The Synthesis And Electrocatalysis Properties Of Trace Tungsten Doped Iron-Nickel Layered Hydroxide Materials

The iron-nickel layered double hydroxide?Fe_xNi_y LDH?catalyst materials have been regarded as one of the most promising catalyst materials in oxygen evolution reaction?OER?,due to their excellent catalytic performance,low cost,simple synthesis method and unique layered structure.However,the large-scale commercial application of Fex Niy LDH was badly limited by the low charge transfer rate,weak binding of oxygenated intermediates and few edge/defective active sites exposure on the surface.In this thesis,a series of FexNiy LDHs have been successfully prepared and the properties of them have also been optimized by the introduction of trace tungsten ions and sodium borohydride chemical immersion.The specific research contents are as follows:?1?Tungsten ion doping is used to promote the interaction among W,Ni,Fe and enhance the intrinsic catalytic activity of Fe_xNi_y LDH.The W-doping Fe_xNi_y LDH nanosheet array was fabricated on the high-conductive carbon cloths or nickel foam substrate by simple hydrothermal synthesis and its electrocatalytic performance in alkaline media were also investigated detailedly.W_0.03Fe_0.2Ni?OH?₂ LDH materials,as the dual-function water-splitting catalyst,have obvious performance improvement than Fe_0.2Ni?OH?₂ LDH without tungsten doping,showing low overpotentials of 271 mV and 208 mV for oxygen and hydrogen evolution reaction at 25 mA cm^-22 current density,respectively.And the corresponding Tafel slopes are 61mV dec^-1 and 181 mV dec^-1.?2?Sodium borohydride immersion has an effect on improving the electrocatalytic activity of tungsten doped Fe_xNi_y LDH materials.The Fe_0.03W_0.03Ni-LDH^B@CC is prepared through soaking the tungsten doped Fe_xNi_y LDH precursor in an aqueous solution of sodium borohydride.In 1M KOH alkaline solution,205 mV overpotential is needed to afford the 10mA cm^-2 current density during the OER,and its corresponding Tafel slope is 60 mV dec^-1.Moreover,there is no obvious performance degradation after more than 50-hours i-t operation or 3000 times cyclic voltammetry for Fe_0.03W_0.03Ni-LDH^B@CC materials,which maintain great chemical reaction stability.?3?The mechanisms for OER performance improvement of Fe_0.03W_0.03Ni-LDH^B@CC materials by tungsten ion doping and sodium borohydride immersion treatment are discussed.The morphology,composition and structure of Fe_0.03W_0.03Ni-LDH^B@CC materials are characterized by means of Scanning Electron Microscope?SEM?,Transmission Electron Microscope?TEM?,X-ray diffraction?XRD?,X-ray photoelectron spectroscopy?XPS?,Raman spectra?Raman?and UV-visible absorption spectrum?UV-vis?.It is worth noting that trace W⁶⁺ions doping can modulate Ni?OH?₂ crystal structure and enhance block electrons interaction,which increase the intrinsic activity of each active site and effectively reduce the overpotential in electrolyzed water.Moreover,immersion treatment with NaBH4 solution could significantly increase the nanosheets surface roughness of Fe_0.03W_0.03Ni-LDH^B@CC,resulting in Ni?OH?2 crystallinity and its order decrease as well as exposing more oxygen/metal vacancies and edges/defective catalytic active sites.In addition,according to the calculation of Arrhenius formula,Fe_0.03W_0.03Ni-LDH^B@CC has the lowest surface activation energy of 23 kJ mol^-1compared with other samples.