Preparation And Study Of Ir Doping Non-Noble Metal Oxides Electrocatalysts For High-Performance Oxygen Evolution In Acid

Hydrogen is a promising clear energy for efficient energy production and storage due to the advantages of high energy density and zero-carbon emissions,with water splitting considered one of the most clean,environmentally friendly,and sustainable approaches to generate hydrogen.Because oxygen evolution reaction（OER）involves four-electron transfer,its reaction kinetic is sluggish,leading to a large reaction energy barrier.Therefore,it is crucial to develop high-efficient and stable OER electrocatalyst for acidic water splitting hydrogen production technology.The precious metal iridium（Ir）and its oxides are the start-of-the-art OER catalysts,but their large-scale application is limited by the high cost and low-abundance of Ir.In this thesis,a highly efficient and stable OER electrocatalyst for Ir doped transition metal oxides（TMOs）was prepared by means of doping Ir atoms to regulate the electronic structure and optimize the adsorption free energy of intermediates.The main contents of this thesis are summarized as follows:（1）In view of the low acidic catalytic activity and sertability of TMOs,the activity and stability of the catalysts are improved by constructing manganese dioxide（MnO₂）nanowire arrays and adjusting the electronic structures.The catalysts were prepared by in-situ growth of MnO₂ nanowire arrays on titanium foam using high temperature hydrothermal method.Then,Ir doped MnO₂ nanowires are prepared by a sol-flame annealing method.OER performance tests show that the optimized Ir_0.05-MnO₂ catalyst（Ir content was only 0.67 wt%）exhibits the best OER activity with an excellent mass activity of 1612.72 A·g^-1 and turnover frequency（TOF）of 4.14 s^-1 at an overpotential of 300 mV in 0.5 M H₂SO₄,and thus reaches 10,50,100 mA·cm^-2 at overpotentials of only 200 mV,243 mV and 314 mV,respectively.More importantly,Ir_0.05-MnO₂ can be stabilized at 10 mA·cm^-2 current density for 100 hours,and the potential change is negligible,indicating excellent electrochemical stability.XPS characterization results show that the formation of high-valence Ir single atoms significantly enhances the catalytic activity of the catalysts,and leads to poor structural stability.（2）Using Ir doped MnO₂ nanowires as template,polypyrrole was coated on the surface of the nanowire by chemical polymerization method,and then Mn elements in MnO₂ were removed by acid-leaching method.Ir-loaded carbon nitride catalysts（Ir-CN_x）were obtained by annealing at air atmosphere.OER performance tests show that the optimized Ir_0.1-CN_xcatalyst requires an overpotential of 205 mV to reaches 10m A·cm^-2.Meanwhile,Ir_0.1-CN_x can be stabilized at 10 mA·cm^-2 current density for 25hours,exhibiting excellent stability.XPS results show that heat treatment increased the contents of pyridine nitrogen in the catalyst,which are favorable for improving OER performance.（3）The activity and stability of cobaltous oxide（Co₃O₄）for acidic OER are improved by constructing Co₃O₄ nanowire arrays and then doping Ir single atom in Co₃O₄ nanowires to regulate the electronic structure.The Co₃O₄ nanowires arrays were prepared by in-situ growing Co₃O₄ nanowire arrays on titanium foam via high temperature hydrothermal and heat treatment methods.The Ir-doped Co₃O₄ nanowires were prepared by a sol-flame annealing method.The OER tests shows that the optimized Ir_0.1-Co₃O₄ catalyst（the content of Ir is 4.15 wt%）exhibited the best OER catalytic performance,and the TOF value of catalysts is 3.48 s^-1 and mass activity is1343.1 A·g^-1 at an overpotential of 300 mV in 0.5 M H₂SO₄.At 10,20 and 50 mA·cm^-2 current density,the overpotentials of the catalyst are 194 mV,223 mV and 282 mV,respectively.Ir_0.1-Co₃O₄ can be stabilized at the current density of 10 mA·cm^-2 for 100hours and the morphology of the nanowires remains well,which indicating excellent stability and stability.Using Pt/C as HER cathode catalyst and Ir_0.1-Co₃O₄ as OER anode catalyst,the overall water decomposition performance of the two-electrode electrolytic cell was tested in 0.5 M H₂SO₄ solution.At the current density of 10m A·cm^-2,the voltage of the cell was only 1.49 V and exhibited excellent stability for 30 h at 10 mA·cm^-2.Density functional theory（DFT）shows that the d band and p band central of Co₃O₄ and the Gibbs free energy of the reaction intermediates are regulated by doping Ir single atoms in Co₃O₄,which enhancing the electron transfer and improving the OER activity.The acidic OER activity and stability of transition metal oxides were significantly enhanced by doping Ir single atom to regulate the electronic structure,which provides a reference for the development of efficient and stable acid OER catalysts.