Fluoride Derived From Iron-based MOF For The Application Of Oxygen Evolution Reaction In Electrochemical Water Splitting

Hydrogen energy has high energy density,clean and environmentally-friendly which can meet the needs of sustainable development.Water electrolysis as an efficient hydrogen production technology consists of anodic oxygen evolution reaction（OER）and cathodic hydrogen evolution reaction（HER）.Oxygen evolution reaction has slower kinetics,which greatly limits the efficiency of water splitting.Therefore,it is very important to explore OER electrocatalysts with low cost and high efficiency.The derivatives of Metal-Organic Frameworks（MOFs）have large specific surface area,high porosity that has application value in oxygen evolution reaction.Fluoridation can modulate the electronic structure of catalysts and further expose more active sites.While fluoride itself has poor electrical conductivity,and the combination of porous conductive materials with fluoridation can effectively improve the catalytic activity of catalysts.Therefore,a series of iron-based MOF precursors were synthesized and then fluorinated in this paper.The structure-activity relationship between the structural composition and catalytic performance of the catalysts were systematically studied.The main research contents are as follows:1.Rod-like Fe MIL MOF was synthesized via hydrothermal method using fumaric acid as ligand,and then nickel was introduced through hydrothermal reaction to obtain nickel doped Fe MIL MOF.Nickel doped FeF₂ was further prepared using low-temperature fluorination strategy based on the as-prepared nickel doped Fe MIL MOF.The OER overpotential to reach the current density of 10 mA cm^-2 was 275 mV in 1M KOH solution,and the Tafel slope was 47 mV dec^-1.The results proved that nickel doping and fluorination cooperatively regulate the electronic structure of iron,thus improving the activity of oxygen evolution reaction.2.Rod-like Fe₂Ni MIL MOF was first prepared through solvothermal method using terephthalic acid as ligand,and further conducted through high-temperature carbonization and low-temperature fluoridation to get carbon-coated FeNi/FeF₂.The effects of carbonization temperature and fluorination on the structure e volution of nanocomposites were studied.XRD and TEM proved that the MOF precursor was partially fluorinated,forming a carbon-coated heterostructure with iron-nickel alloy as the core and iron fluoride as the shell.The FeNi/FeF₂ exhibited a very low overpotential to catalyst OER that only need 253 mV to offer a current density of 10 mA cm^-2 with Tafel slope of 52 mV dec^-1.3.Fe2Ni MIL@ZIF-8 dual MOF was obtained using the dual MOF strategy and Fe2Ni MIL MOF as template for growing ZIF-8.The morphology of MOF was adjusted through changing the ratio of zinc nitrate and 2-methylimidazole during the synthesis process.We finally obtained iron-nickel fluoride with nitrogen doped carbon nanotubes through further high-temperature carbonization and low-temperature fluoridation conduction on the dual MOF.XRD proved the formation of graphitic carbon,SEM and TEM demonstrated that carbon nanotubes were on the surface of nanorods.The OER overpotential to deliver the current density of 10 mA cm^-2 was only of 242 mV in KOH solution,and the Tafel slope was 51.58 mV dec^-1.