Study On Bifunctional Electrocatalysts Based On ZIF–67@yeast Structural Regulation

With the continuous use of fossil fuels,the energy crisis and the intensification of environmental pollution,the transition from traditional fossil fuels to green and efficient clean energy has become a huge challenge.Zn-air batteries have attracted much attention due to their advantages of low-cost,high safety,stable discharge voltage and high energy density.However,the development of Zn-air batteries still faces some challenges,the slow kinctics of oxygen reduction reaction（ORR）and oxygen evolution reaction（OER）on the air electrode.The key to solving this problem is to develop stable and efficient non noble metal bifunctional catalysts.In this paper,Co@NC-3 metal particles,ZIFY-Co-N₄-C-4B single atom and ZIFY Co/Fe-N-C bimetallic composite materials were prepared by electrostatic interaction and functionalization treatment between yeast cells and metal ions.The as-prepared materials are used as positive electrode catalyst for Zn-air batteries,which exhibiting excellent catalytic activity.The details are as follows:（1）This chapter provides a systematic understanding of the cellular structure,composition,and lifestyle of yeast.In particular,different cellular structures of yeast cells can provide different types of functional groups,such as hydroxyl,amino,carboxyl,etc.The presence of functional groups in various cellular structures can provide abundant sites for the anchoring of metals.In addition,amino acids,proteins,phospholipids in yeast cells can provide rich heteroatom doping.We mixed yeast cells with Co（NO₃）₂ solution,adsorbed Co²⁺into yeast cells through the electrostatic interaction between functional groups and Co²⁺.Co@NC-3 was prepared by annealing it under Ar gas and reducing Co²⁺to metallic Co particles.Using Co@NC-3 as an ORR catalyst,the limiting current density at 1600 rpm is 1.56 m A cm^-2,and the corresponding Tafel slope is 93.37 m V dec^-1（2）Based on the study of cell structure in the previous chapter,ZIFY-Co-N₄-C-4B SAC electrocatalysts were synthesized through a two-step route of yeast cell regulation Zeolitic imidazolate framework-67（ZIF-67）and functional treatment.Yeast cells with negatively charged functional groups provide abundant sites for the anchoring of Co²⁺ions.Co²⁺ions in Co（NO₃）₂ solution are selectively adsorbed by activated yeast cells and complexed and fixed by negatively charged functional groups.With the addition of 2-methylimidazole,a willow shaped ZIF-67 sheet structure was formed in situ at the position where Co²⁺ions were anchored on the cellular structure.After functional treatment,the obtained ZIFY-Co-N₄-C-4B monoatomic electrocatalyst provides a low overvpotential of 272 m V at 10 m A cm^-2,a half wave potential of 0.84V,a kinetic current densities of 6.88 m A cm^-2,an OER Tafel slope of 147.8 m V dec^-1and an ORR Tafel slope of 68.38 m V dec^-1.At a current density of 10 m A cm^-2,the charge/discharge voltage gap stabilizes at 0.98 V after 100 h.It providing excellent stability and cycle durability.In order to meet the needs of wearable flexible electronic devices,flexible Zn-air batteries prepared through ZIFY-Co-N₄-C-4B have good flexibility.（3）Based on the experiments in the previous two chapters,a bimetallic Co Fe alloy bifunctional catalyst was designed and synthesized.The obtained ZIFY-Co/Fe-N-C exhibited excellent bifunctional catalytic activity when used as air electrode for Zinc-air batteries.The obtained ZIFY-Co/Fe-N-C electrocatalyst exhibits a low overpotential of 410 m V at 10 m A cm^-2,a half wave potential of 0.809 V,a kinetic current densities of 5.04 m A cm^-2,an OER Tafel slope of 194.24 m V dec^-1 and a ORR Tafel slope of 73.3 m V dec^-1.When the prepared ZIFY-Co/Fe-N-C composite material is used as air electrode material for Zn-air batteries,the discharge voltage can reach 1.28V at a current density of 5 m A cm^-2.After 120 h of charging and discharging cycles,ZIFY-Co/Fe-N-C can still provide a discharge voltage of nearly 1 V.