Study On Preparation And Overall Water Splitting Performance Of FeOOH-based Composite Catalysts

Water electrolysis is one of the effective technologies for hydrogen production,and the commercial precious metal catalysts for electrolyzing water are limited in large-scale application due to their high price and poor stability.Fe based catalysts have the advantages of low price and high catalytic potential for electrolyzing water,but the activity is limited by their special electronic structures and semiconductor properties.This thesis takes the typical Fe-based material FeOOH as the research object,and prepared different types of FeOOH-based composite electrocatalysts.The electrocatalytic performance and electrocatalytic mechanism of FeOOH-based composite catalysts were investigated by surface metal vacancy regulation,interface electron transport regulation,and heterogeneous interface synergy regulation.Firstly,FeOOH catalysts with Fe vacancy defects（D-FeOOH for short）were prepared by Al doping and combining with electrochemical etching of Fe_1-xAl_xOOH,and the effects of different amounts of Fe vacancy defects on electrocatalytic performance were investigated.The results suggest that the Fe vacancy defects improve the charge transfer capability and regulate the inherent electronic structure.The decrease of the overall valence state of Fe and the increase of O atoms with dangling bonds near the defects are the reasons for the improvement of intrinsic electrocatalytic activity.The overpotential of oxygen evolution reaction（OER）and hydrogen evolution reaction（HER）of D_10%-FeOOH at 10m A/cm² is 314 m V and 350 m V,respectively.Secondly,FeOOH was combined with nitrogen doped reduced graphene oxide（N-rGO）,and multifunctional electrocatalytic activities of OER,HER and oxygen reduction reaction（ORR）were improved.In terms of OER and HER,the overpotential at10 m A/cm² is 306 m V and 278 m V,respectively.For the ORR,the half-wave potential of FeOOH/N-rGO composite catalyst is about 730 m V.The energy spectra disclose that there is an electronic interaction between Fe in FeOOH and Pyrrolic N in N-rGO substrate,which leads to the enhancement of interface charge transfer capability and catalytic performance.Finally,FeOOH/Ni₃S₂ heterogeneous composite catalysts with three-dimensional（3D）nanostructure were synthesized by a two-step method,and the heterogeneous interface synergistic effects on the performance of bifunctional catalytic reaction were explored.The composite catalyst has extremely low OER and HER overpotentials of 185 m V and 106 m V at 10 m A/cm²,respectively.The large reduction of Tafel slope indicates that the reaction kinetics are significantly improved,and its overall water splitting potential at 10 m A/cm² is only 1.53 V,which is superior to the commercial precious metal catalysts combination Ru O₂|Pt/C（1.56 V）;and it also has excellent reaction stability.By analyzing the heterogeneous interface structure of the composite catalyst and combining with density functional theory（DFT）calculation,it is found that the interface synergistic effect between FeOOH and Ni₃S₂ significantly improves the adsorption of reactant OH^-and optimize the reaction energy barrier from*O to*OOH in the alkaline OER process;while in the HER process,the interface synergistic effect promotes the dissociation of the O-H bond in the reactant H₂O molecule and enhances the adsorption of hydrogen intermediates(H_ads),thereby enhancing the catalytic activity of electrolyzing water.