Synthesis Of Iron-based Metal/Nanocarbon Materials And The Study Of Charging/Discharging Reaction Mechanism For Zinc-air Battery

Zinc-air batteries（ZABs）exhibit high energy density as well as flexibility,safety,and portability,thereby fulfilling the requirements of power batteries and consumer batteries.Oxygen reduction reaction（ORR）and oxygen evolution reaction（OER）are the two important cathode reactions in ZABs.Noble metal（Pt,Ru,Ir）-based catalysts have excellent activity for ORR and OER reactions,but their poor stability and high cost limit the development of energy technology.Therefore,development of high-efficient,high-stable and low-cost non-noble metal ORR/OER bifunctional catalysts is very important for the commercialization of ZABs.Besides,it is necessary to deeply elucidate the ORR and OER processes,and recognizing the design principles of oxygen electrocatalysts by combining with in-situ characterization techniques.Due to excellent activity and low-cost of Fe-based metals（Fe/Co/Ni）and carbon nanomaterials,it could further improve the electrocatalytic activity and stability by combining the two components.In this paper,the goal is to develop efficient and stable electrocatalyst for oxygen reaction as the goal,the ORR and OER catalysts of Fe series metal and carbon nanotubes（CNTs）,graphene and other carbon materials composites,meanwhile,constructing high-performance ZAB.In-situ X-ray absorption spectroscopy（XAFs）,X-ray photoelectron spectroscopy（XPS）and other characterization methods were used to explore the mechanism of charge and discharge.The main research contents are as follows:1.Due to the difference in charge density and electron spin,the sulfur/nitrogen doped carbon-based catalysts exhibit excellent bifunctional ORR/OER electrocatalytic activity.Herein,the sulfur and nitrogen co-doped carbon-coated Co Ni nanoparticles（RS-Co Ni-Box@CNTs）composite has been prepared by using Co Ni Prussian blue as templates combined with chemical vapor deposition and room temperature vulcanization strategies.It can be used as bifunctional oxygen reaction electrocatalysts.The results show that sulfur doping has the etching effect,which improves the specific surface area of the catalyst and exposes more active sites,and improves the limiting current density of ORR while optimizing the OER performance.It was used to assemble reversible ZAB and the cycle stability of the battery was tested.2.The 3D structure assembled by CNTs and graphene nanosheets is conducive to mass and charge transfer,which can be used as bifunctional oxygen reaction catalyst by further combining with Co Fe catalyst.Herein,melamine was played as carbon source and nitrogen source,Co Fe alloy as the catalytic growth center of CNTs,and graphite oxide as the growth substrate,so a 3D network structure Co Fe/N-GCT tangled with CNTs and graphite nanosheets was synthesized.The ORR/OER activity of Co Fe/N-GCT catalyst was studied,and the liquid reversible and flexible solid ZABs were assembled.The results showed that the battery exhibited the characteristics of high energy efficiency and superior stability.In-situ XAFs proved that the active sites of ORR and OER are respectively on Fe and Co species,while the synergistic effect of Fe/Co bimetals makes the excellent bifunctional activity of Co Fe/N-GCT.3.Sea urchin-like Co Zn-NCNTs derived from bimetallic zeolite imidazole frameworks（ZIFs）were prepared by zinc-assisted epitaxial growth strategy,which can be used as ORR catalyst for ZAB cathode reaction.The synergistic effect between nitrogen-doped CNTs and embedded Co nanoparticles gave the Co Zn-NCNTs catalyst an excellent activity and stability.The assembled ZAB can provide high power density,excellent rate capability and well long-term stability.4.At present,the efficiency of ZAB is difficult to generally less than 65%.Exploration of new positive electrode is the inevitable strategy to solve the current situation.In order to further improve the efficiency and cycling stability of ZAB,Ni Fe hydrotalcite was prepared as OER material and matched with the ORR catalyst of Co Zn-NCNTs as air-cathode.The electrochemical reactions of ZAB and zinc-nickel battery could be combined to construct a new hybrid battery by introducing Ni²⁺/Ni³⁺redox pair,which exhibited a high efficiency.Meanwhile,it solved the problem of ZAB cannot stably operate when the battery was flooded and water evaporated.The off-line XPS further revealed the conversion process of Ni-O?Ni-O-O-H during the charging/discharging process and the operating mechanism of the hybrid battery.The results showed that the hybrid battery performed a high energy efficiency of 79.2%and well environmental adaptability at the current density of 10 m A/cm².