| With development of the society,the demand of global energy is increasing in the foreseeable future.Nowadays,the vast majority of energy sources are mainly from fossil fuels,such as coal,oil and natural gas.The non-renewable energy resource is running out,and the burning of fossil energy has damaged the ecological environment,so people are urgent to develop clean energy to meet energy demand.Hydrogen can be used as one of the clean and high-energy fuel to replace fossil energy,and electrolytic water technology is considered to be an effective method for hydrogen production.At present,commercial electrocatalysts are mainly based on noble metal oxides due to their high catalytic activity,but the weakness such as high price and poor stability further hinder the large-scale application of hydrogen production.Therefore,it is important to develop low cost,corrosion resistance and excellent catalytic activity electrocatalysts.Layered metal hydroxides(LDH)show great potential in electrocatalysis due to their adjustable structure and large interlayer spacing.It has been reported that the morphology and electronic structure of metal nickel are easy to be adjusted,and Ni-Fe LDHs can be prepared on the basis of nickel hydroxide(layered),which is considered as an excellent electrocatalyst because of its unique two-dimensional structure and high intrinsic activity.Most of the methods were used to prepare Ni-Fe LDHs including electrodeposition,co-precipitation and hydrothermal method,but it consumes high energy in the synthesis process with low-yield,even the composition of products is difficult to control.Therefore,it is of great significance to design a method of fabricating Ni-Fe LDHs material with controllable composition,morphology,adjustable electronic structure and high yield.However,Ni-Fe LDHs in alkaline solution still have problems such as slow ion transfer rate and poor stability,which seriously affect the electrocatalytic activity.At present,some progress has been made to enhance the catalytic activity and stability of Ni-Fe LDHs by adjusting the electronic structure,but still need new exploration.A numerous studies have shown that molybdate materials exhibit strong stability.It is theoretically feasible to synthesize NiMoO4/FeMoO4 nanocomposites with stable structure using Ni-Fe LDHs as template by a simple technique,which would further compensate for the weakness of poor stability.In this thesis,a continuous liquid-phase reaction method was designed to synthesize ultra-thin Ni-Fe LDHs nanosheets self-assembled clusters with large specific surface area under mild conditions.The morphology and composition of these clusters were tuned to explore the optimum synthesis condition of Ni-Fe based nanomaterials.In addition,NiMoO4/FeMoO4 nanocomposite with novel structure was prepared by using Ni-Fe LDHs as the template,which achieved the purpose of preparing anode catalyst with high catalytic activity and stability.The main work content and research results are as follows:(1)The self-assembled Ni-Fe LDHs nanosheets clusters with multiple pores were designed and synthesized by a controllable continuous liquid-phase reaction method.The multi-pore structure inhibited the agglomeration of the materials and simultaneously provided a larger active area.The special electronic structure and coupling effect of Ni-Fe LDHs enhanced the catalytic OER performance.In this case,the Ni(OH)2 three-dimensional multi-porosity ultra-thin nanosheets were synthesized by using liquid phase precipitation method,which utilized NaBH4 as precipitator and reducing agent in external environment at room temperature,and simultaneously added Fe into the precursor,the Ni-Fe LDHs nanoclusters were ultimately prepared.The experimental conditions were mild and easy to scale up production.Meanwhile,there was no additional energy consumption during the synthesis process,which is favor to popularize industrial production with great development potential.In addition,the effects of experimental conditions including solvent,reaction time and contents of Fe on the morphology,structure and electrocatalytic performance were investigated.The results show that the Ni-Fe LDHs prepared under the optimal conditions in aqueous solvent exhibits a typical nanocluster structure.This three-dimensional nanocluster inhibited the agglomeration of ultra-thin Ni-Fe LDHs nanosheets,which was favor to the diffusion of electrolyte,and exposed more active sites.In addition,Ni-Fe LDHs prepared at room temperature had abundant defects,which induced higher electron transmission performance of Ni-Fe LDHs.Therefore,the current density of Ni-Fe LDHs reached 10 mA cm-2,the overpotential was only 270 mV when immersed in 1 M KOH solution.(2)NiMoO4/FeMoO4 petal-like ultrathin nanosheets were synthesized using Ni-Fe LDHs as template by continuous liquid-phase reaction method.Molybdate was prepared through ion exchange at room temperature,which maintained the Ni-Fe LDHs' three-dimensional nanometer cluster morphology,which exposed abundant active sites in the materials.Moreover,molybdate ions stabilized the structure of the nanosheets,showing excellent stability in the catalytic process.In addition,We investigated the influence of the amount of(NH4)2MoO4 on the morphology and OER performance of the catalyst samples.In conclusion,the catalyst with the addition of 2.5 mmol ammonium molybdate shows the best morphology and oxygen evolution performance.The synergistic effect of the two components in NiMoO4/FeMoO4 composites optimizes the electronic structure of the materials and enhances the activity of a single active site.When the current density was 10 mA cm-2,the overpotential is only 245 mV.The problems of poor stability and slow reaction kinetics of Ni-Fe LDHs in work(1)have been solved,and also shows a certain application prospect. |
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