Studies Of The Oxygen Evolution Reaction By Ferrious Series Metal Catalyst

The extensive use of fossil resources in modern society has led to increasingly serious environmental problems,and the demand for clean energy is becoming highly urgent.Compared with traditional fossil resources(such as coal,oil and natural gas),hydrogen energy has attracted more and more attention due to its wide source,renewable and clean products.The renewable utilization of clean hydrogen energy can be realized through direct or indirect generation of electricity by solar energy and followed hydrogen production by electrolytic water.The electrochemical reaction in this process involves two half reactions of hydrogen evolution and oxygen evolution.Especially,the overpotential of the electrode process of oxygen evolution reaction is relatively too high,which seriously restricts the energy efficiency of hydrogen production from electrolytic water.It is of great academic value and significant application prospects to study a kind of high-efficiency electrocatalysts which can promote the oxygen evolution reaction and reduce the overpotential of electrodes.At present,in the research of electrocatalysts for oxygen evolution reaction,iron element(Fe,Co,Ni)compounts is one of the most widely reported electrodes.Compared with noble metal catalysts(such as RuO2 and IrO2)with good electrochemical performance,iron group-based metal materials are generally of wide source,low price and stable performance in alkaline solution.In addition,the conductivity of this series of materials is relatively good,so a larger current density can be obtained during the elelctrocvhemical reactions.In this paper,we focus on iron group-based electrode catalysts,using surfactants and chiral amino acid as structure-directing agents,to prepare iron group-based compounds with mesoporous or asymmetrical lamellar morphology.The morphology,modification effects and surface active species of iron group-based materials are studied in order to improve their electrocatalytic oxygen evolution performance.The paper is divided into two parts.The first part is to prepare mesoporous metal oxide materials by surfactant template method,which can adjust the distribution of surface active species by introducing mesoporous and defect,and promote the transfer of reactive substances,thereby improving the electrocatalytic performance.The second part is to use chiral amino acid(such as L-methionine,L-cysteine)to iron group oxide.The structure and function of the compound(represented by cobalt selenide salt)were modified,and the effect of chiral properties on the reaction was studied.The physicochemical and surface properties of the catalysts were characterized by X-ray diffraction(XRD),specific surface analysis(BET),scanning electron microscopy(SEM),X-ray photoelectron spectroscopy(XPS)and Raman.The electrochemical properties of the catalysts were characterized by cyclic voltammetry(CV),volt-ampere characteristic curve(LSV),stability curve(I-T).The main results are as follows:1.Mesoporous iron oxides(meso-NiO/Co3O4/Fe2O3)can be prepared by slow hydrolysis of urea under hydrothermal conditions using a large amount of anionic surfactant sodium dodecyl sulfate as structure-directing agent.The results of characterization confirmed the successful introduction of mesoporous oxide,and the concentration of O species and metal cationic defects on the surface of mesoporous oxide was significantly higher than that of metal oxide prepared by other methods.2.The electrochemical performance of mesoporous metal oxides in oxygen evolution reaction was tested.It was found that the electrocatalytic activity of mesoporous metal oxides was improved compared with other products prepared by other methods.For example,when the current density was 50 mA/cm2,the overpotential of meso-NiO/Co3O4/Fe2O3 was reduced by 84,41 and 60 mV compared with its bulk structure,respectively.Among them,meso-Co3O4 exhibited the best catalytic activity at the current density.The Overpotentials at 10 and 50 mA/cm2 were 313 and 390 mV,respectively.The reason for the improvement of the properties of mesoporous materials is that the regularity of pore channels and the high efficiency of mass transfer can improve the efficiency of electron transfer.On the other hand,the high valence metal cations and O-species content of mesoporous oxides are more abundant,the vacancy content of cations is more,and the reaction process of four-electron system is increased,thus promoting the oxygen precipitation reaction.3.The small nolecule Chiral amino acid(L-methionine/L-cysteime)as structure-directing agent can guide the formation of asymmetric flake-like Coo.gsSe materials.The obtained materials have asymmetric flake-like structure,and the defect sites of the modified samples increase.The L-methionine functionalized LmNs-Coo.ssSe catalyst has lower overpotential(214 mV vs 290 mV@10 mA/cm2),higher Tafel slope(107 mV·dec-1 vs 123 mV·dec-1)and higher active surface area(63.6 mF/cm2 vs 31.9 mF/cm2)than the unmodified Co0.85Se catalyst.Chiral amino acid-guided Co0.85Se asymmetric flake structure has more cationic defect sites,which may lead to the improvement of the electrocatalytic oxygen evolution performance of the modified material.