Synthesis Of Novel Ir/Ru-based Electrocatalysts And Study On Their Performance For Oxygen Evolution Reaction In Acidic Media

With the rapid economic development and people’s pursuit for a happy life,seeking renewable,pollution-free clean energy to replace fossil fuel energy is an important measure to achieve the goal of carbon neutrality,which is also very important for improving the ecological environment and achieving sustainable development goals.Hydrogen is a clean fuel with high energy density and zero carbon emissions.Hydrogen production from water electrolysis based on proton exchange membrane(PEM)technology is a sustainable way to obtain hydrogen for the advantages of high current density and high efficiency.However,the oxygen evolution reaction(OER)on the anode of water electrolysis by PEM,as a four-electron transfer reaction,seriously hinders the progress of the water electrolysis due to it’s slow reaction kinetics and high energy barrier.Additionally,the acidic corrosive environment poses great challenges to the stability of the catalysts,which limits the choice of catalysts components and the exploration of new catalysts.At present,the noble metal-based catalysts such as IrO2 and RuO2 are generally recognized as outstanding electrocatalysts for OER in acidic media.Among them,the stabilities of Ir-based catalysts in acid are generally better than that of Ru-based catalysts,and the activities of Ru-based catalysts are better than that of Ir-based catalysts.Ir and Ru both are noble metals with very low storage capacity,which are expensive.The high price of OER electrocatalysts limits the large scale applications of PEM.Therefore,it is significant to optimize the nanostructure and components of noble metal-based catalysts,enhance the mass activity of the catalysts,and reduce the usage amount of noble metals.In this paper,Ce was dopped into IrO2 to optimize its composition,and N-doped porous carbon material(NPC)was used as a carrier to prepare the Cex-IrO2@NPC catalysts.As a carrier derived from the pyrolysis of ZIF-8,NPC has high surface area,and the adsorption between N and the precursors makes Cex-IrO2 nanoparticles highly dispersed.The Cex-IrO2 nanoparticles display a size about 2 nm,fully exposing the active sites.The XPS results show that Ce exists in the catalyst in the form of Ce3+and Ce4+ oxidation states,optimizes the electronic structure of Ir.After adjusting the Ce doping amount,the representative Ceo.2-IrO2@NPC only need a low overpotential of 224 mV to achieve 10 mA cm-2.After stability test for 100 h in 0.5 M H2SO4,it shows extreme stability.In addition,the mass activity of Ir in Ce0.2-IrO2@NPC reached 6.99 mAμgIr-1,which was more than 11 times that before Ce doping at the 300 mV overpotential.Density functional theory(DFT)calculations show that doping Ce into IrO2 optimizes the binding energy between the active sites and the intermediates,and the energy barrier of rate-determining step(RDS)to OER decreases from 1.83 eV to 1.76 eV,promoting the OER reaction.The collaborative strategy of heteroatom doping regulation and NPC as catalysts support in this work may provide a new idea to explore more electrocatalysts with high activity and long-term stability under acidic conditions.Compared with Ir-based catalysts,Ru-based catalysts have better OER catalytic activity.Ru is one ideal replacement for Ir for its relatively high storage capacity and its cheaper price.In this paper,the Ru-based materials are further studied.The porous Zr-based metal-organic framework UIO-66 was used as a template,and Ru sources were introduced through ion replacement.After pyrolysis,Zr was uniformly doped into RuO2 and formed octahedral Zr-RuO2 carbon nanocomposite with a diameter of about 500 nm.The XPS shows that the Zr dopants modulate the electronic structure of Ru.The morphology and structure of Zr-RuO2 were adjusted by changing the pyrolysis temperature.The representative Zr-RuO2 catalyst only need a low overpotential of 187 mV to achieve 10 mA cm-2.After 50 hours of stability test,it maintains a stable state.Additionally,the mass activity of Zr-RuO2 reached 106.98 mA mgRu-1,which was more than 24 times that of commercial RuO2 at the overpotential of 200 mV,showing outstanding OER performance.The DFT results show that the introduction of Zr optimized the binding energy between the reaction intermediates and the Ru active sites,decreasing the energy barrier of the RDS of the OER reaction from 2.01 eV to 1.73 eV.This greatly promotes the OER performance.This thesis aims at developing high-efficiency noble metal-based OER catalysts in acidic media.In this study,we designed Ir and Ru-based acidic OER catalysts with high mass activity and long-term stability.We also studied the realationship between the electronic structure and morphology of the catalysts and OER performance.The strategy of combining component optimization and structural design used in this article also provides a new methode for the design of more high-performance electrocatalysts.