Preparation And Of Application Of Cobalt-based Bifunctional Electrocatalysts

With the booming development of flexible and wearable electronic devices,the demand for compatible power supply devices with high energy density and safety,as well as the compact structure for driving these wearable electronic devices is growing rapidly.Flexible all-solid-state rechargeable Zn-air battery(F-ZAB)is considered to be one of the most competitive and promising energy storage systems in the future wearable electronic devices due to its high energy density,high safety,low cost and flexible mechanical properties.In recent years,although cathode electrocatalysts have made great progress in improving the electrochemical performance of F-ZAB,but the F-ZAB for wearable applications still faces great technical challenges in terms of mechanical flexibility and durability.In order to solve this problem,this thesis creatively designed to assemble Z-air batteries by preparing cobalt-based bifunctional electrocatalysts with different morphologies as F-ZAB cathode materials,thereby improving the electrochemical performance of the catalyst and the battery performance of Zn-air batteries.According to different morphologies of cobalt-based bifunctional nanocomposite catalysts,the following researches have been done in this thesis:(1)Through rational structural design,a bifunctional catalyst based on non-noble metal materials is studied and prepared in this thesis to achieve efficient and sustainable oxygen reduction(ORR)and oxygen evolution reactions.In this thesis,a novel one-dimensional Co nanoparticles embedded in nitrogen-doped carbon nanotubes nanocomposites(Co-NC CNTs)were successfully prepared by a simple and efficient method,and electrocatalysts containing abundant active sites of cobalt nanoparticles were obtained.Co-NC CNTs are directly used as bifunctional electrocatalysts with a remarkable electrochemical performance,including the positive half-wave potential(0.82 V vs.RHE)compared to the commercial platinum carbon(Pt/C)(0.84 V vs.RHE)for ORR,and the lower overpotential(0.46 V)at the current density of 10 mA/cm2,which is close to the commercial RuO2(0.4 V)for OER.The liquid rechargeable ZABs assembled by Co-NC CNTs catalyst as air cathode material has a large open circuit voltage(1.44V),a special peak power density(115 mW/cm2),a large specific capacity(786.7 mAh/g),and a good cycle stability and durability.(2)Inspired by the single-function electrocatalytic oxygen reduction reaction and oxygen precipitation reaction(ORR/OER),a bifunctional electrocatalyst(labeled Co/NDC)that uniformly embed metal cobalt nanoparticles on nitrogen-doped carbon spheres by simple physical stirring and high temperature pyrolysis is reported in this thesis.Due to its unique nanostructure and chemical material characteristics,the ultra-fine Co nanoparticles embedded on carbon spheres prepared in this thesis have excellent OER and ORR properties.The Co/NDC catalysts have rich pore structure and large surface area(220 m2/g)as excellent oxygen electrocatalysts for liquid and flexible all-solid state Zn-air batteries.At current density of 10 mA/cm2,the catalyst delivering a low overpotential of 460 mV for OER,obtaining a half-wave potential of 0.76 V vs.RHE and the limiting current density of 5 mA/cm2 for ORR.In addition,a home-made flexible all solid-state battery was assembled by using Co/NDC as air cathode has a large open circuit voltage,peak power density,good flexibility and cycle stability,and can drive a LED device.Our work provides a reliable method for fabricating ultrafine metal nanoparticles embedded in carbon based substrate with high activity for next-generation energy conversion and storage devices.Figure 22 table 7 reference 153.