Synthesis Of Porous Carbon-based Catalysts For Zinc-air Batteries

The rapid development of human society has inevitably led to a dramatic increase in the demand for new energy sources,and the most used at present are still traditional non-renewable fossil fuels,leading to an increasingly serious energy crisis and environmental pollution.Zinc-air batteries are regarded as promising next-generation energy storage devices due to their high energy density,high energy conversion efficiency,low cost,environmental friendliness and good safety,and have received great attention.However,the oxygen reduction reaction at the cathode is limited by slow kinetics,resulting in poor high power performance of zinc-air.Although noble metals and their alloy catalysts can accelerate the reaction kinetics of oxygen reduction rection（ORR）at the cathode of zinc-air batteries,their practical application is severely hampered by the high cost and scarcity of noble metals.Therefore,there is an urgent need for this economical and high performance non-precious catalyst as an alternative to precious metal catalysts.In order to accelerate the reaction kinetics of the oxygen reduction process and improve the multiplicative performance of zinc-air batteries,in this paper,Fe-/Co-NC catalysts with a graded porous structure were prepared by the hard template method,and from the microstructure and active sites of the catalysts,highly active porous catalysts were successfully developed to effectively promote the oxygen reduction kinetics of zinc-air batteries.The specific studies in this paper are as follows.1)Three-dimensional nitrogen-doped carbon catalysts with hierarchical porous structure and homogeneous dispersion of Fe-N₄ active sites were synthesized using silica spheres as hard templates.The as-prepared single-atom Fe 3D-ordered porous carbon（SA-Fe-3DOMC）possesses a high specific surface area of 1357.8 m² g^?1 and a high Fe loading of 0.84 wt%.Benefit from these favourable structural properties,the SA-Fe-3DOMC exhibits superior ORR half-wave potential(E_1/2)of 0.901V and negligible activity loss（only 3 mV）after 10000 cycles in alkaline media,surpassing the commercial Pt/C electrocatalyst.Particularly,the integrated zinc-air battery with SA-Fe-3DOMC as air electrode shows a remarkable power density(140 mW cm^-2)and a high specific capacity(786.6 mAh g^?1),representing a great promise in practical application.2)ZnCo-MOF was used as a precursor for the synthesis of the derivative Co-NC catalysts,while silica spheres were used as a template to give them an ordered cross-linked macroporous structure.The use of 2-methylimidazole as a ligand,which is rich in nitrogen,enables in situ doping to obtain an abundance of active sites.The Co-NC catalyst was then ammoniated at high temperature and the synthesised Co-NC/NH₃catalyst had a higher specific surface area and was tested in nitrogen adsorption/desorption to find a greater enhancement in the pore distribution in the mesoporous region,where it was possible that the ammonia etching caused more defects.In the next oxygen reduction performance test the Co-NC/NH₃ catalyst achieved onset and half-wave potentials of 0.962 V and 0.867 V,comparable to commercial Pt/C.The performance in the 10000 accelerated cycle stability test was even better than that of commercial Pt/C catalysts.The zinc-air cell assembled with the Co-NC/NH₃ catalyst as the air cathode exhibited a significantly higher ultimate power density of 126 mW cm^-2 and a specific capacity of 766.2 mAh g^-1 than commercial Pt/C.