Study On The Controlled Synthesis Of Nickel-iron-based Materials And Its Electrocatalytic Water Splitting Performance

Due to the growing demand for energy and attention to environmental protection,hydrogen（H₂）is considered to be one of the sustainable and cleanest energy sources.The electrochemical water splitting method is an environmentally friendly method to provide affordable H₂.The water splitting process includes two parts:hydrogen evolution reaction（HER）and oxygen evolution reaction（OER）.The development of high-efficiency and low-cost catalysts to reduce the electrical energy consumption in the process of water splitting is crucial to the industrialization of hydrogen production from water splitting.Currently,the transition metal Ni Fe-based bifunctional water electrolysis catalyst has been widely studied.Compared with industrial catalysts,the stability and high activity catalysts need to be improved.In this paper,the performance and structure of Ni Fe-based catalysts are optimized by doping with heteroatoms such as sulfur and phosphorus.The specific content is listed as follows:（1）Based on the widespread report that Mo S₂is widely used in hydrogen evolution reactions and Ni Fe S has high oxygen evolution activity,the Fe-Ni S₂/Mo S₂ composite material is synthesized in-situ by a two-step method of formamide solvothermal and high-temperature gas-phase sulfidation.By adjusting the concentration of Ni Fe,the influence of the strong interaction between metal sulfide and molybdenum disulfide on the structure and properties of composite materials was explored.The study found that when a small amount of Ni Fe is added,the metal Ni Fe is dispersed in the material at the atomic level,and the HER performance of the Ni Fe NC-doped Mo S₂ composite material is better than that of pure Mo S₂.With the increase of Ni Fe,the binding energy of Ni is stronger than that of Fe and sulfur,and Ni S₂ is formed.The strong interaction between metal sulfide and molybdenum disulfide,which causes the distortion of the Mo S₂ structure and reconfigures the electronic structure around both Ni and Fe.The Fe-Ni S₂/Mo S₂-12 catalyst shows excellent water splitting catalytic activity and durability.（2）When the powder electrocatalyst is used as an electrode material,there are some disadvantages.Such as,agglomeration of nanoparticles,large resistance of the binder and complicated coating procedure.In order to overcome these shortcomings,Ni foam as the support,a self-supporting nickel-iron sulfide composite electrode material Ni Fe S/NF was synthesized through a two-step process of formamide solvothermal and high-temperature gas-phase vulcanization.Studies have shown that a step-like active layer with a high rough surface is grown in situ on the foamed nickel substrate,which provides a large specific surface area,exposes more active sites,and promotes the rapid departure of bubbles.The seamless contact between the catalyst layer and the foamed nickel substrate realizes rapid charge transfer,and can also prevent the catalyst from falling off.The composite material is superior to most reported alkaline water electrolysis catalysts,and only 1.44 V voltage is required to achieve a current density of 10 m A·cm^-2.（3）Alloying adjusts the electrons on the surface and near-surface atoms of the electrocatalyst,thus optimizing the adsorption/desorption strength of the adsorbate on the catalyst surface and improving the electrochemical performance.Based on this principle,Ni Fe Mo₃-O was synthesized by formamide solvothermal and air roasting,and Fe Ni₃ was synthesized by gas phase phosphating.The research results show that the oxygen interface provided by the Ni Fe Mo₃-O intermediate stabilizes transition metals.After Na H₂PO₂treatment,Mo O₃ is reduced,and Ni Fe two metals are bonded to form a Ni Fe alloy.In this paper,Ni Fe alloying,Ni²⁺is converted to Ni³⁺,and the high oxidation state of Ni³⁺is conducive to the formation of the intermediate product Ni OOH and improves the OER activity.It can reach 10 m A·cm^-2 at a low voltage of 1.5 V.