Preparation Of TiN/NC Catalysts And Their Application In Zinc-air Batteries

The development of new energy storage and conversion devices,such as metal-air batteries,fuel cells,and lithium-ion batteries,is one of the main directions of research into new sustainable energy and conversion systems,which can solve the serious energy and environmental problems from the source.Among them,zinc-air batteries(ZABs)are recognized as one of the promising energy storage and conversion devices with the advantages of high theoretical energy density,low cost and good safety performance.However,the sluggish kinetics(oxygen reduction reaction(ORR)and oxygen evolution reaction(OER))of cathode catalysts have hindered the further development of ZABs.The charge/discharge performance of ZABs can be effectively enhanced by using electrocatalysts with high activity and stability.Noble metal Pt or Ir-based catalysts are a class of highly efficient ORR/OER catalysts.However,their high cost,scarce resources,and insufficient performance of multifunctional electrocatalyst greatly limit their commercial application in ZABs.Therefore,the development non-precious metal catalysts of high-efficiency,low-cost,stable is crucial for the wide application of ZABs.Transition metal nitrides can replace noble metal catalysts for electrocatalysis applications,but currently TiN needs to be prepared by nitriding Ti O₂ with NH₃,which requires high equipment requirements and pollutes the environment.This thesis focuses on the clean synthesis and regulation of titanium nitride/nitrogen doped carbon catalysts,and explores in depth the catalytic performance of the catalysts in ORR and OER,as well as their applications in ZABs.The main studies and conclusions are as follows.(1)P123 was used as the main carbon source,and supramolecular self-assembly occurred under acidic conditions to form gels.Meanwhile,TTIP was hydrolyzed to generate Ti O₂ nanoparticles,and organic nitrogen sources with certain redox characteristics(DCDA,DICY,melamine,carbamide,guanidine hydrochloride)were selected for the preparation of nitrogen-doped carbon materials,and Ti O₂ was reduced to TiN.Through the structural characterization and electrocatalytic performance of the catalyst,it was found that,the catalyst prepared by DICY,carbamide and guanidine hydrochloride not only has TiN but also has Ti O₂.The catalysts prepared by DCDA and melamine as the nitrogen source and reductant contained only TiN,no other transition metal compounds,indicating that the TiN/NC catalysts could be prepared using DCDA and melamine instead of NH₃.The ORR performance of the TiN/NC catalysts made used DCDA was better than that by melamine.(2)On the basis of work 1,the composition,structure,and morphology of TiN/NC catalysts were regulated by adjusted the amount of DCDA added during the preparation process,and then optimized electrocatalytic activity.It was shown that DCDA and P123can inhibit decomposition during the preparation process,which is beneficial to the formation of TiN and N-doped carbon materials.The catalysts prepared used 6 g DCDA have good electrochemical performance,but the catalytic performance is still not satisfactory when compared with other cathode catalysts applied to ZABs.Based on this,the electronic structure of TiN was changed by doped another transition metal Co(Ti_0.95Co_0.05N/NC),which in turn enhanced the catalytic performance of TiN/NC.The onset potential,half-wave potential and limited current density of Ti_0.95Co_0.05N/NC are higher than those of TiN/NC catalysts,which is mainly attributed to the doped cobalt ions.The introduction of Co ions can increase the N content and increase the graphitization degree of N-doped carbon,which is conducive to electron transfer.The application of Ti_0.95Co_0.05N/NC in ZABs has a higher energy density,power density and better cycle stability compared with TiN/NC-based ZABs.(3)Both electronic structure and conductivity of the catalysts are important factors affect the catalyst performance.The Ti_xFe_1-xN/NC/C were successfully prepared by doped a certain amount of Fe and carbon black in the preparation process based on the work 1.The results show that Fe ions can be successfully doped into the TiN lattice and a certain amount of Fe ions can improve the graphitization degree of the catalysts,which is beneficial to electron transfer.Therefore,Ti_0.95Fe_0.05N/NC/C catalyst has higher electrocatalytic performance than TiN/NC/C catalyst(including the initiation site,half-wave potential,ultimate current density,electron transfer number,etc.).The Ti_0.95Fe_0.05N/NC/C catalyst showed excellent stability,after 30,000 s of continuous ORR,the catalyst retained 95.6%of its initial ORR performance.It can be applied as a cathode material in ZABs.Compared with TiN/NC/C,the ZABs performance with Ti_0.95Fe_0.05N/NC/C catalyst as cathode has higher discharge voltage,energy density(966.95 Wh·kg_Zn^-1,close to the theoretical value)and power density.