Preparation Of Metal-Organic Framework-Derived Non-Noble Metal Catalysts And Their Application In Zinc-Air Batteries

Rapid industrial development has led to serious fossil energy consumption,and developing new energy has become an urgent problem around the world.Zinc-air batteries（ZABs）,as a reliable alternative to fossil fuels,has been widely studied because of its high energy density,safety and low cost.Oxygen reduction reaction（ORR）and oxygen evolution reaction（OER）are two fundamental semi-reactions in ZABs,which play important roles in the charging and discharging process of batteries,respectively.However,the slow kinetics of the oxygen reduction and oxygen evolution processes limit its practical application.Currently,noble metal-based catalysts（like Pt/Ru-based catalysts）have been considered as the most effective electrocatalysts,but their large-scale commercial applications are limited by scarcity,high costs and instability.Therefore,developing highly stable non-precious metal（NPM）electrocatalysts for ORR and OER becomes one of the effective solutions to its practical application.Metal-organic frameworks（MOFs）have been extensively studied in recent years because they are excellent nanomaterial precursors that can provide catalysts with the desired composition,high specific surface area,and porosity.In view of this,this paper mainly prepared two MOFs-derived carbon-based materials,and studied their structure,properties application in Zn-air batteries.The specific research contents and results are as follows:1.Co_5.47N/Co₃Fe₇/NC was synthesized by a convenient and low-cost method,and the catalyst exhibited Co_5.47N/Co₃Fe₇heterostructure anchored on porous nitrogen-doped carbon.The as-prepared Co_5.47N/Co₃Fe₇/NC catalyst exhibited remarkable catalytic activity and long-time durability toward ORR and OER processes because of its unique heterostructure.The ORR half-wave potential of Co_5.47N/Co₃Fe₇/NC reaches 0.89 V,which is better than 20%Pt/C in alkaline.The OER overpotential(E_j=10)is 379 m V,which is comparable to Ir O₂.Furthermore,the over-potentialΔE(E_j=10-E_1/2)of the catalyst is only 0.719 V,which is superior to most bifunctional catalysts reported before.Using this catalyst as cathode of ZAB,the ZAB exhibits a maximal power density of 264 m W cm^-2and maintains a stable voltage gap after 180 h,which provides an excellent substitute for the air cathode of Zn-air batteries.The emergence of this novel material provides new ideas for the design of high-performance catalysts.2.An electrocatalyst with ultralong stability（CrN@Fe/NC）was prepared by anchoring CrN on nitrogen-doped carbon substrates by means of secondary carbonization.The research shows that the Fe species on the catalyst provided good catalytically active sites,and the doping of CrN provided the catalyst with ultra-long stability.Compared with the as-prepared Fe/NC catalyst,the CrN-loaded CrN@Fe/NC catalyst has great improvement in stability.After chronoamperometric testing for 80,000 s in alkaline electrolyte,the current retention of the catalyst was 97.47%,exceeding that of Fe/NC（92.41%）and 20%Pt/C（84.90%）.After chronoamperometric testing for 80,000 s in acidic electrolyte,the current retention of the catalyst was 92.76%,exceeding that of Fe/NC（83.91%）and20%Pt/C（61.23%）.And the catalyst can maintain stability for more than500 h in zinc-air batteries.The emergence of this novel catalytic material is expected to open new path for the stability design of energy storage devices.