Design And Structure-activity Relationship Of Oxygen Evolution Reaction Electrocatalyst With High Performance

Since the 21st century,with the rapid increase of the demand for low-carbon emission,the green technology of hydrogen production has attracted the attention of governments all over the world.Electrolysis of water is the most promising technology for hydrogen production from renewable energy sunch as solar energy or wind energy.Oxygen evolution reaction(OER),as the anodic reaction of water electrolysis,suffers from slow reaction kinetics that needs highly efficient catalyst to lower overpotential.At present,the main commercial OER catalysts are the noble metals(IrO2 and RuO2).However,the high cost and scarcity of which hinder the widely used of water electrolysis technology.Therefore,it is vital to develop nonnoble metal catalysts with low cost,high efficiency and performance.On the other hand,proton exchange membrance(PEM)water electrolysis technology has the advantages of high current density,extremely short response time and rapid load change,making it the most promising green hydrogen production technology.However,PEM work in acidic medium,which makes noble metal almost the only choice.Therefore,reducing the utilization of noble metal or improving its mass activity and stability have become the main challenges one needs to solve.In this paper,perovskite oxides,hydroxides and noble metal Ir-based materials with high activity and stability were prepared by polyol synthesis,hydrothermal method,chemical vapor desposition(CVD)and in-situ electrochemical method,respectively.The relationship between the structure and performance of the catalysts was systematically studied,and the deactivation mechanism was studied as well.The specific contents are as follows:Part Ⅰ:a variety of pure perovskite oxide nanoparticles were prepared by polyol method.Compared with the traditional method,the as-prepared materials have smaller size,larger specific surface area and show higher OER activities.By combining their OER performance with the electronic structure,a close relationship between the eg orbital filling of the B-site cation and OER activity has been verified.When the eg orbital filling is closer to 1.2,the OER activity is higher.In addition,nitrogen-doped carbon nanotubes(NCNTs)supported on LaNiO3 nanoparticles was synthesized by in-situ CVD method.The introduction of conductive material accelerates the charge transfer rate between the LaNiO3 surface active sites and electrode,which endows the composite with an overpotential of 390 mV at the current density of 10 mA cm-2.This study guides the direction for the design of perovskite oxides with higher OER performance.Part Ⅱ:β-Ni(OH)2/NiOOH nanosheet composities with superlattice structure have been synthesized using Ni3(PO4)2(NPO)nanowires as precursors by in-situ electrochemical method.The materials show high OER activity and stability with an overpotential of 310 mV@10 mA cm-2 and a long-term stability of 110 h.It has been found that extremely small size is the crucial for the complete conversion of NPO and the formation of the superlattice structure.In addition,the high activity and stability of the composite material are closely related to its superlattice structure,that is,the superlattice structure enables the large amount of highly active NiOOH to exist stably and increases the oxidation potential of Ni on the material surface,thereby decreasing the corrosion rate during the OER.This work provides a valuable addition of study on nickel-based hydroxides as OER catalysts.Part Ⅲ:Ir@TiO2 with core-shell structure was synthesized by one-step polyol method.The monolayer of Ir coating was substantiated by the analysis of accurate loading from inductively coupled plasma mass spectrometer(ICP-MS)combined with morphology/size from TEM and the theoretical model of the most-dense arrangement of Ir nanoparticles on TiO2 surface.Ir@TiO2 shows high OER activity and stability in acidic media with a mass activity of 486 A g-1 at the potential of 1.5 V(vs RHE)and a long-term stability of 500 h.It has been found that its high activity is closely related to the size of Ir nanoparticles and the core-shell structure composed of the external amorphized Ir(OH)4 shell and the internal metallic Ir core.The average size of 1.5 nm ensures that a large amount of active sites are exposed,the existence of amorphous Ir(OH)4 shell greatly improves its extremely high intrinsic activity,and the metallic Ir core enhances the rate of charge transfer between the active sites and electrode.In addition,it is also proved that the dense amorphized Ir(OH)4 shell is the most important factor for the high stability of Ir@TiO2.