Modulated Preparation Of Low-dimensional Iridium-based Nanomaterials And Electrolytic Properties For Water Electrolysis

Proton exchange membrane（PEM）water electrolysis is a sustainable energy conversion technology for hydrogen production.The development of PEM is in line with the current strategic need for clean energy reform and carbon reduction.However,the wide application of PEM electrolyzer is limited by two key challenges:low electrolysis efficiency of the electrolyzer and high cost of the key material.To reduce the energy consumption of hydrogen production and the cost of the key component of the electrolyzer,it is of great significance to develop electrode materials with low overpotentials,simple processes,and prospects for industrialized applications.In this thesis,a series of low-dimensional iridium-based nanomaterials composed of hollandite structures a the basic units were prepared,using strategies such as nanocrystal-support interactions and the design of special structures.Density Functional Theory（DFT）calculations and hydrogen/oxygen evolution（HER/OER）electrochemical performance tests were combined to validate its promising application in PEM water electrolysis.The main research of the thesis is as follows:1.To address the problems of low iridium atom utilization and the limitations of traditional supported methods,low iridium-type catalysts with Ir hyperdispersed supported on hollandite-typeα-Ce Mn O₂ nanorods（NRs）were prepared by ion-exchange method.Sinceα-Mn O₂,which possesses a typical one-dimensional nanorod structure,a higher proportion of oxygen vacancies,and a weaker Mn-O bond strength,is the most promising electrocatalyst support among（α,β,γ,andδ）of Mn O₂;The ordered chains of Ir atoms and randomly distributed Ir clusters in Ir Ce Mn O@Ir NRs prepared by ion-exchange lead to the breaking of structural symmetry,generating more oxygen vacancies and active sites.The adsorption of reactive oxygen intermediates is facilitated by the optimization of the electronic structure of Ir by Ce species to form an Ir（III）-rich surface,while Mn accelerates the electron supply to Ir atoms via O-bridge atoms.The electrochemical test results showed that itsη₁₀(overpotential@10 mAcm^-2)was 261 m V,its mass-normalized activity was 42.3 times higher than that of commercial Ir O₂,and it was stably operated as an anode catalyst for PEM electrolyzer for more than 70 h at a constant current density of 500 mAcm^-2.2.To address the problem of dissolution deactivation due to oxidative corrosion and crystal structure transformation faced by iridium-ruthenium alloy oxides,amorphous Na Ir Ru O_x nanosheets（NSs）enriched with oxygen vacancies have been synthesized by molten-salt pyrolysis as OER catalysts.Electrochemical tests show that ultrathin Na Ir Ru O_x NSs with a thickness of～1.2 nm haveη₁₀ as low as 214 m V.The mass-normalized activities were16.6 and 42.1 times higher compared to commercial Ru O₂ and Ir O₂,respectively.Membrane electrodes prepared by optimizing the slurry process were able to operate stably at a current density of 1 A cm^-2 for 350 h when Na Ir Ru O_x NSs was used as the anode catalyst in the PEM electrolyzer.The results of characterization tests demonstrate that the amorphous phase of Na Ir Ru O_x NSs generated a large number of coordination unsaturated sites and defects as active sites.As well as the intercalation of Na⁺introduces oxygen vacancies to optimize the binding energy of the oxygen intermediates on the catalyst surface,which reduces the reaction barrier of OER.It is also demonstrated that the presence of tunnel-like hollandite structure in amorphous Na Ir Ru O_x NSs plays a key role in enhancing the catalytic activity and stability of OER.3.Aiming at the interfacial rational design and controllable synthesis challenges involved in the bifunctional multicatalyst system for acidic water splitting,ultrathin KIr O_x/Pt heterojunction two-dimensional nanosheets with a thickness of～1.5 nm have been synthesized by optimizing the Pt/Ir ratio.The HER mass-normalized activity of KIr O_x/Pt-10 NSs(η₁₀=21 m V)could be increased by 2.9-fold compared to commercial Pt black,and its OER mass-normalized activity(η₁₀=274 m V)could be increased by 14.8-fold compared to commercial Ir O₂.Membrane electrodes prepared with KIr O_x/Pt-10 NSs as a bifunctional catalyst showed an electrolyzer voltage of only 1.79 V at 1 A cm^-2 and stable operation at constant current density for more than 200 h.DFT calculations and electrochemical experiments show that the KIr O_x/Pt NSs with heterogeneous structures can promote the rapid removal of H*from the Pt site by triggering the hydrogen overflow effect and enhancing the HER catalytic ability of the Pt site.Also through the electron synergistic effect,Pt can accelerate the electron supply to the surface Ir active site of hollandite type KIr O_x and optimize the adsorption energy of surface oxygen-containing intermediates to enhance the OER activity.