Design and Synthesis of ZIFs Derived Carbon Nanocomposites and Their Electrocatalytic Performance for ORR

Author:Hou Ya Nan

Supervisor:zhao zong bin


Degree Year:2019





Oxygen reduction reaction(ORR)occurring at the cathode of metal-air batteries restricts the energy conversion efficiency and performance.Commercial precious metal catalysts,such as Pt/C,have been used as very efficient electrocatalytic catalysts for ORR.Unfortunately,the precious metal-based catalysts still suffer from several disadvantages,including high cost,limited supply and poor stabality.As a result,great attention have been devoted to explore alternative catalysts that are low cost and exhibit comparable catalytic performance for ORR.Based on the merits of ZIFs derived carbon materials such as high conductivity and nitrogen content,herein,we synthesized various ZIFs derived N-doped carbon materials with tunable morphology,porosity and composition as electrocatalysts for ORR,overcame the disadvantages of aggragation and unreasonable pore structure,enhanced the electrocatalytic activity.The main contents and results are summarized as follows:(1)Aiming to address the issue of micropore domination in ZIF-8 derived porous carbon which leading to the difficult diffusion of electrolyte,hierarchical pore structures are introduced into the products.In the synthesis,two-dimensional nitrogen doped carbon nanosheets are prepared via molten salt medium adopting ZIF-8 nanocrystals as precursor.Pro fitting from the mesoporous and two dimensional structure,the investigation of eletrocatalytic performance for ORR demonstrated the enhanced catalytic activity than ZIF-8 derived porous carbon without molten salt,superior stability and methanol tolerance to the commercial Pt/C catalyst.(2)Aiming to address the issue of serious fusion of cobalt metal particles,collapse and aggregation of structural porosity during thermal treatment,three-dimensional ZIF-67 framework were reansformed into two-dimensional carbon sheets are adopted.Ultrathin Co,N-codoped carbon nanosheets are prepared via molten salt medium adopting ZIF-67 nanocrystals as carbon and cobalt source.Investigation on the morphology and contents reveals that the thickness of this ultrathin carbon nanosheets is about 1.0 nm~1.75 nm.During the thermal treatment,liquid state environment of molten salt not only prevents the irreversible fusion and aggregation of carbon sheets,but also dissolves the bulk cobalt metal particle and then doping into the carbon framework in the form of single cobalt atoms.In aqueous electrolyte,the ultrathin carbon nanosheets exhibits excellent stability,competitive catalytic activity,superior durability and methanol tolerance compared to the commercial Pt/C catalyst.(3)Aiming to make full use of the active sites,bifunctional electrocatalyst for ORR and OER is prepared by thermal transforming ZIF-67 hollow nanocubes,which is synthesized under the introduction of n-bulylamine adopting Co3[Co(CN)6]nanocubed as cobalt source and template into cobalt particles embedded N-doped carbon nanocages.Investigation on the electrocatalytic performance demonstrates the merit of hollow structure on facilitating the utilization of active sites and reaction kinetics leading to a lower applicable potential of 860 mV compared to noble metal catalysts.The zinc-air batteries using the nanocages as electrode catalyst exhibits lower initial potential gap and better rechargeable performance than that of noble metal catalysts.