Metal-organic-frameworks-derivatives For Air Electrode And Those Performance Of Li-air Battery

Li-air battery has aroused growing concern as its extremely high theoretical specific energy density.However,the sluggish kinetics of ORR(oxygen reduction reaction)and OER(oxygen evolution reaction)makes higher charge-discharge overpotential of air electrode which decreases the performance of Li-air battery.Researching high efficiency and low cost ORR/OER catalyst is significant to promote the development of Li-air battery.In this thesis,the Metal organic frameworks(MOFs)precursors are synthesized by hydrothermal method and they are made into MOFs derived mesoporous ZnCo2O4-ZIF-67 series catalysts afterwards.ZnCo2O4-ZIF-67-700-2 has the best ORR/OER bifunctional catalytic activity in this catalysts.The current density of OER is 30.02 mA cm-2 at the potential of 0.8 V which shows the best OER performance.The initial voltage,half-wave potential and the Tafel curve slope of ORR are-0.03 V,-0.11 V and-30.47 mV·dec-1,respectively.ZnCo2O4-ZIF-67-700-2 shows the best performance of air electrode in these series:the discharge voltage platform is 2.55 V,the efficiency of Li-air battery(Edischarge/Echarge)is 57.9%,the discharge capacity is 5778 mAh·g-1 for the first time and the higher cycle efficiency.This catalyst shows a lower electrochemical impedance so that the charge transfer ability on the surface of the catalyst is strong.Further research found that the catalyst has higher specific surface area,pore volume and electrochemical specific surface area.Those factors will all help to improve the performance of electrochemistry and Li-air battery.In the MOF(Co/Zn/Fe)series,MOF(Co/Zn/Fe)-600-2 catalyst shows the best oxygen evolution and reduction reaction performance,oxygen evolution and reduction reaction stability and Li-air battery performance.The current density of OER achieves 37.6 mA cm-2 at the potential of 0.8 V.The initial voltage half-wave potential and the Tafel curve slope are-0.029 V,-0:179 V and-59.5 mV·dec-1.The Li-air battery with this catalyst shows the best performance:the discharge potential platform,discharge capacity and batter efficiency(Edischarge/Echarge)for at the current density of 50 mA·g-1 the first time are 2.57 V,5856 mAh·g-1,60.06%,respectively.The cycle performance is quite excellent:the discharge potential at the current density of 100 mA·g-1 after ten cycles hardly decreases.