Preparation, Performance Regulation And Application Of Doped Cobalt-based Transition Metal Nanocatalysts For Water Electrolysis

The ever-increasing energy dilemma and environmental issues caused by the excessive depletion of finite fossil fuels have driven researchers to seek clean,high-efficiency and sustainable new energy.Traditional precious metal catalysts have limited the commercialization of new energy technologies due to their high price and scarce reserves.Therefore,it is of significance to explore cost-effective and earth-abundant excellent non-noble metal electrocatalysts.Transition metal nanomaterials have attracted extensive attention because of their advantages such as large activity improvement space and environmental friendliness.This thesis focuses on cobalt-based nanomaterials,Anion/cation doping is served as a valid engineering strategy to optimize the electronic structure of electrocatalysts,improve the adsorption/desorption process of the catalytic intermediate species,and construct a fast charge and mass transfer channel,thus improving the activity and stability of the catalyst.The prepared model catalyst O-CoP nanorods/Fe0.15Co0.85-TA nanoflowers/Ni doped Co3S4 hollow nanospheres showed good electrocatalytic activity for water splitting.The research in this paper provides ideas for the design and synthesis of efficient,stable and clean catalysts.The main research contents are as follows:1.The Co(OH)2 nanorods were synthesized through a solvothermal method and used as precursors and templates for subsequent low temperature phosphating treatment.CoP nanorods with different amounts of O(O-CoP)were prepared by simply changing the phosphating time in the phosphating process.The prepared O-CoP nanorods have rough surface and a diameter of about 80 nm,rough one-dimensional nanorods facilitate the directional transfer of electrons.The appropriate O doping can efficiently regulate the electronic structure of the catalyst,expose more active sites,and increase the electrochemical active areas.Electrochemical test showed that the hydrogen evolution reaction(HER)overpotential of O-CoP nanorods is only 116 mV at the current density of 10 mA cm-2,Tafel slope is 59 mV dec-1.This work provides an effective way for the preparation of high activity,high stability and low cost electrocatalyst for HER.2.Tannic acid(TA)was used as the complexing agent and morphology regulator with abundant phenolic hydroxyl group(Ph-OH).Fe-doped Co based nanoflowers(FexCo(1-x)-TA)were synthesized by one-step hydrothermal method.The obtained Fe0.15Co0.85-TA sample appears the nanoflower structure with a diameter of about 200 nm which is assembled by the numerous nanosheets.These interconnected nanosheets could enlarge the specific surface area,expose more active sites and provide the highways for mass transfer.Fe doping optimizes the electronic structure of the catalytic active center and provides more O vacancies,which is conducive to charge transfer and catalytic intermediate adsorption/desorption process.Electrochemical test results show that the oxygen evolution reaction(OER)overpotential of the Fe0.15Co0.85-TA nanoflower is only 272 mV at the current density of 10 mA cm-2,and the Tafel slope is 53.9 mV dec-1,which is better than most metal coordination complexes catalysts reported at present.This is mainly attributed to the optimal composition and unique structural advantages of FexCo(1-x)-TA.3.Ni-doped Co3S4(NixCo3-xS4)hollow nanospheres were prepared by one-step solvothermal method using Ni doped cobalt glycerate(NixCo3-xG)nanospheres with different metal ratios as the template and precursor,and thioacetamide as the sulfur source.The prepared Ni doped NixCo3-xS4 hollow nanostructure has the clear internal cavity,abundant porous outer wall,larger surface area,more defects and abundant micropores,which is conducive to better mass transfer and improve electrocatalytic activity.The surface electronic structure of Co3S4 was changed by adjusting the content of metal Ni to improve the intrinsic activity of the catalyst.Thanks to the optimal Ni doping ratio and the structure advantage of the hollow nanospheres,the OER overpotential of the Ni0.9Co2.1S4 hollow nanospheres is only 298 mV at the current density of 10 mA cm-2,and the Tafel slope is 94 mV dec-1.