Preparation Of Iron-based Electrocatalysts And Their Applications In Water Splitting

Hydrogen,characterized by high energy density,has been recognized as one of ideal candidates to fossil fuels.The two half reactions of water splitting are hydrogen evolution reaction?HER?and oxygen evolution reaction?OER?,and catalysts with excellent catalytic properties are desirable to reduce the overpotential in the two half reactions.So far,Pt-based compounds and Ir-based compounds?or Ru?noble metal material have excellent electrocatalytic properties for HER and OER.However,their high cost and susceptibility to deactivation obstruct the widespread application of noble metal-based materials.Compared with noble metal-based materials,the compounds of non-noble transition metals having the advantages of low price and abundant reserves have been studied extensively.The transition metal includes Fe,Co,Ni,Mn and W,etc.elements.Iron is abundant in content,widely used,and has good electrical conductivity.In recent years,it has been widely used as a raw material for preparing catalysts by researchers.This thesis is devoted to the preparation of iron-based composite catalysts using hydrothermal and calcination methods,mainly to study the properties of HER,OER and water splitting.The main research contents are as follows:1?Preparation of nanomaterial Fe₃C/NF and study its OER catalytic property.The catalyst Fe₃C/NF was prepared via a one-step hydrothermal and annealing method.The Fe₃C/NF is nanosheet-like morphology,and the Fe₃C nanosheets perpendicular to Ni foam substrate can increase the specific surface area and the number of active sites,which is beneficial to improve the catalytic activity.The Fe₃C/NF requires overpotentials of 262?372?mV to achieve current densities?j?of 10?100?mA·cm^-2,the Tafel slope is 49 mV·dec^-1.The stability is excellent,and the catalytic performance is only reduced by 2.4%at 100 mA·cm^-2.2?Preparation of nanomaterial Fe₃C@Co₂C/NF and study its OER catalytic property.The Fe₃C@Co₂C/NF electrocatalyst were fabricated through two-step hydrothermal-calcination approach with unique wire-string-cube morphology directly grown on Ni foam,in which Co₂C nanowire stringing Fe₃C nanocube.Due to the synergistic effect of the Fe₃C nanocube and Co₂C nanowire,the Fe₃C@Co₂C/NF electrocatalyst can be thought to be efficient OER catalyst with an overpotential of 254?364?mV at a current density of 10?100?mA·cm^-2 in 1.0 M KOH,the Tafel slope is 65mV·dec^-1,and the catalytic performance is only reduced by 3.0%at 100 mA·cm^-2.3?Preparation of nanomaterial Fe-Co-Ni-S_x/NF and study its HER,OER and water splitting catalytic properties.The catalyst Fe-Co-Ni-S_x/NF was prepared by two-step hydrothermal method.The catalyst Fe-Co-Ni-S_x/NF is loosely porous morphology and uniformly distributed on the Ni foam substrate,this morphology is favorable for the increase of specific surface area and the number of active sites,which is beneficial to the improvement of HER?OER?catalytic performance.The catalyst Fe-Co-Ni-S_x/NF has excellent HER?OER?catalytic properties in 1.0 M KOH solution,the Fe-Co-Ni-S_x/NF catalyst as both anode and cathode for water splitting.The Fe-Co-Ni-S_x/NF requires a cell voltage of 1.70 V to afford the current density of 10 mA cm^-2.