Design Of Transition Metal-based Catalysts And Its Interface Optimization For Air Cathodes In Zinc-air Batteries

Traditional fossil energy sources are facing difficulties such as insufficient natural reserves,low conversion efficiency and toxic byproducts,so the search for new energy sources with sufficient reserves,high conversion efficiency and environmental protection has become a hot topic.Zinc-air batteries have received much attention due to their high theoretical energy density,abundant and inexpensive raw materials,safety,and stability.However,there exist some problems in the practical applications such as sluggish cathodic oxygen reduction reaction（ORR）kinetics and air electrode polarisation.Therefore,this thesis focuses on two research directions.To increase the number of active sites and enhance the mass transfer efficiency,ORR catalysts was designed.Firstly,the solution mixture of Prussian blue analogues K₃[Fe（CN）₆]and Zn Cl₂ was selected for the one-step synthesis of cubic iron nanoparticles,where K₃[Fe（CN）₆]was used as the iron source and Zn Cl₂ dispersed the iron at the atomic level.Next,PANI was used for the nitrogen doping and morphological construction through high temperature pyrolysis.Then the three-dimensional conductive network-like FeZn NPs@3D-CN-10 were prepared with a broad specific surface area(148.32 m² g^-1)and a richly layered mesoporous structure.The FeZn NPs@3D-CN-10 exhibited good catalytic activity and cycling stability:a half-wave potential of 0.81 V and an ultimate diffusion current density of 6.20 m A cm^-2 in a linear voltammetric scan test at 1600 rpm.Secondly,to prepare high-performance ORR catalysts with a shortened catalyst preparation cycle,a three-dimensional conductive network was constructed by nitrogen and phosphorus doped carbon nanotubes using triphenylphosphine and melamine,which facilitate to improve mass and charge transfer.The onset potential and half-wave potential of ZIF67@CNT samples were 0.95 V and0.81 V in the linear voltammetric scan test of 0.1 mol KOH solution at 1600 rpm,respectively,and the four-electron transfer number in 0.3 V-0.7 V was 3.6.To increase the surface area of the catalytic layer and decrease the resistance of oxygen transport,the graphene films were prepared by the coating method for the optimization of the interface.The crumpled and porous structure increased the specific surface area for the loading of catalyts,and the conductive matrix facilitate to increase the charge transfer of catalysts;secondly,by adjusting the ratio of catalyst ink and the volume of drops added to the catalytic layer,the problems of buried active sites and insufficient electrical conductivity were effectively alleviated,and the power density during discharge was increased;Finally,the hydrophobic treatment of the catalytic layer not only expands the interfacial area of the ORR reaction,but also effectively slows.The optimized air electrodes were assembled into a zinc-air cell with an open circuit voltage of1.378 V and a maximum power density of 178.50 m W cm^-2.