The Exploration Of Ni/Fe-based Nanomaterials And Its Electrocatalytic Application In Water Splitting

Pt,Ir and Ru and their compounds are most excellent catalyst for water splitting.However,the rarity and high price limit their practical application in water splitting.It is necessary to develop low-cost,high-performance,stable and resource-rich catalysts for electrocatalytic water splitting.At present,transition metals are widely used in the preparation of electrolytic water catalysts because of their abundant resources and low cost.In this paper,the exploration of Ni/Fe-based nanomaterials and its electrocatalytic application in water splitting.The main contents are as follows:1.A variety of nickel sulfide nanophase materials were prepared by a simple hydrothermal synthesis method and set out to explore the influence of the S:Ni ratio in raw materials on the different nickel sulfides.With the characterizations of XRD,XPS,SEM,TEM and BET,the relevance between the molar ratio of S:Ni in raw materials and stoichiometric ratio,microscopic structure and OER performance are discussed.The specific surface area of all samples was tested.The results showed that the flower-like microstructure had a larger specific surface area than the bulk.It is believed that the formation mechanism of crystals in solution is related to crystal nucleation and crystal growth.According to the results of the experiments,the Ni₃S₄ derived from the 3:1 molar ratio of S:Ni in raw material exhibits the smallest overpotential(245 and 314 mV to achieve 10 and 20 mA cm^-2) and Tafel slope(81.5 mV dec^-1).When the OER curves are normalized by BET surface areas,the absolute high-low tendency isn't changed.Meanwhile,theoretical calculation of?G?H₂O*? indicate that the adsorption energy in Ni₃S₄ is much closer to the IrO₂ than other nickel sulfides,which are in good agreement with the OER performance of electrochemical measurements.2.A bimetallic NiFe₂O₄ was successfully synthesized via confined carburization in NiFe-MOF precursors and characterized by XRD,XPS,SEM,and TEM.The carburization process would be confined within the carbonaceous matrix derived from organic ligands of MOFs,which effectively prevents the agglomeration and coalescence of in situ-generated carbide nanocrystallite.After conducting an investigation of oxygen evolution reaction?OER?,the as-synthesized NiFe₂O₄ material exhibited good catalytic efficiency and high stability and durability in alkaline media.The NiFe₂O₄/NF?Nickel foam? requires overpotentials??? of 293 and 327 mV to achieve 10 and 20 mA cm^-2.As observed,the NiFe₂O₄/NF maintained its current density in 1.0 M KOH even after 20 h,suggesting the strong durability of this electrode for the OER in extremely alkaline solution.We further verified its electrochemically active specific surface area and found that its electrochemical specific surface area is superior to that of similar oxygen evolution electrocatalysts.This study not only expands the utilization rate of transition metals and MOFs precursors,but also enriches the types of oxygen evolution electrocatalysts.3.A Fe_1.89Mo_4.11O₇/MoO₂ material is prepared through the thermal treatment of a ferrimolybdate precursor.Benefiting from the modified electronic structure of Mo sites,the Fe_1.89Mo_4.11O₇/MoO₂ material showed highly efficient HER activity in both alkaline and acidic media.The XPS results also demonstrate that the structure of Mo electrons is changed by the introduction of Fe atoms.The Fe_1.89Mo_4.11O₇/MoO₂ material exhibits a Tafel slope of 79 mV dec^-1 and an exchange current density of 0.069 mA cm^-22 in 1.0 M KOH medium,as well as a Tafel slope of 47 mV dec^-1 and an exchange current density of 0.072 mA cm^-2 in0.5 M H₂SO₄ medium.Compared to original Mo-based oxides,Fe_1.89Mo_4.11O₇ with the regulated Mo electronic structure shows a more suitable Mo-H bond strength for the fast kinetics of the HER process.Density functional theory?DFT? calculations also indicate that the Mo-H bond strength in Fe_1.89Mo_4.11O₇ is similar to the Pt-H bond strength,resulting in the high kinetic activity of Mo-based HER electrocatalysts in alkaline and acidic media.