Self Supporting Oxygen Electrode Materials For Solid/liquid Zinc Air Batteries

The burning of fossil energy and greenhouse gas emissions have brought significant climate change risks.Zinc-air battery,a kind of representative renewable energy conversion system,has the advantages of high corrosion resistance,large capacity and high safety.However,the kinetics of oxygen reduction reaction at its air electrode was slow,which drastically limited the fast development of zinc-air battery.To solve this problem,non-noble metal electrocatalysts with high activity and stability for oxygen reduction became the research focus.Moreover,the solid state zinc-air battery composed of solid electrolyte and self supporting electrode materials is expected to be fast developed due to its practical application in powering micro electronic devices.In this thesis,two kinds of self supporting electrode materials with excellent oxygen reduction catalytic activity were designed.Both of them were used as electrodes for constructing both solid and liquid zinc-air batteries.The main research contents are as follows:(1)Polymer and metal organic framework materials(ZIF-67 and ZIF-8)were used to fabricate uniform nanofibers by electrospinning technology.After mild oxidation and high temperature heat treatment,metal cobalt and a small amount of metal zinc nanoparticles were uniformly wrapped in nitrogen doped carbon fibers,forming a carbon fiber membrane(Co@NCF)with certain mechanical strength and flexibility.Due to Co-N-C active site and unique three-dimensional network structure,Co@NCF showed a high electrocatalytic kinetics and efficiency,comparable with the state-of-the-art noble metal catalysts.After 4000 charge-discharge cycles,the chargedischarge voltage difference of the fabricated liquid zinc-air battery was only 0.64 V,and the voltage efficiency remained as high as 66%.(2)Compared with the single metal,the bimetallic active sites usually show higher electrocatalytic activity.In the second part of study,the bimetallic Co/Ni-ZIFs nanoparticles were first synthesized,and it was then uniformly dispersed with thiourea to fabricated nanofibers by electrospinning technology.In the subsequent pyrolysis process,the catalytic activity of the fabricated flexible carbon fiber film(Co/ Ni@SNCF)towards oxygen reduction was further improved by doping nitrogen atoms.The liquid and solid zinc-air batteries constructed with the as-synthesized electrode material exhibited excellent charge-discharge cycle stability,and the assembled button solid zinc-air battery showed a good stability in the chargedischarge cycle test of 43 h.(3)The high-resolution scanning electrochemical microscopy(SECM)with the redox competition mode and substrate generation/probe collection mode was applied to evaluate the local reactivity of both Co@NCF and Co/Ni@SNCF at different biased sample potentials at room temperature.The influence of working temperature on the electrocatalytic activity of the sample was also studied by the improved temperature-controlled SECM.The research results would guide the design and synthesis of self-supporting catalysts which would be operated in real working environment.