Preparation Of NiFe-based Nanoarray Catalysts And Study On Their Water Splitting Performance

With the continuous increase of the total energy consumption and the increasingly serious environmental pollution caused by industrial production,the development of new and alternative energy sources is urgent.As a secondary energy carrier,hydrogen energy is favored by the public for its non-toxic,abundant sources,and diverse forms of utilization.At present,although the cost of new energy continues to fall,its utilization process（such as wind power generation,etc.）will still cause some excess capacity.Therefore,considering the integration of hydrogen fuel production and power generation in the power plant,so that the excess power can be effectively stored and utilized,which is of great significance to energy conservation,emission reduction,and environmental prevention.However,hydrogen production by electrolysis of water is in a thermodynamically climbing process,especially the oxygen evolution reaction（OER）process involves a four-electron transfer reaction,which becomes the main rate-limiting step for electrolysis of water.Therefore,catalyst assistance is required to lower the reaction energy barrier.Nickel-iron materials have excellent electrocatalytic performance due to their low cost,unique physical and chemical properties,and are considered to be a close partner of water oxidation in recent years.However,common nickel-iron hydroxides/oxides and alloys have problems such as poor conductivity,less exposed active sites,and poor durability.Since porous nickel foam（NF）has a large specific surface area and electrical conductivity,growing the catalyst in situ can help to improve its mechanical strength and promote electron transport.In addition,the synergy with other metals and the adjustment of the morphology are also beneficial to enrich the active sites of the catalyst and increase the contact area with the electrolyte.Based on the above facts,this paper has prepared in-situ nickel-iron sulfides with different morphologies,which proves that morphology adjustment has a greater impact on the catalyst OER performance.Meanwhile,a multi-component,multi-layered NiFe/Co（OH）₂/NF composite nanosheet catalyst was constructed in situ to achieve the purpose of synergistic overall water splitting.The main research contents are as follows:（1）The nickel-iron precursor（NiFe/NF）was designed on NF by electrodeposition,and then NiFe₂O₄-Ni₃S₂ nanorods（NRs）catalyst was prepared by Fe³⁺impregnation and hydrothermal method.Compared with NiFe₂O₄-Ni₃S₂ nanosheets（NSs）obtained by direct hydrothermal of NiFe/NF,the former is exposed to more active sites due to the unique weed-like nanorod array structure,and shows significant water oxidation advantage in 1.0MKOH electrolyte.It only needs 189mV overpotential to drive the current density of 10mAcm^-2,and can maintain stability for more than 80 h at a constant current of 100mAcm^-2.In addition,the difference of morphology may be attributed to the change of element ratio and electron interaction between Ni and Fe by impregnation of Fe³⁺,which indicates that Fe³⁺has an indirect regulation effect on the morphology growth of the catalysts.（2）NiFe-200@Co（OH）₂ and NiFe-500@Co（OH）₂ nanosheet array（NSAs）catalysts for oxygen evolution and hydrogen evolution were prepared on nickel foam by hydrothermal re-electrodeposition method,respectively,and electrochemical tests were carried out in alkaline electrolyte.Thanks to the tight bonding of multilayer composites and the maintenance of the three-dimensional porous array structure,NiFe-200@Co（OH）₂ NSAs/NF only requires an overpotential of 204mV at 10mAcm^-2,and the corresponding Tafel slope is 44.3mV dec^-1.While the optimized NiFe-500@Co（OH）₂ NSAs/NF also shows great hydrogen evolution performance and only 98mV is required to drive the same current density due to the supporting effect of Co（OH）₂.The stability of the catalysts was confirmed by the fact that both of them maintained the morphology of nanosheets after 100h galvanostatic test.Therefore,NiFe@Co（OH）₂ NSAs/NF（500||200）is used to construct a two-electrode system for overall water decomposition test.When the current density reaches 10mAcm^-2,the system only needs a driving voltage of 1.58V,and maintains stability for more than 24h at 10 and 50mAcm^-2,respectively.