Synthesis Of Iridium Baded Nanocomposite Catalysts For Oxygen Evolution And Their Electrocatalytic Performance

Hydrogen energy is high-quality energy that can replace fossil energy in the future,but at present,the source of hydrogen is still mainly obtained from fossil energy.Combining PEM water electrolysis technology with renewable energy is a green and sustainable way to produce hydrogen.However,PEM water electrolysis technology requires high activity and acid stability of anode OER catalyst.At present,Ir-based oxides are used as anode catalysts in the industry.The irreplaceability and high price of precious metal catalysts limit the large-scale application of PEM water electrolysis technology.Therefore,reducing the cost of catalysts has become the key to the development of PEM electrolyzed water technology.The cost of precious metal catalysts can be effectively reduced by increasing the intrinsic activity of the catalyst,reducing the content of noble metals in the catalysts,and enhancing the stability of the catalyst.Meanwhile,the basic research on the mechanism of the catalyst and the construction of the relationship between the structure,and performance of the catalyst are the top priorities for the development of low-cost,high-efficiency and stable precious metal catalysts.In this paper,Ir-based nanocomposite catalysts are synthesized by different methods as OER catalysts in acidic media,and the relationship between catalyst structure and performance is established through characterization and analysis,which provided a new way for the design of acidic OER catalysts.The main work is summarized as follows.Preparation of BaIrO_2.937/La₃Ir O₇ composite oxide electrocatalyst and the study of its performance in oxygen evolution reaction.A double mixed metal oxide composed of BaIrO_2.937 and La₃Ir O₇ is synthesized by a simple solid-state reaction,which can act as an electrocatalyst for OER in acidic electrolytes.The phase composition and crystal structure of the material are firstly determined by XRD.Then,the morphology and element distribution of the material are determined by SEM and TEM.It’s worth noting that the precipitation of Ba and La ions during the OER process leads to the surface reconstruction of the catalyst,and forming an Ir O_xsurface active layer with rich active sites,which are demonstrated by XPS,XANES and EXAFS spectra.More importantly,this surface reconstruction phenomenon makes the catalyst have excellent activity.In 0.1 M HCl O₄,a low overpotential of290 m V is required for BaIrO_2.937/La₃Ir O₇ to achieve the benchmark of 10 m A cm^-2,comparable to commercial Ir O₂.Meanwhile,BaIrO_2.937/La₃Ir O₇ has similar stability with commercial Ir O₂.Particularly,the mass activity of BaIrO_2.937/La₃Ir O₇ is about3.9 times higher than that of commercially available Ir O₂ at 1.63 V（vs.RHE）.Preparation of doped and supported Ir/Ba Ti O₃ electrocatalysts and the study of their oxygen evolution performance.Ir-doped Ba Ti O₃(Ba Ti_1-xIr_xO₃)and Ba Ti O₃supported Ir nanoparticles（Ir/Ba Ti O₃）catalysts are synthesized by one-step hydrothermal and distributed hydrothermal methods,respectively.The successful synthesis of the two catalysts is demonstrated by XRD spectra.The SEM and TEM showed that the microstructures of the two catalysts are beneficial to the mass transport on the catalyst surface and to expose more active sites.Both catalysts have excellent catalytic activity and stability,with the overpotentials of 262 and 250 m V at a current density of 10 m A cm^-2,respectively.In addition,they also deliver high electrochemical stability more than 20 and 45 hours,respectively.The content of Ir in the two catalysts is measured by ICP to be relatively small of 5.2 wt%and 4.4wt%,respectively,indicating their high intrinsic activity.At an overpotential of 300m V,the mass activities of the two catalysts were respectively 15 and 30 times that of commercial Ir O₂.Besides,the doping of Ir at the B site of perovskite Ba Ti O₃ and the interaction of Ir nanoparticles with Ba Ti O₃ are demonstrated by XPS analysis,which result in the redistribution of electrons around the Ir active site in Ba Ti_1-xIr_xO₃and Ir/Ba Ti O₃.The change of oxygen intermediate’s adsorption energy improves the intrinsic activity of the catalyst,and the redistribution of electronic structure suppresses the excessive oxidation of Ir during the electrochemical process,resulting in higher stability of the catalyst.