Controllable Construction Of Iron-based Sulfur (selenium) Nanocrystals And Their Electrocatalytic Properties

With the rapid development of human society,energy shortage and environmental pollution have gradually become the focus of attention.Hydrogen energy sources that producted by electrolyzing water and dye-sensitized solar cells that absorb solar energy into electricity are two effective ways to solve this problem.However,they all require a large amount of precious metal platinum（Pt）as the key catalyst.So looking for other substances as efficient catalysts to replace the platinum（Pt）has gradually become a hot spot for scientists all over the world.Transition metal semiconductor nanocrystals have drawn more and more attentions due to their advantages of small size,high specific surface area,excellent catalytic activity and controllability of morphology and stability.In this dissertation,iron-based materials were used as iron source,and organic materials were used as solvents and ligands.High-temperature pyrolysis method was used to synthesize iron-based sulfur（selenium）nanocrystals with different morphologies by controlling the reaction conditions,and they all have good electrocatalytic activity.The specific research as follows:1)Using iron oleate as iron source and sulfur powder dissolved in oleylamine as sulfur source to synthesize iron sulfide nanocrystals,the nanocrystals with the amount ratio of iron to sulfur is 1:1 and 1:4 are obtained,and the ingredients are all Fe₃S₄.But the morphology of former is sheet and the latter is small particle.The morphology will further change with the extension of reaction time.The electrochemical tests showed that the Fe₃S₄ nanocrystals with particle morphology exhibit more superior catalytic activity because of more specific surface area and more edge positions,which will expose more active sites.2)Using iron oleate as metal source,sulfur powder was dissolved in oleylamine as sulfur source to synthesize iron sulfide nickel nanocrystals.The characterization results show that the(Fe_0.5Ni_0.5)S₂ single component is obtained.The TEM test showed that the obtained iron sulfide nickel nanocrystals were small particles with a diameter of about10 nm.When they were mixed with conductive carbon black at a mass fraction of 57%,they could achieve a photoelectric conversion efficiency of 6.71%when applied to the counter electrode of DSSCs.For the HER and OER reactions,the overpotentials when the current density reached 10 mA/cm² were 250 mV and 270 mV,respectively,shows excellent electrochemical catalytic performance.3)Using ferrous chloride as iron source and ferrous chloride as iron source,selenium powder dissolved in a mixed solution of oleylamine and dodecanethiol as selenium source,and obtain two different types reacted at different temperature of180°C and 220°C for 30 minutes.TEM shows that the former is sheet-shaped,while the latter is irregular morphology,indicating that the reaction needs further control.When two samples were used for the HER and OER reactions,the samples obtained at 180°C performed better.The overpotentials when the current density reached 10 mA/cm² were293 mV and 470 mV,respectively.This work shows that the morphology of the catalyst plays a very important role in the performance of the catalyst,and the excellent performance must correspond to the ordered and regular morphology.