Structural Modulating Of Transition Metal Oxides For Rechargeable Zn-air Batteries

Energy conservation and emission reduction are the premise and guarantee for achieving the grand of“carbon emissions peak”and“carbon neutrality”.One of the most feasible strategies is to explore clean electrochemical energy conversion/storage systems at present.Rechargeable Zn-air batteries have attracted more and more attention since their low cost,zero pollution,and ideal theoretical energy density.The reversible electrochemical reactions（oxygen evolution/reduction reaction:OER/ORR）involved in the cathode of Zn-air cells are multiple electron transfer and slow kinetics processes,resulting in the larger overpotential and lower reaction rate,further seriously affects the actual energy efficiency and service life of Zn-air batteries.In order to improving the bifunctional electrocatalytic performances,it remains key and challenges to optimize the surface active sites and increase the intrinsic conductivity of electrocatalysts.In this paper,on the premise of establishing the“structure-activity”coupling,choosing the transition metal oxides（single metal oxide,spinel,perovskite）as the model electrocatalysts.Synergetic optimizing the bifunctional electrocatalytic activity and stability through micro-structure regulation,d-band center modulation,spin state transition,increasing stability,and in-situ magnetic field assisted strategies.Thus,the overall energy efficiency of Zn-air batteries is improved.The primary contents involved in this paper include:1.The porous Co-doped NiOnanoflowers（Co-NiONFs）was designed and investigated,revealing that the optimization mechanism of electrocatalytic activities by modulation the 2D structure and cation doping in Ni O.At the microscopic scale,the strong 2D hexagonal structure and the abundant nanopores inside the nanosheets cooperate to provide favorable channels and electrocatalytic active surface area for the adsorption and desorption of O₂.At the atomic scale,Co doping enhances the intrinsic conductivity of the pristine Ni O.The electrochemical measurements show that Co-NiONFs exhibits outstanding bifunctional electrocatalytic activities,including the ideal ORR half-wave potential（0.79 V vs.RHE）,and lower OER overpotential（300m V）to driven 10 m A cm^-2.Co-NiONFs based Zn-air battery shows high specific capacity(830 m Ah g_Zn^-1)and good charging/discharging cycling stability（110 h）.2.The Ce-doped Co₃O₄nanospheres was designed and investigated,revealing that the positive effect of Co d-band center on electrocatalytic activities of Co₃O₄.Theoretical calculations indicate that when Ce atoms substitute the octahedral Co sites,the gap between Co 3d-band center and O 2p-band center was reduced,resulting in the decreased potential for the potential-determining step（formation of OOH*）.Thus,achieving the enhanced electrocatalytic reaction kinetics.Besides,Ce doping results in the deepened valence band maximum of Co active sites,further increasing the stability of pure Co₃O₄.When applying in the electrocatalytic reaction,Ce-doped Co₃O₄shows excellent durability and OER/ORR multi-stability in the harst alkaline electrolyte,which are beneficial for the long-term charging/discharging cycling durability（290 h）and flexible nature of Zn-air battery.3.The Ce-doped LaCoO₃was designed and investigated,revealing that the optimization mechanism of electrocatalytic activities by regulation Co³⁺e_g-filling of LaCoO₃.Theoretical calculations indicate that Co³⁺sites of LaCoO₃transition from low spin state(t_2g⁶e_g⁰)to intermidiate spin state(t_2g⁵e_g¹)after Ce doping,giving rise to the optimized adsorption strength between active sites and oxygen-based intermediates,and facilating the electrocatalytic reaction efficiency.Furthermore,Ce dopant increases the conductivity and Co 3d-O 2p covalency of pristine LaCoO₃,thus achieving the promoted electrocatalytic OER/ORR activities.As a result,Ce-LaCoO₃based Zn-air battery exhibits higher specific capacity(783 m Ah g_Zn^-1),stable open-circuit voltage（1.43 V）,and outstanding charging/discharging durability（160h）.4.The Ca-doped LaCoO₃ was designed and investigated,revealing that the dominant role of alkaline-earth metal on the multi-stability and efficient electrocatalytic performances.theoretical calculations indicate that Ca doping optimizes Co³⁺spin state（e_g-filling is 1）and creats more oxygen vacancies,which are conductive to the adsorption/desorption of OH*,accelerating the charge transfer during electrocatalytic process.Moreover,Ca-doped LaCoO₃with oxygen vacancy remains excellent OER/ORR multi-staility after long-term ORR/OER cycling operation,without obvious decline for both half-wave potential（ORR）and overpotential（OER）.This unique performance is beneficail to the charging/discharging cycling stability of Zn-air battery（220 h）.5.The magnetically responsive La_1-xSr_xMnO₃（x=0.1 and 0.2）were designed investaged,revealing that the optimization mechanism of electrocatalytic activities by in-situ modulation the charge and order ordering induced by DC magnetic field.Theoretical calculations indicate that Sr-doped La MnO₃achieves increased inherent conductivity and reduced Mn d-band center,as well as lower energy barrier（0.46 V）after applying magnetic field.The electrochemical measurements show that when applying 1.0 T DC magnetic field,the OER overpotential of La_0.8Sr_0.2MnO₃effectively decreased by 120 m V at 10 m A cm^-2,simultaneously achieves a large negative magnetoresistance effect,MR%value is-16.36%。...