Structural Modulation Of Cobalt-based/Carbon Composite Catalysts And Their Application In Zinc-air Batteries

Zinc-air batteries have received much attention for their high energy density,low cost,high safety and environmental friendliness.However,the oxygen reduction reaction（ORR）occurring at the air electrode during the discharge process involves a complex four-electron reaction process with slow reaction kinetics and excessive overpotential,which greatly impairs the overall performance of zinc-air batteries.Although noble metal catalysts such as platinum exhibit excellent ORR activity,their large-scale applications are greatly limited by high costs and scarce reserves.Therefore,the development of inexpensive and efficient non-precious metal ORR catalysts is a hot research topic at present.However,non-precious metal materials still have problems such as low intrinsic activity and poor stability that need to be solved.To address the above problems,this thesis optimizes the oxygen reduction performance of cobalt-based materials by means of structural modulation and doping,and explores their applications in zinc-air batteries,mainly as follows:（1）Nitrogen and sulfur co-doped carbon aerogels loaded with Co₉S₈ particles（Co₉S₈@NSC）were obtained by a two-step freeze-drying-pyrolysis process using pyrrole-based aerogels as the backbone,ammonium persulfate as the polymerization agent and urea as the nitrogen source.Thanks to the synergistic effect of Co-N_X sites and Co₉S₈ particles,the rich pore structure and large specific surface area of the aerogel as well as the encapsulation of the active sites,Co₉S₈@NSC achieves a half-wave potential（0.85 V）and excellent stability comparable to that of commercial Pt/C catalysts.In a zinc-air cell test,the zinc-air cell with Co₉S₈@NSC as the air electrode exhibited a high specific capacity of 735 m A g_zn^-1 and a high energy density of 150.9 m W cm^-2.（2）The surface Co²⁺aggregation was cleverly utilized to successfully clad the dopamine layer on the outside of the tubular MnO₂ template.A one-dimensional layered composite（MnO@Co/NC）with MnO as the inner core and Co nanocrystal/nitrogen-doped carbon material as the shell layer was obtained after heat treatment.MnO@Co/NC shows excellent oxygen reduction activity(E_1/2=0.85 V)under alkaline conditions due to the internal manganese element with mixed valence of Mn²⁺/⁴⁺,abundant active sites（Co-N_X,pyridine nitrogen and C-N groups,etc.）and high specific surface area and uniform pore size distribution.And also competitive stability under long time operation is achieved.MnO@Co/NC-based zinc-air cells are able to achieve a power density of 145 m W cm^-2 and a specific capacity of 869 m Ah g_zn^-1.（3）Glucose was selected as the carbon skeleton,urea as the nitrogen source and sodium chloride as the hard template to prepare and obtain Fe Co alloy/nitrogen-doped carbon composite catalyst（Fe Co/PNC）.The ORR performance of this Fe Co/PNC was significantly improved due to the alloying effect between Fe Co,N-doping and porous carbon structure with large specific surface area.half-wave potential of Fe Co/PNC was 0.87 V,which was significantly higher than that of commercial Pt/C catalyst（0.83 V）;after 10,000 CV cycles,the half-wave potential only decreased by 6 m V,demonstrating excellent stability.