Synthesis Of Cobalt-based Porous Nanocages And Study Of Their Electrocatalytic Performance For Oxygen Evolution Reaction

Our world is currently facing environmental and energy challenges.Hydrogen is a kind of abundant and clean secondary energy and can effectively alleviate the above crisis.The hydrogen produced by the electrolysis of water using renewable energy has been called"green hydrogen"without carbon emissions during the hydrogen production process,which meets carbon peaking and carbon neutrality goals.The electrolysis of water includes the anodic oxygen evolution reaction（OER）and the cathodic hydrogen evolution reaction.The OER is sluggish and requires high overpotential,resulting in low energy conversion efficiency.Therefore,high-performance OER electrocatalysts are key in determining the energy conversion efficiency and cost of hydrogen production.Therefore,it is desirable to develop cheap and abundant transition metal-based OER electrocatalysts.Studies have found that the low-cost transition metal-based materials,like iron,cobalt,and nickel-based oxides have high electrocatalytic activity for OER and have great potential in alkaline electrolysis of water.However,the activity and durability of transition-metal oxides remain improved for large-scale applications.As the porous structure benefits mass transfer and exposure of active sites,Co layered double hydroxide（LDH）porous nanocages were used as the basis for subsequent structural optimization.Two high-performance Co-based porous nanocages catalysts were prepared by adjusting the synthesis route,catalyst components,and halogen anion dopings,stated specifically as follows.1.SO4^2-intercalated Fex Co OOH porous nanocages:Co LDH porous nanocages were obtained by alcoholysis of ZIF 67,and then Fe was introduced through cation adsorption and exchange strategies.Subsequently,sulfidation was used to transform Fe/Co LDH to Fe_0.07Co_0.93S₂ Finally,the SO₄^2-intercalated Fe_xCo OOH porous nanocages were generated via an electrochemical in-situ reconstruction under the OER condition and characterized by electrochemical and synchrotron X-ray absorption spectroscopy,spherical-aberration electron microscopy,in-situ Raman spectroscopy,and others.Electrochemical results showed that the SO4^2-intercalated Fex Co OOH porous nanocages have the best electrocatalytic OER among the studied catalysts,with an overpotential of only 240 m V at 10 m A/cm² and a Tafel slope of 77.9 m V dec^-1 and the stable operation for at least 400 hours.The structure-performance analysis showed that the SO4^2-intercalated Fex Co OOH porous nanocages have moderate oxygen binding energy,resulting in improved OER kinetics.In addition,the sulfidation method of the precatalyst was expanded to selenization and phosphating and their effect on OER performances has been studied.2.Halogen anions doped-Co LDH porous nanocages:Co LDH porous nanocages were obtained by alcoholysis of ZIF 67,and then doped with F,Cl,and Br halogen anions by an anion impregnation method.Electrochemical tests showed that the Br-Co LDH porous nanocages have the smallest overpotential of 300 m V at 10 m A/cm²among studied catalysts and a Tafel slope of 65 m V dec^-1.The structure-performance analysis showed that the halogen anions not only adjust the electronic structure and conductivity of Co LDH but also etch Co LDH nanocages to expose more active sites.These favorable factors together improve OER kinetics.