High-efficiency Non-noble Metal Catalysts For Zinc Air Batteries

Zinc-air battery has the advantages of low cost,non-toxicity,strong safety,environmental protection and high energy density.It is an ideal candidate for the next generation of energy storage equipment and has received extensive attention.However,the slow oxygen reduction reaction/oxygen evolution reaction（ORR/OER）kinetics on the air cathode is one of the main obstacles that limit the practical application of zinc-air batteries.The development of high-efficiency,stable and inexpensive electrocatalysts is the key to solving these problems.Therefore,this thesis uses transition metals as the metal center to coordinate and bond with the ligands to prepare a series of metal complex precursors,and then prepare high-efficiency zinc-air battery catalysts through high-temperature annealing.The specific work is as follows:Morphology engineering research on nitrogen-doped porous carbon coated Cobalt-based catalyst.4,4’-bipyridine（bpy）and sodium oxalate（ox）are selected as ligands to coordinate with transition metal cobalt,and the growth rate of the material is controlled by changing the addition amount of surfactant sodium citrate,and 4 kinds of materials are prepared Co（ox）（bpy）-x with different morphologies of cobalt-based complexes.After high temperature annealing,Co@NC-x electrocatalysts with different morphologies were obtained.Cobalt metal has good ORR and OER catalytic activity,and the high nitrogen content in the material promotes the excellent dual-functional catalytic performance of Co@NC-x.Electrochemical tests show that the morphology of the catalyst significantly affects the exposure of its effective active sites and the medium transport during the catalytic reaction,which in turn affects the catalytic performance of the catalyst,providing ideas for the preparation of high-performance bifunctional electrocatalysts.Research on preparation and performance of single-atom ORR electrocatalysts.Through the rapid reaction of Fe Cl₃·6H₂O with 4,4’-bipyridine（BPY）at room temperature,a small-sized iron-based complex（Fe-BPY）is obtained.After high temperature annealing and pickling,the Fe-SAs@NC-800 iron single-atom catalyst with ultra-high ORR catalytic activity was obtained.By reducing the size of the metal and creating more metal sites,the utilization of metal atoms can be effectively improved.At the same time,the quantum size effect of the single-atom catalyst and the interaction between the metal atom and the carbon substrate can further improve the catalytic performance of the catalyst.In addition,4,4’-bipyridine is used as a ligand,and a large amount of N element in the ligand is introduced into the material,which can further enhance its ORR activity.The ORR half-wave potential of Fe-SAs@NC-800 is 0.90 V,far exceeding Pt/C（0.85 V）.Therefore,Fe-SAs@NC-800 has excellent discharge performance and shows high catalytic activity in both liquid and flexible zinc-air batteries.This synthesis method can also be used to prepare a nickel-based/cobalt-based single-atom catalysts（Ni-SAs@NC/Co-SAs@NC）,which also have good ORR catalytic activity.