphology of the material,and during the electrolysis process,the metal-phosphorus bond is partially converted to the metal-oxygen bond,density functional theory（DFT）calculations show that:compared to the P site（0.086 e V）,the O site（-0.022 e V）is more conducive to the adsorption of H.We found that the Post-（Co,Ni）₂P sample without NH₄F showed poor HER behavior,which indicates that the incorporation of fluorine can effectively improve the HER performance of transition metal phosphides.In addition,we also found that the incorporation of V can also improve the HER activity of transition metal phosphides.2)A series of metal-organic frameworks for terephthalic acid（TP）have been synthesized using a simple one-step electrodeposition method on the base of foam nickel（NF）,carbon cloth（CC）:M₃（OH）₂（H₂O）₂（tp）₂（M=Ni,Co or Fe）.Among them,Ni-MOF/NF showed an array of porous nanosheets and exhibited excellent catalytic activity for hydrogen evolution reaction（HER）.When the current density is-10 m A cm^-2,The electrode material has an overpotential(η₁₀)of 60 m V,and the material can work continuously for 50 h at a current density of-20 m A cm^-2.In addition,we also studied the formation mechanism of Ni-MOF nanosheet arrays on nickel foam.At the same time,we determined through density functional theory（DFT）calculations that the active site of Ni₃（OH）₂（H₂O）₂（tp）₂ during the hydrogen evolution reaction is the O site of the coordination-OH functional group(ΔG_H*=-0.40 e V).