Controllable Preparation And Catalytic Performance Of Fe-NiSe₂

With the development of the society,the demandfor energyis graduallyincreasingas a basic factor for human survival.However,the fossil fuelsare limited and theycan cause environmental pollution.Therefore,the search for renewable alternatives forclean energy becomes extremely important.For humans,hydrogen fuel is a typical renewable clean energy source.The hydrogen production from electrolyzed water can effectively meet the growing demand because of the water resources are abundant.The product is single in the process of hydrogen production by electrolysis of water.Therefore,electrolysis of water to hydrogen has becomeoneofthe important ways for us to get clean energy.Andit has become the current focus to study catalysts for outstanding performance in electrolyzed water reactions.There are many restrictions on the application of electrolyzed water catalysts.The most important limitation iscost and the second one is that the kinetic process of the water-decomposed anode reaction is very low,whichreduces the overall hydrogen production efficiency of electrolyzed water.Nickel selenide electrocatalytic oxidation catalyst is a promising candidate material due to its low cost and outstanding electrocatalytic activity and stability.In this thesisthree nickel selenide nanostructures are synthesizedin different reaction solvents by wet chemical method:spherical,sea urchin and dendritic nanorods.The synthesized nano-dendritic surface exhibits superior electrocatalytic oxygen evolution?OER? performance over spherical nanoparticles and nanorods.The overpotentials at a current density of 10 mA·cm^-2 for the samples with dendritic nanorods,sea urchins and spherical structures are 300 mV,329 mV and 340 mV,respectively.Since the oxidation reaction of nano-dendritic nickel selenide in electrolyzed water has better catalytic performance and stability,further research is focused on nano-dendritic nickel selenides.The controlled morphologyof nanorods to nano-branches is achieved by adjusting the temperature.The control of structure and aspect ratio is realized by the control variable method?control of reaction time?.Then all samples are used for the electrolysis water test.In this series of experiments,the surface exposed crystal plane can be controlledby adjustingthe morphology and aspect ratio to realiz the tunable catalytic properties.The influence of the ratio of different exposed surfaces and different exposed surfaces on the catalytic properties are systematically studied and found that?200? plane of nickelselenide is the most efficient surface for electrolyzed water.Considering the similarity of properties of iron and nickel as the same group elements and the strong synergistic effect between Fe and Ni,the pure nickel selenide,pure iron selenide and iron-doped nickel selenide are studied,including electrochemical performance of these samples.Firstly,nano-dendritic nickel selenide samples are prepared,and the optimal preparation conditions of the materials are obtained.Secondly,FeSe₂ samples are prepared under the same conditions.After that,the produced NiSe₂ samples are doped with iron to prepare Fe-NiSe samples.Finally,the microstructure and catalytic properties of the three samples are compared and studied in this thesis.In this thesis,after comparing the electrocatalytic properties of nickel selenide produced by different variables,it isfound that the dendritic nanorods formed by reaction for two hours at 140? have best electrochemical performance when thetetrahydronaphthalene and oleylamine used as solvents.In the performance test,when the current density is 10 mA·cm^-2,the corresponding overpotential is 300 mV,which is smaller than the overpotential required by other samples.Fe-NiSe samples are prepared by doping different amounts of iron selenidein the FeSe₂ samples prepared under the same conditions.It is found that Fe-NiSe produced by the doped iron and nickel ratio of 2:5 had the best catalytic performance.At a current density of 10mA·cm^-2,the corresponding overpotential is 231 mV,which is 69 mV lower than that of a pure nickel selenide sample.Compared with other literature,such as Au-Ni?OH?₂?overpotential 300 mV?),the data of IrO₂?overpotential 300 mV?,the overpotential of Fe-NiSe in this thesis is better.As a result,our samples have good electrochemical properties.