Preparation And Electrocatalytic Performance Of Co-doped G-C₃N₄/Graphene Composites

Graphitic carbon nitride（g-C₃N₄）polymer has a graphite-like sp²-bonded C-N structure.Due to its unique thermal stability,appropriate electronic structure and low price preparation method,it has a broad application prospect in the fields of photocatalytic hydrogen production,metal free heterogeneous catalytic reactions in various organic systems and fuel cells.In particular,g-C₃N₄ has rich"melon"molecular structure,so it is called"nitrogen pots",which is an ideal place to modify the molecular electronic structure.In this thesis,two kinds of g-C₃N₄ with different morphologies were used as nitrogen source,cobalt salt was used as the metal source,and graphene was used as the single carrier.A non-noble metal-based catalyst with high bifunctional electrocatalytic activity and stability in alkaline system was prepared by direct polycondensation.The non-precious metal-based catalysts were labeled as Co（X%）-C₃N₄/nG and Co（X%）-ACN/G-n,respectively,depending on the morphology of g-C₃N₄.The morphology,microstructure and optical properties of the two catalysts were characterized by XRD,SEM and TEM.The ORR/OER performance of the samples was characterized by RDE technique.Besides,the bifunctional catalytic activity was optimized by changing the morphology of the catalyst,the amount of metal doping and the composite ratio of carbon support.Subsequently,this samples were used as air electrode cathode catalyst in the rechargeable zinc-air battery to investigate their charge/discharge and cycle performance.The results show that when the Co doping amount accounts for 10 wt%of the prepared Co-doped g-C₃N₄/graphene composite material,and the G:Co-C₃N₄ mass ratio is 3:1,that is,Co（10%）-C₃N₄/3G composite powder has the highest electrocatalytic activity.Co-doped alveolate g-C₃N₄/graphene composites were prepared by sacrificial template method with dicyandiamide as precursor and self-made SiO₂ nanospheres as hard template.Structural optimization and performance optimization of materials through morphology control and composition control.The result is that when the Co doping amount accounts for 20 wt%of the prepared Co-doped honeycomb g-C₃N₄ composite material,and the ACN:G mass ratio is 2:1,that is,Co（20%）-ACN/G-2,the composite powder has a high surface area and a rich pore structure.In addition,a certain number of Co and CoO nanoparticles are embedded in situ,and Co-N and pyridine-N form more defects,which makes Co（20%）-ACN/G-2 have larger electrochemical activity surface area,and the activity of oxygen reduction and oxygen precipitation is the best at the same time.