Synthesis And Electrocatalytic Oxygen Evolution Of Nickel Based Transition Metal Sulfide Nanosheets

Nowadays,it is urgent to develop sustainable green energy because of the increasing energy crisis and environmental pollution.Hydrogen production by water electrolysis is widely concerned thanks to its advantages such as easy availability of raw materials,simple process and environmental friendliness.However,the inherent high reaction energy barrier and four-electron reaction mechanism of oxygen evolution reaction(OER)lead to large overpotential,slow reaction speed and high energy consumption,which greatly limit its practical application.Therefore,the exploration of economic and efficient OER electrocatalyst is the key to realize the wide application of water electrolysis.Transition metal sulfide,as a new type of non-noble metal catalyst,has been widely studied due to its unique physical and chemical properties and low cost.Among them,Ni₃S₂ is an OER electrocatalyst with great potential due to its inherent Ni-Ni metal network with electrical conductivity close to metal.In this paper,we designed and synthesized Ni₃S₂ with high specific surface area on nickel foam,and further improved the catalytic performance of OER by synthesizing Fe S/Ni₃S₂heterojunction.The main contents and conclusion of this thesis are as follows:1.Spherical Ni₃S₂ catalyst composed of nanosheets was synthesized on nickel foam by simple solvothermal method with a new sulfur source of1-Phenyl-1H-tetrazole-5-thiol(Hptt),and the electrochemical performance of Ni₃S₂/NF was tested in 1 M KOH.The results showed that the current density of 100m A cm^-2only required 286 m V overpotential,and the performance decreased by only2.5%during the 25 h stability test.By adjusting the p H value,we found that with the decrease of p H,the number of Ni₃S₂ pellets on the nickel foam showed a trend of first increasing and then decreasing,and the size and morphology of the pellets changed to some extent,and the optimal synthesis conditions of the system were obtained.2.On the basis of the first part,Fe S/Ni₃S₂heterojunction was synthesized by a simple one-step solvothermal method with metal Fe powder as iron source.Cross-linked amorphous sulfide nanosheets were formed on the nickel foam,and the heterojunction structure formed by Fe S and Ni₃S₂ nanocrystal particles was found on the nanosheets.The size of Ni₃S₂ nanoparticles is mostly below 5 nm,which is conducive to increasing the number of active sites.Due to the large number of surface defects provided by amorphous materials and the adjustment of the electronic structure of the heterojunction materials,Fe S/Ni₃S₂/NF has excellent OER electrocatalytic performance.The current density of 100 m A cm^-2 only needs 246 m V over potential,which is 40 m V lower than that of Ni₃S₂/NF.Meanwhile,Fe S/Ni₃S₂/NF has larger electrochemical active area and faster reaction kinetics.This chapter also discussed the effects of using different valence iron sources(Fe~0?Fe²⁺?Fe³⁺)on the morphology and electrochemical properties of Ni₃S₂/NF materials.The results showed that using Fe²⁺and Fe³⁺as iron sources led that Ni₃S₂/NF lose its original morphological advantages,and the reduction of electrochemical active area led to the decline of OER performance.Finally,the morphology and structure of the materials before and after the oxygen evolution reaction were characterized.Fe S and Ni₃S₂ were oxidized to Fe OOH and Ni OOH at high potential,and surface reconstruction took place,forming a smaller nanosheet array on the nickel foam.