Study On The Construction And Electrocatalytic Performance Of Transition Metal Nickel-Based Catalyst

With the development of economy and increasement of population,the problems of environmental pollution and energy shortage have become increasingly serious.In order to alleviate these problems,it is urgent to find new energy sources to replace carbon-based energy sources.As one of the best substitutes for fossil fuels,H₂ has attracted the attention of researchers due to its high energy density and zero environmental pollution over the past few decades.Compared with other methods,electrochemical water decomposition has higher conversion efficiency,hydrogen production purity and commercial value,thus it is considered as the best way to produce hydrogen.The overall water splitting requires much higher potential to overcome the slow kinetics of hydrogen evolution（HER）and oxygen evolution（OER）processes.Therefore,it is necessary to find suitable catalysts to reduce the reaction overpotential of the cathode and anode to effectively accelerate the generation of hydrogen and oxygen.Up to now,noble metal materials have been studied as HER and OER catalysts due to their excellent electrochemical properties and appropriate reaction intermediate adsorption energy.However,the scarcity and high-cost of precious metal materials limit their wide application.Therefore,it is necessary to develop low-cost,resource-rich non-noble metal-based electrocatalysts.An ideal non-noble metal-based catalyst should have the advantages of simple synthesis,excellent performance and stability over a long period of catalytic work,and so on.In this paper,a series of nickel-based composite electrocatalytic materials with high catalytic activity and good stability were designed by doping,interface engineering,morphology control and other strategies based on non-precious metal nickel-based catalysts.The specific contents are summarized as follows:（1）Transition metal phosphides have been widely studied due to their generally good catalytic activity and electrical conductivity.In this work,Ni（OH）₂ is synthesized by in-situ etching of nickel foam substrate,and the CoNiP nanosheets are obtained by phosphating after the introduction of Co ions through ion exchange.The design of the self-supporting electrode could reduce the contact impedance of the material and substrate,and also the sheet morphology could increase the specific surface area of the material and exposes more catalytic active sites.Through DFT calculation,it can be seen that the introduction of Co and P ions could significantly reduce the reaction barrier and improve the electron transfer ability.In alkaline electrolytes,CoNiP nanosheets exhibit excellent HER and OER activity.The overpotential of HER at 10 mA·cm^-2 is 116 mV and the overpotential of OER at 50 mA·cm^-2 is 400 mV.In addition,the timing current test is carried out at room temperature and 80℃,showing long-term stability.（2）Iron hydroxide has the advantages of non-toxicity and high redox activity,especially,theγcrystal phase has attracted much attention because of its layered structure and flaky morphology.While the low conductivity ofγ-FeOOH and the strong interaction with OOH^-lead to poor performance in practical applications.In this work,γ-FeOOH nanosheet array is in situ grown on nickel foam substrate,and it coupled with Ni₃S₂ to construct heterogeneous interface.The self-supporting 3D hierarchicalγ-FeOOH/Ni₃S₂ heterostructure is successfully synthesized.The synergistic effect ofγ-FeOOH and Ni₃S₂ improved the intrinsic catalytic activity of the material.In addition,the heterogeneous interface could increase the catalytic active site and adjust the electronic structure of the surface.The 3D hierarchical structure also could increase the specific surface area and ensure the transmission of electrons and the timely release of gas.Electrochemical tests ofγ-FeOOH/Ni₃S₂ show that the overpotential of OER is279 mV at 50 mA·cm^-2,the overpotential of HER is 92 mV at 10 mA·cm^-2.The overall water splitting performance is 1.66 V at 10 mA·cm^-2.At the same time,it shows high stability for 120hours at a constant voltage.（3）Nickel-based hydroxides are promising electrocatalysts for unique electronic structure,low cost and simple preparation process.However,they usually exhibit poor electrocatalytic activity due to their low conductivity and insufficient active sites.In this work,Ni nanotubes are prepared using Zn O nanorods as template on flexible carbon cloth.Ni（OH）₂ is obtained by hydrothermal method,and Mo is doped into Ni（OH）₂ using hydrothermal method adding Mo source.Finally,the amorphous Fe_xNi_yOH nanosheet is deposited on Mo-Ni（OH）₂.Self-supporting Mo-Ni（OH）₂/Fe_xNi_yOH hollow layered nanotube is successfully prepared.The unique morphology expose the catalytic active sites to the maximum extent,and the doping of Mo can improve the conductivity of Ni（OH）₂ nanotubes.Finally,crystalline Mo-Ni（OH）₂ is coupled with amorphous Fe_xNi_yOH,forming heterogeneous interface that optimizes the electronic structure and enhance the conductivity of the material.Electrochemical tests of Mo-Ni（OH）₂/Fe_xNi_yOH show that the overpotential at 10 mA·cm^-2 of OER and HER is 229 mV and 57 mV,respectively.The overall water splitting performance is 1.54 V at 10 mA·cm^-2.In addition,it also maintains high stability for a long time under constant voltage.